Summary

In the patellar resurfacing, thickening of the medial patella should be avoided, whereas thickness at the lateral side can be tolerated.

Abstract

Introduction

Mal-rotation of femoral and tibial components leads to patellar mal-tracking in total knee arthroplasty (TKA), resulting in anterior knee pain and unstable feeling. However, the effect of patellar cutting in the axial plane on clinical outcomes has not been investigated. The purpose of the current study was to analyze the angle of patellar cutting on patellar tracking and clinical outcomes including knee function.

Materials And Methods

Consecutive 271 knees (40 men and 231 women) with a mean age of 74.8 (standard deviation [SD] = 8.1) years were included in the current study. The mean height and weight were 152.0 (SD =7.7) cm and 61.1 (SD =13.2) kg, respectively. The patella was routinely resurfaced regardless of the status of the patellofemoral joint, and a single posterior-stabilized implant was used. In the merchant view, the patellar cutting angle, patellar tilt, and patellar shift were measured. The patellar cutting angle was defined as the angle between the anterior patellar bony surface and the resection plane. Patellar tilt was defined as the angle between the anterior patellar bony surface and the femoral condyle. Patellar shift was defined as the distance between the center of the patellar component and the femoral groove. Medial thickness of the patella, lateral tilt of patella, and lateral shift were denoted as positive. Clinical outcomes were evaluated using the Knee Society Score (KSS) and the new KSS (2011 KSS) at two years after TKA. To analyze the effect of patellar tracking, correlation between the patellar cutting angle and patellar tilt, patellar shift was calculated. Then correlation between patellar cutting angle and the sub-scales of clinical outcomes was calculated.

Results

The patellar cutting angle was positively correlated with the patellar tilt (r = 0.422, p < 0.001) and patellar shift (r = 0.195, p = 0.001). There were no correlations with the patellar cutting angle and KSS knee score (r = -0.088, p = 0.208) and function score (r = -0.133, p = 0.056). The patellar cutting angle had the tendency with the poor functional score. There were no correlations with the patellar cutting angle and 2011 KSS symptoms (r = -0.070, p = 0.312) and patient satisfactions (r = -0.092, p = 0.179). The patellar cutting angle was negatively correlated with 2011 KSS expectations (r = 0.161, p = 0.018) and functional activities (r = 0.160, p = 0.020).

Conclusion

Thickness at the medial side is correlated with lateral patellar tilt, lateral patellar shift, poor expectations and poor functional activities. In the patellar resurfacing, thickening of the medial patella should be avoided, whereas thickness at the lateral side can be tolerated.