Aims. The use of cementless total knee arthroplasty (TKA) components has increased during the past decade. The initial design of cementless metal-backed patellar components had shown high failure rates due to many factors. The aim of this study was to evaluate the clinical results of a second-generation cementless, metal-backed patellar component of a modern design. Methods. This was a retrospective review of 707 primary TKAs in 590 patients from a single institution, using a cementless, metal-backed patellar component with a mean follow-up of 6.9 years (2 to 12). A total of 409 TKAs were performed in 338 females and 298 TKAs in 252 males. The mean age of the patients was 63 years (34 to 87) and their mean BMI was 34.3 kg/m. 2. (18.8 to 64.5). The patients were chosen to undergo a cementless procedure based on age and preoperative radiological and intraoperative bone quality. Outcome was assessed using the Knee Society knee and function scores and range of motion (ROM), complications, and revisions. Results. A total of 24 TKAs (3.4%) in 24 patients failed and required revision surgery, of which five were due to patellar complications (0.71%): one for aseptic patellar loosening (0.14%) and four for polyethylene dissociation (0.57%). A total of 19 revisions (2.7%) were undertaken in 19 patients for indications which did not relate to the patella: four for aseptic tibial loosening (0.57%), one for aseptic femoral loosening (0.14%), nine for periprosthetic infection (1.3%), one for popliteus impingement (0.14%), and four for instability (0.57%). Knee Society knee and function scores, and ROM, improved significantly when comparing pre- and postoperative values. Survival of the metal-backed patellar component for all-cause failure was 97.5% (95% confidence interval 94.9% to 100%) at 12 years. Conclusion. The second-generation cementless TKA design of metal-backed patellar components showed a 97.5% survival at 12 years, with polyethylene dissociation from the metal-backing being the most common cause of patellar failure. In view of the increased use of TKA, especially in younger, more active, or obese patients, these findings are encouraging at mean follow-up of seven years. Cite this article: Bone Joint J 2023;105-B(12):1279–1285

Introduction. Persistent patellofemoral (PF) pain is a common postoperative complication after total knee arthroplasty (TKA). In the USA, patella resurfacing is conducted in more than 80% of primary TKAs [1], and is, therefore, an important factor during surgery. Studies have revealed that the position of the patellar component is still controversially discussed [2–4]. However, only a limited number of studies address the biomechanical impact of patellar component malalignment on PF dynamics [2]. Hence, the purpose of our present study was to analyze the effect of patellar component positioning on PF dynamics by means of musculoskeletal multibody simulation in which a detailed knee joint model resembled the loading of an unconstrained cruciate-retaining (CR) total knee replacement (TKR) with dome patella button. Material and Methods. Our musculoskeletal multibody model simulation of a dynamic squat motion bases on the SimTK data set (male, 88 years, 66.7 kg) [5] and was implemented in the multibody dynamics software SIMPACK (V9.7, Dassault Systèmes Deutschland GmbH, Gilching, Germany). The model served as a reference for our parameter analyses on the impact on the patellar surfacing, as it resembles an unconstrained CR-TKR (P.F.C. Sigma, DePuy Synthes, Warsaw, IN) while offering the opportunity for experimental validation on the basis of instrumented implant components [5]. Relevant ligaments and muscle structures were considered within the model. Muscle forces were calculated using a variant of the computed muscle control algorithm. PF and tibiofemoral (TF) joints were modeled with six degrees of freedom by implementing a polygon-contact model, enabling roll-glide kinematics. Relative to the reference model, we analyzed six patellar component alignments: superior-inferior position, mediolateral position, patella spin, patella tilt, flexion-extension and thickness. The effect of each configuration was evaluated by taking the root-mean-square error (RMSE) of the PF contact force, patellar shift and patellar tilt with respect to the reference model along knee flexion angle. Results. The analysis showed that the PF contact force was mostly affected by patellar component thickness (RMSE=440 N) as well as superior-inferior (RMSE=199 N), and mediolateral (RMSE=98 N) positioning.. PF kinematics was mostly affected by mediolateral positioning, patellar component thickness, and superior-inferior positioning. Medialization of the patellar component reduced the peak PF contact force and caused a lateral patellar shift. Discussion. Based on our findings, we conclude that malalignment in mediolateral and superior-inferior direction, tilt and thickness of patellar resurfacing are the most important intraoperative parameters to affect PF dynamics. It could be shown that the translational positioning is more critical than rotational positioning regarding PF contact force. Reported findings are in good agreement with previous experimental and clinical studies [2–4]. Our data reveal that patellar component positioning has to be aligned precisely during total knee arthroplasty to prevent postoperative complications. For any figures or tables, please contact authors directly

Introduction:. The widespread use of TKA promoted studies on kinematics after TKA, particularly of the femorotibial joint. Knee joint kinematics after TKA, including the range of motion (ROM) and the physical performance, are also influenced by the biomechanical properties of the patella. Surgeons sometimes report complications after TKA involvinganterior knee pain, patellofemoral impingement and instability. However, only few studies have focused specially on the patella. Because the patella bone is small and overlapped with the femoral component on scan images. In addition, the patellar component in TKA is made of x-ray–permeable ultra-high molecular weight polyethylene. It is impossible to radiographically determine the external contour of the patellar component precisely. No methods have been established to date to track the dynamic in vivo trajectory of the patella component. In this study, we analyzed the in vivo three-dimensional kinematics of the patellar component in TKA by applying our image matching method with image correlations. Methods:. A computed tomography (CT) and an x-ray flat panel detector system (FPD) were used. FPD-derived post-TKA x-ray images of the residual patellar bone were matched by computer simulation with the virtual simulation images created using pre-TKA CT data. For the anatomic location of the patellar component, the positions of the holes drilled for the patellar component pegs were used. This study included three patients with a mean age of 68 years (three females with right knee replacement) who had undergone TKA with the Quest Knee System and achieved a mean passive ROM of 0 to ≥ 130° after 6 or more month post-TKA. We investigated three-dimensional movements of the patellar component in six degrees of freedom (6 DOF) during squatting and kneeling. Furthermore, we simulated the three-dimensional movement of the patellar component, and we estimated and visualized the contact points between the patellar and femoral components on a three-dimensional model. Results:. Average root mean square errors of this technique with the patellar bone of a fresh-frozen pig complete knee joint have been confirmed as 0.2 mm for the translations and 0.2 degrees for the rotation. The 6 DOF analysis results showed that patellar dynamics were similar for all subjects on squatting and kneeling. For the patellar rotation during squatting, only 1 to 2 additional degrees were noted for all subjects. During kneeling, the patellar rotation noted adduction for all subjects. The patellar contact point on the femoral component gradually showed superior shift, increasing the distance with knee flexion during squatting and kneeling (Fig, 1. 2). Discussions and Conclusions:. In this study, no patellar shifts were detected in rotation or tilt during squatting, suggesting that the patellar component remained in the positions designed for early stages of flexion. And the patellar component shifted towards the lateral side during squatting. This finding suggests the idea that the patellar movement reflected the design of the Quest Knee system. This study demonstrated that the analytical method is useful for evaluating the pathologies and post-surgical conditions of the knee and other joints

Aims: The aim of the study was to determine the efþcacy of jet lavage in comparison to syringe lavage with respect to cement penetration and stability of the poly-ethylene patellar component after patellar resurfacing in total knee arthroplasty. Methods: In a cadaver study, we prepared 37 fresh frozen human patella pairs. The retropatellar bed was randomly cleaned with either jet lavage or a bladder syringe. The polyethylene component was cemented using Palacos R. For 12 patella pairs, sagittal sections were obtained at predeþned levels using a diamond saw. Mikroradiograms were digitised and analysed with respect to cement penetration. For the remaining 25 patella pairs, pullout tests were performed on patellar components using a traction-compression device. Results: Cement penetration was signiþcantly greater (P< 0.0001) in the jet lavage specimens compared to the syringe lavage specimens. The maximum force required to cause mechanical failure was signiþcantly greater (P< 0,0001) in jet lavage specimens compared to syringe lavage specimens. Conclusions: Our results support the routine use of jet lavage for cleansing the patellar bed prior to cement application in cemented patellar resurfacing

Purpose: Patellar complications are among the most frequent after total knee arthroplasty. Encasing the patellar piece is one way of resisting the shear forces leading to loosening. Material and Methods: We studied at more than five years the results obtained with a total knee prosthesis implanted with preservation of the posterior cruciate ligament (PCL). This prosthesis has an asymmetric encased patellar insert with a cemented central pivot. The instrumentation ensures patellar thickness. We reviewed 104 implants at more than five years. Six had been lost to follow-up. Ninety-eight implants were still in place. Results: The following complications were observed: four fractures of the upper rim with little displacement (these fractures healed and pain regressed but the insert had moved); three vertical patellar fractures with little displacement (these fractures healed; two were symptomatic temporarily); one transverse fracture of the upper pole with displacement causing a defect in active extension; eight moderate asymptomatic impactions which were visible on the lateral x-ray (modified orientation of the insert with cement fracture). There was no significant difference for functional results (pain 40.9; movement 21.9; knee score 84.3) between patients with or without a patellar complication. Discussion: Insertion of an asymmetric prosthesis increased the risk of an orientation error (two cases early in our experience). Encasing the patellar insert limits medialisation yet the centering was satisfactory (centred patella 95.2%, shift 3.6%, subluxation 1.2%). Encasing provides a peripheral wall protecting against transverse sheer forces. The lateral wall did not fracture, demonstrating its efficacy. The upper wall can fracture under the force of flexion without functional consequences. The other fractures, favoured by section of the lateral patellar wing (p< 0.05), were not treated. Moderate but certain impaction was noted in eight cases at a mean 3.5 years (1–6 years). It was due to failure of bony support under the effect of the compression forces applied on a small surface. The diameter of the encased patellar inserts was rarely more than 25 mm. Once the prosthesis is in place, the periphery of the patella is the only component articulating with the trochlea and its impaction does not cause further aggravation. This contact did not lead to pain in any patients. Conclusions: Complications observed with encased patellar components differ from the better known apposed prostheses

