Influence of dynamic factors in weight-bearing position on the pathogenesis of medial patellofemoral joint cartilage injuries - a radiological in vivo study

Abstract

Objective This study aimed to prospectively compare the changes in the anterior patellofemoral(PF) alignment in the 30°, 60°, and 90° positions of knee flexion in non-weight-bearing and weight-bearing states to understand the pattern of PF joint motion and the causes of medial PF cartilage injury. Methods 22 young volunteers were recruited to participate in this study. PF axial radiographs of the right knee were taken in the prone and standing positions at 30°, 60°, and 90° of knee flexion, and the patellar tilt angle(PTA), Congruence Angle(CA), medial and lateral PF joint space width, patellofemoral index(PI), and patellar shift(PS) were measured. Statistical methods used were paired t-tests, One-Way ANOVA, and chi-square tests were used to prospectively compare the changes in PF joint alignment parameters between the non-weight-bearing and weight-bearing states in the prone and standing positions. Results There was a significant difference in the anterior alignment of the PF joint between the weight-bearing and non-weight-bearing positions at 30°, 60°, and 90° of knee flexion. The PTA was significantly smaller in the weight-bearing position than in the non-weight-bearing position, and the larger the knee flexion angle, the smaller the PTA. The patella was significantly displaced medially at 30°, 60°, and 90° of knee flexion in the weight-bearing position compared with the non-weight-bearing position. The PI was smaller in the weight-bearing than in the non-weight-bearing position at 60° and 90° of knee flexion, and the difference was statistically significant. In the same knee joint with 30°, 60°, and 90° of knee flexion, the number of knees with PI less than 1 with < 2 positions of knee flexion(30°, 60°, and 90° ) was 15 (68.2%) in the non-weight-bearing position compared with 5 (22.7%) in the weight-bearing position, and the number of knees with PI less than 1 with ≥ 2 positions of knee flexion(30°, 60°, and 90° ) was 7 (31.8%) in the non-weight-bearing position compared with 17 (77.3%) in the weight-bearing position; the difference was statistically significant. Conclusion The alignment pattern of the PF joint during dynamic activity in the weight-bearing position reflects the possibility that the medial PF compartment has hyperpressure and is responsible for the high incidence of medial PF cartilage injuries and the development of osteoarthritis(OA) of the medial PF compartment.