Introduction & aims. Resurfacing of the patella is an important part of most TKA operations, usually using an onlay technique. One common practice is to medialise the patellar button and aim to recreate the patellar offset, but most systems do not well control alignment of the patella button. This study aimed to investigate for relationships between placement and outcomes and report on the accuracy of patella placement achieved with the aid of a patella Patient Specific Guide (PSG). Method. A databse of TKR patients operated on by five surgeons from 1-Jan-2014 who had a pre-operative and post-operative CT scan and 6-month postoperative Knee Osteoarthritis and Outcome (KOOS) scores were assessed. Knees were excluded if the patella was unresurfaced or an inlay technique was used. All knee operations were performed with the Omni Apex implant range and used dome patella buttons. A sample of 40 TKRs had a patella PSG produced consisting of a replication of an inlay barrel shaped to fit flush to the patient's patella bone. The centre of the quadriceps tendon on the superior pole of the patella bone and the patella tendon on the inferior were landmarked. 3D implant and bone models from the preoperative CT scans were registered to the post-operative CT scan. The flat plane of the implanted patella button was determined and the position of the button relative to the tendon attachments calculated. Coverage of the bone by the button and patellar offset reconstruction were also calculated. The sample of 40 TKRs for whom a patella PSG was produced had their variation in placement assessed relative to the wider population sample. All surgeries were conducted with Omni Apex implants using a domed patella. Results. A total of 322 patients were identified in the database, and 82 were subsequently excluded as inlay rather than onlay patella. 59% (142) were female and the average age was 68.9 years (+/− 7.2). Coverage percentage of the cut patella surface by the button was 67% (± 7%), with 83% (200) knees having greater than 60%, and 40% (96) greater than 70%. Component position was on average centralised in terms of mediolateral position (0.09mm ± 1.93 lateral). When comparing the alignment of the patients whose knees used PSG guides with those who did not, it was found there was a statistically significant reduction in the variation that both external rotation error and flexional error had (p-values 0.048 and 0.022 respectively.). Excess medialisation of the patella button was found to weakly correlate with reduced postoperative KOOS symptoms scores (coefficient=0.14, p-value = 0.035). When subdivided into patients who reported knee clicking sometimes or more often and those who did not, patients with highly medialised buttons had a 1.5× likelihood of reporting clicking of their knee joint (p-value = 0.036). Conclusions. The patella-femoral joint remains a crucial component in the TKA knee, but the process of resurfacing the bone is not well controlled and can negatively influence patient outcomes. PSG's are one potential mechanism of controlling patella component alignment

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

Patello-femoral arthritis can result in a considerable thinning of the patella. The restoration of an adequate patella thickness is key to the successful outcome of knee arthroplasty. The objectives were (1) to establish a reproducible patella width:thickness index including chondral surface and (2) to investigate whether there is a difference between bone alone and bone/chondral construct thickness as shown by MRI. Forty three MRI scans of young adults, mean age 27 (range 17–38), 34 male and 9 female, were studied. Exclusion criteria included degenerative joint disease, patello-femoral pathology or age under 16/over 40 (102 patients). The bony and chondral thickness of the patella and its width were measured. Inter/intra observer variability was calculated and correlation analysis performed. We found a strong correlation between patella plus cartilage thickness and width (Pearson 0.75, P < 0.001). The mean width:thickness ratio was 1.8 (SD 0.10, 95% CI 1.77–1.83). Without cartilage the ratio was 2.16 (SD 0.15, 95% CI 2.11–2.21), correlation was moderate (Pearson 0.68, P < 0.001). The average patella cartilage thickness was 4.1mm (SD 1.1, 95% CI 3.8–4.5). The narrow confidence intervals for the ratio of patella width:thickness suggest that patella width can be used as a guide to accurate restoration of patella thickness during total knee or patella-femoral replacement. We would recommend a ratio of 1.8:1

