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

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

Introduction. Patellofemoral complications remain a very common post-operative problem in association with total knee arthoplasty (TKA). As malrotation of the femoral component is often considered crucial for the outcome, we analyzed absolute rotational femoral alignment in relation to patellar tracking pre- and postoperatively and matched the results with the two year functional outcome. Methods. Femoral rotation and component rotation was assessed by axial radiography using condylar twist angle (CTA). The lateral patellar displacement, patellar tilt and Insall-Salvati index were measured on conventional radiographs. All assessments were done pre-operatively and at 2-year follow up. The series included 48 consecutive TKA (21 men, 27 women) performed at a single high-volume joint-replacement-center in 2008. All operations were performed using a tibia first-ligament balancing technique without patella resurfacing. The implant used was a condylar unconstrained ultracongruent rotating platform design. Outcome was assessed using the international knee society score (KSS) and the Kujala Score for anterior knee pain. Results. Preoperative CTA showed 6.4±2. 5° (X±SD) of internal femoral rotation (IR) (range, 1° of external rotation (ER) to 12° of IR) compared to postoperative CTA of 3.9°±2.98° (X±SD) of IR (range, 9.5° IR to 3.8°of ER) Preoperative patella lateral displacement showed a mean of 1.1mm (−2mm, 6mm), compared to postoperative patella lateral displacement with a mean of 1.7mm (−3mm, 6mm). Postoperative mean patella tilt was 6.65° (1.8°, 11.7°) postoperatively compared to 8.55° (4.3°,11.5°) preoperatively. No correlation was found between CTA post surgery and patella positioning (r=0.034, 95% CI). IR of the femoral component >3°did not show increased patella lateral displacement/tilt compared to 0° or ER. No correlation was found between the Kujala score and internal rotation of the component (r=0.082, p=0.05). At 2 year post OP KSS reached > 185 of max. 200 points in over 82% of patients. Conclusion. The influence of IR of the femoral component on patellofemoral kinematics remains controversial. As demonstrated, IR does not imperatively lead to patella maltracking and/or patellofemoral symptoms. Functional outcome in this series shows that relative rotation of the femoral component in accordance with natural variations as seen in the pre-operative assessment allows for good and excellent results