title: Mechanical risk of rotator cuff repair failure during passive movements: A simulation-based study.
abstract: BACKGROUND
  Despite improvements in rotator cuff surgery techniques, re-tear rate remains above 20% and increases with tear severity. Mechanical stresses to failure of repaired tendons have been reported. While optimal immobilization postures were proposed to minimize this stress, post-operative rehabilitation protocols have never been assessed with respect to these values. Purpose was to use musculoskeletal simulation to predict when the stress in repaired tendons exceeds safety limits during passive movements. Hence, guidelines could be provided towards safer post-operative exercises.
  
  
  METHODS
  Sixteen healthy participants volunteered in passive three-dimensional shoulder range-of-motion and passive rehabilitation exercises assessment. Stress in all rotator cuff tendons was predicted during each movement by means of a musculoskeletal model using simulations with different type and size of tears. Safety stress thresholds were defined based on repaired tendon loads to failure reported in the literature and used to discriminate safe from unsafe ranges-of-motion.
  
  
  RESULTS
  Increased tear size and multiple tendons tear decreased safe range-of-motion. Mostly, glenohumeral elevations below 38°, above 65°, or performed with the arm held in internal rotation cause excessive stresses in most types and sizes of injury during abduction, scaption or flexion. Larger safe amplitudes of elevation are found in scapular plane for supraspinatus alone, supraspinatus plus infraspinatus, and supraspinatus plus subscapularis tears.
  
  
  CONCLUSIONS
  This study reinforces that passive early rehabilitation exercises could contribute to re-tear due to excessive stresses. Recommendations arising from this study, for instance to keep the arm externally rotated during elevation in case of supraspinatus or supraspinatus plus infraspinatus tear, could help prevent re-tear.
authors: Université de Montréal, Department of Kinesiology, Laboratory of Simulation & Movement Modeling, 1700 rue Jacques Tétreault, Laval QC H7N OB6, Canada. Electronic address: diane.haering@gmail.com.
authors: Diane
authors: D
authors: Haering
authors: Université de Montréal, Department of Kinesiology, Laboratory of Simulation & Movement Modeling, 1700 rue Jacques Tétreault, Laval QC H7N OB6, Canada; Centre de Réadaptation Marie Enfant-Sainte-Justine UHC, Laboratory of Simulation & Movement Modeling, 1700 rue Jacques Tétreault, Laval QC H7N OB6, Canada. Electronic address: yoann.blache@hotmail.fr.
authors: Yoann
authors: Y
authors: Blache
authors: École Polytechnique de Montréal and Centre de Réadaptation Marie Enfant-Sainte-Justine UHC, Research & Engineering Chair Applied in Pediatrics (RECAP), 5200 rue Bélanger, office GR-123, Montreal QC H1T 1C9, Canada. Electronic address: maxime.raison@polymtl.ca.
authors: Maxime
authors: M
authors: Raison
authors: Université de Montréal, Department of Kinesiology, Laboratory of Simulation & Movement Modeling, 1700 rue Jacques Tétreault, Laval QC H7N OB6, Canada; Centre de Réadaptation Marie Enfant-Sainte-Justine UHC, Laboratory of Simulation & Movement Modeling, 1700 rue Jacques Tétreault, Laval QC H7N OB6, Canada. Electronic address: mickael.begon@umontreal.ca.
authors: Mickael
authors: M
authors: Begon
mesh_terms: D000328:Adult; D003198:Computer Simulation; D005081:Exercise Therapy / Q000379:methods; D005260:Female; D006801:Humans; D007592:Joint Diseases / Q000503:physiopathology / Q000534:rehabilitation*; D008297:Male; D019637:Orthopedic Procedures / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D017006:Rotator Cuff / Q000502:physiology* / Q000601:surgery; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000502:physiology; D013314:Stress, Mechanical; D013312:Stress, Physiological / Q000502:physiology; D017211:Treatment Failure; D055815:Young Adult
keywords: Muscle forces; Musculoskeletal modeling; Rehabilitation; Rotator cuff; Shoulder