A Cadaveric Study of Strain on the Subscapularis Muscle

Muraki T, Aoki M, Uchiyama E, Takasaki H, Murakami G, Miyamoto S. A cadaveric study of strain on the subscapularis muscle.ObjectivesTo measure the strain on 3 fiber groups of the subscapularis muscle at various glenohumeral joint positions and to determine the appropriate shoulder position for subscapularis muscle stretching.DesignRepeated-measures design.SettingBiomechanics laboratory.SpecimensNine frozen-thawed glenohumeral joints obtained from 9 fresh cadavers.InterventionsNot applicable.Main Outcome MeasureThe strain on the upper, middle, and lower fiber groups of the subscapularis were measured by precise displacement sensors during 14 different glenohumeral joint positions.ResultsThe glenohumeral joint position that showed the largest strain varied among the 3 fiber groups. Although no position showed significantly large strain on the upper and middle fiber groups, external rotation at 30°, 60°, and 90° of elevation, abduction, flexion, and horizontal abduction revealed significantly greater strain on the lower fiber groups (P<.005). Additionally, except for external rotation at 0° of elevation, the strain on the lower fiber group was significantly greater than that on the upper and middle fiber groups in external rotation (P<.005).ConclusionsThe stretching position of each fiber group of the subscapularis differs depending on the glenohumeral joint position. External rotation at 30° to 60° of glenohumeral elevation, abduction, flexion, and horizontal abduction can significantly stretch the lower fiber group of the subscapularis muscle.