Anterior cruciate ligament reconstruction

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Knees following ACL reconstruction surgery. A patellar tendon graft was used. Discoloration of the left leg is from swelling that drained from the knee to the shin.

Anterior cruciate ligament reconstruction (ACL reconstruction) is surgical repair of a torn anterior cruciate ligament in the knee. Because the ACL does not heal on its own, an ACL reconstruction requires a tissue graft. The torn ligament is removed from the knee before the graft is inserted. The types of surgery differ mainly in the type of graft that is used. In all cases, the surgery is done arthroscopically.

Types of grafts

Patellar tendon

The patellar tendon connects the patella (kneecap) to the tibia (shin). Generally the graft is taken from the injured knee, but in some circumstances (such as a second operation) the other knee may be used. The middle third of the tendon is used, with bone fragments on each end removed. The graft is then threaded through holes drilled in the tibia and femur, and finally screwed into place.

This tendon is large and very strong, and so makes an excellent graft in most patients. A brace often is not even necessary following surgery, so the muscles around the knee have less risk of atrophying from disuse. This option is often used by athletes who wish to return to full performance as fast as possible.

The disadvantage is that the removal of the patellar tendon is more painful than the other options. Strong painkillers may be prescribed for several weeks following the surgery. The patellar tendon also takes about one year to fully recover; until then, there is an increased risk of tendonitis.

Hamstring tendon

For this procedure, two tendons from the hamstring (generally from the injured knee) are the source of the graft. A long piece (about 25 cm) is removed from each of two tendons. Each piece is threaded through the tibia, around a screw in the femur, and then back to the tibia. Finally, the ends of the loops of tendon are screwed into place in the tibia.

Unlike the patellar tendon, the hamstring tendons are not as strong. Therefore, following surgery, a brace is often used to immobilize the knee for one to two weeks while the most critical healing takes place. The removal of hamstring tendons, however, is not as painful as the patellar tendon graft. Evidence suggests that the hamstring tendon graft does just as well, or nearly as well, as the patellar tendon graft in the long-term.

Because this procedure is less painful than the patellar tendon graft, this is often used when a faster recovery is unnecessary. Because the knee must be immobilized for the first week, there is often significant muscle loss, and a long course of physical therapy is necessary to regain strength.


An ACL, patellar tendon, or achilles tendon may be harvested from a cadaver and used as the graft. The achilles tendon is so large it needs to be shaved to fit within the cavity inside the knee. This method has the benefit that the most painful part of the surgery, the harvesting of tendon tissue, is avoided. However, there is a slight chance of rejection which would lead to another surgery to remove the graft and replace it again. Even with the extensive and redundant screening process for donar grafts, there still runs the risk of infection which would be grounds to remove the graft. Therefore, this option runs the largest health risk.


All surgeries have a similar long-term recovery time frame. After surgery, most flexibility of the knee joint is lost. Initial therapy consists of stretching to regain the flexibility and prevent scar tissue from forming, and simple exercises to reduce loss of muscle. Often a continuous passive motion machine is used immediately after surgery to help with flexibility; and the prefered method of preventing muscle loss is isometric exercises that put no strain on the knee.

About three weeks are required for the bone to attach to the graft. After this, the patient can typically walk on their own and perform simple physical tasks without risk. At this stage the first round of physically therapy can begin. This usually consists of careful exercises to regain flexibility, and small amounts of strength back.

One of the more important benchmarks in recovery is the 12 weeks period. After this the patient can typically begin a more aggressive regimine of excersises involving stress on the knee, and increasing resistance. Jogging is often incorperated at or around this time. It should be noted that the patient should be careful though, injuries occur in this time more than any other and the ligament is considered to be at its most vulnerable during this period.

After four months, more intense activities such as running are possible without risk. After six months, the reconstructed ACL is generally at full strength (ligament tissue has fully regrown), and the patient may return to activities involving cutting and twisting. Recovery varies highly from case to case, and sometimes resumption of stressful activities may take a year or longer.

The reconstructed ACL has a high success rate. Studies show that cases in which the ACL retears are generally caused by a traumatic impact. Statistically, it does not appear to matter if the patient uses a brace after recovery. A sufficiently traumatic impact to retear the ACL is unlikely to be mitigated by the use of a brace.


  • Dawn Hastreiter, ACL Reconstruction, University of Washington, UWMC Roosevelt Clinic, Musculoskeletal Radiology.

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