title: Muscle Degeneration Associated With Rotator Cuff Tendon Release and/or Denervation in Sheep.
abstract: BACKGROUND
  The effect of an additional neurological injury (suprascapular nerve traction injury) to a chronically retracted rotator cuff muscle is incompletely understood and warrants clarification.
  
  
  OBJECTIVE
  To investigate the microscopic and macroscopic muscle degeneration patterns caused by tendon release and/or muscle denervation in a sheep rotator cuff model.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Infraspinatus muscle biopsy specimens (for histological analysis) were obtained from 18 Swiss alpine sheep before and 16 weeks after release of the infraspinatus tendon (tenotomy [T] group; n = 6), transection of the suprascapular nerve (neurectomy [N] group; n = 6), or tendon release plus nerve transection (tenotomy + neurectomy [T&N] group; n = 6). Magnetic resonance imaging (MRI) and computed tomography (CT) were used to assess retraction (CT), muscle density (CT), volume (MRI T2), and fat fraction (MRI Dixon). Stiffness of the infraspinatus was measured with a spring scale.
  
  
  RESULTS
  At 16 weeks postoperatively, the mean infraspinatus muscle volume had decreased significantly more after neurectomy (to 47% ± 7% of the original volume; P = .001) and tenotomy plus neurectomy (48% ± 13%; P = .005) than after tenotomy alone (78% ± 11%). Conversely, the mean amount of intramuscular fat (CT/MRI Dixon) was not significantly different in the 3 groups (T group: 50% ± 9%; N group: 40% ± 11%; T&N group: 46% ± 10%) after 16 weeks. The mean myotendinous retraction (CT) was not significantly different in the T and T&N groups (5.8 ± 1.0 cm and 6.4 ± 0.4 cm, respectively; P = .26). Stiffness was, however, most increased after additional neurectomy. In contrast to muscle changes after tendon release, denervation of the muscle led to a decrease in the pennation angle of lengthened muscle fibers, with a reduced mean cross-sectional area of pooled muscle fibers, a slow- to fast-type transformation, and an increase in the area percentage of hybrid fibers, leading to overall significantly greater atrophy of the corresponding muscle.
  
  
  CONCLUSIONS
  Although it is unclear which experimental group (T or T&N) most accurately reflects the clinical scenario in a given case, these findings provide baseline information for clinical differentiation between muscle changes caused by denervation or rotator cuff tendon lesions.
  
  
  CONCLUSIONS
  The findings of this study help to understand how and to which extent a neurological lesion of the supplying suprascapular nerve could influence the pattern of anatomic-physiological muscular changes after rotator cuff tendon tears.
authors.affiliation: Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Gerber
authors.affiliation: Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
authors.forename: Dominik C
authors.initials: DC
authors.lastname: Meyer
authors.affiliation: Laboratory for Muscle Plasticity, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Flück
authors.affiliation: Laboratory for Muscle Plasticity, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
authors.forename: Paola
authors.initials: P
authors.lastname: Valdivieso
authors.affiliation: Musculoskeletal Research Unit, Center for Applied Biotechnology and Molecular Medicine, Equine Department, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Brigitte
authors.initials: B
authors.lastname: von Rechenberg
authors.affiliation: Musculoskeletal Research Unit, Center for Applied Biotechnology and Molecular Medicine, Equine Department, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Mario C
authors.initials: MC
authors.lastname: Benn
authors.affiliation: Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
authors.forename: Karl
authors.initials: K
authors.lastname: Wieser
mesh_terms: D000818:Animals; D003714:Denervation; D004195:Disease Models, Animal; D008279:Magnetic Resonance Imaging; D008297:Male; D009133:Muscular Atrophy / Q000000981:diagnostic imaging / Q000209:etiology*; D059348:Peripheral Nerve Injuries / Q000150:complications* / Q000000981:diagnostic imaging; D000070636:Rotator Cuff Injuries / Q000150:complications* / Q000000981:diagnostic imaging; D012756:Sheep; D058971:Tenotomy; D014057:Tomography, X-Ray Computed; D014143:Traction
keywords: animal model; denervation; muscle degeneration; rotator cuff; shoulder; suprascapular nerve lesion