Background:Muscle edema formation and inflammatory processes are early manifestations of acute rotator cuff lesions in sheep. Histological analysis of affected muscles revealed edema formation, inflammatory changes, and muscle tissue disruption in MRs.Hypothesis:Edema contributes to inflammatory reactions and early muscle fiber degeneration before the onset of fatty infiltration.Study Design:Controlled laboratory study.Methods:Osteotomy of the greater tuberosity, including the insertion of the infraspinatus tendon, was performed on 14 sheep. These experimental animal models were divided into 2 groups: a nontrauma group with surgical muscle release alone (7 sheep) and a trauma group with standardized application of additional trauma to the musculotendinous unit (7 sheep). Excisional biopsy specimens of the infraspinatus muscle were taken at 0, 3, and 4 weeks.Results:Edema formation was histologically demonstrated in both groups and peaked at 3 weeks. At 3 weeks, signs of muscle fiber degeneration were observed. At 4 weeks, ingrowth of loose alveolar and fibrotic tissue between fibers was detected. Fatty tissue was absent. The diameter of muscle fibers increased in both groups, albeit to a lesser degree in the trauma group, and practically normalized at 4 weeks. Immunohistology revealed an increase in macrophage types 1 and 2, as well as inflammatory mediators such as prostaglandin E2 and nuclear factor kappa-light-chain-enhancer of activated B cells.Conclusion:Early muscle edema and concomitant inflammation precede muscle fiber degeneration and fibrosis. Edema formation results from tendon release alone and is only slightly intensified by additional trauma.Clinical Relevance:This study illustrates that early edema formation and inflammation elicit muscle fiber degeneration that precedes fatty infiltration. Should this phenomenon be applicable to human traumatic rotator cuff tears, then surgery should be performed as soon as possible, ideally within the first 21 days after injury.

中文翻译：

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研究冈下肌松解后水肿形成作为绵羊肩袖损伤的实验模型：组织学分析

背景：肌肉水肿形成和炎症过程是绵羊急性肩袖病变的早期表现。对受影响肌肉的组织学分析揭示了 MR 中的水肿形成、炎症变化和肌肉组织破坏。假设：水肿会导致脂肪浸润发生之前的炎症反应和早期肌纤维变性。研究设计：对照实验室研究。方法：截骨术对 14 只羊进行了更大的结节手术，包括插入冈下肌腱。这些实验动物模型被分为两组：仅进行手术肌肉松解的非创伤组（7只羊）和对肌腱单元进行标准化额外创伤的创伤组（7只羊）。在第0、3和4周时取冈下肌切除活检标本。结果：组织学上显示两组均出现水肿形成，并在第3周时达到高峰。3周时，观察到肌纤维退化的迹象。4周时，检测到松散的肺泡和纤维之间的纤维化组织向内生长。没有脂肪组织。两组的肌纤维直径均有所增加，尽管创伤组的程度较小，并且在 4 周时几乎恢复正常。免疫组织学显示巨噬细胞1型和2型以及前列腺素E2和活化B细胞的核因子κ轻链增强子等炎症介质增加。结论：早期肌肉水肿和伴随炎症先于肌纤维变性和纤维化。水肿形成仅由肌腱松解引起，并且仅因额外的创伤而轻微加剧。临床相关性：本研究表明，早期水肿形成和炎症会在脂肪浸润之前引起肌纤维变性。如果这种现象适用于人类创伤性肩袖撕裂，那么应尽快进行手术，最好在受伤后的前 21 天内进行。