What is it?
An ACL sprain occurs when there is damage to the anterior cruciate ligament (ACL), a major knee ligament that is located inside the knee. The ACL is the main stabilizing ligament of the knee for sudden stopping, starting, cutting and pivoting movements. The other major ligaments of the knee are the posterior cruciate ligament (PCL), medial collateral ligament (MCL) and the lateral collateral ligament (LCL). An ACL sprain may range from an injury of a few fibers to a complete tear of the ligament. Most ACL injuries are complete or “3rd-degree” sprains. ACL injuries are usually caused by a twisting motion of a flexed knee, with the foot firmly planted in the ground. About three quarters of these are non-contact injuries, meaning the athlete did not run into something or someone to cause the injury. Collisions can cause ACL injuries as well. Another injury mechanism commonly seen in skiers occurs when the patient lands on an outstretched leg and the heel slips forward. Risk factors include:

• Previous ACL injury
• Female sex
• Intensity of play (more common in games than practice)
• Muscle and strength imbalances of the body
• Genetics

Symptoms
• Pop or snap felt in the knee
• Feeling that the knee shifted out and back into place
• Immediate knee swelling after the injury
• Knee pain may be mild or severe
• Recurrent episodes of instability or a feeling that the knee is giving way
• Limited or painful motion of the knee

Sports Medicine Evaluation and Treatment
ACL injuries can usually be accurately detected by history and exam performed by a medical professional experienced in sports injuries. There are a number of maneuvers designed to test the strength of the knee ligaments. Sometimes pain and swelling make the examination difficult, so repeated exams may be necessary. X-rays and magnetic resonance imaging (MRI) scans can assist with the diagnosis. Initial treatment typically involves rest, ice, elevation, compression, bracing and pain management. If the patient is unable to bear weight on the leg, crutches can be provided. Long-term treatment of ACL injuries is variable. Not every ACL injury requires surgery. At a minimum,
rehabilitation guided by a physical therapist is recommended. Surgery is usually successful at preventing instability episodes but does not prevent osteoarthritis. Surgery consists of reconstructing the ACL with either an “autograft” (using the patient’s own tissue, usually his hamstring or patellar tendon), or an “allograft” (using tissues from an organ donor). Patients who benefit most from surgery are those who participate in pivoting and cutting sports and exercise, those with recurrent episodes of instability and giving way, or those with other associated knee injuries. If surgery is appropriate, it will usually not be done immediately. Time is needed for the swelling, motion and strength to improve. Physical therapy after surgery is vital to a successful outcome.

Injury Prevention
A number exercise activities when properly done have been shown to reduce the risk of an ACL injury. These exercises should be performed under the guidance of a trained professional, such as a certified athletic trainer or physical therapist. Although commonly used in some sports, bracing has not been found to prevent ACL injuries.
• Evaluation by a trained professional may detect at-risk individuals
• Plyometric training exercises (explosive movements to improve performance, such as jumping exercises)
• Strengthening exercises (such as squats, lunges and toe raises)
• Balance training
• Appropriate warm-up routines

Return to Play
Return to play depends on the rate of improvement with rehabilitation.
 

AMSSM Member Authors: Robert Dimeff, MD and Kyle Goerl, MD

References
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