Abstract. Background. The primary objective of the study is to determine the function outcome and survivorship of patellofemoral replacement. The secondary aim is to find the determinants of successful/poor outcome. Methods. This retrospective study involved 45 patients who underwent AVON patellofemoral replacement between January 2015 to December 2020 with the minimal follow-up off for 12 months. The functional outcome was measured using Oxford Knee score (OKS), EuroQol five dimension (EQ-5D). IWANO and Kellgren-Lawrence classification was used to analyse radiographs. To identify determinants of outcome, the following subgroups the presence or absence of normal alignment, tibiofemoral arthritis, trochlear dysplasia and previous surgery. Complications and revision rates were also recorded. Results. The mean follow-up period was 41.7 +/− 8.3 months with no patients lost in follow-up. Patellofemoral replacement significantly improved the Oxford Knee score (OKS), EuroQol five dimension (EQ-5D) (p<0.001). Four out of 45(8.9%) patients underwent revision surgery. Patients with normal alignment preoperatively did worse than those with abnormal alignment with patellar instability. Patients with grade two tibiofemoral arthritis, history of previous surgery did significantly worse with poorer functional outcome. Conclusion. Patellofemoral arthroplasty is reliable treatment option which improves patient function and quality of life with good survivorship in isolated patellofemoral arthritis in mid-term follow-up

Introduction. In knee biomechanics the concept of the envelope of motion (EOM) has proven to be a powerful method to characterize joint mechanics and the effect of surgical interventions. It is furthermore indispensable for numerical model validation. While commonly used for tibiofemoral kinematics, there is very little report of applying the concept to patellofemoral kinematics. EOM measurements require precise and reproducible displacement and load control in all degrees of freedom (DOF), which robotic testing has proven to provide. The objectives of this study were therefore to (1) develop a robotic method to assess patellofemoral EOM as a function of tibiofemoral EOM, (2) compare resulting patellofemoral kinematics to published data, and (3) determine which DOFs in the tibiofemoral EOM mostly account for the patellofemoral EOM. Material and Methods. The developed robotic (KUKA KR140 comp) method was evaluated using 8 post-mortem human leg specimens of both genders (age: 55±11 years, BMI: 23±5). Firstly, tibiofemoral neutral flexion was established as well as the EOM by applying anterior-posterior (±100 N), medial-lateral (±100 N), internal-external (±4 Nm) and varus-valgus (±12 Nm) loads under low compression (44 N) at 7 flexion angles. Secondly, patellofemoral flexion kinematics and EOM were measured during a robotic playback of the previously established tibiofemoral kinematics. During these measurements, the quadriceps tendon was loaded with a hanging weight (20 kg) via a pulley system directing the force to the anterior superior iliac spine. Kinematics were tracked optically (OptiTrack) and registered to CT scans using co-scanned aluminum cylinders and beads embedded in the patella. The overall patellofemoral EOM was calculated as the extent of patellar motion observed during manipulating the tibia inside the tibiofemoral EOM in all DOFs. Additionally, patellofemoral EOMs were calculated for tibial manipulations along individual DOFs to analyze the importance of these DOFs. Results. Trends and magnitudes of patella shift, tilt and rotation during knee flexion were similar to reported in-vivo measurements. Envelopes of patellar shift and tilt during internal-external tibiofemoral rotation closely resembled those reported for in-vitro results despite methodological differences. Tibiofemoral internal-external and varus-valgus rotation had the largest effect on patellofemoral EOM. EOMs in patellar shift and tilt were dominated by internal-external rotation in early flexion and varus-valgus rotation in late flexion. The EOM in patellar rotation was dominated by tibiofemoral varus-valgus rotation throughout flexion. Manipulating the tibia in a combined internal-external and varus-valgus rotation envelope yielded the same patellofemoral EOM as the overall patellofemoral EOM. Conclusion. This study has established a novel robotic method to assess the patellofemoral envelope of motion as a function of tibiofemoral EOM. Resulting patellofemoral kinematics resembled data reported in literature. It was furthermore shown that is sufficient to establish a combined internal-external and varus-valgus envelope of tibiofemoral motion as bases of the patellofemoral EOM, as including the anterior-posterior and medial-lateral tibiofemoral envelopes yielded no additional effect

