Introduction: Fatty degeneration is the most important factor affecting massive rotator cuff tear (RCT) function. However, the mechanism underlying fatty degeneration and treatment after massive rotator cuff injury remains to be elucidated. This study sought to systematically scoping review published animal studies to explore effective treatment options for fatty degeneration following human rotator cuff injury, focusing on fibro-adipogenic progenitor (FAP). Materials and methods: MEDLINE, PubMed, and Embase were systematically searched for articles published in June 2022, using relevant keywords. Animal species, injury and repair types, study duration, and fatty degeneration parameters were summarized. Results: Of the 120 studies, 51 were secondarily evaluated for cell treatment of fatty degeneration in rotator cuff injury. Finally, 6 studies examining the effects of FAP on fatty degeneration were selected for analysis. Six studies showed positive effects on the SS muscle following fibro/adipogenic progenitor (FAP) (n = 3) or pluripotent stem cell (n = 3) injections. Conclusion: Following the review, we concluded the following: 1) FAP cell injections effectively inhibit fatty degeneration after rotator cuff injury. Level of evidence: Level IV, review article.

Introduction: Muscle weakness rotator cuff tear (RCT) after is the most important factor for physical function. However, the mechanism underlying muscle atrophy and treatment after rotator cuff injury remains to be elucidated. This study sought to systematically review published animal studies to explore effective treatment options for muscle weakness following human rotator cuff injury, focusing on fibro-adipogenic progenitors (FAPs). Materials and methods: MEDLINE, PubMed, and Embase were systematically searched for articles published in June 2022, using relevant keywords. Animal species, injury and repair types, study duration, and fatty degeneration parameters were summarized. Results: Of the 120 studies, 51 were secondarily evaluated for cell treatment of muscle weakness in rotator cuff injury. Finally, six studies examining the effects of FAPs on atrophy were selected for analysis. Six studies showed positive effects on the supraspinatus muscle following FAP (n = 3) or pluripotent stem cell (n = 3) injections. Conclusion: Following the review, we concluded that FAP might be effectively inhibit fatty degeneration after rotator cuff injury. However, mechanical stress also should required for prevention of muscle weakness in various article. Overall, there are few FAP injection reports for RCTs, and basic research should proceed in this direction.