Analysis of graft maturation after autologous chondrocyte implantation with T2 mapping

Aims and Objectives: It has been shown in numerous clinical studies that matrix-based autologous chondrocyte implantation (mb-ACI) leads to good clinical results in the medium-term course. But chondrogenic development of ACI grafts and the time of graft maturation are still unclear. The aim of this study was to investigate the graft maturation after mb-ACI with T2 mapping in the postoperative course of four years. Materials and Methods: In a total of 90 patients could be included after matrix-based autologous chondrocyte transplantation of the knee. All cartilage defects were treated with NOVOCART® 3D. The evaluation of the ACI grafts was conducted after 3, 6, 12, 24, 36 and 48 months by MRI. The T2 relaxation time values of the ACI graft and healthy native cartilage areas were determined to assess graft maturation using T2 mapping. MOCART score were used for morphological evaluation of ACI grafts. Results: The T2 relaxation time of ACI grafts showed a significant improvement during the postoperative course at all time points. The T2 relaxation improved from 48.0 ms after 3 months to 34.6 ms after four years. We found a significant influence of the patient’s age and the defect localization on the T2 relaxation time measuring. It could be detected an increasing integration of the ACI grafts into the healthy surrounding cartilage. No significant differences between the T2 relaxation time of ACI grafts and the surrounding healthy cartilage were found after 12 months postoperatively. Conclusion: Graft maturation after ACI in the knee joint needs at least 1 year, with ongoing adjustment of the T2 relaxation time values compared with native surrounding cartilage. Regarding the age and defect localization, significantly worse T2 relaxation times of the ACI grafts could be found with higher age and in cases with treated patellar defects.