Multimodal evaluation of periosteal versus collagen membrane coverage in atelocollagen-associated autologous chondrocyte implantation for large knee cartilage defects.

PURPOSE: Atelocollagen-associated autologous chondrocyte implantation (A-ACI) with periosteal coverage shows favourable outcomes for large knee cartilage defects but is associated with complications such as graft hypertrophy. Collagen membrane coverage remains under-investigated in this technique. This study aimed to evaluate periosteal versus collagen membrane coverage using clinical, radiological, arthroscopic and histological assessments. METHODS: Between 2014 and 2022, patients with ≥4.0 cm2 full-thickness chondral lesions underwent A-ACI using periosteal (n = 13) or collagen membrane (n = 13) coverage in a non-randomized sequential comparative study. Clinical and radiological outcomes were assessed at 12 and 24 months using the Lysholm score, Knee injury and Osteoarthritis Outcome Score and Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) 2.0 score. Second-look arthroscopy included International Cartilage Repair Society (ICRS) and Oswestry Arthroscopy Score (OAS) assessments, with histological analysis using the ICRS II scoring system. Minimum follow-up was 24 months. RESULTS: Both groups demonstrated significant clinical improvement at 24 months without significant between-group differences. MOCART 2.0 scores were significantly higher in the collagen membrane group at 12 and 24 months (83 vs. 60 at 24 months, p = 0.001). OAS scores were significantly higher in the collagen membrane group (8.5 vs. 6.7, p = 0.034), while ICRS scores were comparable. Histological parameters, including tissue morphology, basal integration and subchondral bone quality, were significantly higher in the collagen membrane group. Complication profiles differed: graft hypertrophy and delamination in the periosteal group (46%) versus subchondral bone cysts in the collagen membrane group (15%). Collagen membrane coverage remained associated with higher MOCART 2.0 scores after limited adjustment for concomitant osteotomy. CONCLUSIONS: The primary clinical outcomes improved similarly in both groups at two years without meaningful between-group superiority. While collagen membrane coverage was associated with higher MOCART 2.0 scores after adjustment for concomitant osteotomy, all structural evaluations should be regarded strictly as secondary and exploratory. LEVEL OF EVIDENCE: Level III.