Introduction. The trochlea of a typical patellofemoral replacement or anterior flange of a total knee replacement usually extends past the natural trochlea and continues onto the femoral anterior cortex. One reason for this is that it allows a simple patella button to be permanently engaged in the trochlea groove in an attempt to ensure stability. On the natural patella, the apex helps to guide it into the trochlea groove as the knee moves from full extension into flexion. The aim is to study whether a generalised patella can be created that is close in form to a healthy patella. Method. MRI scans were taken of 30 patellae. Characteristics of these patellae (height, width, thickness, apex angle) were measured. The apex angle was found to be similar between patellae (mean=126 degrees, sd = 8.8), as were the ratios between height and width (mean width/height = 1.05, sd = 0.07) and between thickness and width (mean width/thickness = 1.8, sd = 0.19). These patellae were then segmented to create a surface including cartilage, resulting in 30 STL (stereolithography) files in which the surfaces are represented by triangle meshes. To design the average patella the individual patellae were aligned to a standard frame of reference by placing a set of landmarks on the proximal/distal, medial/lateral and anterior/posterior extents of each (fig.1). The vertical axis was defined as passing parallel to the proximal/distal points and the horizontal as passing parallel to the medial/lateral points when looking along the computed vertical axis. The origin centre of the frame of reference was chosen to be mid-way between these points. The mean width was then computed and each patella scaled linearly around the origin to give them all equal width. All the aligned patellae were then averaged together to provide a composite cartilaginous patella. The averaging process was achieved by taking one patella as a seed. The patella chosen for seed was that whose parameters were closest to the average width, height and thickness. An approximately normal vector was passed a point ‘P’ on the seeds, and the points at which these intersected the other models were then determined. The closest intersection point to ‘P’ on each model was chosen and these averaged together. ‘P’ is then replaced in the model with this average point. The averaging process then continues with all the remaining points on the seed model in the same manner to build the average models. Results and Discussion. The mean patella was compared with individual patellae. This comparison was performed by taking each point on the mean patella and finding the closest point on individual patellae - a colour coded map of differences was obtained (fig.2) along with a mean of the absolute difference for each patella. The absolute mean difference ranged from 0.56mm to 1.33mm, averaging at 0.85mm. This shows a reasonable fit between the average patella and each individual example, raising the possibility of using the average shape in future research to develop anatomical patellofemoral replacements and for planning patella resurfacing

Introduction. Patella femoral joint bearings in total knee replacements have shown low wear (3.1 mm. 3. /MC) under standard gait simulator conditions. 1. However, the wear in retrieval studies have shown large variations between 1.3 to 45.2 mm. 3. /year. 2. Previous in vitro studies on the tibial femoral joint have shown wear is dependent on design, materials and kinematics. 3. . The aim of this study was to investigate the influence of the design (geometry) and shape on the wear rate of patella femoral joints in total knee replacements. Materials and Methods. The Leeds/Prosim knee simulator was used to investigate the wear of two types of commercially available patellae. The PFC Sigma cobalt chrome femoral component was coupled with 2 types of patellae buttons: round and oval dome. The UHMWPE was the same for the both types – GUR1020 GVF (gamma irradiated in vacuum and foiled packed). 25% bovine serum was used as the lubricant. The test were carried out at three conditions – high medial lateral (ML) rotations (<4°) and uncontrolled ML displacement (<4 mm), low ML rotation (<1°) and uncontrolled ML displacement (<4 mm); the physiological gait cycle; and low ML rotation and controlled ML displacement (<1.5 mm). In this abstract the two designs were tested in physiological gait condition (Figure 1). Patella ML displacement and tilt were passively controlled and measured after every 300,000 cycles. A ligament resisting force equivalent to 10 N4 was applied on the lateral side of the patella to avoid patella slip. Five samples of each design were tested for 3 million cycles at a cycle rate of 1 Hz. The wear volume was obtained gravimetrically every million cycles and presented with 95% confidence limits. Statistical significance was taken at p<0.05. Results and Discussions. The wear rate of PFC sigma round dome patella was higher (8.63 ± 3.44 mm. 3. /million cycles) compared to the PFC sigma oval dome patella (6.28 ± 3.89 mm. 3. /million cycles) (Figure 2). However, no significant difference in the wear rates was found between the two shapes (P=0.2). The low area of contact of oval dome patella (31.2% of total surface area) as compared to round dome patella (39.9%) led to low wear. 5. . The wear volume and the patellar tilt were positively correlated for oval dome and round dome patella, R. 2. > 0.9 (Figure 3). Increase in the patellar tilt resulted increase in sliding distance in perpendicular direction of polymer orientation. This led to higher wear volume. Conclusions. Wear rate decreased with change of patella shape from round dome to oval dome although not significantly. Increase in the patellar tilt resulted in increase in the wear volume. Acknowledgement. This research was supported in part by the DePuy and EPSRC. In addition, it was partially funded through WELMEC, a Centre of Excellence in Medical Engineering funded by the Wellcome Trust, under grant number WT 088908/Z/09/Z and additionally supported by the NIHR (National Institute for Health Research) as part of collaboration with the LMBRU (Leeds Musculoskeletal Biomedical Research Unit)

