The Role of Immunologic Response in Fresh Osteochondral Allografting of the Knee

Background:Osteochondral allografting, a restorative treatment option for articular cartilage lesions in the knee, involves transplantation of fresh osteochondral tissue with no tissue matching. Although retrieval studies have not consistently shown evidence of immunologic response, development of anti–human leukocyte antigen class I cytotoxic antibodies has been observed in allograft recipients.Hypothesis:Postallograft antibody formation is related to graft size and may affect clinical outcome.Study Design:Case-control study; Level of evidence, 3.Methods:This study retrospectively compared 42 antibody-positive postallograft patients with 42 antibody-negative patients. Groups were matched for age, sex, and body mass index but not intra-articular disease severity. Seventeen patients (20%) were lost to follow-up. Of the remaining 67 patients (33 antibody-positive and 34 antibody-negative), average follow-up time was 50.3 months (range, 24-165 months). Mean age was 38.1 years (range, 15-68 years) with 58% being male. Graft area was categorized as small (2), medium (5-10 cm2), or large (>10 cm2). Graft survival and Knee Society function scores were used to measure clinical outcome.Results:Of the 84 patients, 80 had graft area data. Of 27 patients with large graft area, 19 (70%) had positive postoperative antibody screens, compared with 1 of 16 (6%) with small graft area ( P < .001). Graft survival rates in the antibody-positive and antibody-negative groups were 64% and 79%, respectively ( P = .152). Mean postoperative Knee Society function scores in surviving antibody-positive and antibody-negative groups were 88.3 and 84.6 points, respectively ( P = .482).Conclusion:Antibody development after fresh, non-tissue-matched osteochondral allograft transplants in the knee appears related to graft size. No difference was observed in clinical outcome between groups. Graft survival is multifactorial, and the effect that the immunologic response has on clinical outcome merits further investigation.