Eight-year clinical and radiographic outcomes after meniscal repair augmented with autologous synovial mesenchymal stem cell transplantation: A long-term follow-up case series.

Abstract

Biological augmentation using synovial mesenchymal stem cells (MSCs) has been proposed to enhance healing after meniscal repair, particularly the repair of degenerative flap and radial tears with poor intrinsic healing potential. This study evaluated the 8-year outcomes after meniscal repair augmented with autologous synovial MSC transplantation, focusing on clinical results, radiographic changes, and adverse events. Nine patients had previously been enrolled in an investigator-initiated clinical trial of autologous synovial MSC transplantation for medial meniscal tears. Of these, six completed the 8-year follow-up and were included. Clinical outcomes were assessed using the Lysholm knee score at screening, 1 year, and 8 years. Radiographic evaluation used standing anteroposterior knee radiographs and a modified Kellgren-Lawrence (KL) grading system. Adverse events and reoperations were assessed through annual follow-ups. All six patients maintained the Lysholm score improvement observed at 1 year throughout the 8-year follow-up. Five of the six patients achieved the maximum Lysholm score of 100, and the remaining patient scored 99. The Lysholm score was significantly higher at 1 and 8 years than at screening (both P=0.031, Wilcoxon signed-rank test). Radiographically, four patients showed no KL grade change, while two demonstrated progression characterized by osteophyte enlargement or onset. No apparent progression of medial joint space narrowing was observed in this cohort. No patient experienced a serious adverse event, reoperation, infection, thromboembolic event, hospitalization, or abnormal radiographic finding, such as ectopic ossification or tumor formation. Meniscal repair augmented with autologous synovial MSC transplantation was associated with sustained clinical improvement over 8 years in this small cohort, with no apparent progression of medial joint space narrowing on plain radiographs or treatment-related serious adverse events. These findings suggest that synovial MSC transplantation is a feasible, safe, and potentially durable biological adjunct to meniscal repair.