Aims. Patient dissatisfaction is not uncommon following primary total knee arthroplasty. One proposed method to alleviate this is by improving knee kinematics. Therefore, we aimed to answer the following research question: are there significant differences in knee kinematics based on the design of the tibial insert (cruciate-retaining (CR), ultra-congruent (UC), or medial congruent (MC))?. Methods. Overall, 15 cadaveric knee joints were examined with a CR implant with three different tibial inserts (CR, UC, and MC) using an established knee joint simulator. The effects on coronal alignment, medial and lateral femoral roll back, femorotibial rotation, bony rotations (femur, tibia, and patella), and patellofemoral length ratios were determined. Results. No statistically significant differences were found regarding coronal alignment (p = 0.087 to p = 0.832). The medial congruent insert demonstrated restricted femoral roll back (mean medial 37.57 mm; lateral 36.34 mm), while the CR insert demonstrated the greatest roll back (medial 42.21 mm; lateral 37.88 mm; p < 0.001, respectively). Femorotibial rotation was greatest with the CR insert with 2.45° (SD 4.75°), then the UC insert with 1.31° (SD 4.15°; p < 0.001), and lowest with the medial congruent insert with 0.8° (SD 4.24°; p < 0.001). The most pronounced patella shift, but lowest patellar rotation, was noted with the CR insert. Conclusion. The MC insert demonstrated the highest level of constraint of these inserts. Femoral roll back, femorotibial rotation, and single bony rotations were lowest with the MC insert. The patella showed less shifting with the MC insert, but there was significantly increased rotation. While the medial congruent insert was found to have highest constraint, it remains uncertain if this implant recreates native knee kinematics or if this will result in improved patient satisfaction. Cite this article: Bone Jt Open 2024;5(7):592–600

Patella instability is a common problem with many surgical options. We prospectively evaluated the results of medial patella femoral ligament (MPFL) reconstruction with an autogenous gracilis or semitendinous graft. With a minimum follow up of one year patients were reviewed using the Kujala scoring system. Twenty MPFL reconstructions were performed on seventeen patients over a two year period, from January 2004 to December 2005. There were 13 females and 4 males. Three patients had bilateral involvement. Thirteen patients had a lateral release with their MPFL reconstruction and three had a distal realignment procedure as well to correct their patella instability. The mean follow up was 17 months (range 12 to 26 months). The average age was 25 years old at operation (range 13 to 47) and the average age of their first dislocation was 16 (range 0-35). Nine patients had previous surgical treatment for patella instability. The average hypermobility score in the patients was 5/9 and six patients scored 9/9. At follow up 18 out of 20 patients (90%) had stable tracking with no further subluxations/dislocations. Of the two with unstable tracking, one had a stable patella before falling several times onto her knee. An MRI confirmed the ligament was intact but a type 2 trochlear dysplasia was present and a Bereiter trochleoplasty was subsequently performed. The other patient described no frank dislocation but instead subluxations. Eighteen of the twenty reconstructions (90%) achieved a stable patella. Overall Kujala scores increased by a third

