Long-term Assessment of Subchondral Bone Changes and Intralesional Bony Overgrowth After Third-Generation Autologous Chondrocyte Implantation: A Retrospective Study

Background: There is an increasing interest in subchondral bone changes and intralesional bony overgrowth (ILBO) after cartilage repair. Their clinical and predictive relevance is unclear and debated. Purpose: To evaluate the long-term development of ILBO and bone marrow edema-like signals (BMELSs) after autologous chondrocyte implantation (ACI) treatment of cartilage defects to find any predictive factors for their appearance. Study Design: Case series; Level of evidence, 4. Methods: A total of 130 patients with 160 cartilage defects in the knee joint treated with third-generation ACI were included in this study. Radiological scores as the MOCART (magnetic resonance observation of cartilage repair tissue), the MOCART 2.0 and the 3D-MOCART using magnetic resonance imaging (MRI), and patient-reported outcome measures such as the Knee injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee (IKDC) score, Noyes Sports Activity Rating Scale (NSARS) score, and Tegner Activity Scale (TAS) score were evaluated between 60 and 120 months (mean, 88 months) postoperatively. The radiological evaluation focused on the occurrence and size of subchondral bone changes, BMELSs, and ILBO during short-, medium-, and long-term follow-up. Results: In long-term evaluation of clinical data, the IKDC score increased preoperatively from 36 to 64, the overall KOOS from 43 to 64, the NSARS score from 30 to 67, and the TAS score from 2 to 3.7. The mean MOCART score was 73; the MOCART 2.0, 69; and the 3D-MOCART, 69 and 70. The authors observed ILBO in 77% and BMELSs in 74% of patients after 60 to 120 months. Previous cartilage surgeries and osteochondral defect buildup showed higher rates of these abnormalities. Early lesions of the subchondral lamina did not predict ILBO in long-term follow-up, but BMELSs predicted later appearance with decreasing size. Conclusion: Subchondral changes frequently appeared in long-term MRI evaluation of patients after ACI. BMELSs showed a decreasing diameter over the years, while the size of ILBO increased in the later follow-ups. These findings did not affect the clinical outcome in the study population. However, osteoarthritis is likely to progress. The degenerative effect and influence on longer-term outcomes needs to be clarified in future studies.