The Coupled Kinematics of Scapulothoracic Upward Rotation

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Abstract

BACKGROUND: Scapulothoracic upward rotation (UR) is an important shoulder complex motion allowing for a larger functional work space and improved glenohumeral muscle function. However, the kinematic mechanisms producing scapulothoracic UR remain unclear, limiting the understanding of normal and abnormal shoulder movements.

OBJECTIVE: The objective of this study was to identify the coupling relationships through which sternoclavicular and acromioclavicular joint motions contribute to scapulothoracic UR.

DESIGN: This was a cross-sectional observational study.

METHODS: Sixty participants were enrolled in this study; 30 had current shoulder pain, and 30 had no history of shoulder symptoms. Shoulder complex kinematics were quantified using single-plane fluoroscopy and 2D/3D shape matching and were described as finite helical displacements for 30-degree phases of humerothoracic elevation (30 degrees-60 degrees, 60 degrees-90 degrees, and 90 degrees-120 degrees). A coupling function was derived to estimate scapulothoracic UR from its component motions of acromioclavicular UR, sternoclavicular posterior rotation, and sternoclavicular elevation as a function of acromioclavicular internal rotation. The proportional contributions of each of the component motions were also calculated and compared between phases of humerothoracic elevation and groups.

RESULTS: Scapulothoracic UR displacement could be effectively predicted using the derived coupling function. During the 30- to 60-degree humerothoracic elevation phase, acromioclavicular UR accounted for 84.2% of scapulothoracic UR, whereas sternoclavicular posterior rotation and elevation each accounted for < 10%. During later phases, acromioclavicular UR and sternoclavicular posterior rotation each accounted for 32% to 42%, whereas sternoclavicular elevation accounted for < 11%.

LIMITATIONS: Error due to the tracking of sternoclavicular posterior rotation may have resulted in an underprediction of its proportional contribution and an overprediction of the proportional contribution of acromioclavicular UR.

CONCLUSIONS: Acromioclavicular UR and sternoclavicular posterior rotation are the predominant component motions of scapulothoracic UR. More research is needed to investigate how these coupling relationships are affected by muscle function and influenced by scapular dyskinesis.

Original languageEnglish (US)
Pages (from-to)283-294
Number of pages12
JournalPhysical therapy
Volume100
Issue number2
DOIs
StatePublished - Feb 7 2020

Bibliographical note

Funding Information:
Research reported in this article was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (F31-HD087069 and L30-HD089226), the National Institute of Arthritis and Musculoskeletal and Skin Diseases (T32-AR050938), the National Center for Advancing Translational Sciences (UL1-TR002494), and the National Institute of Biomedical Imaging and Bioengineering (P41-EB015894). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health (NIH). This work was also supported in part by Promotion of Doctoral Studies (PODS) Scholarships from the Foundation for Physical Therapy, the Minnesota Partnership for Biotechnology and Medical Genomics, a research infrastructure grant from the University of Minnesota Office of the Vice President for Research, and the University of Minnesota Department of Orthopaedic Surgery and Clinical and Translational Science Institute. Neither the NIH nor any of the other funders played a role in the design, conduct, or reporting of this study.

Funding Information:
Research reported in this article was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (F31-HD087069 and L30-HD089226), the National Institute of Arthritis and Musculoskeletal and Skin Diseases (T32-AR050938), the National Center for Advancing Translational Sciences (UL1-TR002494), and the National Institute of Biomedical Imaging and Bioengineering (P41-EB015894). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This work was also supported in part by Promotion of Doctoral Studies (PODS) Scholarships from the Foundation for Physical Therapy, the Minnesota Partnership for Biotechnology and Medical Genomics, a research infrastructure grant from the University of Minnesota Office of the Vice President for Research, and the University of Minnesota Department of Orthopaedic Surgery and Clinical and Translational Science Institute.

Publisher Copyright:
© 2020 2019 American Physical Therapy Association.

PubMed: MeSH publication types

  • Journal Article
  • Observational Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

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