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

Abstract. Optical motion capture (OMC) is the current gold standard for motion analysis, however measuring patellofemoral kinematics is not possible using the technique. One approach to measuring in-vivo kinematics is to use biplane video X-ray (BVX) and 3D models generated from MRI to track the movement of the patellar. Understanding how the patellar is moving during different loaded dynamic activities can help with understanding the effects of different interventions when treating disease or injury. Objective. To develop a protocol and compare patellofemoral kinematics for different activities using biplane video X-ray (BVX). Methods. Two healthy volunteers performed level walk, lunge, and stair ascent activities while simultaneous capturing BVX and synchronised OMC. Participants undertook MR imaging (Magnetom 3T Prisma, Siemens) which was manually segmented into 3D bone models (Simpleware Scan IP, Synopsis). Bone position and orientation for the patellar and femur were calculated by manual matching of 3D Bone models to X-Rays (DSX Suite, C-Motion, Inc.). Patellofemoral kinematics were calculated using Visual 3D (C-Motion, Inc.). Results. Initial results show that patellar flexion(+) (PF) was greatest during lunge (52.1º) compared with stair ascent (49.4º) and stance phase of gait (5.4º), however stair ascent had the largest PF range of motion (ROM) of 48.8º. The lunge activity had the greatest ROM for patellar lateral rotation (12.8º) compared with stair ascent (8.7º) and gait (3.7º). Patellar lateral (+) tilt was found to be greatest during gait (8.4º) compared with stair ascent (6.7º) and lunge (6.8º). Conclusions. These results highlight the variability of patellofemoral kinematics between different loaded dynamic activities. When considering the influence and efficacy of patellofemoral interventions it is important to investigate different activities to fully understand their effects. Future work will look at more dynamic activities and to investigate further the effect of different activities on patellofemoral tracking. 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

Background. Total knee arthroplasty (TKA) surgical techniques attempt to achieve equal flexion and extension gaps to produce a well-balanced knee. Anterior knee pain, which is not addressed by flexion-extension balancing, is one of the more common complaints for TKA patients. The variation in patellofemoral balance resulting from the techniques to achieve equal flexion and extension gaps has not been widely studied. Purpose of study. The purpose of the study is to determine the effects on cruciate retaining (CR) TKA patellofemoral balance when equal flexion and extension gaps are maintained while changing femur implant size and/or adjusting the femur and tibia implant proximal -distal and femur anterior-posterior positions. Methods. A computational analysis was performed simulating knee flexion of two CR TKA designs (JOURNEY II CR and LEGION HFCR; Smith & Nephew) using previously validated software (LifeMOD/KneeSim; LifeModeler). Deviations from the ideal implant position were simulated by adjusting tibiofemoral proximal-distal position and femur anterior-posterior position and size (Table 1). Positioning the femur more proximal was accompanied by equal anterior femur and proximal tibia shifts to maintain equal flexion and extension gaps. The forces in the medial and lateral retinaculum were collected and summed at every 15° knee flexion up to 135° to determine the total patellofemoral retinaculum load which was analyzed versus proximal-distal implant position, implant size, implant design, and knee flexion using an ANOVA in Minitab 16 (Minitab). Results. Patellofemoral retinaculum load was significantly affected by proximal-distal implant position, implant size, and knee flexion angle (p<.001) but was not significantly affected by implant design (p>0.2). Interactions with knee flexion angle were significant for both proximal-distal implant position (p<.001) and implant size (p=.003) indicating that their effects change with knee flexion (Figures 1 and 2). For 15°–30° knee flexion, more proximal tibiofemoral positions corresponding to a more anterior femur increased patellofemoral retinaculum load. Implant position had little effect at 45° knee flexion. For 60°–135° knee flexion, more proximal implant positions decreased patellofemoral retinaculum load. Increased femoral size caused increased patellofemoral retinaculum load with a larger effect for 15–45° knee flexion. Conclusions. Our results indicate that patellofemoral balance should be considered when selecting implant size and position for flexion-extension balancing. The more common adjustment of positioning implants more proximal decreases patellofemoral retinaculum load in flexion, but the anterior femoral shift to balance the flexion space overstuffs the patella near extension. Downsizing the femoral implant is an option to mitigate increased patellofemoral retinaculum load when shifting the femoral anterior. For figures/tables, please contact authors directly.