Purpose: Patellar complications are among the most frequent after total knee arthroplasty. Encasing the patellar piece is one way of resisting the shear forces leading to loosening. Material and methods: We studied at more than five years the results obtained with a total knee prosthesis implanted with preservation of the posterior cruciate ligament (PCL). This prosthesis has an asymmetric encased patellar insert with a cemented central pivot. The instrumentation ensures patellar thickness. We reviewed 104 implants at more than five years. Six had been lost to follow-up. Ninety-eight implants were still in place. Results: The following complications were observed: four fractures of the upper rim with little displacement (these fractures healed and pain regressed but the insert had moved); three vertical patellar fractures with little displacement (these fractures healed; two were symptomatic temporarily); one transverse fracture of the upper pole with displacement causing a defect in active extension; eight moderate asymptomatic impactions which were visible on the lateral x-ray (modified orientation of the insert with cement fracture). There was no significant difference for functional results (pain 40.9; movement 21.9; knee score 84.3) between patients with or without a patellar complication. Discussion: Insertion of an asymmetric prosthesis increased the risk of an orientation error (two cases early in our experience). Encasing the patellar insert limits medialisation yet the centering was satisfactory (centred patella 95.2%, shift 3.6%, subluxation 1.2%). Encasing provides a peripheral wall protecting against transverse sheer forces. The lateral wall did not fracture, demonstrating its efficacy. The upper wall can fracture under the force of flexion without functional consequences. The other fractures, favoured by section of the lateral patellar wing (p< 0.05), were not treated. Moderate but certain impaction was noted in eight cases at a mean 3.5 years (1–6 years). It was due to failure of bony support under the effect of the compression forces applied on a small surface. The diameter of the encased patellar inserts was rarely more than 25 mm. Once the prosthesis is in place, the periphery of the patella is the only component articulating with the trochlea and its impaction does not cause further aggravation. This contact did not lead to pain in any patients. Conclusions: Complications observed with encased patellar components differ from the better known apposed prostheses

Aims. Our intention was to investigate if the highly porous biological fixation surfaces of a new 3D-printed total knee arthroplasty (TKA) achieved adequate fixation of the tibial and patellar components to the underlying bone. Patients and Methods. A total of 29 patients undergoing primary TKA consented to participate in this prospective cohort study. All patients received a highly porous tibial baseplate and metal-backed patella. Patient-reported outcomes measures were recorded and implant migration was assessed using radiostereometric analysis. Results. Patient function significantly improved by three months postoperatively (p < 0.001). Mean difference in maximum total point motion between 12 and 24 months was 0.021 mm (-0.265 to 0.572) for the tibial implant and 0.089 mm (-0.337 to 0.758) for the patellar implant. The rate of tibial and patellar migration was largest over the first six postoperative weeks, with no changes in mean tibia migration occurring after six months, and no changes in mean patellar migration occurring after six weeks. One patellar component showed a rapid rate of migration between 12 and 24 months. Conclusion. Biological fixation appears to occur reliably on the highly porous implant surface of the tibial baseplate and metal-backed patellar component. Rapid migration after 12 months was measured for one patellar component. Further investigation is required to assess the long-term stability of the 3D-printed components and to determine if the high-migrating components achieve fixation. Cite this article: Bone Joint J 2019;101-B(7 Supple C):40–47

Abstract. Patellofemoral Arthroplasty (PFA) is an alternative to TKA for patellofemoral osteoarthritis that preserves tibiofemoral compartments. It is unknown how implant positioning affects biomechanics, especially regarding the patella. This study analysed biomechanical effects of femoral and patellar component position, hypothesising femoral positioning is more important. Nine cadaveric knees were studied using a repeated-measures protocol. Knees were tested intact, then after PFA implanted in various positions: neutral (as-planned), patellar over/understuffing (±2mm), patellar tilt, patellar flexion, femoral rotation, and femoral tilt (all ±6°). Arthroplasties were implemented with CT-designed patient-specific instrumentation. Anterior femoral cuts referenced Whiteside's line and all femoral positions ensured smooth condyle-to-component transition. Knee extension moments, medial patellofemoral ligament (MPFL) length-change, and tibiofemoral and patellofemoral kinematics were measured under physiological muscle loading. Data were analysed with one-dimensional statistical parametric mapping (Bonferroni-Holm corrected). PFA changed knee function, altering extension moments (p<0.001) and patellofemoral kinematics (p<0.05), but not tibiofemoral kinematics. Patellar component positioning affected patellofemoral kinematics: over/understuffing influenced patellar anterior translation and the patellar tendon moment arm (p<0.001). Medially tilted patellar cuts produced lateral patellar tilt (p<0.001) and vice versa. A similar inverse effect occurred with extended/flexed patellar cuts, causing patellar flexion and extension (p<0.001), respectively. Of all variants, only extending the patellar cut produced near-native extension moments throughout. Conversely, the only femoral effect was MPFL length change between medially/laterally rotated components. PFA can restore native knee biomechanics. Provided anterior femoral cuts are controlled and smooth condyle-to-component transition assured, patellar position affects biomechanics more than femoral, contradicting the hypothesis

Abstract. Objectives. Patella resurfacing in primary total knee arthroplasty (TKA) remains a contentious issue. Australian rates of patellar resurfacing are 66.6%, significantly higher compared to UK rates of 8–15% and Swedish rates of 2%. Resurfacing has gained popularity in Australia since registry data has shown decreased revision rates with no increase in patellar component related complications. We present for discussion an analysis of 113,694 total knee arthroplasties using commonly implanted prostheses in the UK. Methods. We included all TKA's since the Australian register's conception on 01/09/1999 for a primary diagnosis of osteoarthritis involving the use of either the Triathlon or Duracon implant with and without patellar components. The primary outcome of the study was time to revision for Triathlon's resurfaced and non-resurfaced prosthesis compared to the Duracon's equivalent data. We also analysed the reasons for revision between the 4 groups, type of revision and complication rates. We then compared minimally stabilised and posterior stabilised prostheses. Results. The cumulative revision rate for Triathlon prostheses with resurfacing after 12 years was 3.2% (95% CI, 2.9% to 3.6%) compared to 5.6% (95% CI, 5.0% to 6.2%) without resurfacing. Duracon's equivalent data was 6.3% with resurfacing and 5.9% without resurfacing. Triathlon prosthesis with resurfacing have much lower rates of revision due to loosening, patellofemoral pain, patellar erosion compared to unresurfaced Triathlon prostheses. Conclusion. Triathlon with re-surfacing has lower revision rates regardless of age or BMI. Previous concerns regarding patellofemoral loosening, tibial wear, maltracking relate to Duracon only, indicating the importance of implant specific studies. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction. We have been re-evaluating patellofemoral alignment after total knee arthroplasty (TKA) by using a weight- bearing axial radiographic view after detecting patellar maltracking (lateral tilt > 5° or lateral subluxation > 5 mm) on standard non-weight-bearing axial radiographs. However, it is unclear whether the patellar component shape affects this evaluation method. Therefore, we compared 2 differently shaped components on weight-bearing axial radiographs. Methods. From 2004 to 2013, 408 TKAs were performed with the same type of posterior-stabilized total knee implant at our hospital. All patellae were resurfaced with an all-polyethylene, three-pegged component to restore original thickness. Regarding patellar component type, an 8-mm domed component was used when the patella was so thin that a 10-mm bone cut could not be performed. Otherwise, a 10-mm medialized patellar component was selected. Twenty-five knees of 25 patients, in whom patellar maltracking was noted on standard axial radiographs at the latest follow-up, were included in this study. Knees were divided into 2 groups: 15 knees received a medialized patella (group M) while 10 received a domed patella (group D). Weight-bearing axial radiographs with patients in the semi-squatting position were recorded with the method of Baldini et al. Patellar alignment (tilt and subluxation) was measured according to the method described by Gomes et al. using both standard and weight-bearing axial views. Results. Patients’ demographic data, such as age at surgery, sex, and disease were similar for both groups. The average follow-up period was significantly longer in group D than group M (5.4 years vs. 2.5 years, respectively; p = 0.0045, Mann- Whitney U-test). The lateral tilt angle decreased significantly (p < 0.0001, paired t-test) from 6.5° ± 2.8° to 1.0° ± 1.2° with weight bearing in group M. However, this parameter in group D changed from 6.7° ± 2.7° to 4.7° ± 3.0° with weight bearing; the difference was not significant. Lateral subluxation also decreased significantly (p < 0.0001, paired t-test) from 5.1 mm ± 2.4 mm to 2.5 mm ± 1.4 mm with weight bearing in group M. However, that in group D changed from 2.8 mm ± 2.7 mm to 2.4 mm ± 2.8 mm with weight bearing, and the difference was not significant. On weight-bearing views, patellar maltracking was noted in 4 knees in group D but no knees in group M. The difference was significant (p = 0.017, Fisher's exact test). One of the 21 patients with adequate patellar tracking (4.8%) and 1 of 4 patients with maltracking (25%) complained of mild anterior knee pain. Discussion. Patellar tracking on axial radiographic views improved better in group M than in group D with weight bearing. The patellofemoral contact area was maintained with a domed patella despite tilting, but not with a medialized patella. Our results indicate that the shape difference affected the degree of radiographic improvement. Thus, the weight-bearing axial radiographic view devised by Baldini et al. is useful for evaluating patellofemoral alignment after TKA, but the shape of the patellar component should be considered for result interpretation

