Natural history of the ACL-deficient knee

A 31-year-old recreational athlete sustained a knee injury while participating in a weekend basketball game. The athlete jumped for a rebound and landed awkwardly on a slightly inverted foot. There was no contact at the time of injury. His knee was flexed similar to 15 degrees and collapsed into a varus position. He felt a pop within his knee, and a tense effusion developed within 24 h. Although the mechanisms resulting in anterior cruciate ligament (ACL) rupture differ, it is commonly due to a non-contact event. Before determining the proper treatment of this lesion, the physician should know the natural history of the untreated ACL-deficient knee. To understand this natural history, the relationship between intraarticular lesions of the knee, clinical symptoms, and time elapsed from the initial injury must be studied.