Aims. It remains controversial whether patellofemoral joint pathology is a contraindication to lateral unicompartmental knee arthroplasty (UKA). This study aimed to evaluate the effect of preoperative radiological degenerative changes and alignment on patient-reported outcome scores (PROMs) after lateral UKA. Secondarily, the influence of lateral UKA on the alignment of the patellofemoral joint was studied. Methods. A consecutive series of patients who underwent robotic arm-assisted fixed-bearing lateral UKA with at least two-year follow-up were retrospectively reviewed. Radiological evaluation was conducted to obtain a Kellgren Lawrence (KL) grade, an Altman score, and alignment measurements for each knee. Postoperative PROMs were assessed using the Kujala (Anterior Knee Pain Scale) score, Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR), and satisfaction levels. Results. A total of 140 knees (130 patients) were identified for analysis. At mean 4.1 years (2.0 to 8.5) follow-up, good to excellent Kujala scores were reported. The presence of mild to moderate preoperative patellofemoral joint osteoarthritis had no impact on these scores (KL grade 0 vs 1 to 3, p = 0.203; grade 0 to 1 vs 2 to 3, p = 0.674). Comparable scores were reported by patients with osteoarthritis (Altman score of ≥ 2) evident on either the medial or lateral patellofemoral joint facet (medial, p = 0.600 and lateral, p = 0.950). Patients with abnormal patellar congruence and tilt angles (≥ 17° and ≥ 14°, respectively) reported good to excellent Kujala scores. Furthermore, lateral UKA resulted in improvements to patellofemoral alignment. Conclusion. This is the first study demonstrating that mild to moderate preoperative radiological degenerative changes and malalignment of the patellofemoral joint are not associated with poor patient-reported outcomes at mid-term follow-up after lateral fixed-bearing UKA. Our data suggest that this may be explained by realignment of the patella and thereby redistribution of loads across the patellofemoral joint. Cite this article: Bone Joint J 2020;102-B(6):727–735

Abstract. Introduction. To investigate the impact medial opening wedge high tibial osteotomy (MOWHTO) has on the progression of patellofemoral OA, patella height and contact pressure within the patellofemoral joint (PF). Methods. A systematic review was conducted in January 2022 according to PRISMA guidelines. Each study was graded as per the MINORS criteria for non-randomised trials. The ICRS cartilage grade of the PF joint at the initial MOWHTO surgery and at second look surgery was compared and relative risk of progression of PF OA was calculated. Evaluation of patella height was assessed by Caton-Deschamps index, Blackburne-Peel index or Insall-Salvati ratio pre and post MOWHTO. Cadaveric studies assessing contact pressures in the PF after MOWHTO were included. Results. Forty-two studies comparing 2,419 patients were included. The mean age was 53.1 years (16–84), 61.3% female. The risk of progression of PF OA was highest in the uniplanar and biplanar MOWHTO with proximal tubercle osteotomy groups (RR= 1.28-1.51, I2= 0%), compared to biplanar MOHWTO with distal tubercle osteotomy (RR= 0.96-1.04, I2 = 0%). Patella height was not affected after biplanar MOWHTO and distal tubercle osteotomy. (P<0.001). Cadaveric studies demonstrate that PF contact pressures increase with more severe corrections (10°) but suggest biplanar MWOHTO and distal tubercle osteotomy induces lower contact pressures within the PF joint than other OWHTO techniques. Conclusion. This novel systematic review demonstrates that biplanar MOWHTO and distal tubercle osteotomy causes lower contact pressures in the PF joint, less severe progression of PF OA and has minimal impact on patella height

Aims. With up to 40% of patients having patellofemoral joint osteoarthritis (PFJ OA), the two arthroplasty options are to replace solely the patellofemoral joint via patellofemoral arthroplasty (PFA), or the entire knee via total knee arthroplasty (TKA). The aim of this study was to assess postoperative success of second-generation PFAs compared to TKAs for patients treated for PFJ OA using patient-reported outcome measures (PROMs) and domains deemed important by patients following a patient and public involvement meeting. Methods. MEDLINE, EMBASE via OVID, CINAHL, and EBSCO were searched from inception to January 2022. Any study addressing surgical treatment of primary patellofemoral joint OA using second generation PFA and TKA in patients aged above 18 years with follow-up data of 30 days were included. Studies relating to OA secondary to trauma were excluded. ROB-2 and ROBINS-I bias tools were used. Results. A total of nine studies were included, made up of four randomized controlled trials (domain 1) and five cohort studies (domain 2). PROMs and knee function specific scores developed for reporting TKA were unable to detect any difference between PFA and TKA. There was no significant difference in complications between PFA and TKA. PFAs were found to have a better postoperative range of motion. Conclusion. TKA and PFA are both viable options for patients with primary PFJ OA. Over time, we have seen an emphasis on patient satisfaction and better quality of life. Recommending sacrificing healthy medial and lateral compartments to treat patellofemoral joint arthritis should be given further thought. Cite this article: Bone Jt Open 2023;4(12):948–956

Aims. Patellofemoral problems are a common complication of total knee arthroplasty. A high compressive force across the patellofemoral joint may affect patient-reported outcome. However, the relationship between patient-reported outcome and the intraoperative patellofemoral contact force has not been investigated. The purpose of this study was to determine whether or not a high intraoperative patellofemoral compressive force affects patient-reported outcome. Patients and Methods. This prospective study included 42 patients (42 knees) with varus-type osteoarthritis who underwent a bi-cruciate stabilized total knee arthroplasty and in whom the planned alignment was confirmed on 3D CT. Of the 42 patients, 36 were women and six were men. Their mean age was 72.3 years (61 to 87) and their mean body mass index (BMI) was 24.4 kg/m2 (18.2 to 34.3). After implantation of the femoral and tibial components, the compressive force across the patellofemoral joint was measured at 10°, 30°, 60°, 90°, 120°, and 140° of flexion using a load cell (Kyowa Electronic Instruments Co., Ltd., Tokyo, Japan) manufactured in the same shape as the patellar implant. Multiple regression analyses were conducted to investigate the relationship between intraoperative patellofemoral compressive force and patient-reported outcome two years after implantation. Results. No patient had anterior knee pain after total knee arthroplasty. The compressive force across the patellofemoral joint at 140°of flexion was negatively correlated with patient satisfaction (R2 = 0.458; β = –0.706; p = 0. 041) and Forgotten Joint Score-12 (FJS-12; R2= .378; β = –0.636; p = 0. 036). The compressive force across the patellofemoral joint at 60° of flexion was negatively correlated with the patella score (R2 = 0.417; β = –0.688; p = 0. 046). Conclusion. Patient satisfaction, FJS-12, and patella score were affected by the patellofemoral compressive force at 60° and 140° of flexion. Reduction of the patellofemoral compressive forces at 60° and 140° of flexion angle during total knee arthroplasty may improve patient-reported outcome, but has no effect on anterior knee pain

We present a prospective review of the two-year functional outcome of 37 Avon patellofemoral joint replacements carried out in 29 patients with a mean age of 66 years (30 to 82) between October 2002 and March 2007. No patients were lost to follow-up. This is the first independent assessment of this prosthesis using both subjective and objective analysis of outcome. At two years the median Oxford knee score was 39 (interquartile range 32 to 44), the median American Knee Society objective score was 95 (interquartile range 90 to 100), the median American Knee Society functional score was 85 (interquartile range 60 to 100), and the median Melbourne Knee score was 28 (interquartile range 21 to 30). Two patients underwent further surgery. Only one patient reported an unsatisfactory outcome. We conclude that the promising early results observed by the designing centre are reproducible and provide further support for the role of patellofemoral joint replacement

Abstract. Introduction. Isolated patellofemoral joint(PFJ) osteoarthritis affects approximately 10% of patients aged over 40 years and treatment remains controversial. Our aim was to evaluate long term functional and radiological outcomes following PFJ arthorplasty with the Femoro Patella Vialli (FPV) prosthesis as this evidence is lacking in literature. Methodology. A retrospective review of prospectively collected PROMS in patients undergoing Patellofemoral arthroplasty. Single centre trial. Between 2004 and 2008, 101 FPV patellofemoral arthroplasties were performed in 80 patients with isolated patellofemoral joint osteoarthritis. Data was collected as a part of routine follow-up for up to 6 years and additional long term data was collected at 16 years. Results. At 6 year follow up the mean OKS was 29 and by 16 year follow up it was 26 which was not a statistically significant drop. 22 patients (29 knees) had died, 32 (32%) had been revised, 25 to total knee replacement using primary arthroplasty components. Mean OKS in the revised group was 27 which was not a statistically significant difference when compared to the unrevised group. Mean time to revision was 4 years. The cumulative survival analysis of the FPV implant was 76% at 5 years, 64% at 10 years. Conclusion. Our findings suggest the FPV patellofemoral prosthesis provides good pain relief and clinical outcomes however, the survivorship for this particular implant maybe lower as compared to the available literature. Patient reported outcomes are maintained over the implant life and are no worse once revised implying a staged approach to arthroplasty is reasonable

Anterior knee pain and/or radiological evidence of degeneration of the patellofemoral joint are considered to be contraindications to unicompartmental knee replacement. The aim of this study was to determine whether this is the case. Between January 2000 and September 2003, in 100 knees (91 patients) in which Oxford unicompartmental knee replacements were undertaken for anteromedial osteoarthritis, pre-operative anterior knee pain and the radiological status of the patellofemoral joint were defined using the Altman and Ahlback systems. Outcome was evaluated at two years with the Oxford knee score and the American Knee Society score. Pre-operatively 54 knees (54%) had anterior knee pain. The clinical outcome was independent of the presence or absence of pre-operative anterior knee pain. Degenerative changes of the patellofemoral joint were seen in 54 patients (54%) on the skyline radiographs, including ten knees (10%) with joint space obliteration. Patients with medial patellofemoral degeneration had a similar outcome to those without. For some outcome measures patients with lateral patellofemoral degeneration had a worse score than those without, but these patients still had a good outcome, with a mean Oxford knee score of 37.6 (SD 9.5). These results show that neither anterior knee pain nor radiologically-demonstrated medial patellofemoral joint degeneration should be considered a contraindication to Oxford unicompartmental knee replacement. With lateral patellofemoral degeneration the situation is less well defined and caution should be observed

Complications involving the patellofemoral joint are a source of anterior knee pain, instability, and dysfunction following total knee arthroplasty. “Overstuffing” the patello-femoral joint refers to an increase in the thickness of the patellofemoral joint after a total knee replacement compared to the preoperative thickness. While biomechanical studies have indicated that overstuffing the patellofemoral joint may lead to adverse clinical outcomes, limited clinical evidence exists to support this notion. The purpose of this study is to evaluate the effect of changing the thickness of the patellafemoral joint on functional outcomes following total knee arthroplasty. Our institutional arthroplasty database was used to identify 1347 patients who underwent a primary total knee arthroplasty between 2006 and 2012 with the same component design. Standard preoperative and postoperative anteroposterior, lateral, and skyline radiographs were collected and measured for patello-femoral overstuffing. These measurements included anterior patellar displacement, anterior femoral offset, and anteroposterior femoral size. These measurements were correlated with patient outcome data using WOMAC, KSS scores, and postoperative range of motion. Multiple linear regression analysis was used to assess the association between stuffing and functional outcomes. A total of 1031 patients who underwent total knee arthroplasty were included. Increased anterior patellar displacement, a measure of patellofemoral joint thickness, was associated with decreased WOMAC scores (p=0.02). Anterior femoral offset (p=0.210) and anteroposterior femoral size (p=0.091) were not significantly associated with patient functional outcomes. Postoperative range of motion (ROM) was not associated with patellofemoral stuffing (p=0.190). The current study demonstrated that functional outcomes are adversely affected by patellofemoral overstuffing. Based on these results, caution is encouraged against increasing the thickness of the patellofemoral joint, particularly on the patellar side of the joint

Aims. The aim of this study was to determine and compare the congruency of the articular surface contact area of the patellofemoral joint (PFJ) during both active and passive movement of the knee with the use of an MRI mapping technique in both the stable and unstable PFJ. Patients and Methods. A prospective case-control MRI imaging study of patients with a history of PFJ instability and a control group of volunteers without knee symptoms was performed. The PFJs were imaged with the use of an MRI scan during both passive and active movement from 0° through to 40° of flexion. The congruency through measurement of the contact surface area was mapped in 5-mm intervals on axial slices. In all, 40 patients were studied. The case group included 31 patients with symptomatic patellofemoral instability and the control group of nine asymptomatic volunteers. The ages were well matched between the case and control groups. The mean age was 25 years (16 to 42; . sd. 6.9) in the case group and 26 years (19 to 32; . sd. 5.1) in the control group. There were 19 female and 12 male patients in the case group. Results. The unstable PFJs were demonstrably less congruent than the stable PFJs throughout the range of knee movement. The greatest mean differences in congruency between unstable and stable PFJ’s were observed between 11° and 20° flexion (1.73 cm. 2. vs 4.00 cm. 2. ; p < 0.005). . Conclusion. The unstable PFJ is less congruent than the stable PFJ throughout the range of knee movement studied. This approach to mapping PFJ congruency produces a measurable outcome and will allow the assessment of pre- and postoperative results following surgical intervention. This may facilitate the design of new procedures for patients with PFJ instability. If a single axial series is to be obtained on MRI scan, the authors recommend 11° to 20° of tibiofemoral flexion, as this was shown to have the greatest difference in contact surface area between the case and control groups. Cite this article: Bone Joint J 2019;101-B:552–558

Introduction. Experimental wear simulation of an all-polymer knee implant has shown an equivalent rate of wear of UHMWPE tibial components against PEEK-OPTIMA™ and cobalt chrome femoral components of a similar initial geometry and surface topography. However, when the patella is resurfaced with an UHMWPE patella button, it is important to also ascertain the wear of the patella. Wear debris from the patella contributes to the total volume of wear debris produced by the implant which should be minimised to reduce the potential for osteolysis and subsequent implant loosening. The aim of this study was to investigate the wear of the patellofemoral joint in an all-polymer knee implant. The wear of UHMWPE patellae articulating against PEEK-OPTIMA™ femoral components was compared to UHMWPE articulating against cobalt chrome femoral components. Materials and Methods. Six mid-size (size C) PEEK-OPTIMA™ femoral components (Invibio Knee Ltd., UK) and six cobalt chrome femoral components of similar initial surface topography and geometry were coupled with 28mm all-polyethylene GUR1020 patellae (conventional, EO sterile) (Maxx Orthopaedics, USA). The implants were set up in a ProSim 6 station electromechanical knee simulator (Simulation Solutions, UK) which was modified for testing the patellofemoral joint. 3 million cycles (MC) of wear simulation was carried out under kinematics aiming to replicate a gait cycle adapted for an electromechanical simulator from previous work by Maiti et al. The simulator used has six degrees of freedom of which four were controlled; axial force up to 1200N, flexion/extension 22°, superior-inferior (SI) displacement (22mm) and Abduction-adduction (AA) (4°). The SI and AA were displacement controlled and driven through the patella. The medial-lateral displacement and tilt (internal/external rotation) of the patella were passive so the patella button was free to track the trochlear groove. The lubricant used was 25% bovine serum supplemented with 0.03% sodium azide to retard bacterial growth. The wear of patellae was determined gravimetrically with unloaded soak controls used to compensate for the uptake of moisture by the UHMWPE. The mean wear rate ± 95% confidence limits were calculated and statistical analysis was carried out using ANOVA with significance taken at p<0.05. Results. The mean wear rates of the UHMWPE patellae were 0.26±0.21 mm. 3. /MC and 0.35±0.17 mm. 3. /MC against PEEK-OPTIMA™ and cobalt chrome femoral components respectively. There was no significant difference in wear rate against the different femoral component materials (P=0.38). Against both femoral component materials, a ‘bow tie’ shaped wear scar was evident on the patellae typical of that seen in retrieval studies and reported in previous experimental wear simulation of the patellofemoral joint. Conclusion. The wear rate of the UHMWPE patellae was low against both PEEK-OPTIMA™ and cobalt chrome femoral components and comparable to previous work by Vanbiervliet et al. This study further shows that in terms of its wear performance, PEEK-OPTIMA™ has promise as an alternative bearing material to cobalt chrome in the femoral component of total knee replacements

Abstract. Introduction. Isolated patellofemoral osteoarthritis accounts for 10% of knee osteoarthritis. Many of these will not require arthroplasty solutions, but for those who are sufficiently symptomatic, patellofemoral joint (PFJ) replacement has been shown to be an effective procedure. The National Joint Registry (NJR) has shown a higher revision rate for this operation, particularly in younger patients (males <55 years 13.3% failure at 5 years, females 9.6%). The aim of this study is to report on the medium-term outcome of the Avon patellofemoral joint arthroplasty in patients under 55 from a non-design centre. There is no other published case series on this young patient cohort. Methodology. 50 Avon PFJ replacements (Stryker, Kalamazoo USA) were undertaken in 46 patients under 55 years old (range 35 – 54, mean 48.8) between 2010 and 2022 for end-stage isolated PFJ arthritis shown on Xray and MRI scan. The outcome measure was all-cause revision rate. This was assessed by review of clinical notes, imaging and NJR data. Results. The mean follow up was 5.8 years (range 6 months to 12.9 years). Only one patient had a revision procedure (for progressive osteoarthritis) which was 3 years after the primary procedure. This patient has had no further surgery. The implant survival rate was 97.2% at 5 years and 97.2% at 10 years. Conclusion. This study shows that patellofemoral joint replacement with the Avon prosthesis can give a satisfactory revision rate in the medium term in patients under 55 if carefully selected

Introduction: The normal relationships of the patellofemoral joint provide a basis for the evaluation of patients with patellofemoral abnormalities. Previous studies have often described the patellofemoral joint using X-rays which are encumbered with projectional inaccuracies. We have used CT to describe the geometry of this joint and its relationship to the tibiofemoral joint in terms of angles and distances. Materials and method: 33 patients had a CT scan prior to medial unicompartmental knee replacement. These patients have minimum patellofemoral joint disease. Special software was used to convert the scans to 3D and measure the distances and angles. The flexion axis of the tibiofemoral joint was found as the line connecting the centres of the spheres fitted to posterior femoral condyles. These two centres and femoral head centre form a frame of reference for reproducible femoral alignment. The trochlear geometry was defined by fitting circles and spheres to slices and surfaces, then constructing an axis through their centres. The geometry of the patella was established by fitting two planes to the proximal and anterior extra-articular surfaces of the patella. The relationships between these planes and the rest of the patella were explored. Results: The deepest points on the trochlear groove can be fitted to a circle with radius of 23mm (stdev 4mm) and an rms of 0.3mm. This centre is offset by 21mm (stdev 3mm) at an angle of 68° (stdev 8°) from the line connecting the midpoint between the centres of the femoral condyles and a point in the piriform fossa. On either end of this line, the articular surface of the trochlea can be fitted to spheres of radius 30mm (stdev 6mm) laterally and 27mm (stdev 5mm) and an rms of 0.4mm medially. The centres of the circle and the two spheres fall on a line with an rms of 1.1mm. The anterior and proximal patellar planes could be described as flat surfaces (rms of 0.4 and 0.3mm). The median ridge could be described as a straight line (rms of 0.2mm). The angle between planes was 112° (stdev 5°); the average angle between the proximal plane and the line on the medial ridge was 62° (stdev4°). The functional centre of the patella was defined as a point in the centre of 2 planes orthogonal to the sagital plane from the midpoint between the most proximal and most distal points on the median ridge. The length, width and thickness of the patellae were measured at 22mm +/−4mm, 47mm +/− 3mm and 24 mm+/− 2 mm. Discussion: This investigation has allowed us to characterise the patello-femoral joint geometry. The knowledge of the shapes of the surfaces of this joint and their relationships may help identify and explain the aetiology of patello-femoral dyplasia and other pathologies. It may also be of use in planning and performing joint reconstruction and may have implications for the design of patello-femoral replacements and the rules governing their position