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

Complications of the patellofemoral (PF) joint remain a common cause for revision of total knee replacements. PF complications, such as patellar maltracking, subluxation, dislocation and implant failure, have been linked to femoral and patellar component alignment. Computational analyses represent an efficient method for investigating the effects of patellar and femoral component alignment and loading on output measures related to long term clinical success (i.e. kinematics, contact mechanics) and can be utilized to make direct comparisons between common patellar component design types. Prior PF alignment studies have generally involved perturbing a single alignment parameter independently, without accounting for interaction effects between multiple parameters. The objective of the current study was to determine critical alignment parameters, and combinations of parameters, in three patellar component designs, and assess whether the critical parameters were design specific. A dynamic finite element (FE) model of an implanted PF joint was applied in conjunction with a 100-trial Monte Carlo probabilistic simulation to establish relationships between alignment and loading parameters and PF kinematics, contact mechanics and internal stresses (Figure 1). Seven parameters, including femoral internal-external (I-E) alignment, patellar I-E, flexion-extension (F∗∗∗∗∗E) and adduction-abduction (A-A) rotational alignment, and patellar medial-lateral (M-L) and superior-inferior (S-I) translational alignment, as well as percentage of the quadriceps load on the vastus medialis obliquus (VMO) tendon, were perturbed in the probabilistic analysis. Ten output parameters, including 6-DOF PF kinematics, peak PF contact pressure, contact area, peak von Mises stress and M-L force due to contact, were evaluated at 80 intervals during a simulated deep knee bend. Three types of patellar component designs were assessed; a dome-compatible patellar component (dome), a medialized dome-compatible patellar component (modified dome), and an anatomic component (anatomic). Model-predicted bounds at 5 and 95% confidence levels were determined for each output parameter throughout the range of femoral flexion (Figure 2). Traditional sensitivity analysis, in addition to a previously described coupled probabilistic and principal component analysis (probabilistic-PCA) approach, were applied to determine the relative importance of alignment and loading parameters to knee mechanics in each of the three designs. The dome component demonstrated the least amount of variation in contact mechanics and internal stresses, particularly in the 30–100° flexion range, with respect to alignment and loading variability. The modified dome had substantially reduced M-L contact force when compared with the dome. The anatomic design, while wide bounds of variability were predicted, had consistently greater contact area and lowered contact pressure than the dome and modified dome designs. The anatomic design also reproduced more natural sagittal plane patellar tilt than the other components. All three designs were most sensitivity to femoral I-E alignment. Thereafter, sensitivity to component alignment was design specific; for the anatomic component, the main alignment parameter was F-E, while for the domed components it was a combination of F-E and translation (M-L and S-I) (Figure 3). Understanding the relationships and design-specific dependencies between alignment parameters can add value to surgical pre-operative planning, and may help focus instrumentation design on those alignment parameters of primary concern

INTRODUCTION. Wear and fracture of patellar components has been frequently reported as a failure mode for cemented and press-fit patellar components. Malalignment of the patellar components may cause higher contact stresses, which may lead to excessive wear, delamination, and/or component fracture. In vitro testing of the patella in a clinically relevant malaligned condition is necessary to demonstrate adequate performance of the patellar component and assess the endurance of its fixation features under severe loading conditions. The purpose of this study was to test in vitro the patellar components under malaligned conditions using a knee joint simulator. MATERIALS AND METHODS. A 6 station MTS (Eden Prairie, MN) knee joint wear simulator and Alpha Calf Fraction serum (Hyclone Labs, Logan, UT) diluted to 50% with a pH-balanced 20-mMole solution of deionized water and EDTA was used (protein level = 20 g/l) for testing. Asymmetric, all-polyethylene, patellar components with an overall construct thickness of 11 mm (Duracon®, Stryker Orthopaedics, Mahwah, NJ) were used. Appropriately sized cobalt-chrome femoral components articulated against the patellae. The patellae were cemented (Simplex, Stryker Orthopaedics, Mahwah, NJ) to delrin fixtures, which placed the patella in 10° of lateral tilt (Figure 1). This angle was chosen based off the work of Huang et al, which was one of the larger average tilt angles reported in vivo. Replicating this scenario in vitro allows for observation of the potential scenario that may occur as the femoral component maintains contact strictly on the thinner lateral edge of the patella, concentrating both the axial and shear loads on a small area of polyethylene. The loading and kinematic profiles used for testing were published previously (maximum axial load: 2450N and maximum patellofemoral angle: 54°. Variations of the loading profile were studied by evaluating the effects of heavier patients, which increased the maximum axial load to 3100N(250lb patient) and 3750N(300lb patient) (Figure 2). Lateral offset was tested to evaluate the effect of malalignment. Increments of 1mm were analyzed starting from the neutral position, eventually reaching a maximum lateral offset of 5mm. A 6-dof load cell was placed beneath the patella fixturing to capture dynamic loads (ATI, Apex, NC). The axial and medial/lateral shear loads where used to calculate the resultant medial/lateral shear force being applied to the patellar pegs. RESULTS. The results of using a heavier loading profile and increasing lateral offset are shown in Figure 3. At neutral alignment, the effect of increasing the axial load caused an increase of 10% in resultant shear force. At 5 mm of lateral offset, the increase in loading caused the shear force to increase by 16%. With each loading profile, increasing the lateral offset from 0 to 5 mm caused the resultant shear force to increase two-fold. DISCUSSION. This test model allows for an aggressive method of testing patellar implants and it includes variables to adjust for severity (lateral offset and joint reaction force). Although increasing the amount of lateral patellar offset increases the resultant shear forces, the patellar wear rates remained minimal and constant. Hence, a femoral component that has a forgiving patellar tracking may demonstrate minimal wear, even when evaluated in extremely aggressive test conditions. Note: These results are specific to the device used since the results will be dependant on the function and design of the patellar implant and patella/femur track

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

Many recent knee prostheses are designed aiming to the physiological knee kinematics on tibiofemoral joint, which means the femoral rollback and medial pivot motion. However, there have been few studies how to design a patellar component. Since patella and tibia are connected by a patellar tendon, tibiofemoral and patellofemoral motion or contact forces might affect each other. In this study, we aimed to discuss the optimal design of patellar component and simulated the knee flexion using four types of patellar shape during deep knee flexion. Our simulation model calculates the position/orientation, contact points and contact forces by inputting knee flexion angle, muscle forces and external forces. It can be separated into patellofemoral and tibiofemoral joints. On each joint, calculations are performed using the condition of point contact and force/moment equilibrium. First, patellofemoral was calculated and output patellar tendon force, and tibiofemoral was calculated with patellar tendon force as external force. Then patellofemoral was calculated again, and the calculation was repeated until the position/orientation of tibia converged. We tried four types of patellar shape, circular dome, cylinder, plate and anatomical. Femoral and tibial surfaces are created from Scorpio NRG PS (Stryker Co.). Condition of knee flexion was passive, with constant muscle forces and varying external force acting on tibia. Knee flexion angle was from 80 to 150 degrees. As a result, the internal rotation of tibia varied much by using anatomical or plate patella than dome or cylinder shape. Although patellar contact force did not change much, tibial contact balances were better on dome and cylinder patella and the medial contact forces were larger than lateral on anatomical and plate patella. Thus, the results could be divided into two types, dome/cylinder and plate/anatomical. It might be caused by the variations of patellar rotation angle were large on anatomical and plate patella, though patellar tilt angles were similar in all the cases. We have already reported that the anatomical shape of patella would contact in good medial-lateral balance when tibia moved physiologically, therefore we have predicted the anatomical patella might facilitate the physiological tibiofemoral motion. However, the results were not as we predicted. Actually our previous and this study are not in the same condition; we used a posterior-stabilized type of prosthesis, and the post and cam mechanism could not make the femur roll back during deep knee flexion. It might be better to choose dome or cylinder patella to obtain the stability of tibiofemoral joint, and to choose anatomical or plate to the mobility

Introduction. Uncemented highly porous titanium implants have been shown to promote osseointegration, and may result in a durable construct for total knee arthroplasty (TKA). Given the mixed results of uncemented TKA, it is important to evaluate the early stability for this product. The objective of the following study was to use radiostereometric analysis (RSA) to assess early fixation of a highly porous tibial baseplate and metal backed patella. Methods. Twenty-seven patients (mean age 64 years, 30% female) undergoing primary TKA consented to participate in this prospective cohort study. All patients received a highly porous tibial baseplate, a metal backed patella and tantalum RSA bone markers. Implant migration was assessed using model-based RSA at 1.5, 3, 6, 12 and 24 months post-operative. Patient reported outcome measures were captured using the same follow-up schedule, and compared to pre-operative measures. Results. There were no adverse events affecting implant fixation, and no revisions. Patient function significantly improved by 3 months post-operation (p < 0.001). The highest rate of tibia and patellar component migration occurred over the first six post-operative weeks, with minimal migration thereafter. Mean maximum total point motion (MTPM) at 24 months was 0.72 (SD 0.34) mm for the tibia, and 0.44 (SD 0.25) mm for the patella. Three tibia baseplates migrated more than 1 standard deviation greater than the mean at 24 months, and also had continuous migration (> 0.2mm of MTPM) in the second post-operative year. One patellar component showed a rapid rate of migration between 6 and 24 months, whereas all other patellar components appeared to stabilize. Conclusions. Osseointegration appears to occur on the highly porous implant surface of the tibia baseplate and metal backed patella, as evidenced by implant stability. Further follow-up is required to determine if clinical loosening will manifest in the continuously migrating implants

