Background: 

Fatty accumulation in the rotator cuff is associated with shoulder dysfunction and a risk of failure of rotator cuff repair. The aims of this study were to (1) describe cellular findings in rotator cuff muscles in patients presenting with varying degrees of rotator cuff tendon pathology by examining fat content and myofiber cross-sectional area of rotator cuff muscles and (2) correlate histologic features to magnetic resonance imaging (MRI) grades derived with the Goutallier classification.

Methods: 

Rotator cuff muscle biopsies were performed in a consecutive series of patients undergoing arthroscopic shoulder surgery. Rotator cuffs were graded according to the Goutallier classification and labeled as either partial-thickness or full-thickness. Patients without a rotator cuff tear undergoing arthroscopic surgery served as controls. The biopsy specimens were examined using LipidTOX to visualize lipid accumulation. Laminin was used to quantify myofiber cross-sectional area.

Results: 

Twenty-seven patients with a rotator cuff tear and 12 without a tear (controls) were included. There were 24 males (62%). The mean age was 55 years. Patients in the control cohort were younger (mean, 46 years) than those in the treatment group (mean, 60 years, p < 0.01). Within the treatment group, 12 and 15 patients were recorded as having partial and full-thickness rotator cuff tears, respectively. Lipid accumulation visualized at the cellular level was fairly-to-moderately correlated with the Goutallier classification on MRI (R_s = 0.705, 95% confidence interval [CI] = 0.513, 0.829). Muscle biopsy specimens with a Goutallier grade of 2+ had significantly more lipid accumulation than those with grade-0 (p < 0.01) or grade-1 (p < 0.01) fatty accumulation. Muscle biopsies at the sites of full-thickness tears showed significantly greater lipid accumulation than those associated with either partial (p < 0.01) or no (p < 0.01) tears. Partial-thickness rotator cuff tears had no difference in lipid accumulation in comparison to the control group. Muscle biopsy specimens from full-thickness tears had significantly smaller myofiber cross-sectional area when compared with partial-thickness tears (p = 0.02) and controls (p < 0.01).

Conclusions: 

Cellular lipid accumulation correlates with the MRI Goutallier grade of fatty accumulation, thus verifying the Goutallier classification at the cellular level. Muscle biopsy specimens from partial-thickness tears are more similar to controls than to those from full-thickness tears, whereas full-thickness tears of all sizes showed significantly greater lipid content and smaller myofiber cross-sectional area compared with partial-thickness tears and controls.

Clinical Relevance: 

Our research confirms the utility of using the Goutallier classification to predict rotator cuff muscle quality and shows that tendon attachment, even if partially torn, protects the muscle from fatty accumulation.

中文翻译：

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基于撕裂特征的人类肩袖肌肉的组织学差异

 背景：

肩袖中的脂肪堆积与肩部功能障碍和肩袖修复失败的风险有关。本研究的目的是（1）通过检查肩袖肌肉的脂肪含量和肌纤维横截面积来描述具有不同程度肩袖肌腱病理学的患者的肩袖肌肉的细胞发现，以及（2）将组织学特征与根据 Goutallier 分类得出的磁共振成像 (MRI) 等级。

 方法：

对一系列接受关节镜肩部手术的患者进行了肩袖肌肉活检。肩袖根据 Goutallier 分类进行分级，并标记为部分厚度或全厚度。接受关节镜手术、没有肩袖撕裂的患者作为对照。使用 LipidTOX 检查活检标本以可视化脂质积累。层粘连蛋白用于量化肌纤维横截面积。

 结果：

其中包括 27 名肩袖撕裂患者和 12 名无撕裂患者（对照组）。其中男性 24 人（62%）。平均年龄为 55 岁。对照组患者比治疗组患者（平均 60 岁，p < 0.01）更年轻（平均 46 岁）。在治疗组中，分别有 12 名和 15 名患者出现部分和全层肩袖撕裂。在细胞水平上可视化的脂质积累与 MRI 上的 Goutallier 分类相当至中度相关（R _s = 0.705，95% 置信区间 [CI] = 0.513，0.829）。 Goutallier 等级为 2+ 的肌肉活检标本比 0 级 (p < 0.01) 或 1 级 (p < 0.01) 脂肪积累的肌肉活检标本具有显着更多的脂质积累。全层撕裂部位的肌肉活检显示，与部分撕裂（p < 0.01）或无撕裂（p < 0.01）相关的脂质积累明显更多。与对照组相比，部分厚度的肩袖撕裂在脂质积累方面没有差异。与部分厚度撕裂 (p = 0.02) 和对照 (p < 0.01) 相比，全层撕裂的肌肉活检标本的肌纤维横截面积明显更小。

 结论：

细胞脂质积累与脂肪积累的 MRI Goutallier 分级相关，从而在细胞水平上验证了 Goutallier 分类。与全层撕裂相比，部分层撕裂的肌肉活检标本与对照组更相似，而与部分层撕裂和对照相比，所有大小的全层撕裂均显示出明显更高的脂质含量和更小的肌纤维横截面积。

 临床相关性：

我们的研究证实了使用 Goutallier 分类来预测肩袖肌肉质量的实用性，并表明肌腱附着即使部分撕裂，也能保护肌肉免受脂肪堆积。