Autologous Chondrocyte Implantation: Natural History of Postimplantation Periosteal Hypertrophy and Effects of Repair-Site Debridement on Outcome

Purpose: Our purposes were to report the clinical outcome of autologous chondrocyte implantation (ACI) patients with graft hypertrophy compared with that of unoperated ACI patients and to longitudinally assess the effects of graft hypertrophy debridement. Methods: We divided 170 knee ACI patients with a minimum of 2 years' follow-up into groups according to the need for reoperation after ACI and the findings at surgery. Group A (n = 73) comprised patients who did not undergo reoperation, group B (n = 61) comprised patients who underwent reoperation and had findings unrelated to the repair, and group C (n = 36) comprised patients who underwent reoperation and had isolated graft hypertrophy. The International Knee Documentation Committee, modified Cincinnati knee rating, and Short Form 36 physical component scores for the 3 groups were compared. Of the repairs debrided because of graft hypertrophy, 41 were longitudinally assessed with arthroscopy or magnetic resonance imaging. Results: The mean follow-up was 42.2 months. Patch-related problems were seen in 73.7% of cases undergoing reoperation less than 2 years after implantation, whereas cartilage-related problems were the dominant finding more than 2 years after implantation (70.2%). Group A patients fared significantly better than group B or C patients with regard to all 3 parameters measured, with no difference between groups B and C. Longitudinal assessment of 41 hypertrophied repairs revealed 18 with signs of pathology after graft debridement. Conclusions: This study shows that reoperation is frequent after ACI and is associated with a less satisfying outcome. Furthermore, debridement of a hypertrophied ACI graft appears to be detrimental as shown by longitudinal assessment of repairs. Level of Evidence: Level IV, therapeutic case series.