Aim. To assess if there is a reproducible relationship between the width and thickness of the normal patella. Method. 43 MRI scans of young adults, average age 27 (range 17–38) were studied. Exclusion criteria included a diagnosis of degenerative joint disease, patella-femoral pathology or age under 16/over 40 (102 patients). The bony thickness of the patella, the chondral thickness and patella width were measured, as was the location of maximal patella thickness. Inter/intra observer variability was calculated and correlation analysis performed. Results. There was a strong correlation between overall patella thickness (bone plus cartilage) and width (Pearson 0.75, P < 0.001). The width: thickness ratio is 1.8:1 (standard deviation 0.102, 95% confidence interval 1.6–2.0). The average patella cartilage thickness is 4.1mm (SD 1.3). The thickest region of the patella lies 54% (SD 2.32) from the lateral border and 54% (SD 7.9) from the superior pole. Conclusion. We propose that the normal “Index of Patella Width: Thickness” = 1.8:1. It can be used as a guide for restoring patella thickness during TKR or patella-femoral replacement to that of a knee free from age related wear and osteoarthritis. This maximal thickness should be slightly medial and distal in the patella. MULTIPLE DISCLOSURES

Aims: The purpose of this study was to determine whether patella replacement or RAP of the patella is advantageous in TKA. Methods: 100 patients were recruited to enter a randomised, prospective, double blind clinical trial to determine the efþcacy of patellar resurfacing during total knee arthroplasty. All patients receive the same posterior cruciatesparing prosthesis, and all operations were performed by, or under the direct supervision of the þrst author. Evaluation consisted of the determination of the HSS-Score, the knee society scores, speciþc questions relating to patellafemoral symptoms, radiographs, measurement of torques and stability of one leg standing. All knees were followed at 3 month and 18 month postoperatively. Results: There was no signiþcant difference between the two groups with regard to the HSS-Score, and the KS-scores. Excentric and concentric torques were higher in the group with RAP of the patella. One leg standing was more stable in the group with RAP of the patella. In both groups one patient complained of severe anterior knee pain. The patient with RAP of the patellar was treated successfully with secondary patella resurfacing. Conclusions: The clinical outcome and the prevalence of anterior knee pain after TKA with the PFC-∑ knee was not inßuenced by whether or not the patella had been resurfaced. Force and balance are slightly better after TKA with RAP of the patella

Abstract. Objectives. The outcomes from patella fracture have remained dissatisfactory despite advances in treatment, especially from operative fixation1. Frequently, reoperation is required following open reduction and internal fixation (ORIF) of the patella due to prominent hardware since the standard technique for patella ORIF is tension band wiring (TBW) which inevitably leaves a bulky knot and irritates soft tissue given the patella's superficial position2. We performed a systematic review to determine the optimal treatment of patella fractures in the poor host. Methods. Three databases (EMBASE/Medline, ProQuest and PubMed) and one register (Cochrane CENTRAL) were searched. 476 records were identified and duplicates removed. 88 records progressed to abstract screening and 73 were excluded. Following review of complete references, 8 studies were deemed eligible. Results. Complication rates were shown to be high in our systematic review. Over one-fifth of patients require re-operation, predominantly for removal of symptomatic for failed hardware. Average infection rate was 11.95% which is higher than rates reported in the literature for better hosts. Nevertheless, reported mortality was low at 0.8% and thromboembolic events only occurred in 2% of patients. Average range of movement achieved following operative fixation was approximately 124 degrees. Upon further literature review, novel non-operative treatment options have shown acceptable results in low-demand patients, including abandoning weight-bearing restrictions altogether and non-operatively treating patients with fracture gaps greater than 1cm. Regarding operative management, suture/cable TBW has been investigated as a viable option with good results in recent years since the materials used show comparable biomechanics to stainless steel. Additionally, ORIF with locking plates have shown favourable results and have enabled aggressive post-operative rehabilitation protocols. TBW with metallic implants has shown higher complication rates, especially for anterior knee pain, reoperation and poor functional outcomes. Conclusion. There is sparse literature regarding patella fracture in the poor host. Nevertheless, it is clear that ORIF produces better outcomes than conservative treatment but the optimal technique for patella ORIF remains unclear. TBW with metallic implants should not remain the standard technique for ORIF; low-profile plates of suture TBW are more attractive solutions. Non-operative treatment may be considered for low-demand individuals however any form of patellectomy should be avoided if possible. 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

