Last week I had a procedure called osteochondral transplantation. Basically, the surgeon took a plug of bone and cartilage from one part of my knee and moved it to fill in a big hole along the place where I put the most weight. I guess they ended up using three bone plugs instead of one because of the size of the hole. I was only expecting to lose a little of the normal cartilage and bone for this graft. Will having three plugs make a difference in my recovery?

There has been some concern that the number of grafts or the graft size harvested makes a difference in the final results of osteochondral transplantation. It’s possible that taking larger grafts or a greater number (sometimes as many as three plugs are transplanted) could negatively affect the outcomes.

But a recent study from Germany involving more than 100 patients found that the size and number of grafts harvested had no bearing on functional results of the donor joint (which happened to be the knee).

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 more of a negative predictor of outcome for the graft donor site than how many bone plugs are taken. Surgeons should take this into consideration when planning osteochondral transplantation from the knee. 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.