There are two main types of grafts: tissue taken from the patient’s own body (autograft) and donated tissue from organ donors (allograft).
The best type of graft used to reconstruct the ACL depends on a variety of patient factors. There is not one ideal graft that is perfect for every patient. Graft selection should be individualized for each patient based on the advantages and disadvantages of the graft type, as well as the patient’s age, lifestyle, activity level and any other associated injuries.
Patellar Tendon Autograft
The bone-patellar tendon-bone autograft, or BPTB, is widely used for ACL reconstruction. The graft is made up of the middle third of the patellar tendon with bone from the top surface of the patella (kneecap) on one end, and bone from the tibia (shinbone) on the other end. BPTB autografts have been used for a long time and have an established track record. The advantages of this type of graft include its ability to reliably restore knee stability, fast incorporation rate and low rate of re-tearing. Potential disadvantages include temporary or permanent pain at the front of the knee, slight loss of motion, a larger incision and more pain immediately after surgery. BPTB is typically recommended for high-level or elite athletes and individuals who have had failed previous ACL reconstructions. Its use should be avoided in patients who have patellar tendonitis, patellofemoral syndrome and individuals who frequently kneel (such as gardeners, floor installers and plumbers) or engage in long-distance or repetitive running, such as marathoners.
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Hamstring Tendon Autograft
Two of the five hamstring tendons (the semitendinosus and the gracilis) are commonly used to reconstruct the ACL. There is no bone harvested with the hamstring tendons, and therefore, the pain immediately after surgery is less compared to BPTB autografts. Other advantages to using hamstring autografts include restoring knee stability, a smaller incision and decreased likelihood of long-term knee pain. The disadvantages are that the reconstructed ligament is not as strong as the BPTB graft, there is a slower rate of graft incorporation and healing and a slight loss in hamstring strength when the knee is at its end range of flexion (bending). Hamstring autograft is typically used in younger individuals who are active and in those who do a lot of kneeling. This graft should be avoided in patients who have very flexible joints throughout their body or have an associated MCL sprain.
Quadriceps Tendon Autograft
This graft uses bone from the kneecap and some of the quadriceps (thigh) tendon and has bone on one end and soft tissue on the other end. This graft is not as widely used, but has a very reliable track record. The advantages include less long-term knee pain compared to BPTB, reliable strength and bony healing at one end. The initial pain may be more than with a hamstring autograft, but it's typically less than what is experienced by a BPTB autograft patient.
In addition to BPTB, hamstring and quadriceps allografts, other tendon grafts are also used, such as the Achilles, tibialis anterior and tibialis posterior. An advantages of allografts is the elimination of donor site pain. However, there are theoretical risks of disease transmission from the donated tissue. Nationally, this risk is about 1:1.5 million for HIV transmission and about 1:470,000 for hepatitis transmission. Donated allografts DO NOT result in a significant immune response and patients do not have to take medication to fight rejection. Allografts tend to have residual laxity (looseness) and therefore have a higher re-rupture rate than BPTB, hamstring and quadriceps tendon autografts. Allografts should be avoided in high-activity individuals and are best suited for older, less active patients.
In general, for young, competitive and highly active individuals, BPTB is recommended. For young patients who are not involved in competitive sports or older patients who are highly active, hamstring autograft is suggested. For older patients who participate in low-impact activities, hamstring autograft or allograft is typically recommended.
Technical Details of ACL Reconstruction
First, three very small (1 cm) incisions are made at the front of the knee. Through these small incisions, the arthroscopic camera and specially designed instruments can enter the knee. The knee joint is continuously irrigated with sterile saline, which “inflates” the joint with clear fluid.
The surgeon will maneuver the camera around the entire joint to evaluate all of the important structures in the joint (for example, ligaments, meniscus, cartilage and bone) and determine if there are any other injuries that may need to be addressed during the surgery. Most often, the surgeon will take photographs and video to help explain to the patient what was found and how it was corrected.
The damaged ACL will then be removed from the knee with small arthroscopic instruments. Sockets or tunnels for the new ACL will be drilled into the tibia (shinbone) and femur (thigh bone). The new ACL graft will then be secured into the two bone tunnels so that it crosses the joint where the injured ligament used to be.