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This has become a very fashionable ligament. Mention an ACL injury at a cocktail party, and you receive grave nods of approval. Everybody recognizes this as an athlete’s injury, and this puts you in the category of the elite skiers, football players and basketball players. You might even have one of those large, glitzy knee braces which come in any number of designer patterns and colors. If you’re a teenager, you’ll demand one.

The Historical Perspective

The pendulum often swings one way and then the other before a happy medium is reached. Until 20 years ago, the medical profession did not take ACL injuries very seriously. There were four reasons for this: 1) MRIs did not exist, nor did arthroscopies, so a number of tears were altogether missed. 2) People with a torn ACL either felt perfectly well, or at most had a “trick knee” - a knee that “goes in and out” when the leg is twisted in a certain way. In short, most people could (and still can) live with a torn ACL, and indeed have done so since the beginning of time. 3) There didn’t seem to be any long-term problems associated with this injury. 4) There were no good operations available.

We now know that a torn ACL predisposes the knee to further meniscal (cartilage) tears and can lead to arthritis. Moreover, the ACL can currently be reconstructed without resorting to lengthy incisions about the knee. This has led to a remarkable flurry of ACL surgery, some of which is unnecessary. See below.

Where is the ACL and What Does It Do?

As noted at the beginning of this chapter, the knee is inherently unstable: it is totally dependent on ligaments and other soft tissues to stay in place.

Contrary to the MCL which runs close to the skin, the ACL lies deep inside the knee. It courses obliquely from the outer part of the thighbone at the back of the knee down to the table-like portion of the upper shinbone tibial plateau (Figure 3). The ACL prevents the knee from hyperextending (bending backwards) and from becoming unhinged during certain twisting motions.

The ACL keeps the knee from shifting during twisting motions. Its absence is more noticeable in some people than in others

The ACL can be likened to a cable made of many strands. These strands are visible to the naked eye and can be seen to subtly twist around each other. There is some elasticity to these fibers and therefore some give when the knee is pushed too far. Some people are loose-jointed, and, by definition, their ligaments tend to have more stretch. Such people are less likely to tear their ACL, but conversely, in the event of such an injury, the other ligaments are less able to pick up the slack.

Can you Prevent an ACL Injury?

By training for a particular activity you can decrease the odds of suffering an ACL injury, but you cannot eliminate the risk. High level athletes tear this ligament with alarming frequency. No brace protects a knee from this injury, and, if it existed, it would probably be too cumbersome and expensive to be prescribed on a routine basis.

Partially Torn Ligament

On occasion, the ligament is partially torn: it appears slightly stretched or just some of the fibers appear torn. This leads to a treatment dilemma: leave it or reconstruct it? The surgeon has to determine whether his reconstructed ligament will be better than your imperfect ACL. I tend to err on leaving the patient’s own ligament unless the patient’s symptoms can only be explained by the partial tear.