A 21-year-old rugby player was tackled on the lateral side of his left lower thigh. During the course of the tackle, the player felt a tearing sensation on the medial part of his knee that was associated with excruciating pain. Immediately after the play, he was unable to get up or walk. On physical examination, there is significant tenderness of the adductor tubercle and joint line. Valgus stress testing (abduction stress test) View image demonstrates some medial instability at 30° of knee flexion, but with a firm endpoint (i.e., resistance is felt). Anterior drawer test View image and Lachman's test View image are negative.
Although rare, it is possible for a patient who had an acute MCL injury to develop chronic valgus (twisting outwards away from the mid-line) instability. Chronic MCL injury is usually defined as symptoms that persist for 3 months or longer after injury.  By this point, injured ligament tissue is beyond its capacity to heal, and anatomical restoration is usually no longer possible due to scar tissue formation and contractures of ligament ends. When combined with anterior cruciate ligament deficiency, chronic MCL injury has been shown to seriously compromise joint stability, and these patients frequently experience symptoms of their knees giving way.