Background Recurrence of massive rotator cuff tears (RCTs) are relatively common due to resultant muscle atrophy and fatty infiltration, possibly caused by scapular nerve (SN) injury. Growing evidence suggests that adipose-derived stem cells (ADSCs) are useful tools for regeneration in chronic RCT models. However, data on the effects of ADSCs on in chronic RCT models with SNI are limited. This study aimed to investigate the effect of ADSCs on tendon-bone healing in a chronic rotator cuff tear (RCT) model with scapular nerve (SN) injury. Methods Overall, 36 adult rats (weight = 344 ± 33 g) were equally divided into the ADSC (+) and ADSC (-) group. Both groups underwent right shoulder surgery in which the supraspinatus was detached, and SN injury was induced; he untreated left shoulder in the ADSC (-) group was used as a control. In the ADSC (+) group, abdominal fat was collected to culture ADSCs. At 6 weeks postoperatively, the ADSC (+) group underwent surgical tendon repair with ADSC injection, whereas the ADSC (-) group underwent tendon repair with saline injection. Shoulders were harvested at 10, 14, and 18 weeks and underwent histological, fluorescent, and biomechanical analyses. Results In bone-tendon junction, a firm enthesis, including dense mature fibrocartilage and well-aligned cells, was observed in the ADSC (+) group. Conversely, decreased cell density and immature fibrocartilage were observed in the ADSC (-) group. Fatty infiltration was more uncommon in the ADSC (+) group compared to that in the ADSC (-) group. The mean maximum stress and linear stiffness was higher in the ADSC (+) group than in the ADSC (-) group at 18 weeks. Neither the mean Young’s modulus nor the cross-sectional area were significantly different throughout the study. Conclusion ADSC injection produced better histological and biomechanical outcomes. Thus, ADSC supplementation showed a positive effect on tendon-bone healing in a chronic RCT model with SN injury; therefore, ADSC injection possibly accelerates recovery in large RCT repair.

Background: Massive rotator cuff tears (RCTs) are complicated by muscle atrophy, fibrosis, and intramuscular fatty degeneration, which are associated with postoperative tendon-to-bone healing failure and poor clinical outcomes. We evaluated muscle and enthesis changes in large tears with or without suprascapular nerve (SN) injury in a rat model. Methods: Sixty-two adult Sprague-Dawley rats were divided into SN injury (+) and SN injury (–) groups (n=31 each), comprising tendon (supraspinatus [SSP]/infraspinatus [ISP]) and nerve resection and tendon resection only cases, respectively. Muscle weight measurement, histological evaluation, and biomechanical testing were performed 4, 8, and 12 weeks postoperatively. Ultrastructural analysis with block face imaging was performed 8 weeks postoperatively. Results: SSP/ISP muscles in the SN injury (+) group appeared atrophic, with increased fatty tissue and decreased muscle weight, compared to those in the control and SN injury (–) groups. Immunoreactivity was only positive in the SN injury (+) group. Myofibril arrangement irregularity and mitochondrial swelling severity, along with number of fatty cells, were higher in the SN injury (+) group than in the SN injury (–) group. The bone-tendon junction enthesis was firm in the SN injury (–) group; this was atrophic and thinner in the SN injury (+) group, with decreased cell density and immature fibrocartilage. Mechanically, the tendon–bone insertion was significantly weaker in the SN injury (+) group than in the control and SN injury (+) groups. Conclusions: In clinical settings, SN injury may cause severe fatty changes and inhibition of postoperative tendon healing in large RCTs. Level of evidence: Basic research, controlled laboratory study

Background: Recurrence of massive rotator cuff tears (RCTs) are relatively common due to resultant muscle atrophy and fatty infiltration, possibly caused by scapular nerve (SN) injury. Growing evidence suggests that adipose-derived stem cells (ADSCs) are useful tools for regeneration in chronic RCT models. However, data on the effects of ADSCs on in chronic RCT models with SNI are limited. This study aimed to investigate the effect of ADSCs on tendon-bone healing in a chronic rotator cuff tear (RCT) model with scapular nerve (SN) injury. Methods: Overall, 36 adult rats (weight=344±33 g) were equally divided into the ADSC (+) and ADSC (-) group. Both groups underwent right shoulder surgery in which the supraspinatus was detached, and SN injury was induced; he untreated left shoulder in the ADSC (-) group was used as a control. In the ADSC (+) group, abdominal fat was collected to culture ADSCs. At 6 weeks postoperatively, the ADSC (+) group underwent surgical tendon repair with ADSC injection, whereas the ADSC (-) group underwent tendon repair with saline injection. Shoulders were harvested at 10, 14, and 18 weeks and underwent histological, fluorescent, and biomechanical analyses. Results:In bone-tendon junction, a firm enthesis, including dense mature fibrocartilage and well-aligned cells, was observed in the ADSC (+) group. Conversely, decreased cell density and immature fibrocartilage were observed in the ADSC (-) group. Fatty infiltration was more uncommon in the ADSC (+) group compared to that in the ADSC (-) group. The mean maximum stress and linear stiffness was higher in the ADSC (+) group than in the ADSC (-) group at 18 weeks. Neither the mean Young’s modulus nor the cross-sectional area were significantly different throughout the study. Conclusion: ADSC injection produced better histological and biomechanical outcomes. Thus, ADSC supplementation showed a positive effect on tendon-bone healing in a chronic RCT model with SN injury; therefore, ADSC injection possibly accelerates recovery in large RCT repair.