title: Comparison of glenohumeral mechanics following a capsular shift and anterior tightening.
abstract: BACKGROUND
  Numerous surgical techniques have been developed to treat glenohumeral instability. Anterior tightening procedures have been associated with secondary glenohumeral osteoarthritis, unlike the anterior-inferior capsular shift procedure, which has been widely advocated as a more anatomical repair. The objective of the present study was to quantify glenohumeral joint translations, articular contact, and resultant forces in cadaveric specimens in order to compare the effects of unidirectional anterior tightening with those of the anterior-inferior capsular shift.
  
  
  METHODS
  Six normal fresh-frozen cadaveric shoulders were tested on a custom rig with use of a coordinate-measuring machine to obtain kinematic measurements and a six-axis load transducer to measure resultant external joint forces. Shoulders were tested in the scapular plane in three configurations (normal anatomical, anterior tightening, and anterior-inferior capsular shift) and in three humeral rotations (neutral, internal, and external). Glenohumeral articular surface geometry was quantified with use of stereophotogrammetry for kinematic and contact analyses. Resultant joint forces were computed on the basis of digitized coordinates of tendon insertions and origins.
  
  
  RESULTS
  Compared with the controls (maximum elevation, 167 degrees 8 degrees ), the anteriorly tightened specimens demonstrated loss of external rotation, significantly restricted maximum elevation (135 degrees 16 degrees , p = 0.002), posterior-inferior humeral head subluxation, and significantly greater posteriorly directed resultant forces at higher elevations (p < 0.05). In contrast, compared with the controls, the specimens that had been treated with the anterior-inferior capsular shift demonstrated a similar maximum elevation (159 degrees +/- 11 degrees , p = 0.8) without any apparent loss of external rotation and with reduced humeral translation.
  
  
  CONCLUSIONS
  Anterior tightening adversely affects joint mechanics by decreasing joint stability, limiting both external rotation and arm elevation, and requiring greater posterior joint forces to attain maximum elevation. The anterior-inferior capsular shift improves joint stability while preserving external rotation with no significant loss of maximum elevation.
authors.affiliation: Leni and Peter W. May Department of Orthopaedics, Mount Sinai School of Medicine, One Gustave Levy Place, Box 1188, New York, NY 10029-6574, USA.
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Wang
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Sugalski
authors.forename: William N
authors.initials: WN
authors.lastname: Levine
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Pawluk
authors.forename: Van C
authors.initials: VC
authors.lastname: Mow
authors.forename: Louis U
authors.initials: LU
authors.lastname: Bigliani
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D017746:Joint Capsule / Q000601:surgery*; D007593:Joint Instability / Q000601:surgery*; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000379:methods*; D012399:Rotation; D012785:Shoulder Joint / Q000503:physiopathology*