Introduction: Patellofemoral joint subluxation is associated with pain and dysfunction. The causes of patel-lofemoral subluxation are poorly understood and multi-factorial, arising from abnormalities of both bone and soft tissues. This study aims to identify which anatomical variables assessed on Magnetic Resonance (MR) images are most relevant to patellofemoral subluxation. Method: A retrospective analysis of MR studies of 60 patients with suspected patellofemoral subluxation was performed. All patients were graded for the severity/ magnitude of radiological subluxation using a dynamic MR scan (Grade 0 [nil] to Grade 3 [subluxed]. The patient scans were assessed using a range of anatomical variables, these included:. Patella alta,. Patella type (Wiberg classification),. Trochlea sulcus angles for bone and cartilage,. The shortest horizontal distance between the most distal part of the vastus medialis obliquis (VMO) muscle to the supra-medial aspect of the patella,. Trochlea and patella cartilage thickness (maximum depth),. The horizontal distance between the tibial tubercle and the midpoint of the femoral trochlea (TTD),. Patella Engagement – represented as the percentage of the patella height that is captured in the trochlea groove when the knee is in full extension,. A Discriminant Analysis test for multi-variant analysis was applied to establish the relationship between each bony/soft tissue anatomical variable and the severity/magnitude of patellofemoral subluxation. Results: The distance of the VMO from the patella (p < 0.001), TTD (p < 0.001) and Patella Engagement (p < 0.001) showed highly significant relationships with patellofemoral subluxation. Conclusions: The following three anatomical variables are associated with patellofemoral subluxation: the distance of the VMO muscle from the patella, TTD and Patella Engagement. This is the first study to establish that patella engagement is related to PFJ subluxation showing that the lower the percentage engagement of the patella in the trochlea, the greater the severity/magnitude of patellofemoral subluxation. The finding provides greater insight into the aetiology and understanding of the mechanism of symptomatic PFJ subluxation

Abstract. Unicompartment knee replacement (UKR) has been an effective treatment of isolated medial compartment osteoarthritis (OA). There has been several studies which suggest that patellofemoral (PFJ) wear may not be a relative contraindication for UKR with no statistical difference in failure rates. There is currently conflicting evidence on the role of BMI. We will review if BMI and PFJ wear impacts on the post operative functional scores following UKR. A retrospective review of a prospectively collected database was performed. Data was collected between 26/6/2014 and 25/8/2022. 159 UKR procedures were identified. BMI and PFJ cartilage wear were collected. Oxford knee scores (OKS) were collected at > 2 years. PFJ wear was split into International Cartilage Research Society (ICRS) grades I&II and III&IV. 159 UKR procedures were identified, of these 115 had 2 year follow up. There were 77 who had OKS recorded at 2 years. For PFJ wear there was no statistical difference in the median OKS at 2 years 45 vs 43.5 (p=0.408). Assessing the BMI the median was 29kg/m. 2. , range 20–43kg/m. 2. Spearman's rank was performed to assess the correlation between BMI and >2 year OKS, this demonstrated a moderately negative correlation p(df)=−0.339 (CI 95% −0.538, −0.104) p=0.004. There is no statistically significant difference in >2 year OKS following UKR regardless of PFJ wear. There is a moderately negative correlation between BMI and >2 year OKS which was significant p=0.004. Therefore BMI is a more important consideration when counselling patients for UKR

