Introduction: Patello-femoral complications are a major problem after total knee arthroplasty (TKA). Purpose of the present study was to analyze patello-femoral complications and function after two different posterior-stabilized TKA designs (Optetrak 913 vs IB-II).

Materials and Methods: This study was performed in two consecutive phases. In the first phase 1410 TKA’s performed by the senior author between 1994 and 1998 were considered for chart review. Within this period, the last 300 IB-II and the first 300 913 performed were analyzed for patello-femoral complication rate. In the second phase, of the 600 charts analyzed, two matched groups (50 patients each of IB-II and 913), were selected for a clinical (Knee Society score), functional (HSS Patellar score) and radiological assessment (AP, Lateral, Merchant, modified-wb Merchant views).

Results: A lateral retinacular release was performed in 30% for the IB-II and 16% for the 913 (p=0.02). The following patello-femoral complications were encountered (phase-1):

IB-II 913

Patellar clunk 3.5% 0.3%

Dislocation 0% 0.3%

Fracture 0% 0.3%

Loosening 0% 0%

Clinical results at follow-up (phase-2) did not show any significant difference between the two matched groups in terms of Knee and Function scores (p=0.7). Patellar score showed a higher rate of excellent and good results in the 913 group (88% vs 81%: p=.043). Anterior knee pain was only mild and activity related in 26% of the IB-II and 14% of the 913 (p=.025). In a multivariate regression analysis, radiographic patellar tilt, subluxation, and height, did not correlate with clinical outcomes, whilst bone-implant contact showed a trend towards a higher incidence of pain, particularly when associated with asymmetric patellar resection.

Discussion: At an intermediate follow-up, the Optetrak 913 prostheses showed fewer complications and an improved patello-femoral function compared to the IB-II prosthesis.

Introduction: Patello-femoral evaluation after total knee arthroplasty (TKA) is not addressed by most knee scoring systems. Patellar radiographic assessment after TKA is obtained with static, unloaded views that may not reproduce the in-vivo patello-femoral kinematics. The purpose of this study was to develop and validate new reliable and reproducible clinical and radiographic assessment tools for analysis of the patello-femoral joint in TKA.

Materials and Methods: The existing axial Merchant view was modified by positioning the standing patient in the semi-squatted position with the knees at 45°. Relationship between X-ray source, the angle of incidence on the joint, and the cassette position, were kept unchanged from the original view. The standing position and consequent muscle involvement were the only differences. The quality of the view was confirmed on a cadaveric knee model with multiple markers. Safety, reproducibility and clinical reliability were obtained in 100 posterior-stabilized TKA’s. These patients were assessed by a new Patella Scoring System (0–100 points). This system considers anterior knee pain, crepitus, stair performance and quadriceps strength. Radiographic abnormalities are calculated as deductions. Intra- and inter-observer variability were obtained comparing the results of two different investigators.

Results: The modified Merchant view showed significant patello-femoral tracking changes in 68% of patients. Twenty-one cases of bone-implant contact were observed when load was applied. Correlation between excellent-good clinical outcome and excellent patello-femoral performance was significantly higher for the Patellar Score compared to Knee Society Clinic or Function scores (p=.022, p=.014). Multivariate regression analysis of radiographic tilt, subluxation, and height, did not correlate with clinical outcomes, whilst bone-implant contact showed higher incidence of pain, particularly when associated with asymmetric patellar resection.

Conclusion: These new patello-femoral clinical and radiological assessment methods employed in the study represent additional valuable tools for the comprehensive evaluation of results in TKA.