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Ever watched in amazement as an athlete fell to the ground in pain when no one even touched him after a jump? It doesn't take a doctorate degree to know this is often the result of an ACL tear.
The ACL is a knee ligament with a significant role in stabilizing the knee. We have it for a reason. Dubbed "the crucial ligament" back in the 1800s, it's better known now as the anterior cruciate ligament due to its configuration within the knee. Its main job is to prevent the lower leg bone from rotating too much or sliding forward on the upper leg bone. It gets assistance from muscles, but it mainly serves the extremely important role of maintaining stability when an athlete cuts, decelerates, jumps and lands.
Hearing a "pop"
After being injured from a jump, athletes often report that they "heard a pop." Although this is not a true symptom, it's a telltale sign that knee damage has occurred. So what specifically are ACL tear symptoms—besides excruciating pain?
Following the injury, a physical therapist, athletic trainer or a doctor will perform specific tests to see if the ligament is still intact. The test results will determine whether an athlete can return to play or must be evaluated further.
Swelling and internal bleeding
A damaged knee will swell and bleed internally. Swelling is not like water; it's more like glue. It bogs down the joint and makes it feel stiff and inflamed, adding to an already painful feeling. Because of the presence of blood, fluid, and other waste products within the joint, surgery is postponed for a time to let this condition resolve itself. This will improve the surgery's outcome.
There's always weakness with a knee injury, making it difficult to walk or fully straighten and bend the knee.
Loss of proprioception
This is the body's ability to balance and sense its position in space. Joint position sense allows you to close your eyes and still determine if your knee is straight or bent. This becomes important in the days leading up to surgery—and afterwards, when you walk without crutches. Proprioception allows for self-correction by the muscles when challenged by walking on uneven surfaces, or if you slip. This is especially important to someone whose knee is at risk for further injury.
These symptoms usually present within 24 hours after the initial injury. What's interesting, and important, is that symptoms of an ACL tear do get better within a few weeks to a month. Swelling and effusion resolve. The knee looks normal. Pain disappears. With training, strength returns as do balance and proprioception. This is actually important. Returning to the fullest possible function prior to surgery will enhance recovery.
However there is still a problem: the knee is not stable. Of all ACL tear symptoms, instability is the most important. It is a subtle effect, persisting even when other symptoms are gone; and in many cases, it is resolved only with surgery.
It is possible to limit instability without an ACL. Although an athlete may return to playing "symptom free" in about nine months, it may take as many as 18 to 24 months before he or she is back playing at pre-injury levels.
(See Returning to Sport after Knee Injury.)
For more information on the ACL please see the STACK ACL Guide.