Background. Despite the excellent clinical success of total knee arthroplasty (TAK), controversy remains concerning whether or not to resurface the patella. This has led to a number of randomized controlled trials. Randomized controlled trials constitute the most reliable source of evidence for the evaluation of the efficacy of a potential intervention. But most of these studies include all degree of osteoarthritis of the patellofemoral joint. So we did this prospective study to compare clinical and radiological outcomes after TKA with or without patellar resurfacing in patients with grade IV osteoarthritis on patellofemoral joint. Materials and Methods. 123 cases (93 patients) with Kellgren-Lawrence grade IV osteoarthritis on patellofemoral joint were enrolled for this study. At the operating room, they were randomly assigned to undergo patella resurfacing (62 cases) or patella retention (61 cases). Among them, 114 cases that could be followed for more than 2 years were included in this study (resurfacing group; 59 cases, retention group; 55 cases). When patellar retention was performed, osteophytes of the patella were removed and marginal electrocauterization was carried out. Preoperative and postoperative clinical outcomes were evaluated and compared regarding the Hospital for Special Surgery Patellar (HSSP) score (total 100 point; anterior knee pain, functional limitation, tenderness, crepitus, Q-strength). We also compared Hospital for Special Surgery (HSS) and WOMAC scores, and range of motion (ROM). We also compared radiological outcomes at the final follow up, with regards to mechanical axis of the lower limb, patella tilt and patella congruence angle between two groups. Results. Average HSSP score was 85 in resurfacing group, 83 in retention group, which were showing no significant differences between groups (p=.75). Anterior knee pain subscale also showed no significant differences between groups (40 in resurfacing group, 36 in retention group, p= 0.52). HSS score improved to 94 points in resurfacing group and 95 points in retention group showing no significant difference (p=.92). While WOMAC score and range of motion was 32 point and 128°±10.5° in resurfacing group, respectively, they were 29 point and 126°±11.5° in retention group, without significant inter-group difference (p>.05). There were no differences between two groups in mechanical axis of the lower limb and patella tilt, patella congruence (p>0.05). Conclusion. Clinical and radiological outcomes were ‘good’ after TKA with or without patellar resurfacing in patients with high grade osteoarthritis of the patellofemoral joint without significant differences. Thus, this study suggested that TKA without patellar resurfacing is a good treatment option in patients with high grade osteoarthritis of the patellofemoral joint

Abstract. INTRODUCTION. 10% of patients with knee osteoarthritis (OA) have disease confined to the patellofemoral joint (PFJ). The main surgical options are total knee replacement (TKR) and PFJ replacement (PFJR). PFJR has advantages over TKR, including being less invasive, bone preserving, allowing faster recovery and better function and more ‘straight forward’ revision surgery. We aim to compare the clinical results of revised PFJR with primary TKR taking into consideration the survival length of the PFJR. METHODOLOGY. Twenty-five patients (21 female) were retrospectively identified from our arthroplasty database who had undergone revision from PFJR to TKR (2006–2019). These patients were then matched with regards to their age at their primary procedure, sex and total arthroplasty life (primary PFJ survival + Revision PFJ time to follow up) up to point of follow-up with a group of primary TKRs implanted at the same point as the primary PFJR. RESULTS. Mean survival of the PFJs revised were 4.2 years. In the PFJR revision group (mean arthroplasty life 7.8 years) mean Oxford knee score (OKS) at latest follow up was 27.8. In the primary knee group (mean arthroplasty life 7.5 years) mean OKS was 32.4. This difference was not statistically significant. All PFJR revisions were performed using primary prostheses. CONCLUSION. PFJR provides comparable clinical outcome even after revision surgery to TKR as primary TKRs at midterm follow up and should be considered in all patients meeting the selection criteria. Given comparable proms and straight forward revisions, staged arthroplasty to preserve bone-stock is a reasonable choice

Between May 1998 and May 2007 we carried out 50 Avon patellofemoral joint replacements in 32 patients with isolated patellofemoral osteoarthritis. There were no revisions in the first five years, giving a cumulative survival of 100% for those with a minimum follow-up of five years. The mean follow-up was 5.3 years (2.1 to 10.2). The median Oxford knee score was 30.5 (interquartile range 22.25 to 42.25). In patients with bilateral replacements the median Euroqol General health score was 50 which was significantly lower than that of 75 in those with a unilateral replacement (p = 0.047). The main complication was progression of disease, which was identified radiologically in 11 knees (22%). This highlights the need for accurate selection of patients. Our findings suggest that the Avon prosthesis survives well and gives a satisfactory functional outcome in the medium term

One of the most controversial issues in total knee replacement is whether or not to resurface the patella. In order to determine the effects of different designs of femoral component on the conformity of the patellofemoral joint, five different knee prostheses were investigated. These were Low Contact Stress, the Miller-Galante II, the NexGen, the Porous-Coated Anatomic, and the Total Condylar prostheses. Three-dimensional models of the prostheses and a native patella were developed and assessed by computer. The conformity of the curvature of the five different prosthetic femoral components to their corresponding patellar implants and to the native patella at different angles of flexion was assessed by measuring the angles of intersection of tangential lines. The Total Condylar prosthesis had the lowest conformity with the native patella (mean 8.58°; 0.14° to 29.9°) and with its own patellar component (mean 11.36°; 0.55° to 39.19°). In the other four prostheses, the conformity was better (mean 2.25°; 0.02° to 10.52°) when articulated with the corresponding patellar component. The Porous-Coated Anatomic femoral component showed better conformity (mean 6.51°; 0.07° to 9.89°) than the Miller-Galante II prosthesis (mean 11.20°; 5.80° to 16.72°) when tested with the native patella. Although the Nexgen prosthesis had less conformity with the native patella at a low angle of flexion, this improved at mid (mean 3.57°; 1.40° to 4.56°) or high angles of flexion (mean 4.54°; 0.91° to 9.39°), respectively. The Low Contact Stress femoral component had the best conformity with the native patella (mean 2.39°; 0.04° to 4.56°). There was no significant difference (p > 0.208) between the conformity when tested with the native patella or its own patellar component at any angle of flexion. The geometry of the anterior flange of a femoral component affects the conformity of the patellofemoral joint when articulating with the native patella. A more anatomical design of femoral component is preferable if the surgeon decides not to resurface the patella at the time of operation

We report the results of patellofemoral joint replacement done at our institution for predominantly patellofemoral arthritis. Patellofemoral joint replacement has always been a controversial subject, particularly in elderly patients where a more predictable result can be obtained with TKA. Patellofemoral joint replacement surgery was commenced at our institute in 2002 using the Avon design (Stryker corp, UK,) pioneered at the Avon Orthopaedic centre, Southmead, Bristol, UK. We report retrospective analysis of 43 consecutive Patellofemoral replacements done in 39 patients between 2002 and 2006, with a minimum of 6 months follow-up. 38 patients (5 bilateral) were available for review while 1 patient died 3 years after the operation following unrelated causes. They were all assessed clinically and radiologically on the last follow up. Follow-up ranged from 6 to 56 months, average being 21 months. Females outnumbered males by 3:1. All patients were scored pre and postoperatively using Melbourne Knee scoring system (Bartlett et al) and Knee Functional Score. The average Melbourne Knee score increased from 10 to 25 postoperatively, while the knee functional score increased from 57 to 85. Postoperative flexion ranged from 100–140°, average being 116°. Commonest complication was clicking (17%), half of which resolved by arthroscopic lateral release. 87% patients graded the result as excellent or good, while 2% (1 patient) rated it as poor. 59% patients had radiologically proven early tibiofemoral arthritis preoperatively, out of which progression was noted in 28% at the last follow-up. No complications related to deep infection or loosening were noted, and one knee needed revision on account of progression of lateral compartment arthritis. With revision as the end point, the survivorship was 97.7% at average of 2 years after surgery

Advanced 3D imaging and CT-based navigation have emerged as valuable tools to use in total knee arthroplasty (TKA), for both preoperative planning and the intraoperative execution of different philosophies of alignment. Preoperative planning using CT-based 3D imaging enables more accurate prediction of the size of components, enhancing surgical workflow and optimizing the precision of the positioning of components. Surgeons can assess alignment, osteophytes, and arthritic changes better. These scans provide improved insights into the patellofemoral joint and facilitate tibial sizing and the evaluation of implant-bone contact area in cementless TKA. Preoperative CT imaging is also required for the development of patient-specific instrumentation cutting guides, aiming to reduce intraoperative blood loss and improve the surgical technique in complex cases. Intraoperative CT-based navigation and haptic guidance facilitates precise execution of the preoperative plan, aiming for optimal positioning of the components and accurate alignment, as determined by the surgeon’s philosophy. It also helps reduce iatrogenic injury to the periarticular soft-tissue structures with subsequent reduction in the local and systemic inflammatory response, enhancing early outcomes. Despite the increased costs and radiation exposure associated with CT-based navigation, these many benefits have facilitated the adoption of imaged based robotic surgery into routine practice. Further research on ultra-low-dose CT scans and exploration of the possible translation of the use of 3D imaging into improved clinical outcomes are required to justify its broader implementation. Cite this article: Bone Joint J 2024;106-B(9):892–897

We studied the anatomy of the patellofemoral joint in the axial plane on cryosections from a cadaver knee and on MR arthrotomograms from 30 patients. The cryosections revealed differences in the geometry and anatomy of the surface of the articular cartilage and corresponding subchondral osseous contours of the patellofemoral joint. On the MR arthrotomograms the surface geometry of the cartilage matched the osseous contour of the patella in only four of the 30 knees. The articular cartilaginous surface of the intercondylar sulcus and corresponding osseous contour of the femoral trochlea matched in only seven knees. Since MR arthrotomography can distinguish between the surface geometry of the articular cartilage and subchondral osseous anatomy of the patellofemoral joint, it allows the surgeon and the radiologist to appraise the true articulating surfaces. We therefore recommend MR arthrotomography as the imaging technique of choice

To assess the clinical outcomes of patients undergoing ACI in the patellofemoral joint. Level of evidence. Therapeutic study, Level II-1 (prospective cohort study). In a prospective study to determine the clinical effectiveness of autologous chondrocyte implantation 130 patients reached a minimum follow up of two years (range, 2–9 years, average 56.5 months) after treatment involving the patellofemoral articulation. There were 77 men (59%) and 53 women (41%) with an average age of 37.5 years (range, 15-57years). The treatment groups included I) isolated patella, n = 14; II) isolated trochlea, n = 15; III) patella plus trochlea, n = 5; IV) weight bearing condyle plus patella n = 19; V) weight bearing condyle plus trochlea, n = 52; VI) weight bearing condyle plus patella plus trochlea n = 25. The average surface area per patella, n = 63, was 4.72 cm2 and per trochlea, n = 98, was 5.8cm2. The average resurfacing per knee, n = 130, was 11.03cm2. This prospective outcome study demonstrated a significant postoperative improvement in quality of life as measured by the SF-36; WOMAC, Knee Society Score, modified Cincinnati Score and a patient satisfaction survey. There were 16 failures (12%) as a result of a patella or trochlea failure. Eighty percent of patients rated their outcomes as good or excellent, 18% rated outcome as fair, and 2% rated outcome as poor. ACI is effective in the patellofemoral joint and specifically is a complementary intervention for those patients that will predictably do poorly with an isolated Fulkerson Tibial Tubercle osteotomy

We report our experience with LCS Patellofemoral joint replacement. Between September 2003 and November 2007, 66 consecutive patients were reviewed retrospectively who underwent LCS patellofemoral joint replacement. There were 13 males and 51 females with a mean age of 61.6 years (range 43–78). The average follow-up was 22 months (range 11–51 months). To assess the outcome, revision for any cause was taken as the end point for this study. A total of 14 (21.2%) revision operations were carried out at an average of 15.6 months (range 8–29 months) from the initial operation. The reasons for revision were mal-tracking of patella (3), dislocated patellar button (2), persistent unexplained pain (5) and progression of arthritis (4). Amongst the remaining 52 patients, 8 are still experiencing pain and not entirely satisfied with the procedure. 42 patients (63%) have a satisfactory outcome so far. All of them who underwent revision to a total knee replacement were satisfied with their outcome with relief in their symptoms. Revision to a total knee replacement is not a straightforward procedure, especially removing the metal backed patellar component. The revision rate of over 21% is unacceptably high to recommend the procedure as a routine. Based on our experience, we conclude that LCS patellofemoral replacement should be used with caution

Aims. Classifying trochlear dysplasia (TD) is useful to determine the treatment options for patients suffering from patellofemoral instability (PFI). There is no consensus on which classification system is more reliable and reproducible for the purpose of guiding clinicians’ management of PFI. There are also concerns about the validity of the Dejour Classification (DJC), which is the most widely used classification for TD, having only a fair reliability score. The Oswestry-Bristol Classification (OBC) is a recently proposed system of classification of TD, and the authors report a fair-to-good interobserver agreement and good-to-excellent intraobserver agreement in the assessment of TD. The aim of this study was to compare the reliability and reproducibility of these two classifications. Methods. In all, six assessors (four consultants and two registrars) independently evaluated 100 axial MRIs of the patellofemoral joint (PFJ) for TD and classified them according to OBC and DJC. These assessments were again repeated by all raters after four weeks. The inter- and intraobserver reliability scores were calculated using Cohen’s kappa and Cronbach’s α. Results. Both classifications showed good to excellent interobserver reliability with high α scores. The OBC classification showed a substantial intraobserver agreement (mean kappa 0.628; p < 0.005) whereas the DJC showed a moderate agreement (mean kappa 0.572; p < 0.005). There was no significant difference in the kappa values when comparing the assessments by consultants with those by registrars, in either classification system. Conclusion. This large study from a non-founding institute shows both classification systems to be reliable for classifying TD based on axial MRIs of the PFJ, with the simple-to-use OBC having a higher intraobserver reliability score than that of the DJC. Cite this article: Bone Jt Open 2023;4(7):532–538

Introduction. Anterior knee pain following total knee arthroplasty continues to be prevalent and may result from abnormal loading of the patellofemoral joint. The kinematics and biomechanics of the patellofemoral joint are complex, and trochlear design likely plays a principle role in affecting patellofemoral contact. As such, understanding the implications of trochlear design on patellofemoral contact remains important. The goal of the present study was to characterize trochlear wear of retrieved femoral components, which may help elucidate the details regarding patellofemoral kinematics and contact properties in relation to design features. Materials and Methods. Retrieved femoral components featuring a single design (cobalt-chrome, posterior stabilized, cemented components with fixed bearing design) were included in the study. Components were selected based on similar time-in-vivo, age, and BMI. The trochlea of femoral components was consistently divided into six equal zones. Trochlear wear and surface damage in each zone were assessed using visual inspection under low-magnification light microscopy and light profilometry. Results. Ten implants were selected and were used for the topographical analysis. The implants were selected based on time-in-vivo (33.6 months±18), BMI (40.4 kg/m. 2. ±13.2), patient age (67.9 years old±13.3) and gender (6 males, 4 females). Revision diagnosis across the implants were infection (n=6), instability (n=2), loosening (n=1), and fracture (n=1). All zones of the trochlea of retrieved femoral components showed evidence of wear on visual assessment, however, surface profilometry showed that the amount of wear in the retrieved components was not significantly different from a new, unused reference component (p>0.05). In fact, surface skeweness was higher in the new component (p=0.026). Modes of wear included scratches (100%), striations (65%), pitting (43%), and delamination (13%). Zone 1, which includes the raised lateral flange, tended to have more damage than the other zones, but this was statistically non-significant (p=0.634). No significant differences were found between the remaining trochlear zones with respect to wear based on visual assessment and light-microscopy (p=0.634) or surface profilometry (p=0.469). No significant differences were found with between proximal and distal wear (p>0.05) as well as medial and lateral trochlear wear (p>0.05). Conclusions. Femoral components exhibit trochlear wear after in-vivo use. The amount of wear, however, is not substantially different from its new state and may represent early polishing. While the raised lateral flange zone trended towards greater wear than other zones, this was not statistically significant. Overall, with modern trochlear design, there was no evidence of asymmetric or abnormal loading of the trochlea. Longer term retrieval studies are required to assess patterns of femoral component wear and determine the clinical correlation of these findings

The aim of this study was to document the thickness of the patellofemoral joint before and after unicompart-mental joint replacement and to correlate these data with knee outcome scores. Seventeen patients (22 knees) who underwent Patello-femoral replacement with FPV (Wright Medical) prosthesis between 2006 and 2008 were identified retrospectively and analyzed using chart and radiological review. Oxford and AKSS knee scores were gathered prospectively pre-operative and at follow-up. Trochlear height was measured using lateral radiograph of the knee by measuring the distance between anterior distal femoral cortex and the highest point of trochlea. Trochlear height was compared pre and postoperatively. The range of movement and the Oxford and American knee society knee scores at six weeks postoperatively were noted. Association between increased trochlear height and improved range of motion was studied. All but two patients regained full knee extension. Postoperative mean range of flexion of the knee joint was 114 degrees. The mean Oxford knee score at 6 weeks postoperatively was 21 points. The mean American Knee Society Knee Score was 85 points and function score 60 points. We found the average trochlear height to be 6.2 mms pre and 9.7 mms post operatively with an average increase of 3.5 mms. We found no relationship between range of motion of the knee and knee function and trochlear height. This is important because there has been concern that ‘overstuffing’ of the patellofemoral joint can lead to stiffness and failure of resolution of pain post-operatively. Rather it appears that the FPV prosthesis restores the previous anatomical thickness of this compartment. We conclude that FPV Patello-femoral replacement results in correct anatomical reconstruction of the trochlear height. This should in turn result in durable improvements in pain and function

Materials and Methods: The institution’s prospective database of unicompartmental knee replacements was reviewed for all Oxford Phase III Unicompartmental Knee Replacement (Biomet, UK) undertaken from January 2004 to July 2007. This identified a total of 645 procedures undertaken. We included all cases where there was pre-operative skyline radiographs and American Knee Scores, Oxford Knee Score and SF-12 data, in addition to skyline radiographs, OKS and SF-12 data with a minimum of 2 years follow-up. All patients without this baseline and follow-up data were excluded. This provided a total of 196 knees (162 patients). Using Altman’s nomogram, the sample size was calculated to be 85 for a power of 90%, with an α significance level of 0.05. Using this database, digital radiographs were assessed using the institution’s PACS system. Pre-operative and follow-up skyline radiographs following Jones et al’s (1993) patellofemoral scoring system were examined by four assessors utilising Jones’ patellofemoral scoring system. In addition, in cases where patellofemoral joint changes were evident, each assessor acknowledged whether this involved the medial, lateral or bilateral aspects of the patellofemoral joint. Intra-observer reliability was made comparing the four assessors. Statistical analysis was performed, using the Statistical Package for the Social Sciences (SPSS) 16.0 for Windows (SPSS Inc, Chicago, Illinois). In order to determine whether changes in patellofemoral joint status related to patients function or quality of life, the difference in OKS and SF-12 from pre-operative to the follow-up period was assessed. Results: There was a statistically significant progression of patellofemoral osteoarthritis as found on the preoperative and postoperative radiographs (p< 0.01, Mann Whitney), there was a correlation between a low OKS and Jones patellofemoral score (P< 0.05, Mann-Whitney). However, there was no correlation between the site of patellofemoral involvement and outcome scores. Conclusion: Due consideration should be taken when offering medial unicompartmental knee replacement to patients with patellofemoral involvement and this is independent of the site of patellofemoral involvement

