Safety and Efficacy of Autologous Bone-Marrow-Derived Mesenchymal Stem Cells for Treating Partial Rotator Cuff Tears: Observational Study with 4-Year Follow-Up

<b>Background/Objectives</b>: Rotator cuff tears (RCTs) are a leading cause of shoulder pain and disability. Management typically involves conservative measures, such as physical therapy and anti-inflammatory medications, or surgery for full-thickness or refractory tears. Regenerative medicine therapies, including platelet-rich plasma (PRP), platelet lysate (PL), and mesenchymal stem cells (MSCs), show promise as alternative treatment strategies, although long-term outcomes remain under investigation. <b>Methods</b>: This cohort included 30 patients with partial rotator cuff tears and were treated with culture-expanded MSC injections. There was no control group. Inclusion criteria included an imaging-confirmed diagnosis of partial-thickness rotator cuff tears. Outcomes were assessed at multiple time points up to 6 years. Pain and function were assessed using the Disabilities of the Arm, Shoulder, and Hand (DASH), a Numeric Rating Scale (NRS), and the modified Single Assessment Numeric Evaluation (SANE)<b>. Results</b>: Thirty patients (37 shoulders) were included in the analysis. Significant improvements in the NRS and DASH scores were observed at 3, 6, 12, 18, and 24 months (<i>p</i> < 0.01). Twenty-four months post-treatment, the mean NRS and DASH decreased by 2.25 and 15.93 points, respectively, and SANE improved by 60%. At six years, among seven respondents, the mean SANE improvement was 75.54%. During this study, no significant adverse events were reported. <b>Conclusions</b>: This study provides the longest known follow-up of MSC therapy for partial-thickness RCTs, finding sustained pain and functional improvements. The findings support further research into MSC-based and combination regenerative therapies as a viable alternative treatment option for partial-thickness rotator cuff tears.