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

Introduction: In this study the optimal angle of fixation or splintage for partially weight bearing fractures of the patella was determined by a gait analysis measurement system. Subjects and Methods: A knee brace was applied to eight subjects and locked at 0, 10, 20 and 30 degrees. Measurements were also taken for an unlocked brace and in the absence of a brace. The subjects were instructed on partial weight bearing mobilisation. Three dimensional motion analyses were performed using an infrared 8-camera system. The ground reaction force was recorded by two 3-dimensional force plates embedded in the walkway. Kinematic and kinetic data was collected and the data was transferred to a computer programme for further analysis and the forces acting on the patella were calculated. Results: The results showed that the forces acting on the patella were directly proportional to the knee flexion angle. The results also showed that the knee flexion angle does not always correspond with the angle set at the knee brace; however they did exhibit a direct relationship. Conclusion: Our findings show that, for partially weight bearing patella fractures, the optimum form of splintage corresponds with a low knee flexion angle

Background: Patella tendonitis is a condition often found in athletes but is also found in less active patients. It usually responds to conservative management (rest, physiotherapy and anti-inflammatory drugs) but some progress to surgery. A retrospective study was done to look at the results of this surgery in our hospital. Patients and Methods: From 2001 to 2007, nineteen knees in sixteen patients had open patella tendon decompression. Eleven patients were still involved in sporting activity. All surgery was performed by the same surgeon. The patients were brought back to a clinic for review, examination and VISA score. Results: All but one patient had an improvement in their pain score. Of the 11 patients that played sport, eight were able to return to sport. Five of these returned to competition. Five patients would not have the surgery again. Only two of these had still played sport. Three of these had other knee pathology found at arthroscopy. Conclusions: The results of the surgery were satisfactory, although they were more favourable in the patients that were still involved in sporting activities. The rehabilitation time was much longer than had been expected by most patients

Abstract. Introduction. There is growing interest in the use of robotic Total Knee Arthroplasty (TKA) to improve accuracy of component positioning. This is the first study to investigate the radiological accuracy of implant component position using the ROSA® knee system with specific reference to Joint Line Height, Tibial Slope, Patella Height and Posterior Condylar Offset. As secondary aims we compared accuracy between image-based and imageless navigation, and between implant designs (Persona versus Vanguard TKA). Methodology. This was a retrospective review of a prospectively-maintained database of the initial 100 consecutive TKAs performed by a high volume surgeon using the ROSA® knee system. To determine the accuracy of component positioning, the immediate post-operative radiograph was reviewed and compared with the immediate pre-operative radiograph with regards to Joint Line Height, Tibial Slope, Patella Height (using the Insall-Salvati ratio) and Posterior Condylar Offset. Results. Mean age of patients undergoing ROSA TKA was 70 years (range, 55 to 95 years). Mean difference in joint line height between pre and post-operative radiographs was 0.2mm (range −1.5 to +1.8mm, p<0.05), posterior condylar offset mean change 0.16mm (range −1.4 to +1.3mm, p<0.05), tibial slope mean change 0.1 degrees (p<0.05) and patella height mean change 0.02 (range −0.1 to +0.1 p<0.05). No significant differences were found between imageless and image-based groups, or between implant designs (Persona versus Vanguard). Conclusion. This study validates the use of the ROSA® knee system in accurately restoring Joint Line Height, Patella Height and Posterior Condylar Offset

