The contribution of the medial retinaculum as a restraining factor to the patella dislocation.

The objective of this study was to evaluate the contribution of the medial retinaculum to the stability of the patella, for several angles of knee flexion. For six cadaveric knees, the patella and patella retinaculum were exposed, and the force required to dislocate the patella laterally by 5 mm was measured, in 0, 45 and 90 degrees of knee flexion, preserving and dissecting the medial retinaculum. Wilcoxon singed rank test (SPSS, version 23, Chicago, USA) was used for data analysis. A p value of < 0.05 was considered as statistically significant. The force required to displace the patella laterally is smaller with the medial retinaculum dissected than intact, in 0, 45 and 90 degrees (p = 0.028, p = 0.046, p = 0.027 respectively). The lateral displacement force is greater as the flexion angle increases, with medial retinaculum intact or dissected (p = 0.028). Thus, an intact medial retinaculum provides more stability against lateral displacement forces to the patella, especially in lower flexion angles. Consequently, surgical methods reinforcing the medial retinaculum combined or not with lateral retinaculum release, are of great importance in the plan of the orthopedic surgeons. The engagement of the bones during flexion of the knee contributes significantly to the stability of the patella.