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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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