Purpose: Osteochondral allograft reconstruction of articular cartilage defects is increasing popular. Currently, freshly harvested osteochondral tissue is screened and refrigerated pending final cultures, with a shelf life of approximately six weeks. Deep frozen allografts have been used less frequently due to diminished cell viability associated with freezing. The purpose of this study was to prospectively analyze the clinical outcome and radiographic findings of patients who underwent refrigerated or frozen allograft transplantation within the knee. Histological and electron microscopic grading of the allograft at the time of implantation was analyzed.

Method: Between 1998 and 2002, twenty-five patients with symptomatic osteochondral lesions of the knee who were treated with a refrigerated or frozen allograft were evaluated. The mean age at the time of surgery was forty-eight years. The mean lesion size was 4.5 cm2. Validated outcome instruments (Knee Society Score (KSS), Western Ontario and McMaster University Score (WOMAC) were used. Clinical and. radiographic evaluation were evaluated pre-operatively and at the most recent follow-up.

Results: The mean duration of clinical follow-up was forty-six months (range twenty-four to sixty months). The mean WOMAC score improved from a baseline of 46 to 66 at the time of final follow-up (p = 0.003). The mean KSS score improved from a baseline of 104 to 132 at the time of final follow-up (p = 0.01). No significant correlation was noted between graft type and histological or electron microscopy scoring. Post-operative mechanical alignment was noted to be statistically correlated with an improvement in WOMAC score (p= 0.004). Six patients (24%), all refrigerated allografts, were failures and underwent knee arthroplasty.

Conclusion: Seventy-six percent of implanted frozen and refrigerated osteochondral allografts are still in place approximately four years after surgery. Currently, frozen allografts appear to be surviving as well as refrigerated grafts. Further follow-up is needed, while the use of magnetic resonance imaging may be beneficial to evaluate graft incorporation and articular cartilage integrity.