Anterior cruciate ligament (ACL) reconstruction can be done with several different graft choices. These include patellar tendon, hamstring tendon, and donor tissue (allograft). Each of these choices has advantages and disadvantages.
ACL reconstruction is not an ACL repair. A repair implies that you can fix something that is broken. If an ACL is completely torn, it will not heal back together, even if the torn ends are sewn together. This has been tried and the result, unfortunately, were poor. What does work well, is to remove the torn ends of the ACL and replace the ligament with a different structure (a graft). To secure the graft into the position of the normal ACL, tunnels are made in the shin bone (tibia) and thigh bone (femur), and the graft is passed through these tunnels to reconstruct the ligament.
The patellar tendon is the structure on the front of your knee that connects the kneecap (patella) to the shin bone (tibia). The patellar tendon averages between 25 to 30 mm in width. When a patellar tendon graft is taken, the central 1/3 of the patellar tendon is removed (about 9 or 10 mm) along with a block of bone at the sites of attachment on the kneecap and tibia. For many years this graft was thought to be the gold standard as the hamstring graft was explored.
Advantages: Many surgeons prefer the patellar tendon graft because it closely resembles what needs reconstruction. The length of the patellar tendon is about the same as the ACL, and the bone ends of the graft can be placed in to the bone where the ACL attaches. This allows for “bone to bone” healing, something many surgeons consider to be stronger than any other healing method.
Disadvantages: When the patellar tendon graft is taken, a segment of bone is removed from the kneecap, and about 1/3 of the tendon is removed. There is a risk of patellar fracture or patellar tendon rupture following this surgery. Also, the most common problem following this surgery is pain on the front of the knee (“anterior knee pain”). In fact, patients sometimes say they have pain when kneeling, even years after the surgery.
The hamstring muscles are the group of muscles on the back of your thigh. When the hamstring tendons are used in ACL surgery, two of the tendons of these muscles are removed, and “bundled” together to create a new ACL. Over the years, methods of fixing these grafts into place have improved. Results of hamstring grafts are essentially the same as patellar tendon grafts in the orthopedic literature.
Advantages: The most common problem following ACL surgery using the patellar tendon is pain over the front of the knee. Some of this pain is known to be due to the graft and bone that is removed. This is not a problem when using the hamstring tendon. The incision is also smaller, and the pain both in the immediate post-operative period, and down the road, is thought to be less.
Disadvantages: A question with this graft is the fixation of the graft in the bone tunnels. When the patellar tendon is used, the bone ends heal to the bone tunnels (“bone to bone” healing). With the hamstring grafts, a longer period of time is necessary for the graft to become rigid. Therefore, people with hamstring grafts are often protected for a longer period of time while the graft heals into place.
Allograft (Donor Tissue)
Allograft is most commonly used in patients who are undergoing revision ACL surgery (when an ACL reconstruction fails) or have other reasons why taking the graft from the patient is not feasible or a poor idea. Biomechanical studies show that allograft (donor tissue from a cadaver) is not as strong as a patient’s own tissue (autograft). For many patients, however, the strength of the reconstructed ACL using an allograft is extremely good.
Advantages: Performing the surgery using allograft allows for decreased operative time, no need to remove other tissue to use for the graft, smaller incisions, and less post-operative pain. Furthermore, if the graft was to fail, revision surgery could be performed using either the patellar tendon or hamstring grafts. Nothing must be sacrificed from your own knee to use this graft.
Disadvantages: More recently, techniques of allograft preparation have improved dramatically, and these problems have greatly improved. However, the process of graft preparation (freeze-drying), kills the living cells, and decreases the strength of the tissue. There is also the risk of disease transmission. While sterilization and graft preparation minimizes this risk, it does not eliminate it entirely. These grafts are thoroughly tested for infection, but what if the test result is incorrect? One can never be 100% sure! The risk of complication from other factors unrelated to allograft tissue is much higher than the risk of disease transmission, but it is still there.
Many surgeons have a preferred technique for different reasons. The strength of patellar tendon and hamstring grafts is essentially equal. There is no right answer as to which is best, at least not one that has been proven in orthopedic studies. The strength of allograft tissue is less than the other grafts, but the strength of both the patellar tendon and hamstring tendon grafts exceed the strength of a normal ACL. The bottom line is 85% to 95% of patients will have clinically stable knees following ACL reconstructive surgery.
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