Aims. It is not clear whether anterior knee pain and osteoarthritis (OA) of the patellofemoral joint (PFJ) are contraindications to medial unicompartmental knee arthroplasty (UKA). Our aim was to investigate the long-term outcome of a consecutive series of patients, some of whom had anterior knee pain and PFJ OA managed with UKA. Patients and Methods. We assessed the ten-year functional outcomes and 15-year implant survival of 805 knees (677 patients) following medial mobile-bearing UKA. The intra-operative status of the PFJ was documented and, with the exception of bone loss with grooving to the lateral side, neither the clinical or radiological state of the PFJ nor the presence of anterior knee pain were considered a contraindication. The impact of radiographic findings and anterior knee pain was studied in a subgroup of 100 knees (91 patients). Results. There was no relationship between functional outcomes, at a mean of ten years, or 15-year implant survival, and pre-operative anterior knee pain, or the presence or degree of cartilage loss documented intra-operatively at the medial patella or trochlea, or radiographic evidence of OA in the medial side of the PFJ. In 6% of cases there was full thickness cartilage loss on the lateral side of the patella. In these cases, the overall ten-year function and 15-year survival was similar to those without cartilage loss; however they had slightly more difficulty with descending stairs. Radiographic signs of OA seen in the lateral part of the PFJ were not associated with a definite compromise in functional outcome or implant survival. Conclusion. Severe damage to the lateral side of the PFJ with bone loss and grooving remains a contraindication to mobile-bearing UKA. Less severe damage to the lateral side of the PFJ and damage to the medial side, however severe, does not compromise the overall function or survival, so should not be considered to be a contraindication. However, if a patient does have full thickness cartilage loss on the lateral side of the PFJ they may have a slight compromise in their ability to descend stairs. Pre-operative anterior knee pain also does not compromise the functional outcome or survival and should not be considered to be a contraindication. Cite this article: Bone Joint J 2017;99-B:632–9

From September 1995 to March 2003, 15 patellofemoral joint replacements were done on 13 patients. The mean age of the one man and 12 women was 62 years. Osteoarthritis was the reason for surgery in 13 of the 15 knees. In the other two it was post-traumatic arthritis. Three different products were used: Avon (eight), Link Lubinus (five) and LCS patellofemoral prostheses (two). One patient has subsequently been revised to a total knee replacement. Recommendations are made regarding selection of patients and implants

We investigated the association between the radiological findings and the symptoms arising from the patellofemoral joint in advanced osteoarthritis (OA) of the knee. Four radiological features, joint space narrowing, osteophyte formation, translation of the patella and focal attrition were assessed in 151 consecutive osteoarthritic knees in 107 patients undergoing total knee replacement. The symptoms which were assessed included anterior knee pain which was scored, the ability to rise from a chair and climb stairs, and quadriceps weakness. Among the radiological features, only patellar translation and obliteration of the joint space had a statistically significant association with anterior knee pain (odds ratio (OR) 4.85; 95% confidence interval (CI) 1.83 to 12.88 and OR 11.23; 95% CI 2.44 to 51.62) respectively. Patellar translation had a statistically significant association with difficulty in rising from a chair (OR 9.06; 95% CI 1.75 to 45.11). Other radiological features, including osteophytes, joint space narrowing, and focal attrition had no significant association. Our study indicates that the radiological findings of patellar translation and significant loss of cartilage are predictive of patellofemoral symptoms and functional limitation in advanced OA of the knee

Aims. Bi-unicondylar arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL)-preserving alternative to total knee arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA. Methods. Bi-UKA subjects (n = 22) were measured on an instrumented treadmill, using standard gait metrics, at top walking speeds. Age-, sex-, and BMI-matched healthy (n = 24) and primary TKA (n = 22) subjects formed control groups. TKA subjects with preoperative patellofemoral or tricompartmental arthritis or ACL dysfunction were excluded. The Oxford Knee Score (OKS) and EuroQol five-dimension questionnaire (EQ-5D) were compared. Bi-UKA, then TKA, were performed on eight fresh frozen cadaveric knees, to investigate knee extensor efficiency under controlled laboratory conditions, using a repeated measures study design. Results. Bi-UKA walked 20% faster than TKA (Bi-UKA mean top walking speed 6.7 km/h (SD 0.9),TKA 5.6 km/h (SD 0.7), p < 0.001), exhibiting nearer-normal vertical ground reaction forces in maximum weight acceptance and mid-stance, with longer step and stride lengths compared to TKA (p < 0.048). Bi-UKA subjects reported higher OKS (p = 0.004) and EQ-5D (p < 0.001). In vitro, Bi-UKA generated the same extensor moment as native knees at low flexion angles, while reduced extensor moment was measured following TKA (p < 0.003). Conversely, at higher flexion angles, the extensor moment of TKA was normal. Over the full range, the extensor mechanism was more efficient following Bi-UKA than TKA (p < 0.028). Conclusion. Bi-UKA had more normal gait characteristics and improved patient-reported outcomes, compared to matched TKA subjects. This can, in part, be explained by differences in extensor efficiency. Cite this article: Bone Joint Res 2021;10(11):723–733

Aim: The aim of this study was to asses the accuracy of skyline radiographs in the assessment of the patellofemoral joint, when compared to open intraoperative assessment. Methods: Eighty nine patients undergoing knee replacement surgery were included in the study. Skyline radiographs were obtained preoperatively. These radiographs were assessed and graded by an experienced musculoskeletal radiologist using the Altman and Ahlbäck classifications. The grades were calculated for both the medial and lateral facets of the PFJ. Intraoperative assessment of the Patellofemoral joint was undertaken at the time of surgery. The damage was graded using the modified Collins classification (0: Normal, 1: Superficial damage, 2: Partial thickness cartilage loss, 3: Focal Full thickness cartilage loss < 2cm2, 4: Extensive full thickness cartilage loss < 2cm2). Data was obtained for the Medial Facet, Lateral Facet and Trochlea. Results: Spearman’s rank correlation coefficient between the radiographic and macroscopic changes within the lateral PFJ were poor with both the Altman 0.22 (p=0.0350) and Ahlbäck 0.24 (p=0.018). The correlation of the medial PFJ was slightly better with a coefficient for Altman 0.42 (P< 0.0001) and Ahlbäck 0.34 (P> 0.001). Conclusion: In conclusion skyline radiographs provide a poor to moderate preoperative assessment of the degree of osteoarthritis within the patella-femoral joint. This has significant implications for establishing radiographic criteria for planning patella-femoral joint replacement

In some regions in Asia or Arab, there are lifestyles without chair or bed and sitting down on a floor directly, by flexing their knee deeply. However, there are little data about the joint angles, muscle forces or joint loads at such sitting postures or descending to and rising from the posture. In this study, we report the knee joint force and the muscle forces of lower limb at deep squatting and kneeling postures. The model to estimate the forces were constructed as 2D on sagittal plane. Floor reacting force, gravity forces and thigh-calf contact force were considered as external forces. And as the muscle, rectus and vastus femoris, hamstrings, gluteus maximus, gastrocnemius and soleus were taken into the model. The rectus and vastus were connected to the tibia with patella and patella tendon. First the muscle forces were calculated by the moment equilibrium conditions around hip, knee and ankle joint, and then the knee joint force was calculated by the force equilibrium conditions at tibia and patella. For measuring the acting point of the floor reacting force, thigh-calf contact force and joint angles during the objective posture, we performed the experiments. The postures to be subjected were heel-contact squatting (HCS), heel-rise squatting (HRS), kneeling and seiza (Japanese sedentary kneeling), as shown in the Fig.1. The test subjects were ten healthy male, and the average height was 1.71[m], weight was 66.1[kgf] and age was 21.5[years]. The thigh-calf contact force and its acting point were measured by settling the pressure distribution sensor sheet between thigh and calf. Results were normalized by body weight, and shown in Fig.1. The thigh-calf contact force was the largest at the heel-rise squatting posture (1.16BW), and the smallest at heel-contact squatting (0.60BW). The patellofemoral and the tibiofemoral joint forces were shown in the figure. Both forces were the largest at the heel-contact squatting, and were the smallest at the seiza posture. And it might be estimated that the thigh-calf contact force acted anterior when the ankle joint dorsiflexed, and the force was larger when the hip joint extended. The thigh-calf contact force might be decided by not only the knee joint angle but also the hip and ankle joints. As a limitation of this study, we should mention about the effect of the neglected soft tissues. It could be considerable that the compressive internal force of the soft tissues behind a knee joint substance the tibiofemoral force, and then the real tibiofemoral force might be smaller than the calculated values in this study. Then, the tensile force of quadriceps also might be smaller, and then the patellofemoral joint force is also small

Normal function of the patellofemoral joint is maintained by a complex interaction between soft tissues and articular surfaces. No quantitative data have been found on the relative contributions of these structures to patellar stability. Eight knees were studied using a materials testing machine to displace the patella 10 mm laterally and medially and measure the force required. Patellar stability was tested from 0° to 90° knee flexion with the quadriceps tensed to 175 N. Four conditions were examined: intact, vastus medialis obliquus relaxed, flat lateral condyle, and ruptured medial retinaculae. Abnormal trochlear geometry reduced the lateral stability by 70% at 30° flexion, while relaxation of vastus medialis obliquus caused a 30% reduction. Ruptured medial retinaculae had the largest effect at 0° flexion with 49% reduction. There was no effect on medial stability. There is a complex interaction between these structures, with their contributions to loss of lateral patellar stability varying with knee flexion

Patellofemoral complications in total knee arthroplasty (TKA) are common. Patellar tracking can be adversely affected by component positioning, soft tissue imbalance and bony deformity. Lateral patellar release rates reported in the literature vary from 6– 40%. Computer assisted surgery has largely been confined to the tibio-femoral component of total knee replacement. However, with recently developed software, it can be used to visualise and quantify patellar tracking and thus guide the precise extent and site of lateral patellar release. The aim of this early study was to define the diagnostic envelope for identification and quantisation of patella maltracking using a current generation patella navigation system. Our previous prospective analysis of 100 patients undergoing primary TKA identified pre-operative radiographic indices that correlate with maltracking of the patellofemoral joint. 20 cases were subsequently selected for computer assisted total knee replacement surgery. The navigation system (Vector Vision (BrainLab) version 1.6) was used to achieve accurate alignment and position of the femoral and tibial components. All knee replacements were performed using a posterior cruciate-retaining prosthesis. The femoral component was of a ‘patella-friendly’ design with inbuilt 3 degrees external rotation, and the patella was resurfaced in all cases with a biconvex inlay patellar prosthesis. Patellar tracking was assessed intra-operatively using an additional patellar array and patella tracking-specific software. Real-time displays of patella shift, tilt, rotation and circle radii during multiple flexion-extension cycles were obtained. Where necessary, an ‘outside-to-in’ release of the lateral retinacular complex was performed. The navigation system was used to provide contemporaneous feedback on the effect of the soft tissue releases on the tracking characteristics of the patella component on the prosthetic trochlea. Primary outcomes included the sensitivity and specificity of the system for peri-operative patella maltracking; secondary outcomes included the definition of interventional endpoints and correlation of intra-operative tracking data with post-operative x-rays. The demographic data for the 20 patients enrolled in this study was essentially unremarkable. As compared to standard intra-operative clinical evaluation of patella tracking, the computer navigation system is equally sensitive and specific, and it can potentially detect more subtle instances of maltracking that may elude conventional clinical evaluation. We present patterns of patellar tracking during the surgery for patient with and without pre-operative patellar maltracking. However, the significance of this is unknown without longer-term outcome data. Patella shift abnormalities that were detected by the system, but not tilt, correlated with clinical judgement of patella maltracking (p< 0.05). Soft tissue balancing of the patella can now be performed by observing precise changes in shift and tilt. This can be as important as component alignment for optimising patellar tracking and minimising patellofemoral complications

Since 1987, autologous chondrocyte implantation (ACI) has been performed in Gothenburg, Sweden in more than 1600 patients. Out of the first 442 patients operated with ACI, 153 (35%) had patella lesions and 91 (21%) had trochlea lesions. Forty two patients (9.5%) had kissing lesions of the patellofemoral joint. The aim of the study was to evaluate the current clinical status of operated patients. Lysholm and Tegner-Wallgren self-assessment questionnaires were used. The patients were requested to compare their current status to previous states and to report whether they would do the operation again. Concomitant realignment procedures of the patellofemoral joint were also recorded and preoperative scores were also assessed from the medical files. Patients were divided into groups according to the location of lesion. All the groups showed a significant improvement compared with the preoperative assessment. Over 90% of the treated patients were satisfied with the ACI and would have undergone the procedure again. It seems that correcting the coexisting background factors with realignment, stabilizing or unloading procedures is improving the results over time. Despite the initial controversy about the results and indication for ACI in patellofemoral lesions, it is clear that ACI provides a satisfactory result even for the difficult cases with concomitant patellar instability. Our study reveals preservation of the good results and of high level of patients’ activities, even 10 to 20 years after the implantation

Traditionally, the results of autologous chondrocyte implantation (ACI) in the patellofemoral joint have been considered inferior to those in the weightbearing femoral condyles. This study investigated the clinical effectiveness of patellofemoral ACI in a large, single-surgeon cohort. This study reviewed prospectively collected data of patients treated with ACI for defects of the trochlea and/ or patella with a minimum follow-up of 2 years. Clinical outcomes were evaluated by SF-36; WOMAC, Knee Society Score, modified Cincinnati Score and a patient satisfaction survey. 130 patients reached a minimum follow-up of 2 years (2–9 years, average 56.5 months) after treatment involving the patellofemoral articulation. There were 77 men (59%) and 53 women (41%), the average age at the time of implantation was 37.5 years (15–57 years). The treatment groups included. isolated patella (n = 14);. isolated trochlea (n = 15);. patella plus trochlea (n = 5);. weight-bearing condyle plus patella (n = 19);. weightbearing condyle plus trochlea (n = 52);. weightbearing condyle plus patella plus trochlea (n = 25). The average surface area of patellar and trochlear defects was 4.7 cm2 (n = 63) and 5.8 cm2 (n = 98), respectively. The average resurfacing per knee was 11 cm2. There were 16 failures (12%) that could be attributed to a patellar or trochlear defect. 80% of patients rated their outcome as good or excellent, 18% rated their outcome as fair, and 2% rated outcome as poor. ACI of the patellofemoral articulation provided a Significant improvement in quality of life as measured by functional scores and patient satisfaction survey. The failure rate was comparable to ACI used in other locations, such as the weightbearing femoral condyles

Purpose of the study: Kinetic studies of total knee arthroplasty (TKA) in vivo have provided divergent data but have agreed on one point: knee kinetics is abnormal after TKA. Restitution of a normal kinetics is thus the goal to reach to improve functional outcome after TKA. The Journey. ®. TKA is specifically designed to induce automatic medial rotation of the tibia during flexion. This would align the extensor system during flexion and would reduce mediolateral shear forces applied to the patellofemoral joint. Fluoroscopic dynamic studies have been conducted in vivo to confirm the reality of the femorotibal kinematics but to date there has been no study of the patellofemoral kinematics. Magnetic resonance imaging (MRI) is the gold standard for exploring the knee. The important artefacts caused by metal implants made of chromium-cobalt alloys make it difficult or impossible to interpret the images in patients with TKA. Oxinium. ®. implants are weakly ferromagnetic, allowing the development of a specific MRI sequence which can be used to explore a TKA. Material and methods: We used this technique in vivo for a 3D exploration of the patellofemoral kinematics of six Jouney. ®. TKA in comparison with five Genesis II. ®. TKA with preservation of the posterior cruciate ligament and with 13 normal knees. We analysed: patellofemoral surface area of contact, patellar translation and shift during weight-bearing flexion. Results: The results showed that the patellofemoral kinematics of the Journey. ®. TKA are close to that observed in normal knees and that the patellofemoral pressures of the posterior cruciate ligament TKA are significantly higher than with the Journey. ®. TKA. Discussion: These findings confirm our initial hypothesis and allow hop for better functional outcome and reduced wear of the patellar implant with the Journey. ®. TKA

Purpose. Little information is available relating to patient demographics, reasons for failure and types of implants used at time of revision following failure of patellofemoral joint (PFJ) replacement. Methods and Results. Using data extracted from the NJR a series of 128 PFJ revisions in whom the index primary procedure was also recorded in the NJR were identified. This cohort therefore represents early failures of PFJ replacements revised over a 2 year period which were implanted after April 2003 and included revisions of 11 different brands of PFJ replacement from 6 different manufacturers. The median age at primary procedure was 59.0 (Range 21.1 to 83.2) of which 43 patients were <55 years old (31 males, 97 females). 19% of the revisions were performed in the first year after implantation, in the second year in 33 cases (26%), in the third year in 39 cases (31%) and between years 4 to 7 in 32 patients (25%). The commonest reasons for revision were pain (35%), aseptic loosening (18%), subluxation, dislocation or instability (11%), PE wear (7%) and component malalignment (6%). No reason for revision was stated in 30% and only 2 cases were revised for infection. Reason for revision differed according to year of failure but was consistent with respect to age at primary surgery. PFJ revision reason differed from those stated for revisions of primary UKR and TKR from the same period with pain being more prevalent and aseptic loosening and infection being less prevalent in the PFJ group. Single stage revision was performed in 124 cases and 118 underwent cemented revision. Conclusion. Limited data exists on the demographics and outcome for patellofemoral arthroplasty revision. This study is the first to identify reasons for failure in a large cohort and relate such to duration of primary component

Patellofemoral Pain Syndrome is characterized by anterior knee pain during activities such as squatting that is thought to be caused by abnormal patellar motion. However, the causative role has yet to be verified since it is difficult to measure the three-dimensional kinematics of the patellofemoral joint (PFJ) in vivo. We developed a fluoroscopy-based method to measure patellar motion as it moves under load through a cycle of flexion and compared the results with those obtained using Roentgen Stereophotogrammetric Analysis (RSA). Our data suggest that the fluoroscopy-based method has sufficient accuracy to detect clinically significant differences in patterns of patellar motion. The purpose of our study was to determine how accurately a fluoroscopy-based method measures patellar tracking. Our method measures three-dimensional PFJ kinematics with sufficient accuracy to be of clinical value in assessing dynamic motion. Patellar tracking can be assessed during aggravating activities to identify specific tracking abnormalities related to anterior knee pain. Four cadaver knees were imaged using computed tomography (CT). Surface models were generated and the coordinates of implanted tantalum beads (in the femur, patella, and tibia) were determined. A series of fluoroscopic images were taken with the knees loaded in a rig at various flexion angles. Each calibrated fluoroscopic image was registered to the CT model using a point-based method such that the high-resolution CT model was matched to the position of knee flexion associated with each fluoroscopic image. The patellar orientation and position relative to the femur was then reconstructed and described using a gyroscopic joint coordinate system. Measurements were made under the same test conditions using the established uniplanar RSA technique. Fluoroscopy-based and RSA-based measures of patellar orientation and position were compared. The mean measurement error (SD) for patellar flexion, spin, and tilt was 1.86 (1.55), 1.16 (1.14), and 1.15 (1.10) degrees, respectively. For proximal, lateral and anterior patellar translation, the mean measurement error (SD) was 2.11 (2.16), 0.59 (0.47), and 1.24 (1.18) mm, respectively. The accuracy of the fluoroscopy-based method of measuring PFJ kinematics was poorer than the reported accuracy of RSA but appears to be sufficiently low to be of clinical value. Funding: Supported by an operating grant from the Canadian Institutes for Health Research and a Strategic Grant from the Natural Sciences and Engineering Research Council. NJM is supported by TAS/CIHR Partnership Fund