“The shortest distance between two points is a straight line.” This explains many cases of patellar maltracking, when the patellar track is visualised in three dimensions. The three-dimensional view means that rotation of the tibia and femur during flexion and extension, as well as rotational positioning of the tibial and femoral components are extremely important. As the extensor is loaded, the patella tends to “center” itself between the patellar tendon and the quadriceps muscle. The patella is most likely to track in the trochlear groove IF THE GROOVE is situated where the patella is driven by the extensor mechanism: along the shortest track from origin to insertion. Attempts to constrain the patella in the trochlear groove, if it lies outside that track, are usually unsuccessful. Physiologic mechanisms for tibial-femoral rotation that benefit patellar tracking (“screw home” and “asymmetric femoral roll-back”) are not generally reproduced. Practical Point. A patellofemoral radiograph that shows the tibial tubercle, illustrates how the tubercle, and with it the patellar tendon and patella itself, are all in line with the femoral trochlea. To accomplish this with a TKA, the femoral component is best rotated to the transepicondylar axis (TEA) and the tibial component to the tubercle. In this way, when the femoral component sits in its designated location on the tibial polyethylene, the trochlear groove will be ideally situated to “receive” the patella. Knee Mechanics. Six “degrees of freedom” refers to translation and rotation on three axes (x,y,z). This also describes how arthroplasty components can be positioned at surgery. The significant positions of tibial, femoral and patellar components are: 1. Internal-external rotation (around y-axis) and 2. Varus-valgus rotation (around z axis). 3. Medial-lateral translation (on x-axis). The other positional variables are less important for patella tracking. Biomechanical analyses of knee function are often broken down into: i. Extensor power analysis (y-z or sagittal plane) and ii. Tracking (x-y or frontal plane). These must be integrated to include the effects of rotation and to better understand patellar tracking. Effect of Valgus. Frontal plane alignment is important but less likely to reach pathological significance for patellar tracking than rotational malposition clinically. For example if a typical tibia is cut in 5 degrees of unintended mechanical valgus, this will displace the foot about 5 cm laterally but the tibial tubercle only 8 mm laterally. An excessively valgus tibial cut will not displace the tubercle and the patella as far as mal-rotation of the tibial component. Effect of Internal Rotation of Tibial Component. By contrast, internal rotation of the tibial component by 22 degrees, which is only 4 degrees in excess of what has been described as tolerable by Berger and Rubash, displaces the tubercle 14 mm, a distance that would place the center of most patella over the center of the lateral femoral condyle, risking dislocation. Dynamically, as the knee flexes, if the tibia is able to rotate externally this forces the tubercle into an even more lateral position, guaranteeing that the patella will align lateral to the tip of the lateral femoral condyle, and dislocate. The design of femoral components, in particular the varus-valgus angle of the trochlear groove, has an effect on patellar tracking. This effect will be accentuated by the surgical alignment technique of the femoral and tibial components. Component positions that mimic the orientation of the normal anatomy usually include more valgus alignment of the femoral component. This rotates the proximal “entrance” of the femoral trochlear groove more medially, making it more difficult for the patella to descend in the trochlear groove

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

Treatment of simple and complex patella fractures represents a challenging clinical problem. Controversy exists regarding the most appropriate fixation method. Tension band wiring, aiming to convert the pulling forces on the anterior aspect of the patella into compression forces across the fracture site, is the standard of care, however, it is associated with high complication rates. Recently, anterior variable-angle locking plates have been developed for treatment of simple and comminuted patella fractures. The aim of this study was to investigate the biomechanical performance of the novel anterior variable-angle locking plates versus tension band wiring used for fixation of simple and complex patella fractures. Sixteen pairs of human cadaveric knees were used to simulate either two-part transverse simple AO/OTA 34-C1 or five-part complex AO/OTA 34-C3 patella fractures by means of osteotomies, with each fracture model created in eight pairs. The complex fracture pattern was characterized with a medial and a lateral proximal fragment, together with an inferomedial, an inferolateral and an inferior fragment mimicking comminution around the distal patellar pole. The specimens with simple fractures were pairwise assigned for fixation with either tension band wiring through two parallel cannulated screws, or an anterior variable-angle locking core plate. The knees with complex fractures were pairwise treated with either tension band wiring through two parallel cannulated screws plus circumferential cerclage wiring, or an anterior variable-angle locking three-hole plate. Each specimen was tested over 5000 cycles by pulling on the quadriceps tendon, simulating active knee extension and passive knee flexion within the range from 90° flexion to full knee extension. Interfragmentary movements were captured by motion tracking. For both fracture types, the articular displacements, measured between the proximal and distal fragments at the central aspect of the patella between 1000 and 5000 cycles, together with the relative rotations of these fragments around the mediolateral axis were all significantly smaller following the anterior variable-angle locked plating compared with the tension band wiring, p < 0.01. From a biomechanical perspective, anterior locked plating of both simple and complex patella fractures provides superior construct stability versus tension band wiring

