title: Postural dependence of passive tension in the supraspinatus following rotator cuff repair: a simulation analysis.
abstract: BACKGROUND
  Despite surgical advances, repair of rotator cuff tears is associated with 20-70% incidence of recurrent tearing. The tension required to repair the torn tendon influences surgical outcomes and may be dependent on the gap length from torn tendon that must be spanned by the repair. Detailed understanding of forces throughout the range of motion (ROM) may allow surgeons to make evidence-based recommendations for post-operative care.
  
  
  METHODS
  We used a computational shoulder model to assess passive tension and total moment-generating capacity in supraspinatus for repairs of gaps up to 3 cm throughout the shoulder (ROM).
  
  
  RESULTS
  In 60° abduction, increased gap length from 0.5 cm to 3 cm caused increases in passive force from 3N to 58 N, consistent with those seen during clinical repair. For reduced abduction, passive forces increased substantially. For a 0.5 cm gap, tension throughout the ROM (elevation, plane of elevation, and rotation) is within reasonable limits, but larger gaps are associated with tensions that markedly exceed reported pull-out strength of sutures and anchors. Peak moment for a large 3 cm gap length was 5.09 Nm, a 53% reduction in moment-generating capacity compared to uninjured supraspinatus.
  
  
  CONCLUSIONS
  We conclude that shoulder posture is an important determinant of passive forces during rotator cuff repair surgery. Choosing postures that reduce forces intraoperatively to permit repair of larger gaps may lead to failure postoperatively when the shoulder is mobilized. For larger defects, loss of strength in supraspinatus may be substantial following repair even if retear is prevented.
authors: Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA. ksaul@wakehealth.edu
authors: Katherine R
authors: KR
authors: Saul
authors: Solomon
authors: S
authors: Hayon
authors: Thomas L
authors: TL
authors: Smith
authors: Christopher J
authors: CJ
authors: Tuohy
authors: Sandeep
authors: S
authors: Mannava