ACL injuries: from tear to repair

By 22nd December 2007 June 28th, 2014 News

I have an interest in knees and while staffing Niseko Physio in the 2006/7 season, decided to begin an extended research program into the biomechanics of snowboarding and the strength of the knee ligaments. As part of this study, I decided to further test the ability of the anterior cruciate ligament (ACL) and the medial co-lateral ligament (MCL) to withstand a blunt force blow – delivered by a tree – to the lateral aspect of the shin while travelling over 30km/h. As I suspected in my hypothesis; the ACL and MCL were unable to withstand this force. The research has continued through the surgical reconstruction phase and now into the end stage rehabilitation. This has been an invaluable research experience for all concerned.

Although some readers may have been diagnosed with a partially torn ACL, experienced knee surgeons know that tearing an ACL is virtually like being pregnant: you’ve either done it completely, or not at all. When the ligament is torn, the knee joint is unstable, and people often complain of a ‘wobbly knee’. If the ACL has been torn, you need to decide whether to have an operation or not. Most active people opt for an operation to replace the ligament. This procedure is commonly known as a knee reconstruction. It involves harvesting a tendon or ligament from another source and inserting it into the bones to replace the torn ACL. There are three main sources for the new ligament: patella tendon (the tendon under the knee cap); hamstring tendon (the rope-like tendon behind the knee); and a patella or Achilles’ tendon allograft (using a cadaver). The pros and cons of each technique are numerous and orthopaedic surgeons are renowned for heated debates on which is the best source of the graft.

Many experts consider the patella tendon to be the strongest graft because it is less elastic and the graft includes bone plugs on either end from the knee cap and the shin bone. Some ongoing anterior knee pain is not an uncommon side effect. Smaller people may not have the substance in the patella tendon to supply the graft without compromising the knee.

The hamstring tendon is more flexible and hence may take more time to change its structure to be the same as the original ACL. The loss of substance in the hamstring requires rehabilitation akin to that of a hamstring tear, but the tendon has enough volume to withstand the loss of the graft well.

The allograft is used extensively in the US however it is still not approved in many countries. The obvious advantage is that there is no additional injury to the body. As the ligament is often harvested and frozen before use, the freezing and time out of the body may result in it not being as healthy as a ligament that has been harvested immediately before the procedure. Let’s hope we never see live ACL donors become a growth market in the transplant tourism business – there are enough people in developing countries getting around with one kidney and half a liver, without having the poor blighters hobbling about with half of their patella tendons missing. The allograft donor is usually reserved for athletes with a special event looming (such as Alisa Camplin before the Winter Olympics) or busy individuals who wish to have minimal time off work and minimum pain.

When it comes to ACL ruptures, women are indeed the weaker sex. Research shows women are between two and seven times more likely to suffer an ACL tear as men. The width of the female pelvis results in a sharper angle at the knee (known as the ‘Q’ angle). The larger the Q angle, the greater the stress placed on the knee. The muscles that support the knee may not be as strong in women, which can leave the knee somewhat unsupported and at risk of injury.
Recent research has shown that fluctuations in hormonal concentrations may be the most important predisposing factor. High estrogen levels can cause   

ligaments and other supporting structures to be more lax and unstable. Interestingly, one study indicated that taking the contraceptive pill decreased the incidence of knee injuries among female athletes – thereby preventing ruptured ACL pain and labour pains – a wonder drug indeed!

Although choosing a surgeon and hospital you are comfortable with is very important, the key to the success of the procedure is how much effort is put into the extended rehabilitation that can take up to 12 months after the operation. Many people begin their rehabilitation with great diligence and gusto, but experience ‘rehab burn out’ three months post-op, give up on the rehabilitation process and never regain full knee function.

Prevention of ACL injuries is difficult. Stretching and generic knee braces do not work. Some motocross riders and extreme skiers find a special brace helps with prevention but it is quite bulky and expensive ($US1500). Strengthening the hip and knee stabilizing muscles will help. Make sure your ski bindings release quickly and of course, try not to hit a tree.

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