It is a not so uncommon clinical scenario: well-fixed, well-aligned, balanced total knee arthroplasty with continued pain. However, radiographs also demonstrate an unresurfaced patella. The debate continues and the controversy remains as whether or not to routinely resurface the patella in total knee arthroplasty. In perhaps the most widely referenced article on the topic, the overall revision rates were no different between the resurfaced (9%) and the unresurfaced (12%) groups and thus their conclusion was that similar results can be obtained with and without resurfacing. However, a deeper look in to the data in this study shows that 4 times more knees in the unresurfaced group were revised for patellofemoral problems. A more recent study concluded that selectively not resurfacing the patella provided similar results when compared to routinely resurfacing. The study does emphasise however, that this conclusion depends greatly on femoral component design and operative diagnoses. This suggests that selective resurfacing with a so-called “patella friendly” femoral component in cases of tibio-femoral osteoarthritis, is a safe and effective strategy. Finally, registry data would support routine resurfacing with a 2.3 times higher relative risk of revision seen in the unresurfaced TKA. Regardless of which side of the debate one lies, the not so uncommon clinical scenario remains; what do we do with the painful TKA with an unresurfaced patella. Precise and accurate diagnosis of the etiology of a painful TKA can be very difficult, and there is likely a strong bias towards early revision with secondary patellar resurfacing in the painful TKA with an unresurfaced TKA. At first glance, secondary resurfacing is associated with relatively poor outcomes. Correia, et al. reported that only half the patients underwent revision TKA with secondary resurfacing had resolution of their complaints. Similarly, only 53% of patients in another series were satisfied with the procedure and pain relief. The conclusions that can be drawn from these studies and others are that either routine patellar resurfacing should be performed in all TKA or, perhaps more importantly, we need to better understand the etiology of pain in an otherwise well-aligned, well-balanced, well-fixed TKA. It is this author's contingency that the presence of an unresurfaced patella leads surgeons to reoperate earlier, without truly identifying the etiology of pain or dissatisfaction. This strong bias; basically there is something more that can be done, therefore we should do it, is the same bias that leads to early revision of partial knee arthroplasty. While very difficult, we as knee surgeons should not revise a partial knee or secondarily resurface a patella due to pain or dissatisfaction. Doing so, unfortunately, only works about half the time. The diagnostic algorithm for evaluating the painful, uresurfaced TKA includes routinely ruling out infection with serum markers and an aspiration. Pre-arthroplasty radiographs should be obtained to confirm suitability and severity of disease for an arthroplasty. An intra-articular diagnostic injection with Marcaine +/− corticosteroid should provide significant pain relief. MARS MRI may be beneficial to evaluate edema within the patella. Lastly, operative implant stickers to confirm implant manufacturer and type are critical as some implants perform less favorably with unresurfaced patellae. To date, no studies of secondary resurfacing describe the results of this, or similar, algorithms for defining patellofemoral problems in the unresurfaced TKA and therefore it is still difficult to conclude that poor results are not simply due to our inherent bias towards early revision and secondary resurfacing of the unresurfaced patella