The patella is a complex sesamoid bone within the quadriceps enhancing mechanical advantage of the extensor mechanism. Depending on activity, the patella magnifies either force or displacement; behaving as a lever, by redirecting quadriceps force it also acts as a pulley. Aim. We describe and validate a device for obtaining consistent dynamic weight bearing views of the patellofemoral joint (PFJ). Materials and Methods. Weight bearing (WB) axial views of 48 knees (24 patients) were performed using the device. The sulcus angle (SA), congruence angle (CA), lateral patellofemoral angle (LPFA), facet angle (FA) and patellofemoral displacement (PD) were measured. These were compared with similar measurements made on prone (PR) and axial (AX) radiographs of same knees. Results. Variance (V=SD2) and Standard error of mean (SEM/95% CI) for all measurements in each of the three views were analysed. For the Sulcus Angle, Congruence angle and LPFA, the WB view had the lowest SEM and the least variance in comparison to PR and AX views (SEM 1.05/V 30.14, SEM 2.52/V 172.39 and SEM 1.34/V 47.61 respectively for the SA, SEM 3.09/V 256, SEM 2.79/V 210.25 and SEM 3.37/V 306.25 respectively for the CA, SEM 0.67/V 11.9, SEM 1.20/V39.06 and SEM 1.03/V 28.83 respectively for the LPFA). SEM and Variance for FA measurements were similar for WB and AX views but superior to PR views (SEM 1.62/V 70.56, SEM 1.6/V 68.9 and SEM 2.3/V 148.84 respectively). Mean PFD was maximum on the WB view compared to the PR and AX views (36.0, −45.62 and 22.23 respectively) with lowest SEM and V (SEM 8.73/V 2052.0, SEM 18.65/V 92959.67 and SEM 9.70/V 2540.16 respectively). Conclusion. The WB view as introduced and reported here has consistently lower Variance, SEM and SD in comparison to Axial and Prone views for all measurements of the PFJ. WB view also gives a more accurate dynamic measure of Patello Femoral displacement. The view is easily obtained and readily reproduced

Introduction. Malrotation of a femoral component is a cause of patellofemoral maltracking after total knee arthroplasty (TKA). We have developed a balanced gap technique in posterior stabilized total knee arthroplasty (PS-TKA) using an original tensor instrument. One of characteristics of this instrument is the ability to measure gaps even if there is a bone defect, because it has two paddles, and we can attach block augmentations. In addition it can measure the gap after a reduction of the patella with an offset mechanism. In the balanced gap technique, the femoral component rotation is decided by a tibial cut surface and ligaments balance using the tensor device. This study investigated retrospectively whether rotational alignment of femoral component rotation influenced patellofemoral joint congruency in PS- TKA. Material and Methods. We evaluated the radiographs of 52 knees of 42 patients, who underwent TKA (NexGen LPS-Flex, fixed surface, Zimmer) by one surgeon (S.A.) for osteoarthritis or rheumatoid arthritis. All procedures were performed through a medial parapatellar approach and a balanced gap technique using a developed versatile tensor device. We measured lateral patella tilt and lateral patella shift at post-op. 6 months. To assess the rotational alignment of femoral component rotation, condylar twist angle (CTA) was measured, and to assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was measured using the epicondylar view radiographs. Results. We performed the lateral release on 4 knees (7.6%). The average lateral patella tilt and CTA, and LOA were 3.00 ± 3.2°, 0.95 ± 2.5°, 1.50 ± 1°, respectively. There were two cases which had more than 10°tilt. We did not find any case of lateral patella shift. There was no statistical correlation with lateral patella tilt and CTA (r=0.17, p=0.2) (figure 1). There was no statistical correlation with the patella tilt and LOA (r=-0.1, p=0.9) (figure2). The case with 13.4°patella tilt was post-traumatic osteoarthritis (ACL and MCL injury). There were two cases which were cut patella obliquely, and each patella tilt was 13.0°and 3.3°. Discussion. Previously we reported that the rate of a lateral release decreased by a balanced gap technique compared with a conventional measured resection technique. Although the balanced gap technique resulted in a patient's specific wide variability for femoral component rotation, this variable rotation was not found to be associated with abnormal patella tilt and patella shift

We have used CT to describe the geometry of the patel-lofemoral joint and its relationship to the tibiofemoral joint.

33 CT scans of patients without patellofemoral disease were performed. 3D images were reconstructed and measured using computer software. The flexion axis of the tibiofemoral joint was found as the line connecting the centres of the spheres fitted to posterior femoral condyles.

The deepest points on the trochlear groove can be fitted to a circle with radius of 23mm (stdev 4mm) and an rms of 0.3mm. This centre is offset by 21mm (stdev 3mm) at an angle of 68° (stdev 8°) from the line connecting the midpoint between the centres of the femoral condyles and a point in the piriform fossa.

On either side of this line, the articular surface of the trochlea can be fitted to spheres of radius 30mm (stdev 6mm) laterally and 27mm (stdev 5mm) and an rms of 0.4mm medially. The centres of the circle and the two spheres fall on a line with an rms of 1.1mm.

The anterior and proximal patellar planes could be described as flat surfaces (rms of 0.4 and 0.3mm). The median ridge could be described as a straight line (rms of 0.2mm). The angle between planes was 112° (stdev 5°); the average angle between the proximal plane and the line on the medial ridge was 62° (stdev4°).

The length, width and thickness of the patellae were measured at 34.2mm +/−4mm, 44.8mm +/− 4.8mm and 22.4 mm+/− 2.3 mm (table).

This investigation has allowed us to characterise the patello-femoral joint geometry which may help identify and explain the aetiology of patello-femoral pathologies. It may have implications for the design of patello-femoral replacements and the rules governing their position.

Aims

The Oswestry-Bristol Classification (OBC) was recently described as an MRI-based classification tool for the femoral trochlear. The authors demonstrated better inter- and intraobserver agreement compared to the Dejour classification. As the OBC could potentially provide a very useful MRI-based grading system for trochlear dysplasia, it was the aim to determine the inter- and intraobserver reliability of the classification system from the perspective of the non-founder.

Introduction: Progressive symptomatic tibiofemoral arthritis following PFJR is an important cause of failure. This study is designed to quantify radiologically the degree of tibiofemoral disease progression in patients who have undergone PFJR in our institution.

Patients and Methods: A prospective series of 102 consecutive Avon PFJRs in 78 patients with a minimum follow-up of five years was analysed.

Available AP weight bearing radiographs of the knee taken at 8 months and 5 years postoperatively were examined in a random order twice by each of two surgeons who were blinded to the patient details and length of follow up. The severity of arthritis was graded using the classifications of Ahlback and Altman, giving a measure of arthritis progression.

Results and Discussion: Arthritis was seen to progress in 8.5–17% of medial and 11–17% of lateral compartments after PFJR. Statistically significant progression was demonstrated using the Altman but not the less sensitive Ahlback scoring system, suggesting that the former should be used in scoring the tibiofemoral joint prior to PFJR. Of those patients who had a preoperative tibiofemoral Altman score of zero, 87% showed no radiological evidence of disease progression at minimum 5 year follow up, suggesting that these are the ideal candidates for PFJR.

Introduction: We have come across a subset of patients with advanced patellofemoral osteoarthritis who also had well defined full thickness cartilage loss lesions on the weight bearing femoral condyle. In these patients the findings or the symptoms are not severe enough to warrant a total knee replacement. In this select group of patients, a combination of patellofemoral arthroplasty (PFA) and Osteochondral Autograft Transfer System (OATS) can be performed to address this unique problem.

Method& Results: Out of 38 PFA procedures performed by the senior author, a concomitant OATS was performed in 6 knees in 5 patients. A retrospective analysis of these patients was carried out with the average follow up being 3.8 years (18 months to 84 months). The average age of the patients in our case study was 48.2 years (36 to 59 years) at the time of surgery. Four of the six knees are doing well in the medium term. One patient had progression of tibiofemoral arthritis and underwent a total knee replacement. The only poor result was a young male, who two years following the PFA, developed a deep infection of the knee. Except for this patient awaiting a second stage revision for an infected knee, all the others have achieved their desired level of activity.

Conclusion: The advantage of this combination is that, the donor tubes for the OATS can be harvested from the trochlea or just adjacent to it, which happens to be the bed for the trochlear implant. This area provides good quality thick donor articular cartilage. As the surgical exposure has already been done for the PFA, the operative time is extended by approximately ten minutes for the OATS procedure. This combination procedure offers an alternative to more invasive options such as total knee replacement in younger patients in whom it is preferable to delay such major surgery.

Introduction

Patellar tracking in total knee replacements has been extensively studied, but little is known about patellar tracking in isolated patellofemoral replacements. We compared patellar tracking and the position of the patellar groove in the natural knee, followed by implantation of the femoral component of a PFR (patella unresurfaced) and after implantation of the femoral & patellar component of the PFR.

Purpose

The purpose of this study was to examine the progression of osteoarthritis (OA) on patella-femoral joint (PFJ) after open wedge high tibial osteotomy (OWHTO) and unicondylar knee arthroplasty (UKA) in correlation with pain and functional outcomes.

Aims. Unicompartmental knee arthroplasty (UKA) has become a popular method of treating knee localized osteoarthritis (OA). Additionally, the posterior cruciate ligament (PCL) is essential to maintaining the physiological kinematics and functions of the knee joint. Considering these factors, the purpose of this study was to investigate the biomechanical effects on PCL-deficient knees in medial UKA. Methods. Computational simulations of five subject-specific models were performed for intact and PCL-deficient UKA with tibial slopes. Anteroposterior (AP) kinematics and contact stresses of the patellofemoral (PF) joint and the articular cartilage were evaluated under the deep-knee-bend condition. Results. As compared to intact UKA, there was no significant difference in AP translation in PCL-deficient UKA with a low flexion angle, but AP translation significantly increased in the PCL-deficient UKA with high flexion angles. Additionally, the increased AP translation became decreased as the posterior tibial slope increased. The contact stress in the PF joint and the articular cartilage significantly increased in the PCL-deficient UKA, as compared to the intact UKA. Additionally, the increased posterior tibial slope resulted in a significant decrease in the contact stress on PF joint but significantly increased the contact stresses on the articular cartilage. Conclusion. Our results showed that the posterior stability for low flexion activities in PCL-deficient UKA remained unaffected; however, the posterior stability for high flexion activities was affected. This indicates that a functional PCL is required to ensure normal stability in UKA. Additionally, posterior stability and PF joint may reduce the overall risk of progressive OA by increasing the posterior tibial slope. However, the excessive posterior tibial slope must be avoided. Cite this article: Bone Joint Res 2020;9(9):593–600

In the unstable patellofemoral joint (PFJ), the patella will articulate in an abnormal manner, producing an uneven distribution of forces. It is hypothesised that incongruency of the PFJ, even without clinical instability, may lead to degenerative changes. The aim of this study was to record the change in joint contact area of the PFJ after stabilisation surgery using an established and validated MRI mapping technique. A prospective MRI imaging study of patients with a history of PFJ instability was performed. The patellofemoral joints were imaged with the use of an MRI scan during active movement from 0° through to 40° of flexion. The congruency through measurement of the contact surface area was mapped in 5-mm intervals on axial slices. Post-stabilisation surgery contact area was compared to the pre-surgery contact area. In all, 26 patients were studied. The cohort included 12 male and 14 female patients with a mean age of 26 (15–43). The greatest mean differences in congruency between pre- and post-stabilised PFJs were observed at 0–10 degrees of flexion (0.54 cm. 2. versus 1.18 cm. 2. , p = 0.04) and between 11° and 20° flexion (1.80 cm. 2. versus 3.45 cm. 2. ; p = 0.01). PFJ stabilisation procedures increase joint congruency. If a single axial series is to be obtained on MRI scan to compare the pre- and post-surgery joint congruity, the authors recommend 11° to 20° of tibiofemoral flexion as this was shown to have the greatest difference in contact surface area between pre- and post-operative congruency

Aims. To fully quantify the effect of posterior tibial slope (PTS) angles on joint kinematics and contact mechanics of intact and anterior cruciate ligament-deficient (ACLD) knees during the gait cycle. Methods. In this controlled laboratory study, we developed an original multiscale subject-specific finite element musculoskeletal framework model and integrated it with the tibiofemoral and patellofemoral joints with high-fidelity joint motion representations, to investigate the effects of 2.5° increases in PTS angles on joint dynamics and contact mechanics during the gait cycle. Results. The ACL tensile force in the intact knee was significantly affected with increasing PTS angle. Considerable differences were observed in kinematics and initial posterior femoral translation between the intact and ACLD joints as the PTS angles increased by more than 2.5° (beyond 11.4°). Additionally, a higher contact stress was detected in the peripheral posterior horn areas of the menisci with increasing PTS angle during the gait cycle. The maximum tensile force on the horn of the medial meniscus increased from 73.9 N to 172.4 N in the ACLD joint with increasing PTS angles. Conclusion. Knee joint instability and larger loading on the medial meniscus were found on the ACLD knee even at a 2.5° increase in PTS angle (larger than 11.4°). Our biomechanical findings support recent clinical evidence of a high risk of failure of ACL reconstruction with steeper PTS and the necessity of ACL reconstruction, which would prevent meniscus tear and thus the development or progression of osteoarthritis. Cite this article: Bone Joint Res 2022;11(10):739–750

Abstract. Objectives. The aim of this study was to develop an in vitro GAG-depleted patella model and assess the biomechanical effects following treatment with a SAP:CS self-assembling hydrogel. Methods. Porcine patellae (4–6 month old) were harvested and subject to 0.1% (w/v) sodium dodecyl sulfate (SDS) washes to remove GAGs from the cartilage. Patellae were GAG depleted and then treated by injection with SAP (∼ 6 mM) and CS (10 mg) in Ringer's solution through a 30G needle. Native, GAG depleted and SAP:CS treated patellae were tested through static indentation testing, using 15g load, 5mm indenter over 1hr period. The degree of deformation of each group was assessed and compared (Mann-Whitney, p<0.05). Native, GAG depleted, sham (saline only) and SAP:CS treated paired patellae and femurs were additionally characterized tribologically through sequential wear testing when undergoing a walking gait profile (n=6 per group). The cartilage surfaces were assessed and compared (Mann-Whitney, p<0.05) using the ICRS scoring system, surface damage was illustrated through the application of Indian ink. Results. Static indentation tests indicated significant increase in indentation deformation of GAG depleted group compared to native group (n=6, p<0.01) and significant reduction in deformation of SAP:CS treated group compared to GAG depleted group (n=6, p<0.05). Sequential wear tests indicated a significant increase in the cartilage damage on the both surfaces of the patellofemoral joint in the GAG depleted group, compared to the native group (n=6, p<0.001), Following SAP:CS treatment, significant protection from damage was observed on femoral surface (n=6, p<0.005), with some non-significant reduction in damage on the patella surface. Sham injections showed no significant increase in damage compared to the native and treated samples. Conclusions. The ∼50% reduction of GAGs represented a moderate osteoarthritic patella cartilage model. This same loss transferred to the dynamic wear tests with significant changes in the damage on the femoral counter face associated with the GAG loss. SAP:CS treatment showed promise in restoring cartilage stiffness to treat Chondromalacia patella in static indentation tests. Sequential wear tests showed that the SAP:CS treatment protects the cartilage layer of both surfaces in the patellofemoral joint from damage in an extreme degeneration model. The sham injections showed that injecting cartilage with a 30G and saline does not cause any significant damage to the cartilage layer. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Aims. The aim of this study was to evaluate medium-term outcomes and complications of the S-ROM NOILES Rotating Hinge Knee System (DePuy, USA) in revision total knee arthroplasty (rTKA) at a tertiary unit. Methods. A retrospective consecutive study of all patients who underwent a rTKA using this implant from January 2005 to December 2018. Outcome measures included reoperations, revision for any cause, complications, and survivorship. Patients and implant survivorship data were identified through both local hospital electronic databases and linked data from the National Joint Registry/NHS Personal Demographic Service. Kaplan-Meier survival analysis was used at ten years. Results. A total of 89 consecutive patients (89 knees) were included with 47 females (52.8%) and a median age of 74 years (interquartile range 66 to 79). The main indications were aseptic loosening with instability (39.4%; n = 35) and infection (37.1%; n = 33) with the majority of patients managed through two-stage approach. The mean follow-up was 7.4 years (2 to 16). The overall rate of reoperation, for any cause, was 10.1% (n = 9) with a rate of implant revision of 6.7% (n = 6). Only two cases required surgery for patellofemoral complications. Kaplan-Meier implant-survivorship analysis was 93.3% at ten years, using revision for any cause as an endpoint. Conclusion. This implant achieved high ten-year survivorship with a low complication rate, particularly patellofemoral complications. These can be avoided by ensuring central patella tracking and appropriate tension of the patellofemoral joint in this posterior hinge design. Cite this article: Bone Jt Open 2022;3(3):205–210

Introduction. The degree of cartilage degeneration assessed intraoperatively may not be sufficient as a criterion for patellar resurfacing in total knee arthroplasty (TKA). However, single-photon emission tomography/computed tomography (SPECT/CT) is useful for detecting osteoarthritic involvement deeper in the subchondral bone. The purpose of the study was to determine whether SPECT/CT reflected the cartilage lesion underneath the patella in patients with end-stage osteoarthritis (OA) and whether clinical outcomes after TKA without patellar resurfacing differed according to the severity of patellofemoral (PF) OA determined by visual assessment and SPECT/CT findings. Methods. This study included 206 knees which underwent TKA. The degree of cartilage degeneration was graded intraoperatively according to the International Cartilage Repair Society grading system. Subjects were classified into four groups according to the degree of bone tracer uptake (BTU) on SPECT/CT in the PF joint. The Feller's patella score and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were assessed preoperatively and postoperative 1 and 2 years. Results. The increased BTU in the PF joint was associated with more severe degenerative cartilage changes underneath the patella (P < 0.001). The risk for the presence of denudated cartilage was greater in the high uptake group (odds ratio = 5.89). There was no association between clinical outcomes and visual grading of patellar cartilage degeneration or the degree of BTU on SPECT/CT. Discussion and Conclusions. The visual assessment of the degree of cartilage degeneration underneath the patella and preoperative SPECT/CT evaluation of the PF joint were not predictive of clinical outcome after TKA with unresurfaced patella

Patellofemoral joint degeneration is often considered a contraindication to medial unicompartmental knee replacement. We examined the validity of this preconception using information gathered prospectively on the intra-operative status of the patellofemoral joint in 824 knees in 793 consecutive patients who underwent Oxford unicondylar knee replacement for anteromedial osteoarthritis. All operations were performed between January 1998 and September 2005. A five-point grading system classified degeneration of the patellofemoral joint from none to full-thickness cartilage loss. A subclassification of the presence or absence of any full-thickness cartilage loss was subsequently performed to test selected hypotheses. Outcome was evaluated independently by physiotherapists using the Oxford and the American Knee Society Scores with a minimum follow-up of one year. Full-thickness cartilage loss on the trochlear surface was observed in 100 of 785 knees (13%), on the medial facet of the patella in 69 of 782 knees (9%) and on the lateral facet in 29 of 784 knees (4%). Full-thickness cartilage loss at any location was seen in 128 knees (16%) and did not produce a significantly worse outcome than those with a normal or near-normal joint surface. The severity of the degeneration at any of the intra-articular locations also had no influence on outcome. We concluded that, provided there is not bone loss and grooving of the lateral facet, damage to the articular cartilage of the patellofemoral joint to the extent of full-thickness cartilage loss is not a contraindication to the Oxford mobile-bearing unicompartmental knee replacement

