Hoshikawa Kyosuke, Yuri Takuma, Giambini Hugo, Mura Nariyuki, Kiyoshige Yoshiro
Graduate School of Health Sciences, Yamagata Prefectural University of Health Sciences, Yamagata, Japan.
Department of Biomedical Engineering and Chemical Engineering, The University of Texas at San Antonio, San Antonio, TX, USA.
JSES Int. 2022 Jun 27;6(5):849-854. doi: 10.1016/j.jseint.2022.05.011. eCollection 2022 Sep.
Knowledge of the morphological and functional differences in the anatomic subregions of the supraspinatus (SSP) and infraspinatus (ISP) muscles during forward flexion will provide useful information in the management of shoulder joint disorders. The purpose of this study was to investigate whether the SSP and ISP muscle subregions exhibit independent roles during forward flexion of the shoulder joint.
Eight healthy male volunteers without any restriction in their shoulder joints were recruited for this study. Participants were instructed to sit on a chair with their back against the backrest. Shear modulus (kPa) was measured as a surrogate for muscle stiffness using shear wave elastography on the SSP and ISP muscle subregions. Active measurements of the nondominant arm were obtained during isometric contraction at a neutral position and every 15° intervals from 30° to 150° during forward flexion. Friedman test and Dunn's post hoc test were used to evaluate differences in measurement outcomes among angles during forward flexion in each muscle subregion.
Active stiffness outcomes of the anterior-middle subregion of the SSP muscle during forward flexion increased from 30° up to 45°, reaching a value of 182.4 ± 32.1 kPa ( < .001). Stiffness of the anterior-superficial subregion of the SSP muscle was highest at 30° (125.0 ± 20.6 kPa; < .019) and linearly decreased up to 105° with increasing shoulder angle position. Stiffness of the superior, middle, and inferior subregions of ISP muscle presented a mountain-shaped trend, with peaks of 99.9 ± 23.5 kPa at 90° ( < .013), 144.2 ± 11.2 kPa at 90° ( < .013), and 122.9 ± 27.9 kPa at 105° ( < .007), respectively. Finally, the stiffness outcomes of the pectoralis major and anterior region of the deltoid muscles showed a mountain-shaped trend with peaks of 89.4 ± 23.5 kPa at 60° ( < .007) and 176.7 ± 22.9 kPa at 90° ( < .026), respectively.
The SSP and ISP muscle subregions play a significant role during active forward flexion motion. While closely overlapped, the activity of the muscle subregions changed during the forward flexion motion range, starting with an active anterior-superficial subregion of the SSP muscle at the initial range of motion and an active inferior subregion of the ISP muscle toward midrange of motion. The SSP and ISP subregions did not demonstrate independent functional behavior during forward flexion.
了解冈上肌（SSP）和冈下肌（ISP）在向前屈曲时各解剖亚区域的形态和功能差异，将为肩关节疾病的治疗提供有用信息。本研究的目的是调查在肩关节向前屈曲过程中，SSP和ISP肌肉亚区域是否发挥独立作用。
招募8名肩关节无任何活动受限的健康男性志愿者参与本研究。参与者被要求背靠椅背坐在椅子上。使用剪切波弹性成像技术测量SSP和ISP肌肉亚区域的剪切模量（kPa），作为肌肉僵硬度的指标。在非优势手臂的等长收缩过程中，于中立位以及向前屈曲过程中从30°至150°每隔15°进行主动测量。采用Friedman检验和Dunn事后检验评估每个肌肉亚区域在向前屈曲过程中不同角度测量结果的差异。
在向前屈曲过程中，SSP肌肉前中部亚区域的主动僵硬度结果从30°增加至45°，达到182.4±32.1 kPa（P<.001）。SSP肌肉前浅表亚区域的僵硬度在30°时最高（125.0±20.6 kPa；P<.019），并随着肩角位置增加至105°呈线性下降。ISP肌肉上、中、下亚区域的僵硬度呈现出山峰状趋势，分别在90°时达到峰值99.9±23.5 kPa（P<.013）、90°时达到144.2±11.2 kPa（P<.013）以及105°时达到122.9±27.9 kPa（P<.007）。最后，胸大肌和三角肌前部区域的僵硬度结果呈现出山峰状趋势，分别在60°时达到峰值89.4±23.5 kPa（P<.007）以及90°时达到176.7±22.9 kPa（P<.026）。
SSP和ISP肌肉亚区域在主动向前屈曲运动中发挥重要作用。虽然各肌肉亚区域密切重叠，但在向前屈曲运动范围内其活动发生变化，在运动初始范围是SSP肌肉的前浅表亚区域活跃，在运动至中间范围时是ISP肌肉的下亚区域活跃。在向前屈曲过程中，SSP和ISP亚区域未表现出独立的功能行为。
