title: Importance of the subscapularis muscle after total shoulder arthroplasty.
abstract: BACKGROUND
  The rotator cuff muscles are the main stabilizer of the glenohumeral joint. After total shoulder arthroplasty using anterior approaches, a dysfunction of the subscapularis muscle has been reported. In the present paper we tested the hypothesis that a deficient subscapularis following total shoulder arthroplasty can induce joint instability.
  
  
  METHODS
  To test this hypothesis we have developed an EMG-driven musculoskeletal model of the glenohumeral joint. The model was based on an algorithm that minimizes the difference between measured and predicted muscular activities, while satisfying the mechanical equilibrium of the glenohumeral joint. A movement of abduction in the scapular plane was simulated. We compared a normal and deficient subscapularis. Muscle forces, joint force, contact pattern and humeral head translation were evaluated.
  
  
  RESULTS
  To satisfy the mechanical equilibrium, a deficient subscapularis induced a decrease of the force of the infraspinatus muscle. This force decrease was balanced by an increase of the supraspinatus and middle deltoid. As a consequence, the deficient subscapularis induced an upward migration of the humeral head, an eccentric contact pattern and higher stress within the cement.
  
  
  CONCLUSIONS
  These results confirm the importance of the suscapularis for the long-term stability of total shoulder arthroplasty.
authors: Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédérale de Lausanne, Station 19, 1015 Lausanne, Switzerland. alexandre.terrier@epfl.ch
authors: A
authors: A
authors: Terrier
authors: X
authors: X
authors: Larrea
authors: V
authors: V
authors: Malfroy Camine
authors: D P
authors: DP
authors: Pioletti
authors: A
authors: A
authors: Farron
mesh_terms: D019643:Arthroplasty, Replacement / Q000009:adverse effects* / Q000379:methods; D001696:Biomechanical Phenomena; D006801:Humans; D058430:Humeral Head / Q000503:physiopathology; D007593:Joint Instability / Q000209:etiology*; D008954:Models, Biological; D009068:Movement / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology; D017006:Rotator Cuff / Q000503:physiopathology*; D012540:Scapula / Q000503:physiopathology; D012785:Shoulder Joint / Q000503:physiopathology / Q000601:surgery*