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. During primary total knee arthroplasty (TKA), surgeons occasionally encounter compromised bone and fixation cannot be achieved using a primary femoral component. Revision knee replacement components incorporate additional features to improve fixation, such as modular connection to sleeves or stems, and feature additional varus-valgus constraint in the post-cam mechanism to compensate for soft tissue laxity. The revision femoral component can be used in place of the primary femur to address fixation challenges; however, it is unclear if additional features of the revision femoral components adversely affect knee kinematics when compared to primary TKA components. The objective of this study was to compare weight-bearing tibiofemoral and patellofemoral kinematics between primary and revision femoral component with the primary tibial insert for a single knee replacement system. The hypothesis of the study was that kinematics for revision femoral components will be similar to kinematics of the primary femoral components. Methods. Eight cadaveric knees (age: 59±10 years, BMI 23.3±3.5) were implanted with a primary TKA system (ATTUNE™ Posterior Stabilized Total Knee Replacement System). Each knee was mounted and aligned in the Kansas Knee Simulator (Fig. 1) [1]. A deep knee bend was performed which flexed the knee from full extension to 110° flexion, while the medial-lateral translation, internal-external, and varus-valgus rotations at the ankle were unconstrained. The femoral component was then replaced with a revision femoral component of the same TKA system, articulating on the same primary insert component, and the deep knee bend was repeated. The translations of the lowest points (LP) of the medial and lateral femoral condyles along the superior-inferior axis of the tibia were calculated. In addition, tibiofemoral and patellofemoral kinematics were calculated for each cycle based on the Grood-Suntay coordinate system [2] [1]. The change in LP and patellofemoral kinematics from the primary to revision femurs were calculated. Student t-tests were performed at 5° increments of knee flexion to identify significant differences between the two implant types. Results. No significant differences were observed between primary and revision femur for both LP and patellofemoral kinematics (Fig 2,3). The revision femoral anterior-posterior lowest point translations were similar to that of the primary femur. Deviations in patellofemoral spin, tilt, and flexion were less than one degree throughout the range of flexion. Patellofemoral translations were less than .5 mm during mid-flexion and greatest deviations were observed during early flexion. Less than .5° deviation was observed in tibiofemoral VV and IE rotations. Discussion. Typical knee revision systems have compromised knee mechanics to improve femoral fixation, yielding poorer functional outcomes and high rates of reoperation [3, 4]. The primary and revision femoral components in this knee system have identical condylar articular geometry which explains the similarity in patellofemoral and tibiofemoral kinematics. Small difference in tibiofemoral kinematics could be a result of implant fixations using bone cement which slightly alters implant alignments between primary and revision surgeries. The revision femur resulted in similar kinematics and can be used during primary TKA when a stem is need for additional implant fixation without affecting the knee contact mechanics. For figures, please contact authors directly

Aims. Medial unicompartmental knee arthroplasty (UKA) is associated with successful outcomes in carefully selected patient cohorts. We hypothesised that severity and location of patellofemoral cartilage lesions significantly influences functional outcome after Oxford medial compartmental knee arthroplasty. Patients and Methods. We reviewed 100 consecutive UKAs at minimum eight-year follow-up (96 to 132). A single surgeon performed all procedures. Patients were selected based on clinical and plain radiographic assessment. All patients had end-stage medial compartment osteoarthritis (OA) with sparing of the lateral compartment and intact anterior cruciate ligaments. None of the patients had end-stage patellofemoral OA, but patients with anterior knee pain or partial thickness chondral loss were not excluded. There were 57 male and 43 female patients. The mean age at surgery was 69 years (41 to 82). At surgery the joint was carefully inspected for patellofemoral chondral loss and this was documented based on severity of cartilage loss (0 to 4 Outerbridge grading) and topographic location (medial, lateral, central, and superior or inferior). Functional scores collected included Oxford Knee Score (OKS), patient satisfaction scale and University College Hospital (UCH) knee score. Intraclass correlation was used to compare chondral damage to outcomes. Results. All patients documented significant improvement in pain and improved functional scores at mid-term follow-up. There were four revisions (mean 2.9 years, 2 to 4; standard deviation (. sd). 0.9) in this cohort, three for tibial loosening and one for femoral loosening. There was one infection that was treated with debridement and insert exchange. The mean OKS improved from 23.2 (. sd. 7.1) to 39.1 (. sd. 6.9); p < 0.001. The cohort with central and lateral grade 3 patellofemoral OA documented lower mean satisfaction with pain (90, . sd.  11.8) and function (87.5, . sd. 10.3) on the patient satisfaction scale. On the UCH scale, patients reported significantly decreased mean overall scores (7.3, . sd. 1.2 vs 9, . sd. 2.3) as well as stair climb task (3.5, . sd. 0.3 vs 5, . sd. 0.1) when cartilage lesions were located centrally or laterally on the PFJ. Patients with medial chondral PFJ lesions behave similar to patients with no chondral lesions. Conclusion. Topographical location and severity of cartilage damage of the patella can significantly influence function after successful Oxford medial UKA. Surgeons should factor this in when making their operative decision, and undertake to counsel patients appropriately. Cite this article: Bone Joint J 2016;98-B(10 Suppl B):11–15

