Patients with diabetes mellitus (DM) often suffered with many musculoskeletal disorders, such as tendon rupture and tendinopathy. However, the understanding of the pathogenesis of these alternations is limited. This study was designed to investigate the role of tendon-derived stem cells (TDSCs) in histopathological alterations of DM tendons. Forty-two SD rats were randomly and equally divided into a diabetes group (DG) and control group (CG). DM was induced by streptozotocin (65 mg/kg). The patellar tendons were isolated at weeks 1, 2, and 4 for histological analysis. TDSCs were isolated at week 2 for osteo-chondrogenic differentiation analysis. Mann-Whitney U test was used with SPSS. p < 0.050 was statistically significant. Micro-tears of collagen fibers and altered appearance of tendon cells were observed in DG tendons. DG tendons exhibited significantly higher expression of OPN, OCN, SOX9, and Col II and decreased expression of Col I and tenomodulin (TNMD) at week 2. Diabetic TDSCs (dTDSCs) demonstrated significantly decreased proliferation ability and increased osteogenic and chondrogenic differentiation ability. Osteo-chondrogenic markers BMP2, ALP, OPN, OCN, Col II, and SOX9 were also significantly increased while tenogenic markers Col I and TNMD were decreased in dTDSCs. These results suggested the erroneous differentiation of dTDSCs might account for the structural and non-tenogenic alternations in DM tendons, which provided new cues for the pathogenesis of tendon disorders in DM.

Background/Objectives: The optimal surgical timing for rotator cuff tears (RCTs) remains controversial, particularly regarding how tear etiology influences the final functional recovery. This study aimed to compare the clinical outcomes of early versus delayed arthroscopic repair stratified by etiology, providing evidence for etiology-specific surgical timing. Methods: A retrospective cohort study was conducted on 183 patients who underwent arthroscopic rotator cuff repair for isolated full-thickness supraspinatus tears. Patients were stratified into traumatic (n = 74) and degenerative (n = 109) groups based on etiology. They were further divided into early-repair and delayed-repair subgroups based on symptom duration (traumatic cut-off: 3 months; degenerative cut-off: 6 months). Clinical outcomes were assessed preoperatively and at the final follow-up using the Visual Analog Scale (VAS) for pain, American Shoulder and Elbow Surgeons (ASES) score, University of California at Los Angeles (UCLA) score, and range of motion. Complications, including retear rates and stiffness, were recorded. Results: In the traumatic group, early repair yielded significantly better postoperative pain relief (VAS) and higher functional scores (ASES and UCLA) compared to delayed repair. Notably, the delayed traumatic group exhibited a significantly higher retear rate compared to the early group (16.7% vs. 2.6%; p = 0.039). Conversely, in the degenerative group, comparisons between early and delayed repair revealed no significant differences in the final functional scores, pain levels, or complication rates (p > 0.05). Conclusions: Surgical timing significantly impacts outcomes in traumatic RCTs, where early repair is critical to optimize functional recovery and minimize retear risks. In contrast, delayed arthroscopic repair for degenerative tears yielded comparable outcomes to early repair, suggesting that an initial trial of conservative management is safe and does not compromise final surgical outcomes.