Persistent Lateral Knee Pain From a 10% Thickness Anterior Cruciate Ligament (ACL) Tear in a 36-Year-Old Runner.

Anterior cruciate ligament (ACL) tears are due to jumping, rapid decelerating, or quick changes in direction, but recent research indicates that accumulated tissue fatigue from repetitive submaximal knee loading can also cause ACL disruption. Partial degenerative ACL tears due to overuse are currently thought to be asymptomatic until the ligament is at least 50% torn. In this case, a 36-year-old female runner presenting with sharp lateral joint line knee pain, which precluded running or hiking over one mile, was found to have an atraumatic 10% thickness ACL tear. After ACL debridement, the patient was able to return to full activity. Females may be more prone to degenerative partial ACL tears due to biomechanical and hormonal factors. Partial ACL tears should be considered in the differential diagnosis of knee pain even without a history of trauma.