Resurfacing the patella is performed the majority of the time in the United States and in many regions it is considered standard practice. In many countries, however, the patella is left un-resurfaced an equal amount of the time or even rarely ever resurfaced. Patella resurfacing is not a simple or benign procedure. There are numerous negative sequelae of resurfacing including loosening, fragmentation, avascular necrosis, lateral facet pain, stress fracture, acute fracture, late fracture, and restricted motion. In a study by Berend, Ritter, et al, failures of the patella component were reported 4.2% of the time at an average of only 2.6 years. A study was undertaken at Washington University in recent years to determine rather more clinical problems were observed following total knee replacement with or without patella resurfacing. Records were maintained on all problem total knees cases with well localised anterior knee pain. The referral area for this clinic is St. Louis which is among the largest American cities, with the highest percentage of total knees that are performed without patella resurfacing. During 4 years of referrals of total knee patients with anterior knee pain, 47 cases were identified of which 36 had a resurfaced patella and 11 had a non-resurfaced patella. Eight of 36 resurfaced patellae underwent surgery while only 2 of 11 non-resurfaced patellae underwent subsequent surgery. More than 3 times as many painful total knees that were referred for evaluation had already had their patella resurfaced. In spite of the fact that approximately equal number of total knees were performed in this area without patella resurfacing, far more patients presented to clinic with painful total knee in which the patella had been resurfaced. The numerous pathologies requiring a treatment following patella resurfacing included patella loosening, fragmentation of the patella, avascular necrosis patella, late stress fracture, lateral facet pain, oblique resurfacing, and too thick of a patellar composite. In a large multi-center randomised clinical trial at 5 years from the United Kingdom in over 1700 knees from 34 centers and 116 surgeons, there was no difference in the Oxford Score, SF-12, EQ-5D, or need for further surgery or complications. The authors concluded, “We see no difference in any score, if there is a difference, it is too small to be of any clinical significance”. In a prospective of randomised clinical trial performed at Tulane University over 20 years ago, no differences were observed in knee score, a functional patella questionnaire, or the incidence of anterior knee pain between resurfaced and un-resurfaced patellae at time intervals of 2–4 years, 5–7 years, or greater than 10 years. Beyond 10 years the knee scores of total knee patients with a resurfaced patella had declined significantly greater than those with a non-resurfaced patella. There are numerous advantages of not resurfacing the patella including less surgical time, less expense, a lower risk of “major” complications (especially late complications), and if symptoms develop in an un-resurfaced patella, it is an easier salvage situation with more options available. A small percentage of total knee patients will be symptomatic whether or not their patella is resurfaced. Not resurfacing the patella retains more options and has fewer complications. The major determinant of clinical result and the presence of anterior knee pain after knee replacement is surgical technique and component design not whether or not the patella is resurfaced. Patella resurfacing is occasionally necessary for patients with inflammatory arthritis, a deformed or maltracking patella, or symptoms and pathology that are virtually restricted to the patellofemoral joint. For the vast majority of patients, however, patella resurfacing is not necessary

The decision to resurface the patella has been well studied. While regional differences exist, the overwhelming choice by most Surgeons in the United States is to resurface the patella. Data supports that this is the correct choice. Articular cartilage on metal has not been shown to be a good long term bearing surface. Cushner et al. has also shown that cartilage in the arthritic knee has significant pathologic abnormalities. Patella surfacing has excellent long-term results with a low complication rate. Anterior knee pain is a common complaint after knee replacement and is even more common in TKA with un-resurfaced patella. Pakos et al. had more reoperations and greater anterior knee pain when the patella was NOT resurfaced. Parvizi et al. also found less patient satisfaction with un-resurfaced patellas. Meta-analysis results indicate higher revision rates with un-resurfaced patellas. Bilateral knee studies also favor resurfaced patella. Higher revision rates were also confirmed in the Swedish Registry with a 140% higher revision rate in TKA with un-resurfaced patellas In addition, second operations to resurface the patella often are unsuccessful at alleviating pain. Surgeons who choose not to resurface the patella must accept that their patients will have the same or greater degree of anterior knee pain and a significantly greater risk for reoperation