Aim. The purpose of this study was to analyze the patellofemoral kinematics in neglected adult developmental dysplasia of the hip patients with patellofemoral symptoms and tried to clarify the affect of the severity of dislocation, the amount of limb length discrepancy, the deviation of mechanical axis and the changes in femoral anteversion on patellofemoral alignment. Methods. The dynamic patellofemoral CT results of 39 patients with DDH suffering from knee pain were reviewed. The mean age was 40.07 (range: 22–61). 14 of them were bilateral and 25 were unilateral neglected DDH patients. The CT results of 12 patients suffering from unilateral patellofemoral pain following the treatment of locked intramedullary nailing was taken as control group. In this patients atraumatic and asymptomatic normal site was taken as control group. Results. In unilateral neglected DDH patients there was significantly higher medial patellar displacement in 0, 15, 30, 60 degrees flexion in the knee at the site of dislocation. Again in uninvolved site medial patellar displacement in 15, 30, 60 degrees flexion was higher with respect to control group. In the involved extremity the PTA angle in 0, 15, 30, 60 degrees flexion were significantly higher than in control group. This increase in PTA angle corresponding to medial patellar tilt was observed only in involved extremity. In the knees of patients with bilateral DDH there was significant medial patellar displacement in every flexion degrees with respect to control group. Besides in bilateral DDH patients, the PTA angle in 15, 30, 60 degrees flexion were significantly higher than control group corresponding to medial patellar tilt. The amount of leg length discrepancy and the severity of dislocation as well as mechanical axis deviation were not affecting the patellofemoral parameters in both unilateral and bilateral DDH patients. Conclusion. Both in unilateral and bilateral DDH patients there are major changes in patellar tracking on femur during knee flexion. Increased medial shift and medial patellar tilt were seen in these patient groups. The neglected DDH patients suffering from knee pain should be analyzed not only for tibiofemoral abnormalities but also for patellofemoral malignment

Patellofemoral unicompartmental joint replacement is a controversial subject with a relatively small evidence base. Of the 50,000 total knee arthroplasties performed each year in the UK, approximately 10% are performed for predominantly patellofemoral arthritis. There are several patellofemoral unicompartmental prostheses on the market with the National Joint Registry recording 745 such prostheses used in 2007. Most evidence in favour of this procedure comes from experience with the Avon prosthesis (Stryker) predominantly from designer-surgeons. The FPV patellofemoral joint replacement (Wright Medical) has been in use in Europe for several years. The instruments have recently been redesigned and the device marketed in the UK. In 2007 the FPV had 5.9% market share (n=44). We present our early experience with the FPV patellofemoral joint replacement, which to our knowledge, is the first clinical outcome series for this prosthesis. 33 consecutive FPV joint replacements in 29 patients were performed between April 2007 and September 2009 for unicompartmental patellofemoral OA. All cases were performed or directly supervised by the senior author. Results are presented with a minimum follow-up of six months. Oxford and American Knee Society scores (AKSS) were obtained on all patients preoperatively and at subsequent outpatient visits. Mean preoperative AKSS knee score was 49.7 points and postoperative scores at 6 months and 1 year were 82.5 and 86.4 respectively. Mean Oxford score preoperatively was 30.4 (37%) and at 6 months and 1 year were 21.3 (56%) and 11.2 (77%) respectively. There were no complications related to the implant. One knee required a secondary open lateral release due to inadequate balancing at the index procedure. Further medium to long-term follow up data are required, but our initial experience with this device is encouraging

