Development of shoulder pain with job-related repetitive load: mechanisms of tendon pathology and anxiety

Abstract

Background: The paucity of longitudinal clinical studies limits our understanding of the development of shoulder pain with repetitive shoulder tasks, and its association with underlying mind and body mechanisms. Tendon thickening characterizes painful shoulder supraspinatus tendinopathy, and the perception of pain can be affected by the presence of psychological factors such as anxiety and depression. This study determined the incidence of shoulder pain in novice individuals exposed to repetitive shoulder tasks, and the associated change in outcomes of supraspinatus tendon morphology and measures of anxiety and depression.

Methods: We recruited dental hygiene (DH) students (n = 45, novice and exposed to shoulder repetitive tasks) and occupational therapy (OT) students (n = 52, novice, but not exposed to shoulder repetitive tasks), following them over their first year of training. We measured shoulder pain, supraspinatus morphology via ultrasonography, and psychosocial distress via the Hospital Anxiety and Depression Scale. We compared the incidence of shoulder pain (defined as a change of visual analog scale for pain score greater than the minimal clinically important difference) between DH and OT students using Fisher exact test. We used mixed effects models to longitudinally compare the change in outcomes between 3 groups: DH students who develop and did not develop shoulder pain, and OT students.

Results: The incidence of shoulder pain is higher in DH students (relative risk = 4.0, 95% confidence interval [CI] 1.4, 11.4). After 1 year, DH students with pain had the greatest thickening of the supraspinatus (0.7 mm, 95% CI 0.4, 0.9). The change in supraspinatus thickness of DH students with pain was greater than both DH students with no pain (0.4 mm, 95% CI 0.1, 0.8) and OT students (0.9 mm, 95% CI 0.5, 1.2). Anxiety score increased 3.8 points (95% CI 1.6, 5.1) in DH students with pain, and 43% of DH students with pain had abnormal anxiety score at 1 year (relative risk = 2.9, 95% CI 1.0, 8.6).

Conclusion: Our results provide support for the theoretical model of repetitive load as a mechanism of tendinopathy. The supraspinatus tendon thickens in the presence of repetitive tasks, and it thickens the most in those who develop shoulder pain. Concurrently, anxiety develops with shoulder pain, indicating a potential maladaptive central mechanism that may impact the perception of pain.

Keywords: Supraspinatus; anxiety; pain; shoulder; tendinopathy.

Copyright © 2021 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

(A) Supraspinatus tendon cross-sectional thickness; the average thickness was calculated at 10, 15, and 20 mm from the biceps tendon (image not to scale). (B) Subacromial space measured as the distance between the acromion and the humeral head distance.

Figure 2

Flowchart of participants within the study. One DH student was excluded from the analysis because of widespread pain in the upper back, shoulder, and neck area.

Figure 3

Effects of overload and pain on (A) supraspinatus cross-sectional thickness, (B) acromiohumeral distance, (C) occupation ratio, (D) the Pennsylvania shoulder score (PENN total score), and the Hospital Anxiety and Depression Scale (HADS) for (E) anxiety and (F) depression. We did not find significant group-by-side interactions; thus, data in panels A-D are collapsed between the dominant and nondominant arms. All data are presented as mean ± standard error of the mean. Baseline values of the supraspinatus cross-sectional thickness (panel A) are in line with normative data collected in young adults. * Significant within-group change from baseline values (P < .05). Brackets indicate that changes from baseline were significantly different between groups (P < .05).

Figure 4

Individual change of supraspinatus tendon cross-sectional thickness from baseline. The DH-pain panel includes 22 data points (10 dominant and 12 nondominant); the DH–no pain panel includes 68 data points (35 dominant and 33 nondominant); the OT panel includes a total of 104 data points, with 5 in red corresponding to the tendons of the 3 dominant and 2 nondominant shoulders that developed pain. The shaded gray area corresponds to the limit of accuracy of the ultrasonography machine for the given tissue depth (0.6 mm). Supraspinatus tendons had an increase in thickness greater than the accuracy of the ultrasonography machine in 50% of the tendons in DH-pain, 32% of the tendons in the DH–no pain, and 8% of the tendons in the OT groups. This figure also supports the theory that tendons can change shape over time, as suggested by the tendons that had a decrease in thickness greater than the limit of accuracy of the ultrasonography machine (DH-pain, 5%; DH–no pain, 15%; OT, 20%).