There has been debate about the role of unicompartmental knee replacement in the presence of radiologically identifiable degenerative changes of the patellofemoral joint. We studied 195 knees in 163 patients in whom an Oxford unicompartmental knee replacement had been performed for medial osteoarthritis between January 2004 and July 2007. The mean age of the patients was 66 years (51 to 93). The degree of degenerative change of the patellofemoral joint was assessed using Jones’ criteria. Functional outcome was assessed at a mean of 3.4 years (2 to 7) post-operatively, using the Oxford knee score and the Short-form 12 score. Degenerative changes of the patellofemoral joint were seen pre-operatively in 125 knees (64%) on the skyline radiographs. There was no statistically significant difference in the Oxford knee or Short-form 12 scores between those patients who had patellofemoral osteoarthritis pre-operatively and those who did not (p = 0.22 and 0.54, respectively). These results support the opinion expressed at the designer’s hospital that degenerative changes of the patellofemoral joint in isolation should not be considered to be a contraindication to medial Oxford unicompartmental knee replacement

Aims. To report mid- to long-term results of Oxford mobile bearing domed lateral unicompartmental knee arthroplasty (UKA), and determine the effect of potential contraindications on outcome. Methods. A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and the presence of full-thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated. Results. Median follow-up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%); 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing, and 12 (4%) were revised for medial osteoarthritis (OA). Ten-year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival. Conclusion. Domed lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. It is recommended that the stability of the bearing is assessed intraoperatively. If the bearing can easily be displaced, the fixed rather than the mobile bearing version of the Oxford lateral tibial component should be inserted instead. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications. Cite this article: Bone Joint J 2020;102-B(8):1033–1040

Introduction. Instability, loosening, and patellofemoral pain belong to the main causes for revision of total knee arthroplasty (TKA). Currently, the diagnostic pathway requires various diagnostic techniques such as x-rays, CT or SPECT-CT to reveal the original cause for the failed knee prosthesis, but increase radiation exposure and fail to show soft-tissue structures around TKA. There is a growing demand for a diagnostic tool that is able to simultaneously visualize soft tissue structures, bone, and TKA without radiation exposure. MRI is capable of visualising all the structures in the knee although it is still disturbed by susceptibility artefacts caused by the metal implant. Low-field MRI (0.25T) results in less metal artefacts and offers the ability to visualize the knee in weight-bearing condition. Therefore, the aim of this study is to investigate the possibilities of low field MRI to image, the patellofemoral joint and the prosthesis to evaluate the knee joint in patients with and without complaints after TKA. Method. Ten patients, eight satisfied and two unsatisfied with their primary TKA, (NexGen posterior stabilized, BiometZimmer) were included. The patients were scanned in sagittal, coronal, and transversal direction on a low field MRI scanner (G-scan Brio, 0.25T, Esaote SpA, Italy) in weight-bearing and non-weight-bearing conditions with T1, T2 and PD-weighted metal artefact reducing sequences (TE/TR 12–72/1160–7060, slice thickness 4.0mm, FOV 260×260×120m. 3. , matrix size 224×216). Scans were analysed by two observers for:. - Patellofemoral joint: Caton-Descamps index and Tibial Tuberosity-Trochlear Groove (TT-TG) distance. - Prosthesis malalignment: femoral component rotation using the posterior condylar angle (PCA) and tibial rotation using the Berger angle. Significance of differences in parameters between weight-bearing and non-weight-bearing were calculated with the Wilcoxon rank test. To assess the reliability the inter and intra observer reliability was calculated with a two-way random effects model intra class correlation coefficient (ICC). The two unsatisfied patients underwent revision arthroplasty and intra-operative findings were compared with MRI findings. Results. In the satisfied group, a significant difference was found between TT-TG distance in non-weight-bearing and weight-bearing condition (p=0.018), with a good interrater reliability ICC=0.89. Furthermore, differences between weight-bearing and non-weight-bearing were found for the CD ratio, however, not significant (p=0.093), with a good interrater reliability ICC=0.89. The Berger angle could be measured with an excellent interrater reliability (ICC=0.94). The PCA was hard to assess with a poor interrater reliability (ICC=0.48). For one unsatisfied patient a deviation was found for tibial component rotation, according to the perioperative findings as, ‘malposition of the tibial component’. For the other unsatisfied patient revision surgery was performed due to aseptic loosening in which the MRI showed a notable amount of synovitis. Conclusion. It is possible to image the patellofemoral joint and knee prosthesis with low field MRI. Patellofemoral measurements and tibial component rotation measurements can reliably be performed. For the two patients with complaints MRI findings were consistent with intra-operative findings. Further research should focus on a larger group of patients with complaints after TKA to verify the diagnostic capacity of low field MRI for peri-prosthetic knee problems. For any figures or tables, please contact authors directly

The biomechanics of the patellofemoral joint can become disturbed during total knee replacement by alterations induced by the position and shape of the different prosthetic components. The role of the patella and femoral trochlea has been well studied. We have examined the effect of anterior or posterior positioning of the tibial component on the mechanisms of patellofemoral contact in total knee replacement. The hypothesis was that placing the tibial component more posteriorly would reduce patellofemoral contact stress while providing a more efficient lever arm during extension of the knee. We studied five different positions of the tibial component using a six degrees of freedom dynamic knee simulator system based on the Oxford rig, while simulating an active knee squat under physiological loading conditions. The patellofemoral contact force decreased at a mean of 2.2% for every millimetre of posterior translation of the tibial component. Anterior positions of the tibial component were associated with elevation of the patellofemoral joint pressure, which was particularly marked in flexion > 90°. From our results we believe that more posterior positioning of the tibial component in total knee replacement would be beneficial to the patellofemoral joint

Introduction. Traditional applied loading of the knee joint in experimental testing of RTKR components is usually confined to replicating the tibiofemoral joint alone. The second joint in the knee, the patellofemoral joint, can experience forces of up to 9.7 times body weight during normal daily living activities (Schindler and Scott 2011). It follows that with such high forces being transferred, particularly in high flexion situations such as stair climbing, it may be important to also represent the patellofemoral joint in all knee component testing. This research aimed to assess the inclusion of the patellofemoral joint during in vitro testing of RTKR components by comparing tibial strain distribution in two experimental rigs. The first rig included the traditional tibiofemoral joint loading design. The second rig incorporated a combination of both joints to more accurately replicate physiological loading. Five implanted tibia specimens were tested on both rigs following the application of strain gauge rosettes to provide cortical strain data through the bone as an indication of the load transfer pattern. This investigation aimed to highlight the importance of the applied loading technique for pre-clinical testing and research of knee replacement components to guide future design and improve patient outcomes. Methods. Five composite tibias (4th Generation Sawbones) were prepared with strain gauge rosettes (HBM), correctly aligned and potted using guides for repeatability across specimens. The tibias were then implanted with Stryker Triathlon components according to surgical protocol. The first experimental rig was developed to replicate traditional knee loading conditions through the tibiofemoral joint in isolation. The second experimental rig produced an innovative method of replicating a combination of the tibiofemoral and patellofemoral joint loading scenarios. Both rigs were used to assess the load distribution through the tibia using the same tibia specimens and test parameters for comparison integrity (Figure 1). The cortical strains were recorded under an equivalent 500 N cyclical load applied at 10° of flexion by a hydraulic test machine. Results. The average results comparing both experimental rigs at three strain gauge locations are shown in Figure 2. Paired t-tests were performed on all results and a p value of p<0.05 was considered significant. No significant differences were found between the rigs. There was a trend towards a reduction in proximal principal strain with the inclusion of the patellofemoral joint (p=0.058). Discussion. The results of this study indicate that there is no significant difference in tibial load transfer between the traditional and novel applied loading techniques at small flexion angles. There is a trend towards a reduction in proximal strain when including the patellofemoral joint. This reduction may be linked to the patella tendon force counteracting the effect of tibiofemoral loading at this small flexion angle. At high flexion angles the patellofemoral reaction load increases significantly relative to the tibiofemoral load. This will have a significant effect on tibial strains and so it is recommended that testing at higher flexion angles should be performed in a combined loading rig

We have developed a new tensor for total knee replacements which is designed to assist with soft-tissue balancing throughout the full range of movement with a reduced patellofemoral joint. Using this tensor in 40 patients with osteoarthritis we compared the intra-operative joint gap in cruciate-retaining and posterior-stabilised total knee replacements at 0°, 10°, 45°, 90° and 135° of flexion, with the patella both everted and reduced. While the measurement of the joint gap with a reduced patella in posterior-stabilised knees increased from extension to flexion, it remained constant for cruciate-retaining joints throughout a full range of movement. The joint gaps at deep knee flexion were significantly smaller for both types of prosthetic knee when the patellofemoral joint was reduced (p < 0.05)

Chronic patellofemoral instability can be a disabling condition. Management of patients with this condition has improved owing to our increased knowledge of the functional anatomy of the patellofemoral joint. Accurate assessment of the underlying pathology in the unstable joint enables the formulation of appropriate treatment. The surgical technique employed in patients for whom non-operative management has failed should address the diagnosed abnormality. We have reviewed the literature on the stabilising features of the patellofemoral joint, the recommended investigations and the appropriate forms of treatment

The patellofemoral joint is an important source of symptoms in osteoarthritis of the knee. We have used a newly designed surgical model of patellar strengthening to induce osteoarthritis in BALB/c mice and to establish markers by investigating the relationship between osteoarthritis and synovial levels of matrix metalloproteinases (MMPs). Osteoarthritis was induced by using this microsurgical technique under direct vision without involving the cavity of the knee. Degeneration of cartilage was assessed by the Mankin score and synovial tissue was used to determine the mRNA expression levels of MMPs. Irrigation fluid from the knee was used to measure the concentrations of MMP-3 and MMP-9. Analysis of cartilage degeneration was correlated with the levels of expression of MMP. After operation the patellofemoral joint showed evidence of mild osteoarthritis at eight weeks and further degenerative changes by 12 weeks. The level of synovial MMP-9 mRNA correlated with the Mankin score at eight weeks, but not at 12 weeks. The levels of MMP-2, MMP-3 and MMP-14 mRNA correlated with the Mankin score at 12 weeks. An increase in MMP-3 was observed from four weeks up to 16 weeks. MMP-9 was notably increased at eight weeks, but the concentration at 16 weeks had decreased to the level observed at four weeks. Our observations suggest that MMP-2, MMP-3 and MMP-14 could be used as markers of the progression of osteoarthritic change

Summary Statement. This project proves that Patellofemoral (PF) joint degeneration is not a contraindication to medial unicompartmental knee replacement. Introduction. Unicompartmental knee arthroplasty (UKA) is a recognised procedure for treatment of medial compartment osteoarthritis. Patellofemoral (PF) joint degeneration is widely considered to be a contraindication to medial unicompartmental knee replacement. We examined the validity of this preconception using information gathered prospectively on consecutive patients who underwent UKA using the Repicci II® UKA prosthesis for medial compartment osteoarthritis. Methods. We prospectively collected data on 147 consecutive patients who underwent the Repicci II® UKA for medial compartment osteoarthritis. All operations were performed between July 1999 and September 2000 by the same surgeon. The status of the PF joint was assessed intra-operatively in all patients, and accordingly patients were divided into two groups, one group with a normal PF joint, and the second group with degenerative changes of the PF joint. Variables measured for outcome included the International Knee Society (IKS) score, limb alignment, and range of motion. Radiographs were assessed for progression of disease or failure of implant. The mean follow-up was 9.4 years (range: 5–10.7 years). Patients were reviewed initially at 2 weeks, and then at 6 months post-operatively. They were subsequently reviewed on an annual basis.. All patients completed an IKS score preoperatively and at last follow-up. Age, gender, BMI, length of hospital stay, perioperative complications, all subsequent surgery, including revision of the prosthesis, and survivorship at 10 years was recorded, and results of the 2 groups compared. Results. A total of 147 patients were included in the study. None were lost to follow-up. Sixty nine had associated PF osteoarthritis (group A) while 78 patients had a normal PF compartment when assessed intra-operatively (group B). Post-operative outcomes of the two groups were compared using the ANCOVA analysis with adjustment for pre-operation values firstly, and adjusting also for gender, age, BMI and follow-up secondly. There were no significant differences in terms of IKS, alignment, and flexion between the two groups. However, patients in group B had significantly better extension post-operatively than patients in group A (p<0.05). Conclusion. We concluded that damage to the articular cartilage of the patellofemoral joint to the extent of full-thickness cartilage loss is not a contraindication to the Repicci II® unicondylar knee arthroplasty for medial compartment osteoarthritis. However, extension is significantly improved post-operatively in those patients with minimal or no PF joint degenerative disease

There have been a large number of studies reporting the knee joint force during level walking, however, the data of during deep knee flexion are scarce, and especially the data about patellofemoral joint force are lacking. Deep knee flexion is a important motion in Japan and some regions of Asia and Arab, because there are the lifestyle of sitting down and lying on the floor directly. Such data is necessary for designing and evaluating the new type of knee prosthesis which can flex deeply. Therefore we estimated the patellofemoral and tibiofemoral forces in deep knee flexion by using the masculoskeltal model of the lower limb. The model for the calculation was constructed by open chain of three bar link mechanism, and each link stood for thigh, lower leg and foot. And six muscles, gluteus maximus, hamstrings, rectus, vastus, gastrocnemius and soleus were modeled as the lines connecting the both end of insertion, which apply tensile force at the insertion on the links. And the model also included the gravity forces, thigh-calf contact forces on the Inputting the data of floor reacting forces and joint angles, the model calculated the muscle forces by the moment equilibrium conditions around each joint, and some assumptions about the ratio of the biarticular muscles. And then, the joint forces were estimated from the muscle forces, using the force equilibrium conditions on patella and tibia. The position/orientation of each segments, femur, patella and tibia, were decided by referring the literature. The motion to be analyzed was standing up from kneeling posture. The joint angles during the motion are shown in Fig.1. This motion included the motion from kneeling to squatting, rising the knee from the floor by flexing hip joint, and the motion from squatting to standing. The test subject was a healthy male, age 23[years], height 1.7[m], weight 65[kgw]. Results were shown in Fig.2. The patellofemoral force was little at standing posture, the end of the motion, however, was as large as tibiofemoral force during the knee joint angle was over 130 degrees. The reason of this was that the patellofemoral joint force was heavily dependent on the quadriceps forces, and the quadriceps tensile force was large at deep knee flexion, at kneeling or squatting posture. The maximum tibiofemoral force was 3.5[BW] at the beginning of standing up from squatting posture. And the maximum patellofemoral force was 3.8[BW] at the motion from kneeling to squatting posture. The conclusion was that the patellofemoral joint force might not be ignored in deep knee flexion and the design of the knee prosthesis should be include the strength design of patellofemoral joint

Introduction. Unicompartmental knee arthroplasty (UKA) is a recognized procedure for treatment of medial compartment osteoarthritis. Patellofemoral (PF) joint degeneration is widely considered to be a contraindication to medial unicompartmental knee replacement. We examined the validity of this preconception using information gathered prospectively on consecutive patients who underwent UKA using the Repicci II® UKA prosthesis for medial compartment osteoarthritis. Methods. We prospectively collected data on 147 consecutive patients who underwent the Repicci II® UKA for medial compartment osteoarthritis. All operations were performed between July 1999 and September 2000 by the same surgeon. The status of the PF joint was assessed intra-operatively in all patients, and accordingly patients were divided into two groups, one group with a normal PF joint, and the second group with degenerative changes of the PF joint. Variables measured for outcome included the International Knee Society (IKS) score, limb alignment, and range of motion. Radiographs were assessed for progression of disease or failure of implant. The mean follow-up was 9.4 years (range: 5–10.7 years). Patients were reviewed initially at 2 weeks, and then at 6 months post-operatively. They were subsequently reviewed on an annual basis. All patients completed an IKS score preoperatively and at last follow-up. Age, gender, BMI, length of hospital stay, perioperative complications, all subsequent surgery, including revision of the prosthesis, and survivorship at 10 years was recorded, and results of the 2 groups compared. Results. A total of 147 patients were included in the study. None were lost to follow-up. Sixty nine had associated PF osteoarthritis (group A) while 78 patients had a normal PF compartment when assessed intra-operatively (group B). Post-operative outcomes of the two groups were compared using the ANCOVA analysis with adjustment for pre-operation values firstly, and adjusting also for gender, age, BMI and follow-up secondly. There were no significant differences in terms of IKS, alignment, and flexion between the two groups. However, patients in group B had significantly better extension post-operatively than patients in group A (p < 0.05). Conclusion. We concluded that damage to the articular cartilage of the patellofemoral joint to the extent of full-thickness cartilage loss is not a contraindication to the Repicci II® unicondylar knee arthroplasty for medial compartment osteoarthritis. However, extension is significantly improved post-operatively in those patients with minimal or no PF joint degenerative disease

Introduction. Torsional malalignment syndrome (TMS) is a unique combination of rotational deformities in the lower limb, often leading to severe patellofemoral joint pain and disability. Surgical management of this condition usually consists of two osteotomies in each affected limb, with simultaneous correction of both femoral anteversion and external tibial torsion. However, we believe that a single supratubercular osteotomy followed by tibial derotation with the Taylor Spatial Frame (TSF) can be used to provide a significant improvement in both appearance and function. Materials and Methods. This is a retrospective case analysis in which we will be reviewing 16 osteotomies performed by one surgeon between 2006 and 2017. The study includes 11 patients with a mean age of 16.7 ± 0.8 years. Pre and post-operatively, patients were fully evaluated through history and physical examination, and CT rotational profiling. Statistical analyses were performed in order to determine whether or not any observed clinical or cosmetic improvements were statistically significant. Results. The results show significant improvements in scores reported on post-operative functional assessment, with mean Oxford Knee Score (OKS) increasing by 18.3 and mean Kujala Anterior Knee Pain Scale (AKPS) also increasing by 31.4. In addition to this, post-operative clinical assessment showed a reduced thigh-foot angle (TFA) in all cases, by a mean value of 31.9o. The angle of the transmalleolar axis (TMA) was successfully reduced in 14/16 cases, by a mean value of 8.6o. Statistical analysis showed all of these results to be statistically significant where p<0.05. Conclusions. The results show that supratubercular osteotomy, followed by gradual correction with TSF, can be used to provide a significant improvement in both appearance and function for patients suffering from TMS

