Anatomy and biomechanics of posterolateral angle structures of the knee joint

BACKGROUND: Structural injuries of the posterolateral angle of the knee are rare. However, these conditions are characterized by high-energy etiologic mechanisms and cause rapidly progressive degenerative processes in the knee joint. There is currently no consensus on the need for reconstructing damaged posterolateral angle structures for effective knee stabilization with surgery. Understanding the effects of anatomical elements of the posterolateral angle on posterolateral knee rotational instability is of theoretical and practical importance. AIM: The aim of this study was to evaluate anatomy and morphometry of the popliteal tendon and the fibular collateral ligament, including their zones of attachment to the femur and the role of these structures in the posterolateral rotational and frontal instability of the knee joint. MATERIALS AND METHODS: A single-center comprehensive topographic and anatomical study used 50 unfixed anatomical specimens of the lower extremities (30 females, 20 males). The mean age was 30 to 60 years. Patients died from causes other than musculoskeletal disorders. Precise dissection of the posterolateral angle components (popliteus tendon and peroneal collateral ligament) was performed with detailed examination and documentation of the morphometric characteristics of the femoral attachment sites of the studied structures. The posterolateral angle structures were then sequentially dissected to determine their effect on posterolateral rotational instability and tibial varus deviation (varus stress test) and posterior tibial translation (posterior drawer test). RESULTS: After dissection of the fibular collateral ligament, the maximum varus deviation of the knee joint was 5° ± 3.0°. A more significant external rotation of the tibia of 11.0° ± 1.5° was achieved after popliteal tendon release. The intersection of the posterior cruciate ligament resulted in a maximum posterior tibial displacement relative to the femur by 9 (7.9–10.2) mm. CONCLUSIONS: This study evaluated in detail the anatomy and function of the posterolateral angle structures of the knee joint. The results obtained highlight the leading role of the popliteal tendon in the pathogenesis of posterolateral rotational instability and the fibular collateral ligament in the pathogenesis of the frontal (varus) instability of the knee joint, which is of great importance for the diagnosis and surgical treatment of these types of knee instability.