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

Patellofemoral unicompartmental joint replacement is a controversial subject with a relatively small evidence base. Of the 50,000 total knee arthroplasties performed each year in the UK, approximately 10% are performed for predominantly patellofemoral arthritis. There are several patellofemoral unicompartmental prostheses on the market with the National Joint Registry recording 745 such prostheses used in 2007. Most evidence in favour of this procedure comes from experience with the Avon prosthesis (Stryker) predominantly from designer-surgeons. The FPV patellofemoral joint replacement (Wright Medical) has been in use in Europe for several years. The instruments have recently been redesigned and the device marketed in the UK. In 2007 the FPV had 5.9% market share (n=44). We present our early experience with the FPV patellofemoral joint replacement, which to our knowledge, is the first clinical outcome series for this prosthesis. 33 consecutive FPV joint replacements in 29 patients were performed between April 2007 and September 2009 for unicompartmental patellofemoral OA. All cases were performed or directly supervised by the senior author. Results are presented with a minimum follow-up of six months. Oxford and American Knee Society scores (AKSS) were obtained on all patients preoperatively and at subsequent outpatient visits. Mean preoperative AKSS knee score was 49.7 points and postoperative scores at 6 months and 1 year were 82.5 and 86.4 respectively. Mean Oxford score preoperatively was 30.4 (37%) and at 6 months and 1 year were 21.3 (56%) and 11.2 (77%) respectively. There were no complications related to the implant. One knee required a secondary open lateral release due to inadequate balancing at the index procedure. Further medium to long-term follow up data are required, but our initial experience with this device is encouraging

Patellofemoral arthroplasty (PFA) has higher revision rates than total knee arthroplasty (TKA) [Van der List, 2015; Dy, 2011]. Some indications for revision include mechanical failure, patellar mal-tracking, implant malalignment, disease progression and persistent pain or stiffness [Dy, 2011; Turktas, 2015]. Implant mal-positioning can lead to decreased patient satisfaction and increased revision rates [Turktas, 2015]. Morphological variability may increase the likelihood of implant mal-positioning. This study quantifies the morphological variability of the anterior-posterior (AP) and medial-lateral (ML) aspects of the patellofemoral compartment using a database of computed tomography (CT) scans. The analysis presented here used the custom CT based program SOMA (SOMA V.4.3.3, Stryker, Mahwah, NJ). SOMA contains a large database of 3D models created from CT scans. Anatomic analysis and implant fitting tools are also integrated into SOMA to perform morphometric analyses. A coordinate system is established from the femoral head center, the intercondylar notch, and a morphological flexion axis (MFA). The MFA is created by iteratively fitting circles to the posterior condyles and creating and axis through the circles' centers. The sagittal plane is created normal to this axis and through the notch. A coronal plane is created from the femoral head center and the flexion axis. The AP measurement is taken normal to the coronal plane from the anterior cortex sulcus to the intercondylar notch (Figure 1). A 5°-flexed anterior resection is created to run-out at the anterior cortex sulcus. The ML measurement is taken normal to the sagittal plane from the most medial to the most lateral points of the anterior resection (Figure 1). The ML measurements are broken down into medial and lateral components divided by a sagittal plane through the trochlea. Means and standard deviations of the AP and ML measurements are calculated. The mean and standard deviation for the AP measurement are 24.9mm and 2.8mm, respectively. The data predicts that 99.7% of the population will have an AP measurement between 16.5mm and 33.3mm. The mean and standard deviation for the ML measurement are 54.6 mm and 5.5mm, respectively. The data predicts that 99.7% of the population will have an ML measurement between 38.1mm and 71.1mm A Pearson Correlation value of 0.134 was calculated for AP/ML indicating a very weak positive correlation between the measures. The correlation value and the large measurement ranges indicate that there is high variability between the AP and ML measurements. A scatterplot was created to graphically represent the high variability between the AP and ML width measurements (Figure 2). A Pearson Correlation value of −0.649 was calculated for the medial and lateral components of ML (Figure 3). The results of this study suggest that patellofemoral morphology is highly variable with respect to the AP and ML dimensions. This variability may impact implant fit and positioning and should be taken into consideration in the design and use of prostheses for PFA. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

