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Anterior Cruciate Ligament (ACL) Reconstruction
The anterior cruciate ligament (ACL) is one of the four major ligaments of the knee. Ligaments are strong, dense structures made of connective tissues that help stabilize a joint. The ACL is in the middle of the knee and is especially important for stabilizing the knee during rotational movements.
ACL tears usually occur in athletes participating in cutting and pivoting sports such as basketball, football, soccer, and skiing. At the time of an ACL injury, the athlete often feels a “pop” or a tearing sensation. This is usually followed by swelling. In some patients, ACL injuries are more subtle and may not be noticed until the knee feels unstable or just “not right” when doing activities or sports. The most common injury associated with ACL tears is a meniscus tear.
It is well recognized that ACL injuries are much more common in females. There are multiple reasons for this including bony anatomy, hormonal differences, muscular balance, and the way girls and women perform certain sports. Of these factors, the ones we can potentially change are muscular balance and the way sporting moves are completed. Females tend to cut and jump with their knees only slightly bent, which can predispose them to ACL injury. The hamstring to quadriceps strength ratio is also different from males. Studies have shown that strengthening exercises and plyometric programs aimed at changing these factors can prevent ACL injuries.
ACL strains and partial tears can sometimes be treated with physical therapy and muscle strengthening. However, most complete tears require surgery in active patients. The surgery is done mostly arthroscopically, with a camera and requires only a few small incisions. The ACL is reconstructed using a tendon graft from the patient or a cadaver.
ACL Reconstruction Grafts
Patellar Tendon Graft
The patellar tendon is a flat, broad tendon with bone attached to both ends. The central third of the tendon can be used along with bone plugs from the patella and tibia for reconstruction of the anterior cruciate ligament.
This graft has a very long track record and has been considered the gold standard for ACL reconstruction. The advantages of this graft include: it is stiff and the bone on both ends allows for rigid fixation and early healing. The downside of patella tendon grafts is there is a higher risk of anterior knee pain and some long-term studies show possible increased risk of arthritis compared to hamstring grafts.
Hamstring Tendon Graft
The hamstring tendons can also be used as a graft for ACL reconstruction. There are four hamstring tendons in the body. Typically two tendons, the gracillis and semitendinosus tendons are used for the ACL graft. These two tendons are doubled over to create a four-stranded graft. Sometimes one tendon can be used and folded over to make a 4 strand graft.
Unlike the patellar tendon graft, the hamstring graft does not involve bone. While the graft itself is very strong there is no bone-to-bone healing. This may allow for more stretching out over time and some studies show a slightly higher risk of graft failure long term. The patient can also have weakness in their hamstrings following tendon harvest. This flexion weakness can be an issue for certain sports, especially in females (who have relatively weaker hamstrings compared to quadriceps). Hamstring grafts have several potential advantages including, smaller incisions, less anterior knee pain, and less likelihood of patellar tendonitis. In long-term studies, patients have less pain in their knees than patients who had patellar tendon grafts, but a higher risk of laxity or graft failure.
Quadricep Tendon Grafts
The Quadricep Tendon has historically been used less frequently than hamstring or patella tendon grafts, but is becoming more popular. The quadriceps is thicker than the patella tendon and has more collagen. It has less propensity to stretch than a hamstring tendon does and also does not cause flexion weakness as a hamstring graft does. Patients initially can have quad weakness, but this resolves over time. There is a lower risk of anterior knee pain than a patella tendon graft. A quadriceps tendon graft does require an additional incision just above the kneecap. The quadriceps graft has not been studied as much as the other grafts, but in short term studies failure rates are similar to patellar tendon grafts and patients have less anterior knee pain than patella tendon grafts do.
Allograft tissue is another option for ACL reconstruction. This avoids taking any additional tissue from a patient and the potential downsides of doing that. There is no tissue matching required for ACL grafts. The downside of allograft tissue is the risk of disease transmission (which is extremely rare), laxity and higher failure rate.