Aims. Commonly performed unicompartmental knee arthroplasty (UKA) is not designed for the lateral compartment. Additionally, the anatomical medial and lateral tibial plateaus have asymmetrical geometries, with a slightly dished medial plateau and a convex lateral plateau. Therefore, this study aims to investigate the native knee kinematics with respect to the tibial insert design corresponding to the lateral femoral component. Methods. Subject-specific finite element models were developed with tibiofemoral (TF) and patellofemoral joints for one female and four male subjects. Three different TF conformity designs were applied. Flat, convex, and conforming tibial insert designs were applied to the identical femoral component. A deep knee bend was considered as the loading condition, and the kinematic preservation in the native knee was investigated. Results. The convex design, the femoral rollback, and internal rotation were similar to those of the native knee. However, the conforming design showed a significantly decreased femoral rollback and internal rotation compared with that of the native knee (p < 0.05). The flat design showed a significant difference in the femoral rollback; however, there was no difference in the tibial internal rotation compared with that of the native knee. Conclusion. The geometry of the surface of the lateral tibial plateau determined the ability to restore the rotational kinematics of the native knee. Surgeons and implant designers should consider the geometry of the anatomical lateral tibial plateau as an important factor in the restoration of native knee kinematics after lateral UKA. Cite this article: Bone Joint Res 2019;8:593–600

The contraindications for unicompartmental knee replacement (UKR) remain controversial. The views of many surgeons are based on Kozinn and Scott’s 1989 publication which stated that patients who weighed more than 82 kg, were younger than 60 years, undertook heavy labour, had exposed bone in the patellofemoral joint or chondrocalcinosis, were not ideal candidates for UKR. Our aim was to determine whether these potential contraindications should apply to patients with a mobile-bearing UKR. In order to do this the outcome of patients with these potential contraindications was compared with that of patients without the contraindications in a prospective series of 1000 UKRs. The outcome was assessed using the Oxford knee score, the American Knee Society score, the Tegner activity score, revision rate and survival. The clinical outcome of patients with each of the potential contraindications was similar to or better than those without each contraindication. Overall, 678 UKRs (68%) were performed in patients who had at least one potential contraindication and only 322 (32%) in patients deemed to be ideal. The survival at ten years was 97.0% (95% confidence interval 93.4 to 100.0) for those with potential contraindications and 93.6% (95% confidence interval 87.2 to 100.0) in the ideal patients. We conclude that the thresholds proposed by Kozinn and Scott using weight, age, activity, the state of the patellofemoral joint and chondrocalcinosis should not be considered to be contraindications for the use of the Oxford UKR

Introduction. Total knee replacement (TKR) is an established and effective surgical procedure in case of advanced osteoarthritis. However, the rate of satisfied patients amounts only to about 75 %. One common cause for unsatisfied patients is the anterior knee pain, which is partially caused by an increase in patellofemoral contact force and abnormal patellar kinematics. Since the malpositioning of the tibial and the femoral component affects the interplay in the patellofemoral joint and therefore contributes to anterior knee pain, we conducted a computational study on a cruciate-retaining (CR) TKR and analysed the effect of isolated femoral and tibial component malalignments on patellofemoral dynamics during a squat motion. Methods. To analyse different implant configurations, a musculoskeletal multibody model was implemented in the software Simpack V9.7 (Simpack AG, Gilching, Germany) from the SimTK data set (Fregly et al.). The musculoskeletal model comprised relevant ligaments with nonlinear force-strain relation according to Wismans and Hill-type muscles spanning the lower extremity. The experimental data were obtained from one male subject, who received an instrumented CR TKR. Muscle forces were calculated using a variant of the computed muscle control algorithm. To enable roll-glide kinematics, both tibio- and patellofemoral joint compartments were modelled with six degrees of freedom by implementing a polygon-contact-model representing the detailed implant surfaces. Tibiofemoral contact forces were predicted and validated using data from experimental squat trials (SimTK). The validated simulation model has been used as reference configuration corresponding to the optimal surgical technique. In the following, implant configurations, i.e. numerous combinations of relative femoral and tibial component alignment were analysed: malposition of the femoral/tibial component in mediolateral (±3 mm) and anterior-posterior (±3 mm) direction. Results. Mediolateral translation/malposition of the tibial component did not show high influence on the maximal patellofemoral contact force. Regarding the mediolateral translation of the femoral component, similar tendencies were observed. However, lateralisation of the femoral component (3 mm) clearly increased the lateral patella shift and medialisation of the tibial component (3 mm) led to a slightly increased lateral patella shift. Compared to the reference model, pronounced posterior translation of the tibial and femoral component resulted in a lower patellofemoral contact force, further increasing with higher anterior translation of the components. The translation of the tibial component showed smaller influence on the patellofemoral contact force than the translation of the femoral component. Discussion. In our present study, the mediolateral malposition of the femoral and tibial component showed no major impact on patellofemoral contact force and contribution to anterior knee pain in patients with CR TKR. However, the influence of implant component positioning in anterior-posterior direction on patellofemoral contact force is evident, especially for the femoral component. Our generated musculoskeletal model can contribute to computer-assisted preclinical testing of TKR and may support clinical decision-making in preoperative planning

We have examined the differences in clinical outcome of total knee replacement (TKR) with and without patellar resurfacing in a prospective, randomised study of 181 osteoarthritic knees in 142 patients using the Profix total knee system which has a femoral component with features considered to be anatomical and a domed patellar implant. The procedures were carried out between February 1998 and November 2002. A total of 159 TKRs in 142 patients were available for review at a mean of four years (3 to 7). The patients and the clinical evaluator were blinded in this prospective study. Evaluation was undertaken annually by an independent observer using the knee pain scale and the Knee Society clinical rating system. Specific evaluation of anterior knee pain, stair-climbing and rising from a seated to a standing position was also undertaken. No benefit was shown of TKR with patellar resurfacing over that without resurfacing with respect to any of the measured outcomes. In 22 of 73 knees (30.1%) with and 18 of 86 knees (20.9%) without patellar resurfacing there was some degree of anterior knee pain (p = 0.183). No revisions related to the patellofemoral joint were performed in either group. Only one TKR in each group underwent a re-operation related to the patellofemoral joint. A significant association between knee flexion contracture and anterior knee pain was observed in those knees with patellar resurfacing (p = 0.006)

Introduction: Anterior knee pain is a commonly encountered orthopaedic symptom. Textbooks list a number of clinical symptoms and physical signs that are specific for the PF joint in the assessment of the patient with knee pain. Radiological evaluation of the PF joint is rarely helpful. The authors have investigated the value of these symptoms and signs in predicting the presence of PF pathology. Patients and Methods: All patients presenting for diagnostic knee arthroscopy were enrolled prospectively. A detailed proforma was completed with each patient pre-operatively recording the presence or absence of specific PF symptoms and clinical signs. A blinded independent observer recorded the operative findings of the PF joint, the presence / absence of a plica and / or anterior synovitis. Chondromalacia (CM) was graded using the Outerbridge classification and grade 2 or greater was considered a positive finding. Pre-operative symptoms and signs were correlated with arthroscopic findings and their positive predictive value (PPV) was determined. Results: Thirty patients were enrolled over a 2-month period. Pure anterior knee pain was present in 10 patients. The remainder had medial (15), lateral (2) or generalised pain (3). 20 of the thirty patients had degenerative changes in the PF joint. One patient had a plica and no patients had significant anterior synovitis. 20 of the 30 patients had pathological findings elsewhere in their joint. In the prediction of PF degenerative changes, the PPV of symptoms exacerbated by squatting was 0.53; stairs – 0.55; kneeling – 0.57; rising from low chair – 0.6 and night pain – 0.5. Analysis of specific signs in predicting PF changes showed that the PPV of PF crepitus was 0.5; pain exacerbated by patellar compression 0.6; and patellar facet compression was 0.62. Conclusion: Degenerative changes of the PF joint are common in our patient population. The value of knee arthroscopy in patients with isolated PF symptoms is questionable. Our assessment of these patients with specific questions and physical signs has been shown to have a low PPV in predicting ultimate arthroscopic findings in the PF joint

Abstract. Objective. Explore whether high tibial osteotomy (HTO) changes knee contact forces and to explore the relationship between the external knee adduction moment (EKAM) pre and 12 months post HTO. Methods. Three-dimensional gait analysis was performed on 17 patients pre and 12-months post HTO using a modified Cleveland marker-set. Tibiofemoral contact forces were calculated in SIMM. The scaled musculoskeletal model integrated an extended knee model allowing for 6 degrees of freedom in the tibiofemoral and patellofemoral joint. Joint angles were calculated using inverse kinematics then muscle and contact forces and secondary knee kinematics were estimated using the COMAC algorithm. Paired samples t-test were performed using SPSS version 25 (SPSS Inc., USA). Testing for normality was undertaken with Shapiro-Wilk. Pearson correlations established the relationships between EKAM1 to medial KCF1, and EKAM2 to medial KCF2, pre and post HTO. Results. Total knee contact force peak 1 significantly reduced from 2.6 x body weight pre-HTO to 2.3 x body weight 12-months post-HTO. Medial contact force peak 1 significantly reduced from 1.7 x body weight pre-HTO to 1.5 x body weight 12-months post-HTO. Second peak lateral knee contact force significantly increased from 0.9 body weight pre-HTO to 1.1 x body weight 12-months post-HTO. Furthermore, this study found very strong correlations between EKAM1 and medial KCF1 pre-HTO (r=0.85) as well as post-HTO (r=0.91). There was a significantly moderate relationship between EKAM2 and medial KCF2 pre-HTO (r=0.625). Conclusion. HTO significantly reduced overall and medial KCF during the first half of stance whilst increasing second half of stance peak lateral knee contact force. This study demonstrated a strong relationship between EKAM peaks and respective medial KCF peaks, supporting the usefulness of EKAM as a surrogate measure of medial compartment tibiofemoral contact forces. This demonstrates HTO successfully offloads the tibiofemoral joint overall, as well as offloading the medial compartment

Introduction. Recurrent patellar dislocation is often reported in bilateral knees in young active individuals. The medial patellofemoral ligament (MPFL) tear is the attributable cause behind many of them and warrants reconstruction of the ligament to stabilize the patellofemoral joint. Besides, trochleoplasty and Fulkerson's osteotomy are some other procedures that are performed to treat this problem. This study aimed to compare the clinical and functional outcomes in a cohort of patients with single-stage bilateral realignment procedures vs staged procedures. Methods. It was a retrospective matched cohort study with prospectively collected data. A total of 36 patients (mean age-26.9 years, range 13 years to 47 years) with recurrent patellar dislocations, who underwent a surgical correction in both the knees, were divided into two matched groups (age, sex, follow-up, and type of procedure). Among them, 18 patients had surgeries in one knee done at least six months later than the other knee. The remaining 18 patients had surgical interventions for both knees done in a single stage. Lysholm, Kujala, Tegner, and subjective knee scores of both groups were compared and analyzed. The rate of complications and return to the theatre were noted in both groups. Results. With a mean follow-up of 7.3 years (2.0 years to 12.3 years), there was a significant improvement in PROMS observed in both the groups (p<0.05). No significant difference could be found between the two groups in terms of the Lysholm, Kujala, and subjective knee scores (p> 0.05). The rate of complication and the re-operation rate was comparable in both the groups (p>0.05). Conclusion. The outcomes of staged vs simultaneous surgeries for bilateral patellofemoral instability are comparable. Our results indicate that simultaneous bilateral surgical correction is safe. This can potentially be an option to reduce the surgical cost and perioperative morbidity. However, careful selection of cases, choice of the patient, and the scope of rehabilitation facilities are some of the other factors that should be considered

Objectives. The aim of the current study was to analyse the effects of posterior cruciate ligament (PCL) deficiency on forces of the posterolateral corner structure and on tibiofemoral (TF) and patellofemoral (PF) contact force under dynamic-loading conditions. Methods. A subject-specific knee model was validated using a passive flexion experiment, electromyography data, muscle activation, and previous experimental studies. The simulation was performed on the musculoskeletal models with and without PCL deficiency using a novel force-dependent kinematics method under gait- and squat-loading conditions, followed by probabilistic analysis for material uncertain to be considered. Results. Comparison of predicted passive flexion, posterior drawer kinematics and muscle activation with experimental measurements showed good agreement. Forces of the posterolateral corner structure, and TF and PF contact forces increased with PCL deficiency under gait- and squat-loading conditions. The rate of increase in PF contact force was the greatest during the squat-loading condition. The TF contact forces increased on both medial and lateral compartments during gait-loading conditions. However, during the squat-loading condition, the medial TF contact force tended to increase, while the lateral TF contact forces decreased. The posterolateral corner structure, which showed the greatest increase in force with deficiency of PCL under both gait- and squat-loading conditions, was the popliteus tendon (PT). Conclusion. PCL deficiency is a factor affecting the variability of force on the PT in dynamic-loading conditions, and it could lead to degeneration of the PF joint. Cite this article: K-T. Kang, Y-G. Koh, M. Jung, J-H. Nam, J. Son, Y.H. Lee, S-J. Kim, S-H. Kim. The effects of posterior cruciate ligament deficiency on posterolateral corner structures under gait- and squat-loading conditions: A computational knee model. Bone Joint Res 2017;6:31–42. DOI: 10.1302/2046-3758.61.BJR-2016-0184.R1

Background. Lateral Unicompartmental Knee Arthroplasty (UKA) is a recognised treatment option in the management of lateral Osteoarthritis (OA) of the knee. Whilst there is extensive evidence on the indications and contraindcations in Medial UKA there is limited evidence on this topic in Lateral UKA. The aim of this study was to assess our experience of mobile lateral UKR and to look specifically at the effect of Contraindications on the outcome. Method. A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and presence of full- thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated. Results. Median follow- up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%). In total, 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing. In all, 12 (4%) were revised for medial osteoarthritis (OA). Ten- year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival. Conclusion. Mobile (domed) lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications

Background. Secondary osteonecrosis of the knee (SOK) generally occurs in relatively young patients in their working years; at advanced stages of SOK, the only viable surgical option is total knee arthroplasty (TKA). We conducted a retrospective study to investigate implant survivorship, clinical and radiographic outcomes, and complications of cemented TKA with/without patellar resurfacing for SOK. Methods. Thirty-eight cemented TKAs in 27 patients with non-traumatic SOK with a mean age 43 years (range 17–65) were retrospectively reviewed. Twenty-one patients (78%) were female. Mean body mass index was 31 kg/m. 2. (range 20–48); 11 patients (41%) received bilateral TKAs. Twenty patients (74%) had a history of corticosteroid use and 18% had a history of alcohol abuse. Patellar osteonecrosis was coincidentally found in six knees (16%), all of which had no anterior knee pain and had no patellofemoral joint collapse. The mean follow-up was 7 years (range 2–12). Knee Society Score (KSS) and radiographic outcomes were evaluated at 6 weeks, 1 year, then every 2–3 years thereafter. Results. Ninety-two percent had implant survivorship free from revision with significant improvement in KSS. Causes of revision included aseptic tibial loosening (one), deep infection (one), and instability with patellofemoral issues (one). Four of six cases also with patellar osteonecrosis received resurfacing, including one with a periprosthetic patellar fracture after minor trauma, with satisfactory clinical results after conservative treatment. None of the unrevised knees had progressive radiolucent lines or evidence of loosening. Non-resurfacing of the patella, use of a stem extension or a varus-valgus constrained prosthesis constituted 18%, 8% and 3% of knees, respectively. Conclusion. Cemented TKAs with selective stem extension in patients with SOK had satisfactory implant survivorship and reliable outcomes at a mean of 7 years. Patellar resurfacing is unnecessary in younger patients with no symptoms of anterior knee pain and no patellar collapse radiographically. For any figures or tables, please contact the authors directly

Introduction. Persistent anterior knee pain, subluxation or dislocation of the patella as well as early aseptic loosening and increased polyethylene wear of the patella implant are common clinical problems after total knee arthroplasty (TKA) which are associated with the patellofemoral joint. In addition to patellar resurfacing, the design of the patellofemoral joint surfaces is attributed a large influence. While for patients without patella resurfacing, the native patella is sliding on the standardized femoral component and therefore the possibility of a reduced surface matching is high, patella resurfacing has been shown to decrease the joint contact area and yield to increased patellofemoral pressure. With regard to a further design optimization, the current study examined patellar biomechanics after TKA without and with resurfacing, comparing 5 differently designed patellofemoral joint surfaces of the femoral implant. Methods. The femoral implant of the Genesis II prosthesis (Smith & Nephew) was scanned and an adaptable CAD-model was built using CATIA. Five different designs of the patellofemoral groove were created:. original. completely flat. laterally elevated (+2mm lateral, −1mm medial). medially elevated (+2mm medial, −1mm lateral). laterally & medially elevated (+3mm lateral+medial). The tibiofemoral joint as well as patellofemoral groove path and radius remained unchanged. Rapid Prototyping was used to produce prototypes made of polyamide. A dynamic muscle loaded knee squat was simulated on 10 fresh frozen knee specimens with an upright knee simulator. The patellofemoral pressure distribution was measured using a flexible, resistive force sensor (TEKSCAN) while tibiofemoral and patellofemoral kinematics were recorded with an ultrasonic motion tracking system (ZEBRIS). In addition, patellar stability was measured in different flexion angles on another 10 specimens using a robot (KUKA). Measurements were taken on the native knee as well as after TKA and after additional patellar resurfacing with alternating femoral implant. Results. Considering patellofemoral kinematics, the largest influence was found for the flat design where increased lateral tilt (up to 6°) and medial shift (up to 5mm) were measured after TKA compared to the native knee. Similar results were achieved for patellar stability, where increased lateral displacement (up to +6mm) was measured for the flat design. The other designs only had a small effect on patellar kinematics and patellar lateral stability. Regarding maximal peak pressure, on average, only a small influence of the designs was found. However, for the individual knee specimens, the pressure distribution and peak pressures varied clearly among the different designs. After additional patellar resurfacing, patellofemoral peak pressures significantly increased (almost doubled), but for the different designs, similar results as before were achieved regarding patellar kinematics, stability and pressures. Conclusions. Increased mediolateral motion was found for the flat design compared to the others and the native knee concluding that a moderate groove is necessary but also sufficient to guarantee stable motion. Especially for maximal patellofemoral peak pressures, large individual differences between the designs were measured while the average influence was small. Therefore, an individual choice between some standard implants might be an interesting option, if appropriate criteria can be found

Background. Flexion-extension gap balancing is recognized as an essential part of total knee arthroplasty (TKA). The gap is often evaluated using spacer blocks, laminar spreader, or tensor device. The evaluation of gap balancing with the patella in the reduced position is more physiological and reproducible than with patellofemoral (PF) joint everted. However, in the knee with a reduced PF joint, it is difficult to comprehend the anteroposterior position of the tibia to the femur. So, we developed a new tensor to lift up the tibia ahead and fix the anteroposterior position of the tibia to the femur with the PF joint reduced [Fig.1]. Purpose. To investigate how accurate the extension and flexion gaps would be measured by comparing our new tensor with the conventional tensor which could not fix the position of the tibia to the femur. Methods. This study includes 60 knees in 48 patients underwent TKA using the Posterior Stabilized (PS) Prosthesis (Striker), for varus osteoarthritis. The mean age of patients was 78.2 (62 to 88) at the time of surgery. All knees were exposed using a standard medial parapatellar approach. The posterior cruciate ligament was sacrificed at the beginning of the procedure. A balanced gap technique was used for the femoral and tibial bone cuts. After the completion of bony resection, osteophyte removal, and soft-tissue balancing by the release of the medial collateral ligament (MCL), the offset knee balancer which consisted of an upper seesaw plate and a lower platform plate, and allowed the PF joint reduction during the measurement was inserted into the knee to balance on the knee flexion angles of 0 deg and 90 deg at 30 pounds. We prepared two plate types, one plate which was flat and conventionally-known plate, the other plate to which the claw hook was attached at the end. The tension device provides two measurements: the central gap length (mm) between femur and tibia which was cut, and as the ligament balance, the angle (°) between the seesaw plate and the platform plate with positive values representing varus imbalance. The joint gap measurement was performed at full extention or 90°of flexion using the both tensors. We calculated difference between the two extreme values of the values measured 3 times repeatedly using each tensor, and defined the difference as error span. Results. In the joint gap at full extention, the error span on the value measured with the claw hook type was 0.9±0.8mm, significantly small compared with the conventional type, 2.8±1.4mm [Fig.2]. On the other hand, the joint gap at 90°of flexion and the ligament balance at full extention and 90°of flexion were not significantly different between the claw hook type and the conventional type [Fig.3]. Conclusion. The tensor of claw hook type have proved to be useful in the joint gap measurement especially at full extention than the conventional type by preventing the tibia from falling posterior to the femur by gravity

