PT Classroom - A Brief Review of Grafts Utilized for Anterior Cruciate Ligament Reconstruction ׀ by Anthony Laurenzi SAT & Chai Rasavong, MPT, MBA

Introduction
The anterior cruciate ligament (ACL) connects the front part of the shin bone (tibia) to the back part of the thigh bone (femur) and assists with stability at the knee by restraining excessive forward movement of the shin bone (tibia) in relation to the thigh bone (femur). About 200,000 ACLs are injured in the United States each year, resulting in approximately 100,000 ACL reconstructions (1). Most orthopedic surgeons advocate ACL reconstruction for patients with an ACL tear associated with knee instability. There are several choices that could be made when deciding what type of graft to be used for reconstruction of the ACL. Each graft has its benefits, including no harvest-site morbidity, rapid biological incorporation, secure fixation, and consistent restoration to the patient’s pre-injury levels (2). No graft has clearly been shown to provide a faster return to athletic participation. The purpose of this article is to provide a review of the various grafts that may be utilized in the reconstruction of the ACL.

Cadaver Graft
The cadaver graft (allograft) requires less surgical time and doesn’t require harvesting of the patient’s patellar tendon and bone. In addition, placement of the cadaver graft is done arthroscopically using a 2 cm incision with minimal disturbance to the knee joint and quadriceps extensor tendon mechanism. The cadaver graft is safe as it is tested extensively for viral disease like hepatitis and AIDS. The allograft takes more time for bone-to-bone healing (>6 mos) (3).

Hamstring Graft
The hamstring graft is increasing in popularity. The hamstring graft is taken from the same leg but may be harvested from the non-injured extremity. Advantages of hamstring grafts include less donor site complications, small incision, and high load to failure rates when compared to the native ACL. Disadvantages include slower tendon-to-bone healing in the tunnel (8-12 weeks) and weakness in the hamstrings following surgery (3, 4).

Patellar Tendon Graft
Considered the “gold standard”, the bone-patellar tendon-bone graft is taken from the patient's own injured knee (autograft). The autograft is considered very safe and is the most common graft used for all reconstruction. Advantages of this graft are its strength as compared to the patient’s native ACL (168%) and the healing time of the graft is much faster with a patella tendon bone block than with a free ligament (6 weeks) (3). Disadvantages of using the patellar tendon graft may include donor site morbidity, anterior knee pain, patellar fractures, patella tendonitis, scar formation, quadriceps dysfunction, and numbness caused by the division of the infrapatellar branch of the saphenous nerve (5).

Gortex Graft
The fourth type of graft is a synthetic ligament which may be made of Gortex, or some other synthetic material. Some believe that synthetic grafts offer the advantage of early return to sports activity. However, synthetic ligaments have been known to fail and are rarely utilized now. These ligaments also have a limited blood supply and have shown extreme intra-articular knee joint wear and a high incidence of severe synovitis (6).

Tibialis Anterior and Posterior Graft
The tibialis anterior and posterior grafts are not as commonly used as the patellar tendon graft or the hamstring graft. When comparing the tibialis graft, the tensile strength and stiffness are similar to or greater than the hamstring graft (7). Another advantage of using this type of graft is low surgical morbidity. Although grafts from the tibialis tendons are not as commonly used as the hamstring or patellar tendon grafts, it is an appropriate alternative.
 

Conclusion
In general, when examining the grafts available, it can take at least 6 months for the various grafts to achieve normal strength and stiffness. The grafts will heal into tunnels at various rates, but that doesn’t mean the ligament is strong (8). All are weaker at 2-3 months than when they were put in due to remodeling of the graft (8). Therefore, allowing sufficient time for the healing and maturation of the graft along with adequate rehabilitation will maximize return to previous level of function.