Introduction A biomechanical model was developed to measure wear of all-polyethylene patellar components as it relates to femoral component mal-rotation. The model, based on high load and flexion activities such as stair climbing, was used to differentiate the effects of femoral mal-rotation and differing materials on a single patellar design. Methods The patellar components (Scorpio®, Stryker-Howmedica-Osteonics) were cemented onto metal fixtures and articulated against “aligned” and “mal-aligned” (six degrees internally rotated) femoral components. The patellar components were subjected to a constant force and articulated against femoral components flexing from 600 to 1200. Patellae of identical geometry, made of conventional and highly cross-linked ultra-high molecular weight polyethylene, were tested to 1x106 cycles. Following testing, patellar wear was determined by gravimetric measurement relative to soaked control specimens. Results All conventional polyethylene patellae demonstrated damage in the form of burnishing and scratching of the articular surface. The mal-aligned conventional ultra-high molecular weight patellae demonstrated increased weight loss or wear relative to the aligned components (p=.048). All rotationally mal-aligned highly cross-linked polyethylene components sustained polyethylene fracture or catastrophic failure of the cement-polyethylene construct. Conclusions Rotational mal-alignment of the femoral component will result in increased wear of polyethylene patellar components. The newer highly cross-linked materials failed to resolve this wear problem and sustained catastrophic failure when mal-aligned. Attention needs to be given to the patella-femoral articulation when implanting knee components and when developing new polyethylene as the forces in this articulation may result in polyethylene behaviour that varies dramatically from the femoraltibial articulation. In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits

INTRODUCTION: Following Total Knee Arthroplasties, patellofemoral complications have shown to be responsible for approximately 50% of re-operations. Contemporary patellar designs employ both “onlay” and “inset” configurations. The latter promotes ease of placement, reduced bone removal and a heralded theoretic advantage of increased strength at the fixation interface. However, to date, no reports have compared the disassociation strengths of these two patellar component modes of fixation. The purpose of this study is to quantify the shear disassociation strength for both onlay and inset patellar fixation techniques. METHODS: Two sets of synthetic solid foam patellae were prepared using standard milling techniques for symmetrical, three-peg onlay and inset polyethylene cylinders of identical dimension. The use of synthetic bones in mechanical testing was validated in the past. The cylinders were cemented to the synthetic patellae, using standard cementing techniques. The fixation resistance of both groups was measured using an Instron Testing Machine. A compressive joint force simulating chair rise was applied perpendicular to the anterior surface of the patellar component model. A shearing displacement was then applied to the composite until patellar component disassociation. RESULTS: The mean shear strength of the onlay group was 2540 N SD 236 N, (n=7) and 3180 N SD 186 N, (n=6) for the inset group. The inset patellae was 25% (640 N) stronger than the onlay patellae, (p=0.0002, two-tailed student t-test). DISCUSSION/CONCLUSION: The results of the study demonstrated a significantly higher resistance of inset patellar fixation to shear stress compared to onlay patellar fixation. Although further in-vivo studies are indicated, the data suggests that the use of inset patella in total knee replacements may offer stronger fixation and consequently decreasing morbidity associated with patella implant loosening

Purpose. Measurements of patellar kinematics are essential to investigate the link between anterior knee pain following knee arthroplasty and patellar maltracking. A major challenge in studying the patellofemoral (PF) joint postoperatively is that the patellar component is only partially visible in the sagittal and close-to-sagittal radiographs. The narrow angular distance between these radiographs makes the application of conventional bi-planar fluoroscopy impossible. In this study a methodology has been introduced and validated for accurate estimation of the 3D kinematics of the PF joint post-arthroplasty using a novel multi-planar fluoroscopy approach. Method. An optoelectronic camera (Optotrak Certus) was used to track the motion of an ISO-C fluoroscopy C-arm (Siemens Siremobil) using two sets of markers attached to the X-ray source and detector housings. The C-arm was used in the Digital Radiography (DR) mode, which resembles an ordinary X-ray fluoroscopy image. A previously-developed technique (Cho et al., 2005; Daly et al., 2008) was adapted to find the geometric parameters of the imaging system. Thirty-eight DRs of the calibration phantom were obtained for the 190 of rotation of the C-arm at 5 rotational increments while data from motion markers were recorded continuously at a frequency of 100 Hz. A total knee replacement prosthesis was implanted on an artificial bone model of the knee, and the implant components and bones were rigidly fixed in place using a urethane rigid foam. For the purpose of validation, positions of the implant components were determined using a coordinate measuring machine (CMM). Sagittal and obliquely sagittal radiographs of the model were taken where the patellar component was most visible. For each DR the geometric parameters of the system were interpolated based on the location of the motion markers. The exact location of the projection was then determined in 3D space. JointTrack Bi-plane software (Dr. Scott Banks, University of Florida, Gainesville) was used to conduct 2D-3D registration between the radiographs and the reverse-engineered models of the implant components. Results of the registration were directly compared to the ground-truth obtained from the CMM to calculate the accuracies. Results. The accuracies for the PF were found to be 0.48 mm and 1.32 for position and orientation of the components. For the tibiofemoral joint these values were found to be 0.89 mm and 1.43, respectively. Conclusion. The multi-planar method can be used to assess the sequential kinematics of the patellofemoral and tibiofemoral joints including the mediolateral translation and tilt of the patellar component, which are obscured in standard 2D sagittal measurements and are not possible using the traditional bi-planar setup. A limitation is that it can only be used for static imaging of the joint. It has the advantage of a relatively low radiation dose. This methodology can be used to investigate the relationship between maltracking of the patella and anterior knee pain as well as other postoperative complications

Introduction/Aim. Outcomes for guided motion primary total knee arthroplasty (TKA) in obese patients are unknown. Materials and Methods. 1,684 consecutive patients underwent 2,059 primary TKAs with a second-generation guided motion implant (Journey II Bi-Cruciate Stabilized Knee System, Smith & Nephew, Inc., Memphis) between 2011–2017 at three European and seven US sites. Results. Of 2,003 (97.3%) TKAs in 1,644 patients with BMI data: average age 64.5 years; 58.4% females; average BMI 32.5 kg/m. 2. ;13.4% had BMI ≥ 40 kg/m. 2. Subjects with BMI ≥ 40 kg/m. 2. had longest length of hospital stay (LOS) at European sites; LOS similar at US sites. Subjects with BMI ≥ 40 kg/m. 2. (P=0.0349) had longest surgery duration. BMI ≥ 40 kg/m. 2. had more re-hospitalizations or post-TKA reoperations than BMI < 40 kg/m. 2. (12.7% and 9.2% at five-year post-TKA, P<.0495). 62 TKAs were revised (3.39/100 TKA at five years) with no differences in revision risk between groups. 17 (27.4%) revisions involved femoral or tibial component removal; 45 (72.6%) involved tibial insert or patellar component removal only with revision risk similar between groups. Discussion. Our results corroborate literature-reported revision outcomes of standard TKAs in obese patients. Conclusion. Surgery duration and long-term complication rates are higher in patients with BMI ≥ 40 kg/m. 2. , but device revision risk is not elevated

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. Methods. Computer navigation was used to track the patella in eight whole lower extremities of four cadavers in the natural knee, in the same knee with the femoral component of the PFR (PFR-P) and with the femoral and patellar component of the PFR (PFR+P, patella resurfaced) (Depuy Sigma PFR). The form and position of the trochlea in the natural knee and the patellar groove of the femoral component was also analysed. Values are means+/−SD, two tailed Student's t-test for paired samples. Results. With a PFR-P the patella had a slightly more lateral tilt (0.8+/−0.8° to 2.8+/−2.5° at 40–100° of flexion, p<0.05 vs. Nat), this was more pronounced with the PFR+P (2.0+/−0.7° to 4.9+/−1.8° at 20–90° flexion, p<0.05 vs. Nat., p<0.05 vs. PFR-P at 20–80° flexion). No differences in patella rotation were seen between the three groups. In the PFR-P group the patella tracked a little more medially compared to the natural knee (0.6+/− 0.7mm to 1.3+/−2.6mm, p<0.05 at 20°,80°,90° flexion). The difference was more pronounced after patella resurfacing (PFR+P) (2.1+/−2.0mm to 3.0+/−2.2mm, p<0.05 vs. Nat. at 10°–100°, p<0.05 vs. PFR-P from 10–100°). When analysed relative to the patellar groove of the trochlea/femoral component the patella in the natural knee tracked slightly lateral to the groove (2.0+/−1.7mm to 2.9+/−2.0mm at 50–100° p<0.05), so did the patella of PFR-P (2.0+/−2.3mm to 2.3+/−2.3mm at 60–90° flexion, p<0.05), whilst the PFR+P tracked right on the groove (0.6+/−3.7mm medially to 0.6+/−2.9mm laterally, p<0.05 vs Nat at 10–30° & 70–100°, p<0.05 vs. PFR-P at 10–100°). Distance from the patellatot the epicondylar axis was slightly larger in the PFR-P group (0.6+/− 0.7mm to 1.3+/−1.4mm, p<0.05 vs. Natu at 20,80 & 90°. This was more pronounced with patellar resurfacing (2.1+/−2.0 to 3.0+/−2.2mm, p<0.05 vs. Nat at 10–100°, p<0.05 vs. PFR-P at 20–100°) The patella groove on the natural knee and the implanted femoral component of the implanted PFR had the same radius, inclination relative to the femoral mechanical axis, antero-posterior position and medio-lateral orientation. As intended by the designers the groove of the patellar component extended about 13mm further superiorly and 0.5mm more inferiorly. Discussion. The patella groove on the femoral component of the PFR reproduces the natural trochlear anatomy well. Patella tracking in the PFR-P shows only minor differences compared to the natural knee. Resurfacing of the patella in the PFR+P group causes the patella to tilt a little more laterally and track a little more medially, the distance to the epicondylar axis is slightly larger but this allows the patella to engage better in the patellar groove of the femoral component