Introduction. A large number of total knee arthroplasty (TKA) patients, particularly in Japan, India and the Middle East, exhibit anatomy with substantial proximal tibial torsion. Alignment of the tibial components with the standard anterior-posterior (A-P) axis of the tibia can result in excessive external rotation of the tibial components with respect to femoral component alignment. This in turn influences patellofemoral (PF) mechanics and forces required by the extensor mechanism. The purpose of the current study was to determine if a rotating-platform (RP) TKA design with an anatomic patellar component reduced compromise to the patellar tendon, quadriceps muscles and PF mechanics when compared to a fixed-bearing (FB) design with a standard dome-shaped patellar component. Methods. A dynamic three-dimensional finite element model of the knee joint was developed and used to simulate a deep knee bend in a patient with excessive external tibial torsion (Figure 1). Detailed description of the model has been previously published [1]. The model included femur, tibia and patellar bones, TKA components, patellar ligament, quadriceps muscles, PF ligaments, and nine primary ligaments spanning the TF joint. The model was virtually implanted with two contemporary TKA designs; a FB design with domed patella, and a RP design with anatomic patella. The FB design was implanted in two different alignment conditions; alignment to the tibial A-P axis, and optimal alignment for bone coverage. Four different loading conditions (varying internal-external (I-E) torque and A-P force) were applied to the model to simulate physiological loads during a deep knee bend. Quadriceps muscle force, patellar tendon force, and PF and TF joint forces were compared between designs. Results. The RP design demonstrated consistently lower medial-lateral (M-L) force at the PF joint than the FB design, with greater differences between designs in later flexion once the patella was engaged in the sulcus groove; root-mean-square (RMS) differences in M-L force averaged 50 N less in the RP design throughout the flexion cycle, and 70 N less after 45° flexion (Figure 2). The FB design aligned for optimal bone coverage demonstrated 15% higher M-L forces than the FB design aligned with the tibial A-P axis. RMS load required by the quadriceps muscle was 60 N lower with the RP design than the FB design throughout the cycle (Figure 2). Discussion. Comparing a RP design with an anatomic patellar component and a FB design with a domed patellar component, the RP design demonstrated lower M-L PF joint and soft-tissue extensor mechanism forces. Differences were more pronounced under conditions of high I-E torque where the RP design accommodated large relative TF rotation. Differences in FB alignment resulted in substantially different PF M-L forces; when the FB component was mal-aligned with respect to the tibial A-P axis (and the line-of-action of the patellar tendon) the resulting M-L PF force was increased. The RP design reduced the demands on the extensor mechanism and loads on the PF joint and facilitated better coverage of the resected tibial bone surface

The influence of soft tissue balance in mobile-bearing posterior-stabilized (PS) total knee arthroplasty (TKA) on the patellofemoral (PF) joint was investigated in thirty varus-type osteoarthritis patients. Intraoperative soft tissue balance including joint component gap and varus/valgus ligament balance and the medial/lateral patellar pressure were measured throughout the range of motion after the femoral component placement and the PF joint repair. The lateral patellar pressure, which was significantly higher than the medial side in the flexion arc, showed inverse correlation with the lateral laxity at 60° and 90° of flexion. The lateral patellar pressure at 120° and 135° of flexion also inversely correlated with the postoperative flexion angle. Surgeons should take medial and lateral laxity into account when considering PF joint kinematics influencing postoperative flexion angle in PS TKA

Although complications associated with patello-femoral (PF) joint account for up to 50% of total knee replacement (TKR) revision procedures (Lee), the PF joint has been overlooked in wear simulations. The goal of this study was to develop an in vitro model to simulate patella wear in TKR’s. This report describes the concepts of an in vitro model for normal gait and the preliminary results of experimental validation. The primary consideration in the development of the current model was modeling of the in vivo kinetics and kinematics. Since the in vivo kinetics are not well documented, the current model adapted a PF joint force pattern of gait measured one year postoperatively in a telemetric distal femoral replacement (Taylor et al). The maximum force was increased from 571N to 1780N (2.5xBody Weight) to compensate for muscle deficiency and to better reflect a maximum load representative of the in vivo situation. In vivo kinematics were adopted from measurements of Lafortune. Only the PF flexion was included in the model as a simplification of the complex patella motions. The phase relationship between the kinematic and kinetic waveforms was adjusted to replicate the in vivo situation. A 6-station knee simulator carried out the experimental validation with a test frequency of 1.5Hz. The test was intended to run for 5 million cycles, with CMM wear measurements (Muratoglu et al.) taken every million cycles. The preliminary measurements showed wear patterns in the tested patellae similar to retrieved patellae. Currently there are no standards for wear testing the PF joint. The current in vitro wear model presents a useful tool to critically assess the PF joint during gait. Future work should incorporate testing for adverse loading conditions, such as PF mal-alignment, rising from a chair or deep knee flexion

Important factors affecting quality of life (QOL) after total knee arthroplasty (TKA) include postoperative knee kinematics and geometry, influenced by implant design and placement (Matsuda 2001; Nishikawa 2013; Noble 2005). Although specific design factors and their effect on kinematics or QOL have been investigated previously, the inter-relationships between preop-postop changes in kinematics, geometry and the resulting QOL have not been studied to our knowledge. These are essential to understand the interplay between the different factors, and to determine which factors manufacturers and surgeons should focus on when designing and implanting knee prostheses. In addition, the majority of TKA studies focus on the tibiofemoral (TF) joint, although the patellofemoral (PF) joint is routinely the source of postop complications; the PF joint is difficult to study due to polyethylene radio-transparency and because the femoral component obscures the patella from most directions. The purpose of this pilot study was to correlate changes in knee articular shape, over which the implant designers and surgeons have some control, to changes in kinematics and postop QOL, with a particular focus on the PF joint, to answer the following research questions for a sample population with a given implant design and surgeon: (1) Do changes in knee shape affect knee kinematics? In particular, is patellar tracking affected by groove location? (2) Do changes in knee kinematics affect QOL? (3) Do changes in knee shape (resulting from implant design and placement) affect QOL? (4) Do individuals with worse QOL differ from those with better QOL?

Purpose: Our purpose was to study the 10-year results of a proximal soft-tissue procedure combined with a Lateral Patellar Facetectomy technique for an isolated osteoarthritis of patellofemoral joint. Methods: The study group included 39 knees (30 patients). There were 19 female and 11 male patients. Mean age 52 years old (range 40–65). All patients were evaluated at a mean follow-up of 10 years. The indications for surgery were instability of patellofemoral joint with isolated arthritis. Patient outcome scores, patient demographics, and data from a physical examination, x-Ray and TC were collected before and after surgery. A release of the lateral patellofemoral ligament and a retinacular release were performed, leaving the synovial tissue intact to isolate the joint. The lower fibers of the vastus lateralis were released as well, and the release was carried down to the level of the tubercle. Medially, an imbrication of the medial retinacular tissue from the medial aspect of the quadriceps tendon to the proximal aspect of the tibial tubercle, as Insall described, was performed. Results: At final follow-up, the results were excellent or good in 89% of the knees, fair in 7%, and poor in 3%. Subjective improvement was reported by 90% of patients. Follow-up radiographs showed slow progression of osteoarthritis in the patellofemoral and tibiofemoral compartments, but radiographic appearance did not always correlate with clinical symptoms. The success of this procedure depends largely on relief of pain. Conclusions: proximal soft-tissue realignment combined with a Lateral Patellar Facetectomy for a severe isolated osteoarthritis of patellofemoral joint is a powerful way to correct malalignment and offload the lateral and distal parts of the patella. This technique relief pain and improved the activity level. Is an effective surgical treatment for middle-aged to elderly active patients with isolated lateral patellofemoral osteoarthritis who want to maintain activity level

The aim of this study was to assess the benefit and durability of isolated lateral release for advanced osteoarthritis of the lateral facet of the patellofemoral joint. A retrospective study of 23 knees in 20 patients who had isolated lateral patellofemoral joint arthrosis treated with arthroscopic debridement and limited open lateral release was carried out. Patients completed a specific patellofemoral questionnaire (35 points) including questions for pain and functional improvement and pain and functional Fisual Analogue Scores (VAS). Eighteen knees in 15 patients were clinically and radiologically examined. Patients averaged 50 years of age and 2 years from surgical treatment. Visual analogue scores for pain improved 28% and function 40% with little radiological change. Similar improvements were seen in the patello femoral specific questionnaire. The results appeared to be durable over the 2 year follow up period. Lateral release for treatment of isolated arthrosis of the lateral compartment of the patellofemoral joint is an effective, reliable, durable procedure in carefully selected patients

Total knee arthroplasty (TKA) has produced excellent results, but many surgeons are hesitant to perform TKA in younger patients with isolated patellofemoral arthritis. In properly selected patients, patellofemoral arthroplasty (PFA) is an effective procedure with good long-term results. Contemporary PFA prostheses have eliminated many of the patellar maltracking problems associated with older designs, and short-term results, as described here, are encouraging. Long-term outcome and prospective trials comparing TKA to PFA are needed. Incidence. Isolated patellofemoral arthritis occurs in as many as 11% of men and 24% of women older than age 55 years with symptomatic osteoarthritis (OA) of the knee; Isolated patellofemoral arthritis found in 9.2% of patients older than age 40 years; 7% to 19% of patients experience residual anterior knee pain when TKA is done for isolated patellofemoral arthritis. Imaging. Weight bearing AP radiographs as supine radiographs can underestimate the extent of tibiofemoral arthritis; Midflexion posteroanterior radiographs to rule out posterior condylar wear; Lateral radiographs to identify the presence or absence of patella alta or baja; Axial radiographs identify the presence of trochlear dysplasia, patellar tilt or subluxation, and extent of patellofemoral arthritis; Magnetic resonance imaging and arthroscopic photographs should be reviewed if available. Indications. Osteoarthritis limited to the patellofemoral joint; Symptoms affecting daily activity referable to patellofemoral joint degeneration unresponsive to lengthy nonoperative treatment; Posttraumatic osteoarthritis; Extensive Grade-III chondrosis; Failed extensor unloading surgical procedure; Patellofemoral malalignment/dysplasia-induced degeneration. Contraindications. No attempt at nonoperative care or to rule out other sources of pain; Arthritis of greater than Grade 1 involving tibiofemoral articulation; Systemic inflammatory arthropathy; Osteoarthritis/chondrosis of the patellofemoral joint of Grade 3 or less; Patella baja; Uncorrected patellofemoral instability or malalignment; Uncorrected tibiofemoral mechanical malalignment; Active infection; Evidence of chronic regional pain syndrome or evidence of psychogenic pain; Fixed loss of knee range of motion, minimum 10–110 degrees ROM. Results. Majority of failures related to patellar instability from uncorrected patellar malalignment, soft-tissue imbalance, or component malposition; With improved implant designs tibiofemoral arthritis has become the primary source of failure; Failure from component subsidence or loosening occurring in <1% of knees. Our Series. Retrospective review 34 patients, 40 knees average 30 month follow-up using Natural Knee II Patello-femoral Joint System (Zimmer, Warsaw, IN); Average age 61, ranging from 34–84 years of age; Average subset KOOS scores were 93 for pain, 94 for symptoms, 94 for ADL's, 70 for sports and recreation, 82 for quality of life; Average pre-operative Tegner score 2.6, increasing to 4.7 post-operatively; 38/40 survival over 30 months with the two failures undergoing revision for traumatic injuries; No revisions to TKA; At most recent follow-up no progression of OA to involve tibiofemoral compartments; No evidence of component loosening

The effects of advancement of the tibial tuberosity by inserting bony wedges was studied on cadaveric specimens of the knee. The geometry, the contact areas and the forces acting on the patellofemoral joint were investigated, and the forces acting on the tibiofemoral compartment were calculated. A 1 cm advancement was found to be optimal in reducing the high patellofemoral joint forces occurring at 90 degrees and 110 degrees of flexion, whilst causing least reduction of the contact areas; the stresses on the joint were reduced significantly. Advancement by 2 cm and by 3 cm drastically reduced the congruity and the size of the contact area. It was also shown that 2 cm and 3 cm advancement caused an increase in forces at the patellofemoral joint and also in the tibiofemoral joint in a direction tangential to the articular surfaces

Background. More and more patients with end-stage knee OA are treated with total knee replacements (TKR). A modern TKR (Persona PS system, Zimmer Inc.) was designed with the hope to improve fit by providing additional sizing options on the femur and tibia. To date, there is very little information regarding the knee strength and knee mechanics during gait after the TKR. Furthermore, as a great percentage of knee OA patients have OA limited in one knee compartment and in the patellofemoral joint, a bi-compartmental knee replacement (BKR) (iDUO system, ConforMIS Inc.) was designed to treat OA at these affected areas. The BKR re-creates the individual's knee shape while correcting for any deformity. In addition, the BKR procedure results in less bone loss and retains the cruciate ligaments. To date, the influence of the BKR on knee strength and knee mechanics remains unknown. The purpose of the study was to evaluate knee strength and mechanics during level walking after the TKR and BKR surgeries. Methods. Twelve healthy control participants (age=57±6 yr.; mass=82±11 kg; height=175±11 cm), eight patients (age=63±10 yr.; mass=87±20 kg; height=166±8 cm) with ten BKR systems (post-op time = 17±9 mo.), and nine patients (age=65±9 yr.; mass=90±35 kg; Height=169±12 cm) with twelve TKR systems (post-op time = 14±5 mo.) participated in the study. In a laboratory setting, maximal isometric knee strength was evaluated. Motion capture and 3D kinematic and kinetic analyses were conducted for level walking. One way ANOVA was used to determine differences among the BKR, TKR, and the healthy control knees. Findings. The TKR knee extensor strength was 34% and 20% less than that of the control limb (p<0.05) and the BKR limb (p=0.07), respectively. The TKR limb had less knee extensor moment during walking than both the control limb (40% less) and the BKR limb (24% less) (p<0.05). The TKR knee displayed smaller internal rotation at stance than that of the control knee (60% less) and the BKR knee (50% less) (p<0.05). Both the control and BKR groups walked at a faster pace (24% and 17% faster, respectively) than the TKR group (p<0.05). No differences were found for peak knee abduction and abduction moment among the TKR, BKR, and control limbs during walking (p0.05). Interpretations. BKR patients saw their knee extensor strength returned to a normal level and were able to produce the same level of knee extensor moment of the healthy control limbs during walking. The TKR patients still experienced knee strength deficit after one year post-surgery. Both the TKR and BKR groups exhibited similar frontal plane mechanics when compared to the control limbs during walking. However, BKR patients were able to walk significantly faster than their TKR counterparts, at speeds similar to the control subjects. Patients with OA limited in the medial/lateral compartment and the patellofemoral joint may consider the BKR procedure for better knee strength recovery and functional outcomes. Acknowledgement. Funding source: ConforMIS Inc

Introduction. Patellar resurfacing affects patellofemoral (PF) kinematics, contact mechanics, and loading on the patellar bone. Patients with total knee arthroplasty (TKA) often exhibit adaptations in movement patterns that may be linked to quadriceps deficiency and the mechanics of the reconstructed knee [1]. Previous comparisons of PF kinematics between dome and anatomic resurfacing have revealed differences in patellar sagittal plane flexion [2], but further investigation of PF joint mechanics is required to understand how these differences influence performance. The purpose of this study was to compare PF mechanics between medialized dome and medialized anatomic implants using subject-specific computational models. Methods. A high-speed stereo radiography (HSSR) system was used to capture 3D sub-mm measurement of bone and implant motion [3]. HSSR images were collected for 10 TKA patients with Attune® (DePuy Synthes, Warsaw, IN) posterior-stabilized, rotating-platform components, 5 with medialized dome and 5 with medialized anatomic patellar components (3M/7F, 62.5±6.6 years, 2.2±0.6 years post-surgery, BMI: 26.2±3.5 kg/m. 2. ), performing two activities of daily living: knee extension and lunge (Figure 1). Relative motions were tracked using Autoscoper (Brown University, Providence, RI) for implant geometries obtained from the manufacturer. A statistical shape model was used to predict the patella and track motions [4]. Subject-specific finite element models of the experiment were developed for all subjects and activities [5]. The model included implant components, patella, quadriceps, patellar tendon, and medial and lateral PF ligaments (Figure 2a). While tibiofemoral kinematics were prescribed based on experimental data, the PF joint was unconstrained. A constant 1000N quadriceps load was distributed among four muscle groups. Soft tissue attachments and pre-strain in PF ligaments were calibrated to match experimental kinematics [5]. Model outputs included PF kinematics, patellar and contact force ratios, patellar tendon angle, and moment arm. Results and Discussion. Load-bearing activities presented larger variations in PF kinematics and mechanics between dome and anatomic subjects. Consistent with previous findings [2], patients with medialized anatomic geometry achieved greater patellar flexion than those with the medialized dome during lunge (16±3° from 40–100° knee flexion), and demonstrated PF kinematics closer to that of the natural knee (Figure 2b) [6]. Dome subjects experienced greater PF internal-external range-of-motion compared to the anatomic subjects (8±5°). Model PF kinematics closely replicated the experiment with average root-mean-square differences of flexion-extension<5°, internal-external<3°, and medial-lateral<2 mm. Dome subjects demonstrated larger contact force ratios than anatomic, but presented smaller patellar force ratios in deep flexion (–60°). Smaller PF flexion angles in dome implants likely influenced the increase in contact force ratio, which may increase implant forces and decrease quadriceps efficiency. In contrast, the flexed position of the anatomic design distributed load to the patellar tendon at deeper flexion angles, which may improve extensor function (Figure 3). The current modeling framework can inform implant designers on the impact of articular geometry on quadriceps efficiency

