Bone Marrow Edema in the Knee and Its Influence on Clinical Outcome After Matrix-Based Autologous Chondrocyte Implantation

Background: Third-generation autologous chondrocyte implantation (ACI) is an established method for treatment of full-thickness cartilage defects in the knee joint. Subchondral bone marrow edema (BME) is frequently observed after ACI, with unknown pathogenesis and clinical relevance. Purpose: To investigate the occurrence and clinical relevance of BME after third-generation ACI in the knee joint during the postoperative course of 36 months. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 38 circumscribed full-thickness cartilage defects in 30 patients were included in this study. All defects were treated with third-generation ACI (Novocart 3D). A standardized MRI examination was carried out after 1.5, 3, 6, 12, 24, and 36 months. Bone marrow edema was observed in 78.9% of defects over the postoperative course, with initial occurrence in the first 12 months. The size of the BMEs were determined according to their maximum diameter and were classified as small (4 cm). Clinical outcomes in patients were analyzed by use of the International Knee Documentation Committee (IKDC) scoring system and a visual analog scale for pain. Results: There were 5.3% (n = 2) small, 28.9% (n = 11) medium, 34.2% (n = 13) large, and 10.5% (n = 4) very large BMEs. In a subgroup analysis, cartilage defects of the medial femoral condyle showed significantly higher frequency of BME than did patellar defects. Clinical scores showed significant improvements throughout the entire study course (P .05). Conclusion: Midterm clinical results of the matrix-based third-generation ACI showed a substantial amount of BME over a 36-month follow-up, but this did not correlate with worse clinical outcome. Patients with femoral cartilage defects were more often affected than were those with patellar cartilage defects