Background: Kinematic patterns of knees after total knee arthroplasty (TKA) are different from those of healthy knees. We hypothesised that these changes cause a relevant shift in the medial and lateral epicondyles and, consequently, the insertion sites of the collateral ligaments. Any alterations, however, violate the law of Burmester, which states a close relation between the course of the collateral and cruciate ligaments, and the articular surfaces.
Methods: Ten healthy knees of whole body cadavers were investigated. The positions of the medial and lateral epicondyles in relation to the tibia were compared before and after cruciate retaining fixed bearing TKA between 0 and 90° of flexion using a navigational device.
Results: After TKA, the medial and lateral epicondyles significantly shifted laterally (~3-5mm) between 0° and 40° of flexion. Additionally, the lateral epicondyle was located significantly more dorsal (~3-5mm) during 0° and 20° of flexion and significantly shifted proximally (~2.5-3mm) between 0° and 30° of flexion.
Conclusions: By changing the epicondylar positions relative to the articular surfaces, the law of Burmester is violated in the present study setting. This might explain the impairment in motion, instability, or mid-flexion instability and the persistent pain in the knees after TKA.
Keywords: Burmester; TKA; kinematics; knee; mid-flexion instability; total knee arthroplasty.