Natural History

The natural history of an ACL injury without surgical intervention varies from patient to patient and depends on the patient’s activity level, degree of injury and instability symptoms. The prognosis for a partially torn ACL is often favorable, with the recovery and rehabilitation period usually spanning 2 to 3 months. However, some patients with partial ACL tears may still have instability symptoms. Close clinical follow-up and a complete course of physical therapy helps identify those patients with unstable knees due to partial ACL tears. Complete ACL ruptures have a much less favorable outcome. After a complete ACL tear, some patients are unable to participate in cutting or pivoting-type sports, while others have instability during even normal activities such as walking. There are some rare individuals who can participate in sports without any symptoms of instability. This variability is related to the severity of the original knee injury as well as the physical demands of the patient. About half of ACL injuries occur in combination with damage to the meniscus, articular cartilage or other ligaments. Secondary damage may occur in patients who have repeated episodes of instability due to ACL injury. With chronic instability, up to 90 percent of patients will have meniscus damage when reassessed 10 or more years after the initial injury. Similarly, the prevalence of articular cartilage lesions increases up to 70 percent in patients who have a 10-year-old ACL deficiency.