Compensatory mechanisms for acromiohumeral distance by increased scapulothoracic joint motion during scapular plane abduction: A musculoskeletal model simulation study

Daichi Shimose, Hisanori Matsuura, Ryoji Kiyama, Rikuto Suzuki, Tomohisa Nishikawa, Shobu Nakashima, Masayuki Kawada, Masafumi Fukuda, Yasufmi Takeshita
Purpose:

This study aims to analyze the changes in GH stability and AHD by increased ST motion during scapular plane abduction, using a musculoskeletal model.

Methods:

Fifteen healthy males (age 23.5 ± 1.8 years) participated in this study. Participants performed 5 right shoulder abduction along scapular plane. Motion capture was performed using 8-camera OptiTrack Flex 13 system (NaturalPoint, Corvallis, OR, USA), and obtained marker trajectories were entered to the musculoskeletal model simulation software (AnyBody7.4, AnyBody Technology A/S, Denmark) to calculate GH stability, and to obtain the point cloud data of the humeral head and the acromion. GH stability ratio quantified from positional relationship between the joint force and the glenoid fossa. The ratio ranges from 0 to 1, with a ratio close to 0 indicating serious joint instability. AHD was obtained by calculating the shortest distance between the point cloud data of the acromion and the humeral head. Musculoskeletal models were used the following 3 models with altered ST motion: normal ST motion model (normal model), mild ST motion increased model (mild model), and large ST motion increased model (large model). One-dimensional statistical parametric mapping was used to compare GH stability and AHD from 30° to 120° in arm elevation angle in 3 models. Differences among models were analyzed using a one-way repeated measures ANOVA. As a post hoc test, paired t-tests with Bonferroni correction for multiple comparisons were used for further significance testing. A Type I error rate of 0.05 was used in this study.

Results:

GH stability was significant differences among 3 models. Post hoc analysis showed significant decreased stability in mild and large model compared to normal model from 57° to 120°. GH stability in large model was significantly lower compared to mild model from 60° to 120°. AHD was also significant differences among 3 models. Post hoc analysis showed significant increased AHD in mild model from 46° to 106°, and in large model from 46° to 109°, comparing to normal model. AHD in large model was significant greater compared to mild model from 49° to 112°.

Conclusion(s):

Increased ST motion decreased GH stability during scapular plane abduction. Excessive glenoid fossa upward rotation due to increased ST motion would increase superior joint force acting on humerus head, resulting in decreased GH stability. Conversely, increased ST motion increase AHD. Increased AHD depending on increased ST motion would contribute to pain avoidance due to impingement.

Implications:

During shoulder elevation, increased ST motion would magnify AHD for pain avoidance, but on the other hand, it decreases GH stability. Therapist engaging in shoulder rehabilitation must pay attention to this issue.

Funding acknowledgements:
No funding was received for this study.
Keywords:
Musculoskeletal model simulation
scapulothoracic joint motion
acromiohumeral distance
Primary topic:
Musculoskeletal: upper limb
Second topic:
Musculoskeletal
Did this work require ethics approval?:
Yes
Name the institution and ethics committee that approved your work:
The Ethics Committee on Epidemiological and Related Studies at the Sakuragaoka campus of the Kagoshima University
Provide the ethics approval number:
180113Epi ver. Revision 2
Has any of this material been/due to be published or presented at another national or international conference prior to the World Physiotherapy Congress 2025?:
No

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