Introduction: Patellar complications after total knee arthroplasty (TKA) remain a common reason for failure. Fully congruent patellar components, with larger contact areas and a polyethylene articular surface that is free to rotate in the frontal plane (LCS design), were designed to accommodate patellar mechanics and decrease wear. However, it remains to be determined whether the perceived advantages of a mobile-bearing, fully congruent patella design are realized in-vivo. The purpose of this study is correlate wear patterns on congruent mobile-bearing patellar components with patellar mechanics that existed after TKA. Methods: Uncemented metal-backed patellar components were retrieved at revision surgery from 26 knees with meniscal bearing (23 knees) and rotating platform (3 knees) LCS mobile bearing prostheses (DePuy Orthopaedics). Mean patient age and time in-situ was 75+11 years and 11+4 years, respectively. Revision reasons included bearing wear (11), patella wear (7), instability (2), pain (3), loosening (1), osteolysis (1), and unknown (1). Polyethylene damage was assessed using optical microscopy. Articular wear area was measured using digital image analysis and the % area, location and incidence of each damage mode was calculated. Results: The average damage area on the retrieved patella occupied 69%+15% of the surface. Burnishing, delamination and scratching modes occupied the largest areas. Delamination was noted on 58% of the retrieved patellae, predominantly located in the superior-medial quadrant. Nine (35%) patellae were fractured, with the fracture plane typically oriented in the medial-lateral direction or along the lateral edge. Twently one (81%) patellae had subsurface cracks oriented along the superior-inferior axis on the extreme lateral edge and along the medial-lateral axis. None of the patellae had embedded third body debris, but the embedded superior metal pin was exposed due to extreme damage in 4 patellas. The original femoral and tibial components were left in-situ in all knees at the time of revision, such that only the polyethylene tibial and patellar articulations were exchanged. Discussion: Despite severe wear of the components, there was only a 5% incidence of osteolysis noted intra-operatively. Cyclic compressive and tensile forces during knee flexion likely caused initiation and propagation of cracks resulting in patellar bearing fracture. The delami-nation patterns on the retrieved patellae are consistent with bearing rotation into an incongruent bearing position during knee flexion, with presumably high contact stresses occurring in the delaminated superior-medial quadrant. Fully congruent mobile-bearing patella components must maintain mobility between the articular surface and metal back so that areas of incongruent contact, and associated high contact stresses and delamination, do not occur during in-vivo function

There is no question that at some point many TKAs will be cementless-the question is when. The advantages of cementless TKA include a shorter operative time, no need for a tourniquet, more suitability for MIS, no concern for cement extrusion, and the history of THA. The concerns for cementless TKA include the history to date with cementless TKA (tibia and metal-backed patella), variable bony substrate, surgical cut precision, cost, revision concerns, and the patella (for patella component resurfacers). Cemented total knee arthroplasty remains the gold standard and has proven to provide durable results in most patients. The early experience with cementless tibial fixation was problematic due to tibial micromotion leading to pain and loosening. Screw fixed tibial components had additional problems as portals for polyethylene debris leading to tibial osteolysis. Moreover, metal-backed patellar components were associated with a high failure rate and most surgeons began to cement all three components. Renewed interest in cementless tibial fixation is driven in part by newer materials felt to be more suitable for ingrowth and by the perceived benefit of minimally invasive surgery. One of the concerns in limited exposure total knee arthroplasty is the difficulty in preventing the extravasation of cement posteriorly. If there is evidence-based data that quad sparing non-patella everting and limited incision length facilitates rehabilitation and does not jeopardise outcome, cementless tibial fixation will be a more attractive option in some patients. An additional concern is that the tibial surface is frequently quite variable in terms of the strength of the cancellous bone. Bone cement stabilises those differences and provides a homogeneous platform for load bearing through the tibial component

The low contact stress patellofemoral replacement consists of a trochlear component and a modular patellar component which has a metal-backed mobile polyethylene bearing. We present the early results of the use of this prosthesis for established isolated patellofemoral arthritis in 51 consecutive patellofemoral replacements in 35 patients. The mean follow-up was 25 months (5 to 60). The estimated survival rate at three years was 63% (95% confidence interval 47 to 80) with revision as the endpoint and 46% (95% confidence interval 30 to 63) with revision and ongoing moderate or severe pain as the endpoint. The early results of the use of the low contact stress patellofemoral replacement are disappointing with a high rate of revision. We cannot therefore recommend its use

Total knee arthroplasty (TKA) is a successful operation associated with a high rate of clinical success and long-term durability. Cementless technology for TKA was first explored 30 years ago with the hope of simplifying the performance of the procedure and reducing an interface for potential failure by eliminating the use of cement. Poor implant design and the use of first generation biomaterials have been implicated in many early failures of these prostheses due to aseptic loosening and reflected the failure of either the tibial or patellar component. Despite this, many excellent intermediate and long-term series have clearly demonstrated the ability of cementless TKA to perform well with good to excellent survival, comparable to that of cemented designs. Lessons learned from the initial experiences with cementless technology in TKA have led to improvements in prosthetic design and materials development. One of the most innovative biomaterials introduced into orthopaedics for cementless fixation is porous tantalum. Compared to other commonly used materials for cementless fixation, porous tantalum has the highest surface friction against bone, optimizing initial stability at the implant-bone interface as a prerequisite for long-term stability of the reconstruction. At the 2013 AAOS Annual Meeting, Abdel presented the 5-year Mayo Clinic experience with cementless TKA utilizing a highly porous monoblock tibial component in 117 knees and found NO difference in survivorship compared to cemented fixation with a re-operation rate of 3.5% in both groups. They had no revisions for aseptic loosening. These early to intermediate results reflect our own experience with all cementless TKA utilizing a cobalt-chromium fibermesh femoral component, as well as monoblock porous tantalum tibial and patellar components with up to 11-year follow up. In that series of 115 patients, there was a 95.7% survival of implants, with no revisions of any components for aseptic loosening. Further advantages to using cementless fixation include the elimination of concerns with regard to monomer-induced hypotension, thermal necrosis from PMMA polymerization, and third body wear secondary to retained or fragmented cement. Savings are also realised from elimination of the costs of cement, a PMMA mixing system, cement gun, pulse lavage system, and irrigation solution. Perhaps the greatest cost savings is derived from the reduction in operating room time. At our institution–a Level 1 county trauma center with an orthopaedic residency training program–we typically spend an average of 19 minutes of operating room time for the cementing of a total knee arthroplasty. Our average time expended for insertion of all three cementless implants is 47 seconds–representing a significant savings in the hospital operating room time charge. From the standpoint of the patient, the shorter operating time reduces the time under anesthesia, the blood loss, the risk of venous thromboembolism, as well as the infection risk–optimizing the conditions for a reduction in post-operative complications, directly impacting a potential reduction in morbidity and mortality. Overall, the performance of all cementless TKA at our facility is cost-saving, is easily performed and reproduced by orthopaedic residents, and brings potential advantages to the patient in the form of a reduction in complications and an improvement in outcomes. Cementless fixation is the wave of the future, and the future is now

General Principles. All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute tibial tuberosity avulsion. Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilization. Augmentation with a semitendinosus graft or Marlex mesh can provide additional support. Acute Patella Tendon Rupture. End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture. These can be repaired end-to-end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture. Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag, non-operative treatment in extension. A loose component and/or > 20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions. While standard repair techniques are possible, tissue retraction usually prevents a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate. In chronic disruptions with loss of the patella, allograft extensor mechanism reconstruction may be considered. Marlex mesh repair has also been shown to be effective in reconstruction of chronic patellar and quadriceps tendon defects

Complications involving the patellofemoral joint, caused by malrotation of the femoral component during total knee replacement, are an important cause of persistent pain and failure leading to revision surgery. The aim of this study was to determine and quantify the influence of femoral component malrotation on patellofemoral wear, and to determine whether or not there is a difference in the rate of wear of the patellar component when articulated against oxidised zirconium (OxZr) and cobalt-chrome (CoCr) components. An in vitro method was used to simulate patellar maltracking for both materials. Both rates of wear and changes in height on the patellar articular surface were measured. The mean rates of wear measured were very small compared to standard tibiofemoral wear rates. When data for each femoral component material were pooled, the mean rate of wear was 0.19 mm. 3. /Mcycle (. sd. 0.21) for OxZr and 0.34 mm. 3. /Mcycle (. sd. 0.335) for CoCr. The largest change in height on each patella varied from -0.05 mm to -0.33 mm over the different configurations. The results suggest that patellar maltracking due to an internally rotated femoral component leads to an increased mean patellar wear. Although not statistically significant, the mean wear production may be lower for OxZr than for CoCr components

