Pietroski Alexander, Zhou Yang, Kasto Johnny, Obinero Chimdindu, Zhu Kai, Mazeh Mahdi, Chen Chaoyang, Muh Stephanie
Department of Orthopaedic Surgery, Henry Ford Health System, Detroit, USA.
Department of Biomedical Engineering, Wayne State University, Detroit, USA.
Cureus. 2025 Mar 7;17(3):e80229. doi: 10.7759/cureus.80229. eCollection 2025 Mar.
Reverse total shoulder arthroplasty (RSA) increases deltoid muscle fiber recruitment and tension to compensate for deficient rotator cuff activity; however, it is unclear whether the anterior or middle deltoid becomes dominant and how the muscle activation profile changes postoperatively. Using minimally invasive electromyography, this study evaluated the activity of the deltoid and surrounding muscles during shoulder motion to assess muscle activation changes post-RSA.
In this observational study, we assessed change in preoperative to postoperative shoulder muscle activation in 10 patients over six months. Muscle activation was measured using eight surface electrodes. Activation of the anterior, middle, and posterior deltoid, along with surrounding muscles, was recorded and quantified during shoulder abduction, flexion, and external and internal rotation. One-way analysis of variance was used to identify significant differences in activation and time or speed. The least significant difference post hoc test was used to determine specific differences in muscle activation at subsequent time points.
RSA shoulders at six months postoperatively showed a significant increase in activity of the middle deltoid predominantly. Middle deltoid activation increased during abduction (p<0.001), flexion (p=0.008), external (p<0.001), and internal (p<0.001) rotation.
Our study highlights the middle deltoid as the primary contributor to rotator cuff function in reverse shoulder arthroplasty (RSA), characterized by quantitative activation, significant involvement in all shoulder motions, and increased activation over time. These findings could inform future RSA designs to enhance deltoid wrapping, maximizing strength and efficiency.
反式全肩关节置换术（RSA）可增加三角肌肌纤维募集和张力，以代偿肩袖活动不足；然而，目前尚不清楚是三角肌前部还是中部占主导地位，以及术后肌肉激活模式如何变化。本研究采用微创肌电图评估了肩关节运动期间三角肌及周围肌肉的活动，以评估RSA术后肌肉激活的变化。
在这项观察性研究中，我们评估了10例患者在6个月内术前至术后肩部肌肉激活的变化。使用8个表面电极测量肌肉激活情况。在肩关节外展、前屈、外旋和内旋过程中，记录并量化三角肌前、中、后部以及周围肌肉的激活情况。采用单因素方差分析来确定激活、时间或速度方面的显著差异。使用最小显著差事后检验来确定后续时间点肌肉激活的具体差异。
术后6个月的RSA肩关节主要表现为三角肌中部活动显著增加。三角肌中部在肩关节外展（p<0.001）、前屈（p=0.008）、外旋（p<0.001）和内旋（p<0.001）时激活增加。
我们的研究强调了三角肌中部是反式肩关节置换术（RSA）中肩袖功能的主要贡献者，其特征为定量激活、参与所有肩部运动且随着时间推移激活增加。这些发现可为未来RSA设计提供参考，以增强三角肌包裹，最大化力量和效率。
