*For a description of ligaments of the knee, see the blog titled “The Knee Explained”. The anterior cruciate ligament (ACL) is one of 4 main ligaments of the knee. It runs diagonally in the knee joint and prevents the tibia from sliding forward and also provides rotational stability of the knee.
CAUSES: Most ACL injuries are sports-related, non-contact injuries. Only roughly 25% of sports ACL tears are due to direct contact to the knee. Mechanism of injury usually involves deceleration with cutting, pivoting, or awkwardly landing. Female athletes are more likely to sustain these injuries, possibly due to decreased strength in the surrounding musculature.
SIGNS/SYMPTOMS: The knee usually gives out immediately after a tear. Swelling, pain, and decreased range of motion are present. Often, the person hears a pop when the ACL is completely torn. A feeling of instability occurs leaving the patient often unable to bear any weight.
DIAGNOSIS: Physical examination and MRI are the most conclusive diagnostic procedures.
TREATMENT: Rest, ice (about 15 minutes at a time), compression, and elevation (RICE), physical therapy, adjustment of the knee to align the joint for proper healing, bracing for support, and surgery in some cases to reconstruct the ligament. For athletes who are trying to get back to a competitive activity, surgery has been shown to be the best way. The key whether you get surgery or not is to properly rehab the knee.
COMPLICATIONS: Other injuries often occur with an ACL tear such as meniscus tears, MCL tears, or even fractures of the tibia or femur. With chronic instability due to an ACL tear, upwards of 90% of patients may exhibit meniscus damage years after the initial injury.
PROGNOSIS: Once a ligament is torn, it heals with scar tissue which is inflexible and weaker than the original tissue. Little or no rehab will almost certainly lead to future problems. Prognosis depends on the severity of the tear. Full tears rarely, if ever, heal on their own. Partial tears will heal with scar tissue. Surrounding muscular strength is necessary to protect the injured ligament.