[Effect of critical shoulder angle on deltoid muscle strength reduction in patients with rotator cuff tears].

To investigate the synergistic interaction between the deltoid muscle and the rotator cuff muscle group in patients with rotator cuff tears (RCT), as well as the impact of the critical shoulder angle (CSA) on deltoid muscle strength.A retrospective analysis was conducted on clinical data from 42 RCT patients who met the selection criteria and were treated between March 2022 and March 2023. There were 13 males and 29 females, with an age range of 42-77 years (mean, 60.5 years). Preoperative visual analogue scale (VAS) score was 6.0±1.6. CSA measurements were obtained from standard anteroposterior X-ray films before operation, and patients were divided into two groups based on CSA measurements: CSA>35° group (group A) and CSA≤35° group (group B). Handheld dynamometry was used to measure the muscle strength of various muscle group in the shoulder (including the supraspinatus, infraspinatus, subscapularis, and anterior, middle, and posterior bundles of the deltoid). The muscle strength of the unaffected side was compared to the affected side, and muscle imbalance indices were calculated. Muscle imbalance indices between male and female patients, dominant and non-dominant sides, and groups A and B were compared. Pearson correlation analysis was used to examine the relationship between muscle imbalance indices and CSA as well as VAS scores.Muscle strength in all muscle groups on the affected side was significantly lower than on the unaffected side ( P<0.05). The muscle imbalance indices for the supraspinatus, subscapularis, infraspinatus, and anterior, middle, and posterior bundles of the deltoid were 14.8%±24.4%, 5.9%±9.7%, 7.2% (0, 9.1%), 17.2% (5.9%, 26.9%), 8.3%±21.3%, and 10.2% (2.8%, 15.4%), respectively. The muscle imbalance indices of the anterior bundle of the deltoid, supraspinatus, and infraspinatus were significantly lower in male patients compared to female patients ( P<0.05); however, there was no significant difference in muscle imbalance indices among other muscle groups between male and female patients or between the dominant and non-dominant sides ( P>0.05). There was a positive correlation between the muscle imbalance indices of infraspinatus and VAS score ( P<0.05), and a positive correlation between CSA and the muscle imbalance indices of middle bundle of deltoid ( P<0.05). There was no correlation between the muscle imbalance indices of other muscle groups and VAS score or CSA ( P>0.05). Preoperative CSA ranged from 17.6° to 39.4°, with a mean of 31.1°. There were 9 cases in group A and 33 cases in group B. The muscle imbalance indices of the anterior bundle of the deltoid was significantly lower in group A compared to group B ( P<0.05), while there was no significant difference in muscle imbalance indices among other muscle groups between group A and group B ( P>0.05).Patients with RCT have a phenomenon of deltoid muscle strength reduction, which is more pronounced in the population with a larger CSA.探讨肩袖损伤（rotator cuff tear，RCT）患者三角肌与肩袖肌群的协同作用，以及肩关键角（critical shoulder angle，CSA）对肩袖三角肌肌力的影响。.回顾分析2022年3月—2023年3月收治且符合选择标准的42例RCT患者临床资料。男13例，女29例；年龄42～77 岁，平均60.5岁。术前疼痛视觉模拟评分（VAS）为（6.0±1.6）分。于术前标准正位X线片上测量CSA，根据所测CSA大小将患者分为CSA>35° 组（A组）和CSA≤35° 组（B组）。使用手持测力计测量患者肩部各肌群（包括冈上肌、冈下肌、肩胛下肌以及三角肌前、中、后束）肌力，记录并比较健侧与患侧肌力并计算肌力失衡指数，比较男性与女性、优势侧与非优势侧及A、B组间各肌群肌力失衡指数。使用Pearson相关分析各肌群肌力失衡指数与CSA及VAS评分的相关性。.患者患侧各肌群肌力均显著低于健侧（ P<0.05）。冈上肌、肩胛下肌、冈下肌及三角肌前、中、后束肌力失衡指数分别为14.8%±24.4%、 5.9%±9.7%、7.2%（0，9.1%）、17.2%（5.9%，26.9%）、8.3%±21.3%、10.2%（2.8%，15.4%）。男性患者三角肌前束、冈上肌及冈下肌肌力失衡指数显著低于女性患者（ P<0.05）；男女性患者间其他肌群肌力失衡指数以及优势侧与非优势侧间所有肌群肌力失衡指数比较差异均无统计学意义（ P>0.05）。患者冈下肌肌力失衡指数与VAS评分成正相关（ P<0.05），CSA与三角肌中束肌力失衡指数成正相关（ P<0.05）；其余肌群肌力失衡指数与VAS评分和CSA均无相关性（ P>0.05）。术前CSA为17.6°～39.4°，平均31.1°；其中A组9例、B组33例。A组三角肌前束肌力失衡指数显著小于B组（ P<0.05），A、B组间其余肌群肌力失衡指数比较差异无统计学意义（ P>0.05）。.RCT存在三角肌肌力下降现象，在CSA更大人群中更为明显。.