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Okamune R1,2, Miyashita K1,3, Koyama T2, Tani Y4, Ota K5, Emon Y1, Matsushita Y6
1Chubu University, Rehabilitation Science, Graduate School of Life and Health Sciences, Kasugai-shi, Japan, 2Matsushita Orthopedics, Department of Rehabilitation, Kasugai-shi, Japan, 3Chubu University, College of Life and Health Sciences, Department of Physical Therapy, Kasugai-shi, Japan, 4Advanced Reha Co., Ltd., Kitamuro-gun, Japan, 5Shigakkan University, Baseball Club, Obu-shi, Japan, 6Matsushita Orthopedics, Kasugai-shi, Japan
Background: During shoulder movement, the motion of the scapula is influenced by the contour of the thorax. Thus, it is well accepted that thorax movement is related to the shoulder movement. However, little is known regarding the kinematics of the thorax during shoulder movement, and it is unclear how the shoulder movement is affected by restricted thorax movement.
Purpose: We aimed to investigate the effects of restricted thorax movement on the scapulohumeral rhythm.
Methods: We included 20 male college students without shoulder pain in this study under the following two conditions: 1) restricted thorax movement (restricted) and 2) unrestricted thorax movement (unrestricted). We restricted the movements using a non-elastic athletic tape that was circumferentially applied around the thorax. The restricted parts of the thorax were at the level of a point located immediately under the angulus inferior scapulae and the spinous process of the 12th thoracic vertebra. Subjects executed a bilateral shoulder flexion in the standing posture. We collected data using four high-speed cameras and established three-dimensional coordinates of each landmark with a direct linear translation method. Then, we obtained angles of the shoulder flexion, glenohumeral joint flexion, and upward scapula rotation on the dominant hand side in each condition. In addition, we calculated the motion ratio of the glenohumeral joint to the scapula (the glenohumeral joint flexion/the upward scapula rotation) and defined it as the scapulohumeral rhythm. We conducted paired Student's t-tests to detect differences in the scapulohumeral rhythm between restricted and unrestricted conditions and compared the scapulohumeral rhythm at 30°, 60°, 90°, and 120° of the shoulder flexion position, maximum shoulder flexion position of the restricted condition, and maximum shoulder flexion position of each condition. Values are presented as mean ± standard deviation of the mean.
Results: The shoulder flexion position of each condition was 145.1°±14.8° and 152.1°±15.6° for the restricted and unrestricted conditions, respectively. The mean (±SD) values of the scapulohumeral rhythm were as follows (restricted/unrestricted): 30° flexion, 1.49±1.08/1.66±1.46; 60° flexion, 1.33±0.71/1.31±0.75; 90° flexion, 1.43±0.62/1.41±0.67; 120° flexion, 1.50±0.50/1.44±0.51; maximum flexion position of the restricted condition, 1.45±0.53/1.34±0.39; maximum flexion position of each condition, 1.45±0.53/1.31±0.36. Values of the scapulohumeral rhythm were significantly greater in the restricted condition than in the unrestricted condition at the maximum flexion position of the restricted condition and of each condition (p 0.05).
Conclusion(s): We observed significant differences in the scapulohumeral rhythm between the restricted and unrestricted conditions only during the last phase of shoulder flexion. Our results suggest that shoulder movement was remarkably affected by thorax movement just after 120° of the shoulder flexion. During shoulder flexion with restricted thorax movements, the motion ratio of the glenohumeral joint to the scapula increases after 120° flexion and can lead to various injuries in the glenohumeral joint.
Implications: We revealed compelling evidence of a relationship between the scapulohumeral rhythm and thorax movement and further suggest that the assessment of the thorax movement is necessary to understand the pathologies of the shoulder related to abnormal scapulohumeral rhythm.
Keywords: scapulohumeral rhythm, thorax, shoulder flexion
Funding acknowledgements: No funding acknowledgement was available for this study.
Purpose: We aimed to investigate the effects of restricted thorax movement on the scapulohumeral rhythm.
Methods: We included 20 male college students without shoulder pain in this study under the following two conditions: 1) restricted thorax movement (restricted) and 2) unrestricted thorax movement (unrestricted). We restricted the movements using a non-elastic athletic tape that was circumferentially applied around the thorax. The restricted parts of the thorax were at the level of a point located immediately under the angulus inferior scapulae and the spinous process of the 12th thoracic vertebra. Subjects executed a bilateral shoulder flexion in the standing posture. We collected data using four high-speed cameras and established three-dimensional coordinates of each landmark with a direct linear translation method. Then, we obtained angles of the shoulder flexion, glenohumeral joint flexion, and upward scapula rotation on the dominant hand side in each condition. In addition, we calculated the motion ratio of the glenohumeral joint to the scapula (the glenohumeral joint flexion/the upward scapula rotation) and defined it as the scapulohumeral rhythm. We conducted paired Student's t-tests to detect differences in the scapulohumeral rhythm between restricted and unrestricted conditions and compared the scapulohumeral rhythm at 30°, 60°, 90°, and 120° of the shoulder flexion position, maximum shoulder flexion position of the restricted condition, and maximum shoulder flexion position of each condition. Values are presented as mean ± standard deviation of the mean.
Results: The shoulder flexion position of each condition was 145.1°±14.8° and 152.1°±15.6° for the restricted and unrestricted conditions, respectively. The mean (±SD) values of the scapulohumeral rhythm were as follows (restricted/unrestricted): 30° flexion, 1.49±1.08/1.66±1.46; 60° flexion, 1.33±0.71/1.31±0.75; 90° flexion, 1.43±0.62/1.41±0.67; 120° flexion, 1.50±0.50/1.44±0.51; maximum flexion position of the restricted condition, 1.45±0.53/1.34±0.39; maximum flexion position of each condition, 1.45±0.53/1.31±0.36. Values of the scapulohumeral rhythm were significantly greater in the restricted condition than in the unrestricted condition at the maximum flexion position of the restricted condition and of each condition (p 0.05).
Conclusion(s): We observed significant differences in the scapulohumeral rhythm between the restricted and unrestricted conditions only during the last phase of shoulder flexion. Our results suggest that shoulder movement was remarkably affected by thorax movement just after 120° of the shoulder flexion. During shoulder flexion with restricted thorax movements, the motion ratio of the glenohumeral joint to the scapula increases after 120° flexion and can lead to various injuries in the glenohumeral joint.
Implications: We revealed compelling evidence of a relationship between the scapulohumeral rhythm and thorax movement and further suggest that the assessment of the thorax movement is necessary to understand the pathologies of the shoulder related to abnormal scapulohumeral rhythm.
Keywords: scapulohumeral rhythm, thorax, shoulder flexion
Funding acknowledgements: No funding acknowledgement was available for this study.
Topic: Human movement analysis; Musculoskeletal: upper limb; Musculoskeletal: upper limb
Ethics approval required: Yes
Institution: Chubu University
Ethics committee: Chubu University Research Ethics Committee
Ethics number: 280074
All authors, affiliations and abstracts have been published as submitted.
