Christian Gerber1, Dominik C Meyer1, Martin Flück2, Mario C Benn3, Brigitte von Rechenberg3, Karl Wieser4. 1. Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland. 2. Laboratory for Muscle Plasticity, Balgrist University Hospital, University of Zurich, Zurich, Switzerland. 3. Musculoskeletal Research Unit, Center for Applied Biotechnology and Molecular Medicine, Equine Department, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland. 4. Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland karl.wieser@balgrist.ch.
Abstract
BACKGROUND: Chronic rotator cuff tendon tearing is associated with irreversible atrophy, fatty infiltration, and interstitial fibrosis of the corresponding muscle. HYPOTHESES: Anabolic steroids can prevent musculotendinous degeneration during retraction and/or can reverse these changes after operative repair of the retracted musculotendinous unit in sheep. STUDY DESIGN: Controlled laboratory study. METHODS: The infraspinatus tendon was released in 18 alpine sheep. All sheep underwent repair of the retracted musculotendinous unit after 16 weeks and were sacrificed after 22 weeks; 6 sheep served as controls, 6 sheep were treated with weekly intramuscular injection of 150 mg of nandrolone decanoate after infraspinatus (ISP) repair (group N6W), and 6 sheep were treated with 150 mg of nandrolone decanoate immediately after tendon release (group N22W). Muscle biopsy specimens were taken before tendon release and after 16 and 22 weeks. Muscle volume and fatty infiltration (on MRI), myotendinous retraction, and muscle density (on computed tomography) were measured immediately after ISP release, after 6 weeks, and before ISP repair and sacrifice. RESULTS: Muscle volume on MRI decreased to a mean (±SD) of 80% ± 8% of the original volume after 6 weeks, remained stable at 78% ± 11% after 16 weeks, and decreased further to 69% ± 9% after 22 weeks in the control group. These findings were no different from those in group N22W (72% ± 9% at 6 weeks, 73% ± 6% at 16 weeks, and 67% ± 5% at 22 weeks). Conversely, the N6W group did not show a decrease in ISP volume after repair; this finding differed significantly from the response in the control and N22W groups. Fatty infiltration (on MRI) continuously increased in the control group (12% ± 4% at tendon release, 17% ± 4% after 6 weeks, 50% ± 9% after 16 weeks, and 60% ± 8% after 22 weeks) and the N6W group. However, application of anabolic steroids at the time of tendon release (N22W group) significantly reduced fatty infiltration after 16 (16% ± 5%; P < .001) and 22 weeks (22% ± 7%; P < .001). CONCLUSION: In a sheep model of rotator cuff tendon tear, further muscle atrophy can be prevented with the application of anabolic steroids starting immediately after tendon repair. In addition, fatty muscle infiltration can largely be prevented if the steroids are applied immediately after tendon release. CLINICAL RELEVANCE: Study findings may lead to the development of treatment strategies to prevent or reduce muscle degeneration caused by rotator cuff tendon tearing.
BACKGROUND: Chronic rotator cuff tendon tearing is associated with irreversible atrophy, fatty infiltration, and interstitial fibrosis of the corresponding muscle. HYPOTHESES: Anabolic steroids can prevent musculotendinous degeneration during retraction and/or can reverse these changes after operative repair of the retracted musculotendinous unit in sheep. STUDY DESIGN: Controlled laboratory study. METHODS: The infraspinatus tendon was released in 18 alpinesheep. All sheep underwent repair of the retracted musculotendinous unit after 16 weeks and were sacrificed after 22 weeks; 6 sheep served as controls, 6 sheep were treated with weekly intramuscular injection of 150 mg of nandrolone decanoate after infraspinatus (ISP) repair (group N6W), and 6 sheep were treated with 150 mg of nandrolone decanoate immediately after tendon release (group N22W). Muscle biopsy specimens were taken before tendon release and after 16 and 22 weeks. Muscle volume and fatty infiltration (on MRI), myotendinous retraction, and muscle density (on computed tomography) were measured immediately after ISP release, after 6 weeks, and before ISP repair and sacrifice. RESULTS: Muscle volume on MRI decreased to a mean (±SD) of 80% ± 8% of the original volume after 6 weeks, remained stable at 78% ± 11% after 16 weeks, and decreased further to 69% ± 9% after 22 weeks in the control group. These findings were no different from those in group N22W (72% ± 9% at 6 weeks, 73% ± 6% at 16 weeks, and 67% ± 5% at 22 weeks). Conversely, the N6W group did not show a decrease in ISP volume after repair; this finding differed significantly from the response in the control and N22W groups. Fatty infiltration (on MRI) continuously increased in the control group (12% ± 4% at tendon release, 17% ± 4% after 6 weeks, 50% ± 9% after 16 weeks, and 60% ± 8% after 22 weeks) and the N6W group. However, application of anabolic steroids at the time of tendon release (N22W group) significantly reduced fatty infiltration after 16 (16% ± 5%; P < .001) and 22 weeks (22% ± 7%; P < .001). CONCLUSION: In a sheep model of rotator cuff tendon tear, further muscle atrophy can be prevented with the application of anabolic steroids starting immediately after tendon repair. In addition, fatty muscle infiltration can largely be prevented if the steroids are applied immediately after tendon release. CLINICAL RELEVANCE: Study findings may lead to the development of treatment strategies to prevent or reduce muscle degeneration caused by rotator cuff tendon tearing.
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