Background. Multiple retrospective studies have compared UC with traditional bearings and shown comparable results and outcomes when looking at clinical and radiologic variables, complications rates, and implant survivorship; however, debate still exists regarding the optimum bearing surface. The present study seeks to determine whether there are any preoperative patient demographic or medical factors or anatomic variables including femoral condylar offset and tibial slope that may predict use of a UC bearing when compared to a standard CR group. Methods. The study cohort consisted of 117 patients (41 males, 76 females) who underwent primary TKA with the senior author. The implants utilized were either the CR or UC polyethylene components of the Zimmer Persona Total Knee System. Insert selection was based on intraoperative assessment of PCL integrity and soft tissue balancing. Patient demographics (age, gender, BMI) and co-morbidities (hypertension, diabetes, depression, cardiac disease, and lung disease) were recorded. Intraoperative variables of interest included extension and flexion range of motion, estimated blood loss (EBL), tourniquet time, and polyethylene and femoral component sizes. We calculated change in tibial slope and femoral condylar offset from pre- to post-surgery and computed the percentage of patients for whom an increase in tibial slope or femoral condylar offset was determined. Postoperative variables, including length of stay, complication rates and reoperation rates, were recorded. All dependent variables were compared between patients who received the UC component and patients who received the CR component. Continuous variables were assessed using independent samples t-tests, while categorical variables were compared using the chi-square test of independence. Results. There were 39 patients who received a UC insert and 78 patients who received CR insert. Patient age (p = 0.58), BMI (p = 0.34), or sex distribution (p = 0.84) did not differ between the UC and CR groups. Mean LOS (3.59 vs. 3.08; p = 0.017), EBL (54.5 vs. 46.7; p=0.021), and tourniquet time (61.2 vs. 57.4; p=0.032) were greater for the UC group. Intraoperative implant variables, including polyethylene component (p = 0.49), femoral component (p = 0.56), use of a narrow femoral component (p = 0.85), and patellar component size (p = 0,83), were similar between groups. Additionally, preoperative (p = 0.46) and postoperative (p = 0.19) condylar offset and preoperative (p = 0.66) and postoperative (p = 0.23) tibial slope were not different between the groups. However, the proportion of patients for whom tibial slope increased postoperatively was greater for the UC group compared to the CR group (43.6 vs. 21.8% respectively, p=0.018). Conclusions. Our results showed that no preoperative medical co-morbidities or demographic factors predicted use of the UC bearing; however, postoperative tibial slope was increased for a greater number of patients who received the UC implant. Patients who have an increase in their slope from their native anatomy during tibial preparation may require additional balancing of the flexion gap, and use of a UC component may be beneficial in this particular group of patients

A retrospective review was performed of patients undergoing primary cementless total knee replacement (TKR) using porous tantalum performed by a group of surgical trainees. Clinical and radiological follow-up involved 79 females and 26 males encompassing 115 knees. The mean age was 66.9 years (36 to 85). Mean follow-up was 7 years (2 to 11). Tibial and patellar components were porous tantalum monoblock implants, and femoral components were posterior stabilised (PS) in design with cobalt–chromium fibre mesh. Radiological assessments were made for implant positioning, alignment, radiolucencies, lysis, and loosening. There was 95.7% survival of implants. There was no radiological evidence of loosening and no osteolysis found. No revisions were performed for aseptic loosening. Average tibial component alignment was 1.4° of varus (4°of valgus to 9° varus), and 6.2° (3° anterior to 15° posterior) of posterior slope. Mean femoral component alignment was 6.6° (1° to 11°) of valgus. Mean tibiofemoral alignment was 5.6° of valgus (7° varus to 16° valgus). Patellar tilt was a mean of 2.4° lateral (5° medial to 28° lateral). Patient satisfaction with improvement in pain was 91%. Cementless TKR incorporating porous tantalum yielded good clinical and radiological outcomes at a mean of follow-up of seven-years. Cite this article: Bone Joint J 2014;96-B(11 Suppl A):87–92

Introduction. Patellar resurfacing during Total Knee Arthroplasty (TKA) is controversial. Problems unique to patellar resurfacing may be influenced by available patellar component design. These issues include; over-stuffing (the creation of a composite patellar-prosthesis thickness greater than the native patella) that may contribute to reduced range of motion; and over-resection of the native patellar bone that may contribute to post-operative fracture. Prosthesis design may play a role in contributing to these problems. Component diameter and thickness are quite variable from one manufacturer to another and little information has been previously published about optimal component dimensions. This anatomic study was performed to define the native patellar anatomy of patients undergoing TKA, in order to guide future component design. Methods. This retrospective, IRB approved study reviewed 797 Caucasian knees that underwent primary TKA by a single surgeon. Data recorded for each patient included: gender; patellar thickness before and after resurfacing, and the size of the component that provided the greatest patellar coverage without any overhang. The residual patellar bone thickness after resection was also calculated. Results. Mean (SD) native patellar thickness was 25.24 mm (2.11) in males, versus 22.13 mm (1.89) in females (P = <0.001). 84 of 483 females (17 %) had a native patellar thickness less than or equal to 20 mm. Only 3 male patients had a native patellar thickness less than or equal to 20 mm (1%). 374 females (78%) could only accommodate a round patellar button less than or equal to 32 mm. Conclusions. These findings suggest that patellar component design can be improved for Caucasian female patients. Round components between 26 and 32 mm that measure no more than 7 mm thick would be required to avoid systematic over-stuffing or over-resection of the native patellar in female patients. Most contemporary knee systems do not meet these needs

Implant selection in TKA remains highly variable. Surgeons consider pre-operative deformity, patient factors such as BMI and bone quality, surgical experience, retention or substitution for the PCL, type of articulation and polyethylene, cost, and fixation with or without cement. We have most frequently implanted the same implant for the majority of patients. This is based on the fact that multiple large series of TKAs have demonstrated that the most durable TKAs have been non-modular metal-backed tibial components, retention of the PCL, with a cemented all-polyethylene patellar component. Polymer wear must be addressed for long-term durability. One method for reducing polyethylene wear is eliminating modularity between a metal-backed tray and the articular bearing surface. This can be done with a metal-backed implant as with the IB-1, AGC, Vanguard Mono-lock, or with elimination of the metal backing via a one piece all-polyethylene tibial component. The all-polyethylene implants appear design and patient sensitive. We observed higher clinical failure rates in a flat-on-flat design. Other authors have observed improved survivorship with coronal dishing of the articular surfaces which centralises osseous stresses. All-polyethylene implants have promise in the future but require proven design and fixation design features

We analysed at a mean follow-up of 7.25 years the clinical and radiological outcome of 117 patients (125 knees) who had undergone a primary, cemented, modular Freeman-Samuelson total knee replacement. While the tibial and femoral components were cemented, the patellar component was uncemented. A surface-cementing technique was used to secure the tibial components. A total of 82 knees was available for radiological assessment. Radiolucent lines were seen in 41 knees (50%) and osteolytic lesions were seen in 13 knees (16%). Asymptomatic, rotational loosening of the patellar implant was seen in four patients and osteolysis was more common in patients with a patellar resurfacing. Functional outcome scores were available for 41 patients (41 knees, 35%) and the mean Western Ontario McMasters Universities score was 77.5 (. sd. 19.5) and the cumulative survival was 93.4% at ten years with revision for aseptic loosening as an endpoint. Increased polyethylene wear from modular components, a rotationally-loose patella, and the surface-cementing technique may have contributed to the high rate of osteolysis seen in our study

Success in knee revision begins in the office. The initial evaluations determine the implant design and pre-operative diagnosis. The physical examination identifies the presence of instability, stiffness, extensor mechanism malfunction and previous incisions all of which influence the planned procedure. Prior to surgery arrangements are made to have all manner of revision implants, removal tools, and allograft material available. Removal of implants must be done with a focus on preserving bone stock and the extensor mechanism. Initial exposure involves release of the gutters, lateral subluxation of the patella and removal of the polyethylene insert. These maneuvers combined with a quadriceps snip provide exposure for implant removal in 80–90% of cases. More extensive exposure options include quadriceps turndown, tibial tubercle osteotomy, medial epicondylar osteotomy and a femoral peel. Tools needed for implant removal include thin osteotomes, offset osteotomes, thin saws and a high-speed bur. After polyethylene removal the femur followed by the tibia are removed. In many cases the existing well-fixed patellar component can remain. The implant cement or implant bone interface is approached for cemented and cementless implants, respectively. Tools are always directed parallel to the fixation surface. Offset osteotomes are helpful gaining access to the femoral notch when femoral pegs prevent access from the sides. Central keels or peripheral pegs can complicate tibial removal. Working completely around the keel from medial and lateral disrupts the peripheral tibial interface leaving just the central posterior metaphysis. Stacked osteotomes or a slap hammer can be used to lift the baseplate from the tibia

