Do you think it makes any difference whether I have a hamstring or patellar tendon graft for an ACL tear? I know that the patellar tendon graft sometimes makes it difficult to kneel after surgery. Are there any problems with the hamstring tendon graft?

The increased risk of an infection after a hamstring autograft for the reconstruction of an anterior cruciate ligament (ACL) is a potential concern. According to a recent study, the risk of infection is 8.24 times higher for someone receiving a hamstring tendon graft compared with a bone-patellar tendon-bone (BPTB) autograft.

These are the results of a very large study from well-known and respected institution: Kaiser Permanente in California. Almost 11,000 patients from the Kaiser Permanente ACLR registry were involved in the study. These patients were treated in 41 different medical centers in six different geographical regions.

By reviewing the patient records, they were able to determine how many patients who had any kind of ACL graft surgery developed an infection afterwards.

The three main types of ACL grafts included: 1) hamstring autograft, 2) bone-patellar tendon-bone (BPTB) autograft, and 3) allograft. An autograft refers to tendon material taken from the patient and used to replace the torn ligament. An allograft is tendon graft material from a donor bank.

Although the overall infection rate was low (0.48 per cent), the fact that there was an obvious and statistically important difference between the autografts is very significant. In more simpler terms: graft choice does make a difference. There was no apparent difference in the infection rates between autografts and allografts. These findings support (agree with) other previous studies but now provide the added information of how often this happens.

Some additional details from the study also included the fact that there was a 2:1 ratio of deep (deep soft tissue or joint) to superficial (skin only) infections. The superficial infections occurred early on (first month after surgery). Deep infections were more likely to develop up to one year after the procedure.

Further analysis of all the data also revealed that in most cases, hamstring tendon grafts were the source of both superficial and deep infections. Staphylococcus bacteria accounted for half of the deep and three-fourths of the superficial infections. More obese patients (higher body mass index) had a greater chance of developing a superficial infection. The reason for this is unknown but may be linked with the need to remove more soft tissue in larger patients.

What is behind this observed increase in superficial and deep infections associated with hamstring tendon grafts used for ACL reconstruction? There may be more than one possible avenue for this occurrence. The authors suggest the following possibilities:

  • The graft tissue is contaminated during the harvest procedure.
  • The graft tissue is contaminated after harvest but while it is being prepared for use.
  • Hamstring tendon grafts take longer to prepare giving more time for possible contamination during graft preparation.
  • Hamstring grafts require the use of a multifilament suture, which could be the source of the bacteria.
  • If the graft or hardware used to fix the graft in place comes in contact with the skin, then contamination is more likely.
  • The tools (e.g., screwdriver) used to insert the screws that hold the graft in place could be an external (environmental) source of contamination.

    The purpose of this study was not to identify risk factors for infection after ACL reconstruction. The authors’ intent was to determine the incidence of such infections and that was accomplished successfully. They suggest future studies to evaluate the many possible risk factors and determine the source and cause of infections. Although the infection rate is fairly low, preventing infections is still an important goal.