Anterior cruciate ligament (ACL) reconstruction involves surgical removal and replacement of the damaged tissue with a substitute graft made of tendon. The following two types of grafts are commonly used to repair a torn ACL:

Patellar tendon graft

This type of graft is prepared from a strip of the patellar tendon below the kneecap. For a long time, the patellar tendon was the preferred choice because it is easy to get to, holds well in its new location and heals fast. One big drawback to grafting the patellar tendon is pain at the front of the knee after surgery. This can be severe enough to prevent any pressure on the knee, such as kneeling.

Hamstring tendon graft

To overcome the issues from the patellar graft, the semitendinosus hamstring tendons on the inner side of the knee are used to create the hamstring tendon autograft for ACL reconstruction. The hamstring graft is an entirely soft tissue graft with no bone plug on either end, unlike the case with the patellar tendon graft. Thus, the fixation of the graft to the knee is slightly less rigid than the patellar tendon graft with its bone plugs.

In some cases, surgeons use an additional tendon, the gracilis, which is attached below the knee in the same area. This creates a two- or four-strand tendon graft. Hamstring graft proponents claim there are fewer problems associated with harvesting the graft compared to the patellar tendon autograft, including:

  • Less anterior knee pain or kneecap pain after surgery
  • Less postoperative stiffness problems
  • Smaller incision
  • Faster recovery

The graft function may be limited by the strength and type of fixation in the bone tunnels, as the graft does not have bone plugs. There have been conflicting results in research studies as to whether hamstring grafts are slightly more susceptible to graft elongation (stretching), which may lead to increased laxity during objective testing. Recently, some studies have demonstrated decreased hamstring strength in patients after surgery. There are some indications that patients who have intrinsic ligamentous laxity and knee hyperextension of ten degrees or more may have increased risk of postoperative hamstring graft laxity on clinical exam. Therefore, some clinicians recommend the use of patellar tendon autograft in these hypermobile patients.

Additionally, since the medial hamstrings often provide dynamic support against valgus stress and instability, some surgeons believe that chronic or residual medial collateral ligament laxity (grade two or more) at the time of ACL reconstruction may be a contra-indication for use of the patient’s own semitendinosus and gracilis tendons as an ACL graft.

Experts believe that the hamstring graft is an excellent choice as a substitute during ACL reconstructions. There are no major differences in the outcomes of these two grafting (patellar tendon and hamstring tendon) methods in the repair of a torn ACL. Both grafting approaches have similar symptoms after surgery, joint strength and stability, and ability to use the knee. However, with the hamstring tendon graft, there are generally no problems kneeling and no pain in the front of the knee. The rehabilitation and physical therapy just goes more easily in general with a hamstring ACL graft compared to a patellar tendon graft.