Introduction: Patellar crepitus (PC) has been reported in 13% of cruciatesubstituting total knee arthroplasty (TKA) patients resulting from synovial tissue impingement within the femoral component intercondylar box (IB). Patient factors, component design, and technical errors have been implicated in PC. We compared primary TKA patients with PC requiring surgery against matched controls to identify significant variables. Methods: The databases of 2 institutions were reviewed to identify patients requiring surgery for PC. A control group matched for age, sex, and BMI was identified. Patient charts and radiographs were reviewed. Statistical analysis was performed. Significant variables associated with patient anatomy, implant size and alignment were subsequently investigated in a computational model to evaluate tendofemoral contact. Results: Between 2002 and 2008, over 4000 primary TKAs were performed using the Press Fit Condylar Sigma (DePuy, Warsaw, Indiana) TKA. Of these, 59 knees developed PC requiring surgery. The mean time to presentation was 10.9 months. The incidence of PC correlated with greater number of previous surgeries (1.18 vs. 0.44, p= 0.002), decreased patellar button size (35.7 vs. 37.1mm, p=0.003), shorter patellar tendon length (54.5 vs. 57.9mm, p=0.01), and increase in posterior femoral condylar offset (1.27mm vs. 0.17mm, p=0.022). Using a patellar component of 32 or 35mm significantly increased the risk of PC compared to the use of a 38 or 41mm component (p< 0.01, RR=1.61, OR 2.63). Modeling results demonstrated decreased patellar tendon length created increased tendofemoral contact near the IB, while larger buttons increased separation between the tendon and the box edge. Conclusion: Shortened patellar tendon length and use of smaller patellar components may expose the quadriceps tendon to increased irritation as it traverses across the femoral component IB. Increasing posterior femoral offset may increase quadriceps tendon tension, further risking synovial tissue impingement within the IB

We report the incidence of osteolysis in the femur, tibia, and patella of 44 consecutive patients (60 knees) who were followed for more than seven years after cementless knee arthroplasty with a Porous-Coated Anatomic prosthesis. The average age of the patients was 56.5 years (17 to 73); the operative diagnosis was osteoarthritis (33 knees), rheumatoid arthritis (17), tuberculous arthritis (7) and post-traumatic arthritis (3). All patellae were resurfaced. No femoral or tibial component was loose at the final follow-up examination. Thirty patellar components were loose of which six had been revised. Radiographs revealed osteolysis in 90% of the tibial plateaux and in 80% of the 30 intact patellar prostheses. No osteolysis was seen around any femoral component. In 50 knees (83%) the average wear of the polyethylene liner was 2.5 mm in the medial compartment and 1.7 mm in the lateral compartment. Four of 60 knees (6.7%) were revised for complete wear of the polyethylene liner of the tibial component. Fixation of the tibial and patellar components without cement fails to seal the interface between bone and prosthesis and allows the migration of polyethylene particulate debris which causes osteolysis

The August 2023 Knee Roundup³⁶⁰ looks at: Curettage and cementation of giant cell tumour of bone: is arthritis a given?; Anterior knee pain following total knee arthroplasty: does the patellar cement-bone interface affect postoperative anterior knee pain?; Nickel allergy and total knee arthroplasty; The use of artificial intelligence for the prediction of periprosthetic joint infection following aseptic revision total knee arthroplasty; Ambulatory unicompartmental knee arthroplasty: development of a patient selection tool using machine learning; Femoral asymmetry: a missing piece in knee alignment; Needle arthroscopy – a benefit to patients in the outpatient setting; Can lateral unicompartmental knees be done in a day-case setting?

General Principles: All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex Mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute tibial tuberosity avulsion: Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilization. Augmentation with a semitendinosus graft or Marlex can provide additional support. Acute Patella Tendon Rupture: End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture: These can be repaired end-to-end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture: Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag, non-operative treatment in extension. A loose component and/or > 20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions: While standard repair techniques are possible, tissue retraction usually prevents a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate. In chronic disruptions with loss of the patella, allograft extensor mechanism reconstruction may be considered. Marlex mesh repair has also been shown to be effective in reconstruction of chronic patellar and quadriceps tendon defects

Aims

Revision total knee arthroplasty (rTKA) is a technically challenging and costly procedure. It is well-documented that primary TKA (pTKA) have better survivorship than rTKA; however, we were unable to identify any studies explicitly investigating previous rTKA as a risk factor for failure following rTKA. The purpose of this study is to compare the outcomes following rTKA between patients undergoing index rTKA and those who had been previously revised.

Introduction. Tibial tuberosity and trochlear groove (TT-TG) distance has been investigated for the patients with primary patellofemoral subluxation/dislocation. To date, TT-TG distance after TKA has not been evaluated, and the effect of postoperative TT-TG distance on patellar tracking is unknown. The purpose of the current study was to investigate the effect of TT-TG distance and rotational position of the femoral and tibial components on patellar tilt after TKA. Methods. Consecutive 115 knees for the diagnosis of osteoarthritis were included in the current study. TKA was performed using posterior cruciate ligament sacrificed prosthesis. A total of 17 men and 96 women with an average age of 75.3 years were included at the time of the surgery. Computed tomography (CT) was taken after TKA in full extension. Postoperative TT-TG distance was measured as a reference of surgical epicondylar axis (SEA) of the femur. Patellar tilt was defined as the angle of the patellar component relative to SEA. Femoral and tibial component rotation was measured as the angle relative to SEA and tibial antero-posterior (AP) axis. Tibial AP axis was defined as the line connecting medial one-third of the tibial tuberosity and center of medial-lateral width. Pearson correlation coefficients were calculated to determine the correlations between patellar tilt and TT-TG distance and between patellar tilt and femoral and tibial component rotation. Results. TT-TG distance had significant correlation with patellar tilt (Figure 1; r = 0.254, p = 0.006), whereas femoral component rotation (p = 0.092) and tibial component rotation (p = 0.062) were not correlated with patellar tilt. Concerning the effect on TT-TG distance, femoral component rotation (r = 0.248, p = 0.008) and tibial component rotation (r = −0.567, p < 0.001) were correlated with TT-TG distance. Conclusion. The current study investigated the effect of TT-TG distance on patellar tilt with postoperative CT scan. Greater TT-TG distance resulted in more patellar tilt, which might have negative effects on patellar tracking. In previous clinical studies, femoral component and tibial component rotation affected patellar maltracking. In the current study, however, component rotation itself did not affect patellar tilt. Postoperative TT-TG distance includes information of rotational and medial-lateral positioning of the femoral and tibial components, and can be a useful indicator to predict patellar maltracking after TKA. For any figures or tables, please contact authors directly

The battle of revision TKA is won or lost with safe, effective, and minimally bony-destructive implant removal, protecting all ligamentous stabilisers of the knee and, most importantly, the extensor mechanism. For exposure, incisions should be long and generous to allow adequate access. A standard medial parapatellar capsular arthrotomy is preferred. A synovectomy is performed followed by debridement of all scar tissue, especially in the medial and lateral gutters. All peripatellar scar tissue is excised followed by release of scar tissue within the patellar tendon, allowing for displacement or everting of the patella. As patellar tendon avulsion at any time of knee surgery yields disastrous results, the surgeon should be continuously evaluating the patellar tendon integrity, especially while displacing/everting the patella and bringing the knee into flexion. If displacement/eversion is difficult, consider rectis-snip, V-Y quadricepsplasty, or tibial tubercle osteotomy. The long-held requisite for patellar eversion prior to component removal is inaccurate. In most cases simple lateral patellar subluxation will provide adequate exposure. If a modular tibial system is involved, removal of the tibial polyethylene will decompress the knee, allowing for easier access to patellar, femoral, and tibial components. For patellar component removal, first identify the border of the patella, then carefully clean and debride the interface, preferably with electrocautery. If the tibial component is cemented all-polyethylene, remove using an oscillating saw at the prosthetic-bone interface. Debride the remaining cement with hand tools, ultrasonic tools, or burrs. Remove the remaining peg using a low-speed burr. If the tibial component is metal-backed, then utilise a thin saw blade or reciprocating saw to negotiate the undersurface of the component between the pegs. If pegs are peripherally located, cut with a diamond disc circular cutting tool. Use a trephine to remove the pegs. For femoral component removal, identify the prosthetic-bone/prosthetic-cement interface then remove soft tissue from the interface, preferably with electrocautery. Disrupt the interface around all aspects of the component, using any of following: Gigli saw for cementless components only, micro saw, standard oscillating saw, reciprocating saw, a series of thin osteotomes, or ultrasonic equipment. If the femoral component is stemmed, remove the component in two segments using an appropriate screwdriver to remove the screw locking the stem to the component. Remove the femoral component with a retrodriver or femoral component extractor. Debride cement with hand tools or burr, using care to avoid bone fracture. If a stem is present, then remove with the appropriate extraction device. If “mismatch” exists, where femoral (or likewise, tibial) boss is smaller in diameter than the stem, creating a cement block prohibiting stem removal, remove the cement with hand tools or burr. If the stem is cemented, use hand tools, ultrasonic tools, or a burr to debride the cement. Curette and clean the canals. For tibial component removal, disrupt the prosthetic-cement/prosthetic-bone interface using an oscillating or reciprocating saw. Gently remove the tibial component with a retrodriver or tibial extractor. If stem extensions are utilised, disengage and debride all proximal cement prior to removing the stem. If stem is present, then remove stem with appropriate extraction device. If stem is grit-blasted and well-fixed, create 8mm burr holes 1.5 to 2.5cm distal to tibial tray on medial aspect and a small divot using burr, then drive implant proximally with Anspach punch. Alternatively, a tibial tubercle osteotomy may be performed. If the stem is cemented, use hand tools, ultrasonic tools or burr to debride cement

