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Body Mass Index is a Risk Factor in Cartilage Repair

When joint cartilage is damaged and needs repair, surgeons can take a plug of cartilage and subchondral bone from a healthy joint and transfer it to the defect. A special tool called the Osteochondral Autograft Transfer System (OATS) is used to harvest the bone-cartilage plug. The graft is called autologous because it is taken from the patient. This technique has been used for several different sites such as the shoulder, elbow, and knee. In this report, surgeons from Germany examine the harvest site for plugs taken from the knee to treat the ankle.

There is some concern that taking these osteochondral plugs can have a negative effect on the knee. Even though the donor material is harvested from a non-weightbearing area in a healthy knee, it's not replaced by normal tissue. Previous studies have shown that the donor site fills in with fibrous tissue rather than actual cartilage. That could lead to problems later -- especially at the knee where the grafts in this study were taken from.

There have been a few long-term studies looking at donor site morbidity (problems and complications). But the number of patients included was very small. This is the first large study of over 100 patients who were followed for at least two years and some for as long as four and a half years. The authors thought that perhaps the number of grafts or the graft size harvested made a difference in the final results. It's possible that taking larger grafts or a greater number (some had as many as three plugs transplanted) could negatively affect the outcomes.

What they found was that these factors had no bearing on functional results of the knee (the ankle receiving the osteochondral plug was not evaluated). Instead, a higher body mass index (BMI) indicating obesity was the major negative factor in the outcomes. A secondary factor was patient satisfaction. Two specific tools were used to measure function and patient satisfaction. The first was the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). The second was the Lysholm score. They also looked at age as a possible factor, but age did not have a significant effect on donor site recovery.

The WOMAC is a standardized set of questions that evaluates 17 functional activities. It was designed as a pain scoring system for patients with osteoarthritis. The Lysholm is a well-validated questionnaire used to evaluate knee function after injury (including after surgery). It includes questions about limping, need for support when standing or walking, locking or catching sensations within the knee, and stability (knee gives way). Previous studies of donor site morbidity following autologous osteochondral grafts for similar problems used these two measures as well. This helps researchers study and measure the same variables in the same way thus making research more consistent across the board.

A closer look at the results of this study showed that for every point increase in the body mass index, the Lysholm score dropped a point and the WOMAC scores went up slightly (an indication of worse function). The authors concluded that a higher body mass index is a negative predictor of outcome for the donor graft site. Surgeons should take this into consideration when planning osteochondral transplantation from the knee to some other area. Patients should be chosen carefully for this procedure with special attention to the presence of obesity. Patients who are overweight should be cautioned that this is a risk factor for less than optimal results.


J. Paul, MD, et al. Donor-Site Morbidity After Osteochondral Autologous Transplantation for Lesions of the Talus. In The Journal of Bone and Joint Surgery. July 2009. Vol. 91-A. No. 9. Pp. 1683-1688.

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