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

The LCS RPS knee system is based on the successful LCS mobile bearing prosthesis, and has been introduced with the intention of improving post-operative knee flexion. The aim of this study is to report a high incidence of significant patellofemoral crepitus when this prosthesis is used without patella resurfacing. A successful arthroscopic technique to treat this complication will be described. We present a retrospective review of a single surgeon series of LCS RPS knee arthroplasty. All procedures were performed using a standard technique with cemented components. The patella was not resurfaced in any of the presented cases. The knee society score, patellofemoral score (Baldini et al, 2006), BMI, range of motion, and post-operative radiographs were obtained for all patients. In addition the presence of patellofemoral crepitus was assessed and rated as either none, mild (for limited ROM), moderate (throughout entire ROM), or severe(catching/clunk). An arthroscopic technique to treat this complication was developed. A total of 56 patients were reviewed at a mean follow-up of 16 months (range 9–22). The mean age at time of operation was 70 (range 50–87), and mean BMI was 29 (range 18–42). A lateral release was performed in 7 cases (12%). Mean knee society score was 77 (range 35–92), patellofemoral score 73 (range 25–100), and ROM 115 degrees (range 85–135). Significantly, patellofemoral crepitus was severe in 12 (21%) patients, moderate in 21 (37%), mild in 15 (26%), and absent in 9 (16%). In 4 patients arthroscopic resection of the proximal pole of the patella has resulted in complete resolution of severe crepitus with increases in patellofemoral (mean 25) and knee society (mean 7) scores, and, ROM (mean 15 degrees). One of these patients at 6 month follow-up has reported return of moderate crepitus. Similar resolution of crepitus has been seen in 3 cases which were revised to resurface the patella. As part of this ongoing study a non-randomised comparison group who received patellar resurfacing at the primary procedure has produced no cases of moderate or severe crepitus. In conclusion patella resurfacing is required when using the LCS RPS prosthesis to prevent an unacceptably high rate of moderate to severe patellofemoral crepitus. Both arthroscopic patelloplasty and revision to resurface the patella have resulted in resolution of this problem. Potential biomechanical causes for this problem will be presented

Quadriceps moment arm is one of the factors determining quadriceps force. Total knee arthroplasty designs with larger quadriceps moment arms should generate less quadriceps and patellofemoral forces. A study was conducted to measure knee kinematics, quadriceps and patellofemoral forces in two knee designs with differing centers of rotation. In addition, the effect of a central dome-shaped versus a medialized patella component was determined. Six human cadaver knees were tested before implantation and after sequential implantation with two posterior cruciate retaining designs: Scorpio and Control. The quadriceps moment arm of the Scorpio design was 1 cm longer than that of the Control design. Knee kinematics was measured with an eletromagnetic tracking device while the knee was put through dynamic simulated stair climbing under peak flexion moments of 40 N-m. Quadriceps tension and patellofemoral compressive and shear forces were measured for both conditions and for the central and medialized patella components. The normal unimplanted condition showed increasing rollback with flexion while both implanted conditions displayed relatively less rollback. Overall, quadriceps tension was highest in the unimplanted condition and lowest in the Scorpio condition. The Scorpio design showed a 10-20% reduction in quadriceps tension at angles greater than 40° when compared to the Control design. Patellofemoral forces were also significantly reduced in the Scorpio design when compared to Control. There were no differences noted between the central and medialized patella component. The Scorpio design, with its more posterior center of rotation, reduced quadriceps tension and patellofemoral forces. Reduced quadriceps forces may facilitate postoperative rehabilitation and activities such as stair climbing. Reduction in patellofemoral forces could reduce patellar complications such as anterior knee pain, component wear and loosening. These results are currently undergoing validation with a prospective clinical study

