Evaluation of Shoulder Strength and Kinematics as Risk Factors for Shoulder Injury in United States Special Forces Personnel

Caleb D Johnson; Branco K J F Nijst; Shawn R Eagle; Marijn W M Kessels; Mita T Lovalekar; Kellen T Krajewski; Shawn D Flanagan; Bradley C Nindl; Christopher Connaboy

doi:10.1177/2325967119831272

Evaluation of Shoulder Strength and Kinematics as Risk Factors for Shoulder Injury in United States Special Forces Personnel

Orthop J Sports Med. 2019 Mar 13;7(3):2325967119831272. doi: 10.1177/2325967119831272. eCollection 2019 Mar.

Authors

Caleb D Johnson¹, Branco K J F Nijst², Shawn R Eagle¹, Marijn W M Kessels², Mita T Lovalekar¹, Kellen T Krajewski¹, Shawn D Flanagan¹, Bradley C Nindl¹, Christopher Connaboy¹

Affiliations

¹ Neuromuscular Research Laboratory, Department of Sports Medicine and Nutrition, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
² Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, the Netherlands.

Abstract

Background: Musculoskeletal injuries at the shoulder are highly prevalent and place a large burden on United States Special Forces personnel. Literature is lacking regarding the risk factors for these types of injuries.

Purpose/hypothesis: The purpose of this study was to evaluate the association of shoulder strength and kinematic characteristics, which have shown retrospective associations with shoulder conditions/injuries, with prospectively collected shoulder injuries. We hypothesized that lower strength and abnormal kinematics would be predictive of future shoulder injury.

Study design: Case-control study; Level of evidence, 3.

Methods: A total of 140 male Special Forces operators underwent a musculoskeletal evaluation of the shoulder that included a scapular kinematic assessment during a humeral elevation task and isokinetic strength testing of the scapular protractors/retractors, external/internal rotators, and elevators of the shoulder. From strength assessments, ipsilateral strength ratios and bilateral strength asymmetries were also calculated. Musculoskeletal injuries of the shoulder were collected prospectively by use of medical chart reviews at 365 days following the evaluation. Separate generalized estimating equations (GEEs) and simple logistic regressions were used to analyze the association between baseline predictors and development of shoulder injury.

Results: Results of the GEEs showed no significant prediction of shoulder injury by shoulder strength (odds ratio [OR], 1.00-1.03), ipsilateral strength ratios (OR, 0.43-2.12), or scapular kinematics (OR, 0.99-1.01). Logistic regression indicated that none of the bilateral asymmetries were significantly predictive of shoulder injury (OR, 1.00-1.04).

Conclusion: The results indicate that shoulder strength and kinematic characteristics are not risk factors for shoulder injury in the Special Forces population. These findings are in opposition to the general findings of previous research using a retrospective analysis.

Keywords: biomechanics; isokinetic; military; prospective; upper extremity.