Introduction. Complications related to the patellofemoral joint continue to be a substantial source of patient morbidity, causing anterior knee pain, instability, and dysfunction following total knee arthroplasty. One of the principle factors affecting patellofemoral outcomes may be trochlear design. The optimal design is currently unknown. The purpose of the present study was to study patellofemoral joint contact by analysing areas of wear in retrieved femoral components of three modern designs. Materials and Methods. Eighteen retrieved femoral components featuring three different designs (constant radius of rotation, multiple radii of rotation, and multiple radii of rotation with built-in external rotation design) were matched on the basis of time-in-vivo, age, BMI and gender. All implants were cobalt chrome, posterior stabilized, cemented components with fixed bearing design with a resurfaced patella. Trochlear wear and surface damage were assessed using visual inspection, low-magnification light microscopy, and light profilometry. Results. Six implants from each group were successfully matched and were used for the topographical analysis. The femoral components were closely matched on the basis of time-in-vivo (TIV) (2.4 years±1.2), age (71.6 years±11.3), and BMI (33.0 kg/m. 2. ±7.0). There were 9 males and 9 females in the sample. Infection was the most common reason for revision (n=14) followed by instability (n=3) and loosening (n=1). There were no significant differences in TIV, age, and BMI between the groups (p=0.366, p=0.829, and p=0.586, respectively). When compared with unused, reference components, both the retrieved constant radius implants (p<0.05) and multiple radii implants (p<0.05) were significantly rougher than the new components. The retrieved components with multiple radii and built-in external rotation were not substantially rougher than the reference component (p>0.05). Visual inspection of the femoral components showed evidence of damage in all implant types. Modes of damage included scratches, striation, pitting, and delamination. No significant differences between the groups were found with respect to overall damage and wear on visual inspection (p=0.480). However, light profilometry analysis showed significantly increased roughness of multiple radii components compared to constant radius or multiple radii components with built-in external rotation (p<0.05). This was particularly significant in the proximal middle (p=0.045) and medial zones of the trochlea (p=0.017). Conclusions. All retrieved femoral components show evidence of damage in the trochlear area. While retrieved constant radius and multiple radii components showed increased wear compared to new components, retrieved components with multiple radii and built-in external rotation did not differ significantly from their new state. Retrieved multiple radii components appeared to have increased roughness compared with constant radius or multiple radii with built-in external rotation, particularly in the proximal zones of the trochlea. The long term effects of increased trochlear roughness requires further investigation and correlation with clinical outcomes. As the volume and patient demands for total knee arthroplasty increase, a greater understanding of the effect of trochlear design on clinical outcomes is warranted

Multiple studies have shown that the symptomatology of knee osteoarthritis weakly correlate to radiographic severity of disease. Current literature however does not have much in the way of comparing functional outcomes of those with OA knees with radiographic severity. Our objective was to compare radiographic measurements of OA knees with self-reported functional outcomes and determine if radiographic severity of OA knees correlated with loss of functional ability. A retrospective review of prospectively collected registry data of 305 patients with osteoarthritis of the knee was collected. The patient's x-rays were reviewed, and radiographic measurements were taken to include medial, lateral and patellofemoral joint space distance measured in millimetres. The Kellgren and Lawrence, and Ahlback classifications of radiographic knee OA were computed. These were correlated with severity of functional limitations was measured using the SF36, Knee society score (KSS) and Oxford knee scores. Statistical analysis were conducted with SPSS V22.0 statistical software. Demographic characteristics and functional assessments were analysed using one way ANOVA test. Post-hoc test using Tukey HSD and effect size (partial-eta squared η. 2. ) was performed if one-way ANOVA was found to be statistically significant. A p-value of 0.05 or less was considered statistically significant. Pre-operative patient demographics are shown in table 1. Patients in with Grade 2 osteoarthritis were significantly younger than Grade 4 patients (post-hoc p=0.003). There were no statistically significant differences in age between the other Grades, and there were no differences in BMI or gender or operative site between all grades. There were significant differences in KSS Function scores between Grade 2 and Grade 3 patients (post-hoc p=0.017) and Grade 2 and 4 patients (post-hoc p < 0 .001). Statistically significant differences were also found between Grade 1 and Grade 4 patients for the KSS Knee score (post-hoc p=0.016). There were significant differences in Oxford knee score (post-hoc p=0.026) and SF- Physical Function (post-hoc p < 0 .001) between Grade 2 and Grade 4 patients too. The effect size η. 2. for KSS Function, KSS Knee and Oxford knee score was 0.05, 0.06 and 0.33 respectively. When comparing the loss of joint space with the functional scores, there were no statistically significant correlations. Our study show that the radiological severity of knee osteoarthritis based on the two scoring methods was able to correlate with worsening functional scores. Most notably, the differences in KSS function scores correlated strongly between Grade 2 and Grade 3 patients. Of note, there was no correlation between the loss of joint space and the severity of functional limitations across any of the scoring systems. Our study showed that although both the Kellgren and Lawrence and Ahlback radiological grading of Osteoarthritis were able to correlate with worsening functional scores, this was not due to loss of joint space alone and further studies need to be conducted on the other contributors to the scoring system such as osteophytes and subchondral sclerosis. Our study show that the radiological severity of knee osteoarthritis based on the two scoring methods was able to correlate with worsening functional scores. Most notably, the differences in KSS function scores correlated strongly between Grade 2 and Grade 3 patients. Of note, there was no correlation between the loss of joint space and the severity of functional limitations across any of the scoring systems. Our study showed that although both the Kellgren and Lawrence and Ahlback radiological grading of Osteoarthritis were able to correlate with worsening functional scores, this was not due to loss of joint space alone and further studies need to be conducted on the other contributors to the scoring system such as osteophytes and subchondral sclerosis. For any figures or tables, please contact authors directly

Introduction. The assumption that symmetric extension-flexion gaps improve the femoral condyle lift-off phenomenon and the patellofemoral joint congruity in total knee arthroplasty (TKA) is now widely accepted. Conventional understanding of knee kinematics suggests that the femoral component should be rotationally aligned parallel to the surgical epicondylar axis (SEA). On the other hand, the theory of the balanced gap technique suggests the knee be balanced in extension and flexion to achieve proper kinematics and stability of the knee without reference to fixed bony landmarks. The purpose of our study was to evaluate the relationship between rotation alignment of the femoral component and postoperative flexion gap balance, and the femoral rotational alignment in relation to the tibial mechanical axis in patients when implanted using a balanced gap technique. Materials and Methods. The subjects presented 53 consecutive osteoarthritic (OA) varus knees underwent primary Posterior-Stabilised (PS) -TKA (NexGen LPS-flex, Zimmer). All subjects completed written informed consent. The patient population was composed of 7 men and 35 women with a mean age of 72.5 ± 8.3 years. The average height, weight, BMI, weight-bearing FTA, and the patella height (Insall-Salvati ratio: T/P ratio) were 151.7 ± 7.7 cm, 62.6 ± 11.8 kg, 27.2 ± 4.5, 184.9 ± 5.9° and 0.93 ± 0.14 respectively. All procedures were performed through a medial parapatellar approach and a balanced gap technique used a newly developed versatile tensor device which can measure the medial and lateral gaps individually and make use of the balanced gap technique guide with patellofemoral joint reduction, which had been introduced in 56. th. ORS 2010. Pre- and post-operatively, a condylar twist angle (CTA) was evaluated using computed tomography (CT). To assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was evaluated using the epicondylar view radiographs by adding a 1.5 kg weight at the ankle. Coronal alignment of the tibial component in reference to the tibial mechanical axis (angle θ) was evaluated using plain AP radiography. Data were expressed as mean ± SD and analysed with Stat View version 5.0. Results. Extension gap was well balanced within 3 mm in all cases. The average of the preoperative CTA, the postoperative CTA, the LOA and the angle θ. were 6.0 ± 1.5°, 1.2 ± 2.4°, 0.8 ± 1.4° and 89.7 ± 1.2° respectively. No significant correlation was observed in between the postoperative CTA, the LOA and the angle θ. The degree of the clinical epicondylar axis (CEA) to the tibial machanical axis was 90.1 ± 2.9°. Only one knee needed lateral retinaculum release, because of poor patella tracking evaluated by no thumb test or one stitch method. Discussion. This study demonstrated that our balanced gap technique, using a newly developed tensor device, achieved good patellofemoral joint congruity and balanced flexion gaps postoperatively. Rotation alignment of the femoral component was slight internal rotation in reference to the CEA but not parallel to the SEA. Conclusion. The CEA was perpendicular to the tibial mechanical axis in PS-TKA with well balanced extension-flexion gap achieved by a balanced gap technique

The August 2024 Trauma Roundup³⁶⁰ looks at: Does topical vancomycin prevent fracture-related infections in closed fractures undergoing open reduction and internal fixation? A randomized controlled trial; Is postoperative splinting advantageous after upper limb fracture surgery?; Does suprapatellar nailing resolve knee pain?; Locking versus non-locking plate fixation in comminuted talar neck fractures: a biomechanical study using cadaveric specimens; Revolutionizing recovery metrics: PROMIS versus SMFA in orthopaedic trauma care; Dorsal hook plating of patella fractures: reliable fixation and satisfactory outcomes; The impact of obesity on subtrochanteric femur fracture outcomes; Low-dose NSAIDs (ketorolac) and cytokine modulation in orthopaedic polytrauma: a detailed analysis.

Aims

To assess the incidence of radiological lateral osteoarthritis (OA) at 15 years after medial unicompartmental knee arthroplasty (UKA) and assess the relationship of lateral OA with symptoms and patient characteristics.

Modifiable factors contributing to stiffness include alignment, implant size, implant position and rotation, and soft tissue tightness or laxity. Less modifiable factors include genetics as in predisposition to inflammation and fibrosis, aberrations in perception and experience of emotional pain, and preoperative range of motion. We reviewed 559 knees undergoing revision between 2007 and 2014, selecting out patients with a diagnosis of stiffness and greater than one-year follow-up. Stiffness was defined as greater than 15 degrees of flexion contracture or less than 75 degrees of flexion or less than 90 degrees of active motion and a chief complaint of limited motion and pain. Radiographic analysis used a set of matched controls with greater than 90 degrees and full extension prior to surgery and were further matched by age, gender, BMI. Flexion contracture changed from an average of 9.7 to an average of 2.3 degrees, flexion changed from an average of 81 to an average of 94 degrees, active motion changed from an average of 72 to an average of 92 degrees, pain scores improved from 44 to 72 points, and Knee Society function scores improved from an average of 49 to an average of 70 points. There were four failures for stiffness, two knees underwent additional manipulation, gaining an average of 10 degrees; and two knees were revised. Radiographic analysis demonstrated stiffness to be strongly correlated to anterior condylar offset ratio and to patellar displacement by multivariant regression analysis, suggesting that overstuffing the patellofemoral joint by anteriorization of the femoral component is associated with stiffness. Using modern revision techniques, revision for stiffness creates reliable improvements in pain, Knee Society clinical and functional scores, and motion

Recurrent patella dislocation is a well-recognized complication after primary dislocation of the patellofemoral joint. We propose that acute surgical management of the injury minimizes this risk. Between February 2006 and August 2010 47 patients (49 knees) with a mean age of 17.9 (range 12–31) at the time of surgery who sustained a patellofemoral joint dislocation for the first time were treated with an acute repair of the medial patellofemoral ligament. Patients presenting to our fracture clinic following a primary lateral dislocation of the patella were investigated with an MRI scan and with consent, proceeded to have an examination under anaesthesia and arthroscopy of the injured knee. An easily dislocatable patella in the presence of a confirmed medial patellofemoral ligament rupture was the indication for open repair. All patients treated surgically were followed up for a period of 24–72 months where the primary outcome measure was further dislocation. An evaluation of symptoms, functional recovery, restoration of range of movement and patient satisfaction was made supported by the Lysholm knee score. Our results confirm that acute repair of the medial patella femoral ligament in selected patients reduces the risk of further dislocations and results in a overall good functional outcome and patient satisfaction with minimal complications

Although cartilage repair has been around since the time of open Pridie drilling, clinical outcomes for newer techniques such as arthroscopic debridement, microfracture (MFX), osteochondral autograft transfers (OATS), osteochondral allograft transplantation and Autologous Chondrocyte Implantation (ACI) are still finding their place in treating injured knees. Early mechanical symptoms are best managed by a gentle arthroscopic debridement of loose articular flaps. This allows the surgeon to assess the defect size, location in the tibio-femoral or patellofemoral joint, status of the cartilage overall and patients response to the intervention. If the symptom improvement is not satisfactory to the patient, after assessing background factors that will influence the results of a cartilage repair procedure, (alignment of the patellofemoral joint or axial alignment, ligament stability and status of the meniscus), the surgeon can choose the best procedure for that individual based on the expected outcomes of the various cartilage repair techniques while addressing the background factors. As all the techniques have failures and informed discussion with the patient prior to performing the procedure is critical in avoiding disappointment for the patient and the surgeon. The repair technique used should incorporate considerations of the defect size, location, and the patient age, activity level, expectations and ability to comply with the longer rehabilitation needed for biological procedures as compared to prosthetic implants

Introduction. Knee arthroplasty is an effective intervention for painful arthritis when conservative measures have failed. Despite recent advances in component design and implantation techniques, a significant proportion of patients experience problems relating to the patella-femoral joint (PFJ). Detailed knowledge of the shape and orientation of the normal and replaced femoral trochlea groove is critical when considering potential causes of anterior knee pain. Furthermore, to date it has proved difficult to establish a diagnosis due to shortcomings in current imaging techniques for obtaining satisfactory coronal plane motion data of the patella in the replaced knee. The aim of this study was to correlate the trochlea shape of normal and replaced knees with corresponding coronal plane PFJ kinematic data. Method. Bony and cartilagenous trochlea geometries from 3T MRI scans of 20 normal healthy volunteers were compared with both anatomical and standard total knee replacements (TKR) and patellofemoral joint replacement (PFJR) geometries. Following segmentation and standardized alignment, the path of the apex of the trochlea groove was measured using customized Matlab software. (Fig1). Next, kinematic data of the 20 normal healthy volunteers (Normal) was compared with that of 20 TKR, and 20 PFJR patients using the validated MAUS. TM. system (Motion Analysis and UltraSound) comprising a 12-camera, motion capture system used to capture images of reflective markers mounted on subjects lower limbs and an ultrasound probe. A mapping between the ultrasound image and the motion capture system allows the ultrasound probe to be used to determine the locations of the patella relative to bony landmarks on the femur during a squat exercise. Results. In normal knees the arc of the trochlear groove apex was orientated progressively laterally for both cartilage and. Neither of these trends were reproduced by any of the knee prostheses. Indeed far from being a laterally directed trochlea groove, both the anatomic TKR and PFJR have a medially orientated trochlea, whilst the TKR showed a neutral straight path (Figure 2). The direction of displacement in the replaced knee is significantly different (opposite) to that of the native knee (p<0.05). The accuracy of the MAUS technique registering the ultrasound images within the motion capture system is 1.84 mm (2 × SD). The three groups showed very different patella tracking patterns which matched the orientation of the underlying trochlea (Figure 3). The sine wave pattern of coronal plane patella motion displayed by the Normal group was not recreated in the TKR or PFJR groups. Movements of the Normal group were significantly different from the TKR group (p=0.03) and the PFJR group (p<0.01), whilst there was no significant difference between the TKR and PFJR groups (p=0.27). Discussion. We present a new, accurate, reliable in vivo technique for measuring 3D patellofemoral kinematics in native and replaced knees. Our data suggest that many aspects of patellofemoral kinematics are absent following TKR and PFJR. This can be explained by the differences in shape of the underlying femoral component. Anterior knee pain problems might be addressed by alterations to the patellofemoral joint in future designs of knee arthroplasty

Enhanced appreciation of normal knee kinematics and the inability to replicate these in the replaced total knee has led to increased enthusiasm for partial knee arthroplasty by some. These arthroplasties more closely replicate normal kinematics since they inherently preserve the anterior cruciate ligament (ACL). Indications for medial UKA are: anteromedial osteoarthritis with an intact ACL, posterior cruciate ligament, and medial collateral ligament (MCL), full thickness cartilage loss, and correctable deformity demonstrated radiographically with valgus stress view; full thickness cartilage laterally with no central ulcer; <15 degrees of flexion contracture, < 15 degrees varus and > 90 degrees flexion. The state of the patellofemoral joint, chondrocalcinosis, obesity, age and activity level are NOT contraindications to medial mobile-bearing UKA. The only certain contraindications are the presence of inflammatory arthritis or a history of previous high tibial osteotomy (HTO). Advantages of medial UKA are that it preserves undamaged structures, it is a minimally invasive technique with low incidence of perioperative morbidity, preservation of the cruciate mechanism results in more “normal” kinematics versus TKA, it normalises contact forces and pressures in the patellofemoral joint, and it provides better range of motion than TKA. Furthermore, medial UKA results in better function than TKA in gait studies, with demanding activities, such as climbing stairs, having a better “feel”. Pain relief with medial UKA is equivalent or better than TKA, and morbidity and mortality are decreased compared with TKA, as well as venous thromboembolism. Recommended preoperative imaging studies consist of plain radiographs with the following views obtained: standing AP, PA flexed, lateral, Merchant or axial, and valgus stress. There are several surgical perils associated with performing medial UKA. First, in regard to patient selection, avoid medial UKA in patients with residual hyaline cartilage – the joint must be bone on bone. Second, perform a conservative tibial resection with respect to depth to prevent tibial collapse as well as excessive overload of weakened bone, and avoid excessive posterior slope. Perform the tibial resection coplanar with tibial spine/ACL insertion to maximise tibial coverage. Avoid overcorrection of deformity. Do not perform a medial release. Balance flexion/extension gaps meticulously. For mobile-bearing designs, remove all impinging osteophytes. Over 55 published studies report results with mobile-bearing medial UKA, with survival ranging 63.2–100% at mean follow-up ranging from 1 to 17.2 years

Introduction. MERA Quest Knee System (Quest Knee) is a posterior cruciate ligament–retaining prosthesis considering the anatomical features and lifestyles of the Japanese. As for the anatomical features, we reduced the size of prosthesis and set a smaller interval of sizes because Japanese knees are smaller and flatter than those of Caucasians. As for the lifestyles, we evaluated in vivo patellar tracking during deep knee flexion and the condylar geometry in the axial plane of magnetic resonance imaging. It was found that the patella sank deeply into the intercondylar notch and that the articular surface of the lateral condyle began to curve steeply. We adopted this shape and engraved the lateral condyle deep to reduce the pressure of the patellofemoral joint and to get better range of motion (ROM). For the contact pressure rise in the femorotibial joint by engraving the lateral condyle, the insert was suited to the shape of the femoral component. Furthermore, we increased the thickness of the posterior flange of the femoral component and changed the posterior radius of curvature gradually, and this shape allowed the flexion of 155°. We have used Quest Knee for clinical applications from October 2009. We studied the short-term results of Quest Knee. Methods. Between June 2010 and July 2013, the same senior surgeon performed 59 consecutive primary operations with Quest Knee. Forty patients (44 knees) were women, and 14 patients (15 knees) were men. The mean patient age was 72.5 years (range, 59–89 years). All were osteoarthritis knees. Coronal deformity was varus in 58 knees and valgus in one knee. All operations were performed with a measured resection technique, and all patellae were resurfaced. Clinical evaluations were assessed using the Japanese Orthopaedic Association knee rating score (JOA score), and clinical ROM and standing femorotibial angle (FTA) were measured. Additionally, three-dimensional motion analysis of the patellar component during squatting was performed by the image matching method with image correlations. Results. The mean follow-up period was 17.4 months (range, 6–43 months). The JOA score at preoperative and follow-up were 57.5 ± 10.1 and 87.5 ± 5.6 points, respectively (P < 0.0001) (Fig. 1). The ROM at preoperative and follow-up were 127.4 ± 11.1 and 126.2 ± 9.0° (P = 0.47) (Fig. 2). The mean FTA at preoperative and follow-up were 184.2 and 172.3°. With regard to the three-dimensional motion analysis, the patella showed lateral shift during squatting (Fig. 3). Discussion. As for the patellofemoral contact pressure at flexion in total knee arthroplasty, a biomechanical study has reported that the pressures of posterior cruciate ligament–retaining and posterior-stabilized knees were 3.2 and 2.8 times as much as the body weight. This report suggests that the reduction of the pressure of the patellofemoral joint during deep knee flexion results in better ROM. We suppose that Quest Knee reduced the pressure, led the patella to the lateral side, and achieved better ROM. Conclusions. Short-term results of Quest Knee were good. More detailed studies are needed to get better function and long-term durability