Current concepts in isolated and combined injuries of the medial collateral ligament complex-Part I: Anatomy, biomechanics, clinical and radiological examination of the medial collateral ligament of the knee.

Injuries involving the medial collateral ligament (MCL), or combined injuries to both the anterior cruciate ligament (ACL) and MCL, are common and present considerable diagnostic and therapeutic challenges. Better understanding of MCL anatomy and biomechanics, especially in combined ACL-MCL injuries, has driven the need for updated clinical examination and treatment approaches. The MCL complex comprises the superficial MCL (sMCL), deep MCL (dMCL), and the posteromedial complex (PMC), which includes the posterior oblique ligament (POL). Additional contributors to medial knee stability include the AMR and dynamic structures such as the semimembranosus, semitendinosus, and gracilis tendons. Biomechanically, the sMCL serves as the primary restraint against valgus loading and resists anterior tibial translation, particularly at higher degrees of knee flexion with external tibial rotation. The dMCL functions as a key stabiliser against external tibial rotation at low flexion angles and plays a significant role in anteromedial rotatory instability (AMRI), while the PMC/POL primarily limits internal tibial rotation. Accurate diagnosis requires an integrated approach, including thorough patient history, detailed physical examination, magnetic resonance imaging (MRI), and selective use of stress tests. Clinical assessment remains essential, as overreliance on imaging alone may misrepresent injury severity. Evaluation of medial-sided structures should be performed bilaterally and for each structure separately, based on their distinct biomechanical roles. The POL should be evaluated in full patient-specific knee extension. Assessment for AMRI should involve testing both valgus laxity at 20° of knee flexion, anteromedial drawer at 20° and anterior tibial translation at 90° with the tibia in neutral and then externally rotated. Findings of increased anterior tibial translation accompanied by excessive external tibial rotation relative to the contralateral side strongly indicate AMRI. This current concept article reviews the current literature and provides evidence-based recommendations to develop guidance and optimize treatment strategies for isolated MCL injuries and combined MCL-ACL injuries LEVEL OF EVIDENCE: Level V.