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Related Experiment Videos

Shoulder electromyography in multidirectional instability.

Alfred D Morris1, Graham J Kemp, Simon P Frostick

  • 1University Department of Musculoskeletal Science, Royal Liverpool University Hospital, Liverpool, United Kingdom.

Journal of Shoulder and Elbow Surgery
|January 22, 2004
PubMed
Summary
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Altered shoulder muscle activity, particularly in the deltoid, is linked to shoulder instability. This study highlights deltoid dysfunction in multidirectional instability (MDI) and laxity (MDL) rather than rotator cuff muscles.

Area of Science:

  • Orthopedics
  • Sports Medicine
  • Biomechanics

Background:

  • Multidirectional instability (MDI) and multidirectional laxity (MDL) are common shoulder conditions.
  • Altered shoulder muscle activity is hypothesized to contribute to the pathogenesis of MDI and MDL.

Purpose of the Study:

  • To investigate and compare shoulder muscle activity patterns in individuals with MDI, MDL, and healthy controls.
  • To identify specific muscle groups and movement patterns associated with shoulder instability.

Main Methods:

  • Intramuscular dual fine-wire electromyography was used to record activity in six shoulder muscles.
  • Participants performed various exercises on an isokinetic dynamometer at different speeds.
  • Electromyography signals were processed and normalized for analysis.

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Main Results:

  • Subjects with MDI showed altered anterior, middle, and posterior deltoid activity during specific rotation and abduction movements compared to controls.
  • Individuals with MDL exhibited increased posterior deltoid activity during adduction.
  • Rotator cuff muscles (supraspinatus, infraspinatus, subscapularis) showed similar activity patterns across all groups.

Conclusions:

  • Impaired coordination and inefficiency of dynamic shoulder stabilizers, particularly the deltoid muscle, are implicated in the etiology of MDI.
  • Electromyography provides valuable insights into shoulder girdle muscle function in instability.
  • Abnormalities in deltoid muscle activity, not rotator cuff muscles, are key findings in shoulder instability.