Basic science
Superior humeral head migration occurs after a protocol designed to fatigue the rotator cuff: A radiographic analysis

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Hypothesis

Awkward postures and repetitive work have been suggested to lead to shoulder fatigue, which may in turn decrease the subacromial space. The aim of this study was to quantify changes in humeral head position relative to the glenoid after rotator cuff fatigue. We hypothesized that the humeral head would migrate superiorly with fatigue due to the inability of the rotator cuff muscles to balance the upward pull of the deltoid.

Materials and methods

Four anterior-posterior radiographs (at 0°, 45°, 90°, and 135° of elevation in the scapular plane) of the glenohumeral joint were taken before and after a fatiguing task. The fatiguing task was a simulated job task intended to exhaust the entire rotator cuff.

Results

The position of the humeral head with respect to the glenoid cavity was significantly affected both by arm elevation angle and fatigue state. In the prefatigued state, increasing arm elevation angle was related to superior translation until 90°, after which the humeral head moved inferiorly to a more central position. In the postfatigued state, the inability of the rotator cuff to centralize the humeral head led to increasing translations with higher elevations.

Discussion

Superior humeral head migration was associated with the fatigued state. This implies that overhead or repetitive work, or both, may accelerate the development of subacromial impingement through reduction of the subacromial space.

Conclusions

Continuous overhead work demonstrably created rotator cuff fatigue, which apparently inhibited the ability of the shoulder musculature to resist upward humeral translation.

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.

References (41)

  • G.A. Paletta et al.

    Shoulder kinematics with two-plane x-ray evaluation in patients with anterior instability or rotator cuff tearing

    J Shoulder Elbow Surg

    (1997)
  • B. Bernard

    Chapter 3:Shoulder Musculoskeletal Disorders. Musculoskeletal disorders and workplace factors. DHHS (NIOSH) Publication No. 97-141

    (1997)
  • D.C. Boone et al.

    Normal ranges of motion of joints in male subject

    J Bone Joint Surg Am

    (1979)
  • G.A. Borg

    Psychophysical bases of perceived exertion

    Med Sci Sports

    (1982)
  • J.N. Chopp et al.

    On the feasibility of obtaining multiple muscular maximal voluntary excitation levels from test exertions: a shoulder example

    J Electromyogr Kinesiol

    (2009)
  • J. Cohen

    Statistical power analysis for the behavioral sciences

    (1988)
  • R.E. Cotton et al.

    Tears of the humeral rotator cuff

    J Bone Joint Surg Br

    (1964)
  • J.R. Cram et al.

    Introduction to surface electromyography

    (1998)
  • R. Girometti et al.

    Supraspinatus tendon US morphology in basketball players: correlation with main pathologic models of secondary impingement syndrome in young overhead athletes. Preliminary report

    Radiol Med

    (2006)
  • F.C. Golding

    The shoulder—the forgotten joint

    Br J Radiol

    (1962)
  • Cited by (0)

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