February 19, 2013

Collateral Damage

Pop Goes the Knee Joint

by Corey Dawkins and Stephani Bee

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Some players can’t escape the injury prone label, and Mat Gamel might earn it soon. On Monday, we learned that Gamel suffered a mid-portion tear of the ACL graft in his surgically repaired right knee. Despite his knee receiving a green light twice within the last month, Gamel suffered the ACL tear during the first full-squad workout on Saturday.

ACL surgery, while one of the more prevalent surgeries in sports medicine, is both never routine and not guaranteed to be 100 percent successful. Among top sports medicine surgeons, the failure rate ranges up to three percent, while 10 percent is a commonly cited figure for most others. Even though failure is unlikely, the primary cause for ACL graft failure is a technical error by the surgeon that causes additional stress across the graft. The surgeon can make several errors including, but not limited to: improper drill hole angles in the femur or tibia, too much or too little tension in the graft after securing it, and a failure to recognize a concomitant injury such as a partial PCL tear. These mistakes can lead to the ACL getting too much force or getting force too quickly.

Given that his surgeon, Dr. William Raasch, is a world-renowned surgeon, the likelihood of a technical error is minimal. Graft failure can also result from a person rushing through rehabilitation. Returning before knee strength is approximately the same as the other side diminishes the effectiveness of dynamic stability. Even though there are static stabilizers such as ligaments and two menisci, dynamic stability is an important factor as well. The hamstring muscles are the most important dynamic stabilizer for the ACL, as they directly resist anterior translation of the tibia when contracting. The traditional recovery time to cutting and pivoting sports is about six months, and Gamel had over eight months before re-injuring his ACL, so improper rehabilitation length is unlikely to be the culprit.

Even if the procedure was performed correctly and the rehab was carried out appropriately, ACL grafts can fail due to physiologic reasons. Every surgeon has his/her own technique and preference for performing each surgery, and different surgeons use different hardware components for securing the ACL graft. Every patient runs the risk of rejecting the hardware used in the surgery. This occurs when the graft loosens and the knee becomes unstable again. This can lead to both ACL re-injury and a higher risk for structural damage in the knee. The physiology inside the knee also affects how well the graft acts like the original ACL in terms of tensile strength.

Infections pose a risk, too. Most infections are superficial in the skin and are easily treated with antibiotics; the ACL graft itself is fine. However, the joint itself can become infected. Contaminated hardware and/or graft preparation tables can lead to septic joints, or infections inside the joint. The condition tends to worsen rapidly, and the patient has to return the operating room to have the joint drained and cleaned out, and then get started on strong antibiotics. Failure to do so can increase the risk of structural damage. This was not what caused Gamel to re-tear his ACL.

The last major reason for the ACL graft to fail is that there was simply too much force applied to it. The rehab was done correctly, but if the athlete returns to his/her sport, they will likely have the similar—or greater—forces applied that caused the original injury. Nothing can prevent it; it just happens because of the traumatic forces across the knee joint. Braces can provide some protection, but they don’t guarantee safety.

The most likely cause for Gamel’s injury was a combination of physiologic and mechanical problems, and a small strength deficit could have played a role. Gamel’s physiology likely caused the graft to heal slightly lax but also with a weakened tensile strength. Then, when Gamel started ramping up his activities this spring, the ACL graft sustained too much force and was torn.

Gamel is now facing another surgery this week and will likely miss the entire season. The process is similar, but a different graft type is usually used. If the athlete wishes to remain active in a cutting or pivoting sport, they will likely use autologous tissue; non-autologous grafts have a much higher failure rate in the athletic population, sometimes approaching 20 percent. The surgeon will check all structures of the knee again while the patient is under anesthesia to ensure that there are no concomitant injuries. The rehab will be similar.

Returning from a revision ACL is not as difficult as returning from a revision Tommy John surgery, but it isn’t as easy as the first one. We will have to wait to see whether 2014 will be the year Gamel can shake the infamous “injury prone” label.

Corey Dawkins is an author of Baseball Prospectus. Follow @CoreyDawkinsBP
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Stephani Bee is an author of Baseball Prospectus. 
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