Avoidance of extensor mechanism complications is best obtained by using components with an appropriately designed femoral trochlea and patellar component and where internally rotated components are avoided. Residual valgus deformity may also lead to patellar dislocation or more subtle subluxations, which may manifest as pain along the medial patellar retinaculum. Because rotational abnormalities are difficult to detect on plain x-ray, CT scans are a useful way to diagnose this problem. Peripatellar crepitation may cause symptoms and can be avoided by aggressive peripatellar synovectomy at the time of surgery. In its most severe form, the patellar clunk syndrome, most commonly seen in posterior stabilised knees, arthroscopic debridement of the offending fibrous nodule may be needed. Patellar fracture is best treated on the basis of residual extensor mechanism function. Maintenance of active extension following fracture (with no loss of component fixation) is a good sign that conservative therapy will yield better function than ORIF. Loss of extension indicates that surgery will be required. In this setting restoration of extensor continuity is more important than retention of the patellar component. Patellar tendon avulsion can be avoided by careful attention to the tendon during surgical exposure. Intraoperative repair alone is rarely successful and should be reinforced by semitendonosis, or fascia lata grafting. Late rupture may be treated by this type of grafting alone. But if the patella is necrotic or the failure results in a high riding patella, mechanism transplant is preferred. In this setting attention to fixing the graft in full extension is mandatory to prevent severe extensor lag, as the allograft will stretch out overtime

Purpose: The purpose of this study was to determine the clinical and radiographic outcomes at a minimum follow-up of ten years of patients who underwent a total knee arthroplasty with an inset patellar component. The incidence of anterior knee pain and the factors which may contribute to were also studied. Method: Patients who had genesis I/II TKA with an inset patellar button with a minimum follow-up of 10 years were identified. 448 patients with 521 knees were identified. Patients were excluded if they were deceased, had incomplete data, were unable to be contacted or had a known or impending revision. Those who had revision were included in a Kaplan-Meier survivorship analysis. The included patients, deceased patients and those lost to follow-up were named group1, 2, and 3 respectively. Demographics and Knee society scores(KSS) were studies for all 3 groups. This was to identify any exclusion bias. Presence and severity of anterior knee pain as well as radiographic factors were collected for group 3. Logistic regression analysis was used to identify and variables that influenced the KSS and presence of anterior knee pain. Kaplan-Meier survivorship analysis was performed for patellar revision and tibial/femoral revision endpoints. Results: 144 patients with 175 TKA were included in this study. They were on average 66 years old, 64% female, had a BMI of 30 and had a diagnosis of OA 92% of the time. Their average f/u was 11.3 years. Groups 2 and 3 had similar demographics but of course a much shorter f/u. Group 1 had a pre-op KSS of 84 a post-op KSS of 151 and a KS change score of 67. Groups 2 and 3 had similar pre-op, post-op and KSS change scores. We found anterior knee pain occurred in 5% of patients with an average severity of 5/10. Linear regression analysis did not identify any variables including radiographic parameters that had an independent influence on KSS or anterior knee pain. Kaplan-Meier survivorship with patellar revision for any reason as an endpoint was 96% at 10 years and 94% at 17 years. 20 patella were known to have had a revision or were undergoing a revision. Conclusion: We conclude that use of an inset patellar component can give excellent durable results over time with a low rate of anterior knee pain and complications

Introduction: The aim of introducing mobile-bearing knee replacements was to improve long term survival by maintaining large areas of surface contact, while allowing motion to occur at the bearing-metal interface on the tibial and patellar components. Despite wide use of these implants, there are only a few intermediate or long-term follow-up studies. Aims: To present the intermediate follow-up results of a cementless, posterior cruciate ligament retaining, low contact-stress, knee replacement system (LCS). Methods: Between 1987 and 1991 the senior author (U.W.) performed 134 cementless LCS total knee arthroplasties in 121 patients. Twenty of the patients were male, 101 female, with an average age of 70 years (range: 49 years to 91years). In 40% of the cases the patella was resurfaced. The patients were evaluated with clinical knee rating (Insall score) and radiographic analysis, between six and nine years postoperatively. Results: At the time of the follow-up 94 patients were alive. Twelve patients (10%; 14 prostheses) were contacted by phone after an average of 77 months. Evaluation was possible in 82 patients (68%; 91 prostheses) after an average of 74 months. Ninety percent of these patients had an Insall score of > 80 (good to very good). One patient had a score of < 70 (insufficient). Average flexion was 114 degrees (range: of 70 to 135 degrees). Two patients had flexion of < 90 degrees. There were no radiographic signs of aseptic loosening. The meniscal bearing of four prostheses and one patellar component were replaced. Complications like haematoma, fibrotic arthritis and infection due to endocarditis lenta lead to three revisions. Conclusion: Our study has shown that the non-cemented posterior cruciate ligament retaining LCS knee replacement system produced very satisfactory results with few complications in the medium term

Introduction: Although the problems of patello-femoral kinematics in contemporary total knee arthroplasty are multifactorial, meticulous surgical technique is pivotal in providing optimal and durable function. The goal of this study was to evaluate the incidence of lateral release comparing fixed and mobile bearing posterior stabilized modular press-fit condylar TKA’s with patellar resurfacing. Materials and methods: Cohort 1 comprised 100 consecutive cemented Press-Fit Condylar Sigma, (Johnson & Johnson, Raynham, Massachusetts) modular total knee prostheses with a posterior cruciate substituting design and dome shaped single peg patellar component implanted prospectively by a single surgeon. Cohort 2 comprised 100 consecutive cemented Press-Fit Rotating Platform Sigma (Johnson & Johnson, Raynham, Massachusetts) modular total knee prostheses with the same posterior cruciate substituting design and patellar component. The surgical technique comprised cutting the tibial surface perpendicular to the long axis, ligament balancing in extension followed by femoral component rotation referenced off the proximal tibial cut to produce a rectangular flexion gap. The patella was cut to the level of the lateral facet and tibial component rotation was referenced off the center of the ankle. Lateral release was performed if congruent patello-femoral contact was not attained in knee flexion. Clinical and radiographic review was performed as per Knee Society criteria. Additional radiographic evaluation included patellar displacement, tilt, residual bone thickness and coverage ratio. A patient-administered questionnaire was used to evaluate anterior knee pain and patello-femoral function 1 year after surgery. Results: The incidence of lateral release in the fixed-bearing cohort was 10% 1 compared to 0% in the mobile bearing cohort (p< 0.05). There were no significant differences in terms of clinical or radiographic parameters at short term. Discussion: This study demonstrates the benefit of self-correction of tibiofemoral rotational mismatch with mobile bearing TKA’s and improvement in patello-femoral tracking. Longer follow-up is necessary to confirm the effect on patello-femoral wear, fixation and durability

A series of 100 consecutive osteoarthritic patients was randomised to undergo total knee replacement using a Miller-Galante II prosthesis, with or without a cemented polyethylene patellar component. Knee function was evaluated using the American Knee Society score, Western Ontario and McMaster University Osteoarthritis index, specific patellofemoral-related questions and radiographic evaluation until the fourth post-operative year, then via questionnaire until ten years post-operatively. A ten-point difference in the American Knee Society score between the two groups was considered a significant change in knee performance, with α and β levels of 0.05. The mean age of the patients in the resurfaced group was 71 years (53 to 88) and in the non-resurfaced group was 73 years (54 to 86). After ten years 22 patients had died, seven were suffering from dementia, three declined further participation and ten were lost to follow-up. Two patients in the non-resurfaced group subsequently had their patellae resurfaced. In the resurfaced group one patient had an arthroscopic lateral release. There was no significant difference between the two treatment groups: both had a similar deterioration of scores with time, and no further patellofemoral complications were observed in either group. We are unable to recommend routine patellar resurfacing in osteoarthritic patients undergoing total knee replacement on the basis of our findings

Extensor mechanism complications after or during total knee arthroplasty are problematic. The prevalence ranges from 1–12% in TKR patients. Treatment results for these problems are inferior to the results of similar problems in non-TKR patients. Furthermore, the treatment algorithm is fundamentally different from that of non-TKR patients. The surgeon's first question does not focus on primary fixation; rather the surgeon must ask if the patient needs surgery and if so am I prepared to augment the repair? Quadriceps tendon rupture, periprosthetic patellar fracture, and patellar tendon rupture have similar treatment algorithms. Patients who are able to perform a straight leg raise and have less than a 20-degree extensor lag are generally treated non-operatively with extension bracing. The remaining patients will need surgical reconstruction of the extensor mechanism. Loose patellar components are removed. Primary repair alone is associated with poor results. Whole extensor mechanism allograft, Achilles tendon allograft, and synthetic mesh reconstruction are the current techniques for augmentation. In the acute setting if these are not available hamstring tendon harvest and augmentation is an option. Achilles tendons and synthetic mesh are easier to obtain than and entire extensor mechanism but are limited to patients that have an intact patella and the patella that can be mobilised to within 2–3 cm of the joint line. No matter which technique is used the principles are: rigid distal/tubercle fixation, coverage of allograft/mesh with host tissue to decrease infection, tensioning the augment material in extension, no flexion testing of reconstruction and post-operative extension bracing

Aims

We have previously reported the mid-term outcomes of revision total knee arthroplasty (TKA) for flexion instability. At a mean of four years, there were no re-revisions for instability. The aim of this study was to report the implant survivorship and clinical and radiological outcomes of the same cohort of of patients at a mean follow-up of ten years.

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.

General Principles - All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex Mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute Tibial Tuberosity Avulsion - Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilisation. Augmentation with a semitendinosus graft or Marlex can provide additional support. Acute Patella Tendon Rupture - End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture - These can be repaired end to end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture - Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag. A loose component and/or >20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions - While standard repair techniques are possible, tissue retraction usually prevent a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate while in any patellar tendon defect, mesh repair has been shown to be effective. In most chronic disruptions with loss of the patella allograft extensor mechanism reconstruction may be considered