Clinical examination of knee instability

Background: The knee joint lacks inherent bony congruency and relies on a complex network of ligamentous and capsular structures for stability. While magnetic resonance imaging serves as a primary diagnostic tool, clinical examination remains essential for identifying multi-ligamentous and rotatory instabilities that may be under-detected by standard imaging protocols.

Objective: This review aims to delineate the anatomical contributions to knee stability and provide a systematic framework for the clinical diagnosis of straight, rotatory, and patellofemoral instabilities through specific physical examination maneuvers.

Key Points: Tibiofemoral instability is categorized into straight and rotatory patterns. Straight instabilities, including varus, valgus, anterior, and posterior laxity, are assessed using stress tests at 0° and 30° of flexion to differentiate between isolated and combined ligamentous injuries. Anterior cruciate ligament deficiency is primarily evaluated via the Lachman and pivot shift tests, while the posterior drawer and sag tests identify posterior cruciate ligament compromise. Rotatory instabilities involve abnormal subluxations of the tibial condyles relative to the femur. Anteromedial, anterolateral, and posterolateral rotatory instabilities require specialized maneuvers, such as the Slocum, jerk, and dial tests, to assess the integrity of the posteromedial and posterolateral corners. Patellofemoral assessment focuses on the Q-angle, patellar tracking (J-sign), and the apprehension test to evaluate medial patellofemoral ligament integrity and trochlear morphology.

Conclusion: A comprehensive understanding of knee anatomy and biomechanics is fundamental for accurate clinical diagnosis. Systematic physical examination is the primary method for identifying complex injury patterns, which is critical for effective surgical planning and preventing ligamentous reconstruction failure.