Test-retest reliability of isometric shoulder muscle strength during abduction and rotation tasks measured using the Biodex dynamometer

Eleonora Croci; Patrik Born; Franziska Eckers; Corina Nüesch; Daniel Baumgartner; Andreas Marc Müller; Annegret Mündermann

doi:10.1016/j.jse.2023.03.025

Test-retest reliability of isometric shoulder muscle strength during abduction and rotation tasks measured using the Biodex dynamometer

J Shoulder Elbow Surg. 2023 Oct;32(10):2008-2016. doi: 10.1016/j.jse.2023.03.025. Epub 2023 May 11.

Authors

Eleonora Croci¹, Patrik Born², Franziska Eckers², Corina Nüesch³, Daniel Baumgartner⁴, Andreas Marc Müller², Annegret Mündermann³

Affiliations

¹ Department of Biomedical Engineering, University of Basel, Basel, Switzerland; Department of Orthopaedics and Traumatology, University Hospital Basel, Basel, Switzerland. Electronic address: eleonora.croci@unibas.ch.
² Department of Orthopaedics and Traumatology, University Hospital Basel, Basel, Switzerland.
³ Department of Biomedical Engineering, University of Basel, Basel, Switzerland; Department of Orthopaedics and Traumatology, University Hospital Basel, Basel, Switzerland; Department of Spine Surgery, University Hospital Basel, Basel, Switzerland; Department of Clinical Research, University of Basel, Basel, Switzerland.
⁴ IMES Institute of Mechanical Systems, Zurich University of Applied Sciences, Winterthur, Switzerland.

PMID: 37178965
DOI: 10.1016/j.jse.2023.03.025

Abstract

Background: The Constant score (CS) is often used clinically to assess shoulder function and includes a muscle strength assessment only for abduction. The aim of this study was to evaluate the test-retest reliability of isometric shoulder muscle strength during various positions of abduction and rotation with the Biodex dynamometer and to determine their correlation with the strength assessment of the CS.

Methods: Ten young healthy subjects participated in this study. Isometric shoulder muscle strength was measured during 3 repetitions for abduction at 10° and 30° abduction in the scapular plane (with extended elbow and hand in neutral position) and for internal and external rotation (with the arm at 15° abduction in the scapular plane and elbow flexed at 90°). Muscle strength tests with the Biodex dynamometer were measured in 2 different sessions. The CS was acquired only in the first session. Intraclass correlation coefficients (ICCs) with 95% confidence interval, limits of agreement, and paired t tests for repeated tests of each abduction and rotation task were calculated. Pearson's correlation between the strength parameter of the CS and isometric muscle strength was investigated.

Results: Muscle strength did not differ between tests (P > .05) with good to very good reliabilities for abduction at 10° and 30°, external rotation and internal rotation (ICC >0.7 for all). A moderate correlation of the strength parameter of the CS with all isometric shoulder strength parameters was observed (r > 0.5 for all).

Conclusion: Shoulder muscle strength for abduction and rotation measured with the Biodex dynamometer are reproducible and correlate with the strength assessment of the CS. Therefore, these isometric muscle strength tests can be further employed to investigate the effect of different shoulder joint pathology on muscle strength. These measurements consider a more comprehensive functionality of the rotator cuff than the single strength evaluation in abduction within the CS as both abduction and rotation are assessed. Potentially, this would allow for a more precise differentiation between the various outcomes of rotator cuff tears.

Keywords: Constant score; abduction; dynamometer; external rotation; internal rotation; isometric tests; shoulder.

MeSH terms

Humans
Isometric Contraction / physiology
Muscle Strength / physiology
Muscle Strength Dynamometer
Reproducibility of Results
Rotator Cuff / physiology
Shoulder Joint* / physiology
Shoulder*