Introduction. The constitutional knee anatomy in the coronal plane includes the distal femoral joint line obliquity (DFJLO) which in most patients is in slight valgus positioning. Despite this native anatomy, the mechanical positioning of the femoral component during primary total knee arthroplasty (TKA) often ignores the native DFJLO opting to place the femur in a set degree of valgus that varies upon the practitioner's practice and experience. Unfortunately, this technique is likely to generate high rate of distal lateral femoral overstuffing. This anatomical mismatch might be a cause of anterior knee pain and therefore partly explain the adverse functional outcomes of mechanically aligned (MA) TKA. Our study aims at assessing the relationship between constitutional knee anatomy and clinical outcomes of MA TKA. We hypothesized that a negative relationship would be found between the constitutional frontal knee deformity, the distal femoral joint line obliquity, and functional outcomes of MA TKA with a special emphasize on patellofemoral (PF) specific outcomes. Methods. One hundred and thirteen patients underwent MA TKA (posterior-stabilized design) for primary end-stage knee osteoarthritis. They were prospectively followed for one year using the New KSS 2011 and HSS Patella score. Residual anterior knee pain was also assessed. Knee phenotypes using anatomical parameters (such as HKA, HKS, DFJLO and LDFA (Lateral distal femoral angle)) were measured from preoperative and postoperative lower-limb EOS® images (Biospace, Paris, France). We assessed the relationship between the knee anatomical parameters and the functional outcome scores at 1 year postoperatively. Results. We investigated four groups according to the preoperative obliquity of the distal femur and HKA. The group with high DFJLO and varus knee deformity demonstrated lower HSS scores (drop>10%, p=0.03) and higher rate of anterior knee pain (p=0.03). Higher postoperative variation of LDFA was associated with lower HSS scores (r = −0.2367, p=0.03) and with higher preoperative DFJLO (p=0.0001) due to the MA technique. Knee phenotypes with LDFA<87° presented higher risk of variation of LDFA. No correlation was found using New KSS 2011 outcomes at one-year follow-up. Discussion/Conclusion. Disregard of the constitutional knee anatomy (LDFA and DFJLO) when performing a MA TKA may generate a non-physiologic knee kinematics that impact patellofemoral outcomes and resulting in residual anterior knee pain. While these results are restricted to modern posterior-stabilized TKA design, recent in silico and in vitro studies supported the negative effect of the lateral overstuffing of the femoral component in the coronal plane during knee flexion. This study provides further evidence that suggest patient-specific anatomical considerations are needed to optimize component position and subsequent outcomes following primary TKA. Additional studies are needed to integrate the rotational status of the femoral component in this analysis. For any figures or tables, please contact authors directly

Introduction. Epidemiologic studies indicate that isolated patellofemoral (PF) arthritis affects nearly 10% of the population over 40 years of age, with a predilection for females. A small percentage of patients with PF arthritis may require surgical intervention. Surgical options include non-arthroplasty procedures (arthroscopic debridement, tibial tubercle unloading procedures, cartilage restoration, and patellectomy), and patellofemoral or total knee arthroplasty (PFA or TKA). Historically, non-arthroplasty surgical treatment has provided inconsistent results, with short-term success rates of 60–70%, especially in patients with advanced arthritis. Although TKA provides reproducible results in patients with isolated PF arthritis, it may be undesirable for those interested in a more conservative, kinematic-preserving approach, particularly in younger patients, who may account for nearly 50% of patients undergoing surgery for PF arthritis. Due to these limitations, patellofemoral arthroplasty (PFA) has become utilised more frequently over the past two decades. Indications for PFA. The ideal candidate for PFA has isolated, non-inflammatory PF arthritis resulting in “anterior” pain and functional limitations. Pain should be retro- and/or peri-patellar and exacerbated by descending stairs/hills, sitting with the knee flexed, kneeling and standing from a seated position. There should be less pain when walking on level ground. Symptoms should be reproducible during physical examination with squatting and patellar inhibition testing. An abnormal Q-angle or J-sign indicate significant maltracking and/or dysplasia, particularly with a previous history of patellar dislocations. The presence of these findings may necessitate concomitant realignment surgery with PFA. Often, patients with PF arthritis will have significant quadriceps weakness, which should be treated with preoperative physical therapy to prevent prolonged postoperative pain and functional limitations. Tibiofemoral joint pain suggests additional pathology, which may not be amenable to PFA alone. Conclusion. PFA is effective for the treatment of arthritis localised to the PF compartment. Outcomes can be optimised with proper patient selection, meticulous surgical technique, and selection of an onlay-style implant that can be positioned perpendicular to the AP axis of the femur. Minimizing the risk of patellar instability by using onlay-design PFAs has enhanced mid- and long-term results, and leaves progressive tibiofemoral arthritis as the primary failure mechanism beyond 10–15 years