Supraspinatus and deltoid muscle fiber composition in rotator cuff tear conditions

Morten Kjaer Ravn; Trine Ivarsen Ostergaard; Henrik Daa Schroeder; Jens Randel Nyengaard; Kate Lykke Lambertsen; Lars Henrik Frich

doi:10.1016/j.jseint.2020.04.016

Supraspinatus and deltoid muscle fiber composition in rotator cuff tear conditions

JSES Int. 2020 May 26;4(3):431-437. doi: 10.1016/j.jseint.2020.04.016. eCollection 2020 Sep.

Authors

Morten Kjaer Ravn^{1

2}, Trine Ivarsen Ostergaard^{1

2}, Henrik Daa Schroeder³, Jens Randel Nyengaard⁴, Kate Lykke Lambertsen^{5

6

7}, Lars Henrik Frich^{1

2

5}

Affiliations

¹ Department of Orthopaedics, Odense University Hospital, Odense, Denmark.
² The Orthopaedic Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.
³ Department of Pathology, Odense University Hospital, Odense, Denmark.
⁴ Department of Clinical Medicine - Core Centre for Molecular Morphology, Section for Stereology and Microscopy, Center for Stochastic Geometry and Advanced Bioimaging, Aarhus University, Aarhus, Denmark.
⁵ Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark.
⁶ Department of Neurology, Odense University Hospital, Odense, Denmark.
⁷ BRIDGE - Brain Research - Inter-Disciplinary Guided Excellence, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.

Abstract

Background: Rotator cuff (RC) tears are associated with RC muscle atrophy and changes in composition that are crucial to the prognosis of RC repair. The aim of this study was to characterize muscle fiber composition in the supraspinatus (SS) muscle under tear conditions.

Methods: Muscle biopsies were obtained from 21 patients undergoing surgery for an RC tendon tear. Biopsies were obtained from the musculotendinous junction of the SS muscle, and control biopsies were harvested from the deltoid muscle (DT). Biopsies were immunohistochemically processed for detection of type 1 (slow type) and type 2 (fast type) fibers and analyzed using unbiased, stereological principles. We counted the total numbers of type 1 and 2 muscle fibers/mm², and fiber diameter was used to estimate muscle fiber atrophy and hypertrophy.

Results: We found significantly more type 2 cells/mm² in the SS compared with the DT (P < .01). In addition, we found a significantly higher fraction of type 1 fibers than type 2 fibers in the DT (P < .01), whereas both fiber types were equally present in the SS. The diameters of SS cells were generally smaller than those of DT cells. Atrophy of especially SS type 2 fibers was also demonstrated. Fiber atrophy was more pronounced in men than women.

Conclusion: The changes in the composition of SS muscle cell types suggest a shift from type 1 to type 2 muscle fibers and atrophy of both type 1 and 2 fibers. This composition indicates loss of endurance and rapid fatigue of the SS muscle under RC tear conditions.

Keywords: Muscle fiber type; atrophy factors; fiber diameter; stereology; type 1; type 2.