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What's a partial tear of the anterior cruciate ligament? Either I tore it or I didn't, right?

With soft tissue injuries such as the anterior cruciate ligament (ACL), there are degrees of damage. Some experts categorize strains and sprains differently. Others claim these are on a continuum from mild to severe. The American Medical Association (AMA) has defined ligament damage as first degree, second degree, or third degree sprains. First degree is a mild sprain with a minor tear of the ligament fibers. Patients present to the physician with pain and/or tenderness but usually without swelling or much (if any) loss of motion. A second-degree sprain is a partial tear of the ligament resulting in a moderate sprain. There is pain, moderate loss of function and disability, and slight-to-moderate abnormal knee motion. There is a risk of reinjury. Third-degree sprains are severe and involve a complete rupture of the ligament. Tenderness, pain, swelling, hemorrhage, instability, and loss of motion are typical with a full-thickness tear of the ligament. Some physicians prefer to estimate how much of the ligament is torn in terms of a percentage (e.g., 25 per cent, 50 per cent, 75 per cent). Anything 75 per cent or less is considered a partial tear. Others refer to partial ligament tears as low-grade (less than 50 per cent) or high-grade (50 per cent or more). And finally, there are articles published on this topic showing orthopedic surgeons' preferences for a battery of clinical findings necessary before a diagnosis of partial ACL tear can be made. There are clinical tests such as the Lachman test or the pivot-shift test that help guide the diagnosis. Several other diagnostic tests are available when the surgeon suspects a partial ACL tear. The first is the KT-1000 arthrometer test. This test provides a measure of joint laxity or looseness. Some people have naturally loose ligaments, so the injured knee is always compared to the uninjured side. More than three millimeters of difference from side-to-side is a red flag sign of pathologic injury. This test can fool the clinician. It simply isn't always a sensitive enough test. Results of the test can appear normal when there is a partial ACL tear. Some suggest relying on MRIs for the diagnosis. But even with today's more advanced MRI systems, up to half (or more) of the partial ruptures will be missed using MRIs. A more reliable (but still not always 100 per cent accurate) method of identifying partial ACL tears is the arthroscopic exam. Even with a scope inside the joint, if the outer covering of the ligament is intact, the surgeon won't see the torn fibers inside the sheath. And sometimes scar tissue mimics a normal appearing ligament support structure. Surgeons are advised to perform the pivot-shift test under anesthesia when the ligament appears to be torn. In this way, the effects of muscle spasm and guarding are eliminated and the results are more accurate. Studies show that the pivot-shift test is only 24 per cent sensitive when the patient is awake compared to 92 per cent sensitive when under anesthesia. Results of the pivot-shift test while in the operating room can be misleading if there is other soft tissue damage inside the joint. The surgeon must take the opportunity to double-check for problems such as cartilage, bone, or meniscal fragments in the joint. Seeing is believing, and that's the benefit of an arthroscopic exam. The surgeon can get a direct look at the ligament and determine whether or not it is torn and by how much (either in degrees or percentages). Ask your surgeon to tell you what criteria he or she used to make your diagnosis. That's the only way to know for sure how severe the injury is.


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