Basic scienceSuperior humeral head migration occurs after a protocol designed to fatigue the rotator cuff: A radiographic analysis
Section snippets
Materials and methods
This study was approved by the Office of Research Ethics of the University of Waterloo (ORE #15505) and by the Research Ethics Board at St. Joseph's Healthcare Hamilton (REB #09-3174), where data collection took place. All participants read and signed a consent form before beginning the study.
Results
Humeral head position with the respect to the glenoid cavity was significantly affected by arm angle and fatigue state. A fatigue-arm angle interaction effect was not significant, thus only main effects will be discussed. Further, infraspinatus and middle deltoid had conclusive evidence of fatigue (increased EMG amplitude and decreased MPF) 31, 35, 36, 38 in 95% of participants after the fatigue protocol.
Humeral head excursion with respect to past literature
Results indicated that most of the participants displayed superior humeral head excursion as an effect of arm angle and fatigue. With respect to arm angle, a characteristic trend for excursion existed as healthy patients elevated their arm above 0°. Previously, Graichen et al17 examined humeral head excursion during active and passive abduction and found that an initial superior migration was present during active abduction, but at 90° and further at 120° of abduction, the humeral head had
Conclusions
Both research hypotheses for this study were accepted. The humeral head migrated superiorly after fatigue, implying that industrial jobs requiring overhead or repetitive work, or both, may help to accelerate the development of upper extremity musculoskeletal disorders, particularly impingement. Characteristic and different trends in excursion magnitude with changes in arm elevation support this contention. Thus, workers should be aware that working in overhead postures for an extended period
Acknowledgements
We thank Glenn Madill and the team of technologists at St. Joseph's Hospital for their assistance during data collection.
Disclaimer
Partial project support came from a Centre of Research Expertise for the Prevention of Musculoskeletal Disorders grant, on which Dr Clark Dickerson was the principle investigator. Jaclyn Chopp was supported through a PGS-M award through NSERC.
The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
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