title: Biomechanical Evaluation of Glenoid Version and Dislocation Direction on the Influence of Anterior Shoulder Instability and Development of Hill-Sachs Lesions.
abstract: Abnormal glenoid version is a risk factor for shoulder instability. However, the degree to which the variance in version (both anteversion and retroversion) affects one's predisposition for instability is not well understood.
  
  
  
  To determine the influence of glenoid version on anterior shoulder joint stability and to determine if the direction of the humeral head dislocation is a stimulus for the development of Hill-Sachs lesions.
  
  
  
  Controlled laboratory study.
  
  
  
  Ten human cadaveric shoulders (mean age, 59.4 ± 4.3 years) were tested using a custom shoulder dislocation device placed in a position of apprehension (90° of abduction with 90° of external rotation). Glenoid version was adjusted in 5° increments for a total of 6 version angles tested: +10°, +5°, 0°, -5°, -10°, and -15° (anteversion angles are positive, and retroversion angles are negative). Two humeral dislocation directions were tested. The first direction was true anterior through the anterior-posterior glenoid axis. The second dislocation direction was 35° inferior from the anterior-posterior glenoid axis based on the deforming force role of the pectoralis major. The force and energy to dislocate were recorded.
  
  
  
  Changes in glenoid version manifested a linear effect on the dislocation force. The energy to dislocate increased as a second-order polynomial as a function of increasing glenoid retroversion. Glenoid version of +10° anteversion and -15° retroversion was highly unstable, resulting in spontaneous dislocation in one-quarter (10/40) and one-half (25/40) of the specimens anteriorly and posteriorly, respectively, in the absence of an applied dislocation force. The greater tuberosity was observed to engage with the anterior glenoid rim, consistent with Hill-Sachs lesions, 40% more frequently when the dislocation direction was true anterior compared with 35° inferior from the anterior-posterior glenoid axis. The engagement of the greater tuberosity caused an increase in the energy required to dislocate.
  
  
  
  Glenoid version has a direct effect on the force required for a dislocation. An anterior-inferior dislocation direction requires less energy for a dislocation and results in a lower risk of the development of a Hill-Sachs lesion than a direct anterior dislocation direction.
  
  
  
  Consideration should be given to glenoid version when choosing a surgical treatment option for anterior shoulder instability.
authors: Department of Orthopaedic Surgery, Medical University of South Carolina, Charleston, South Carolina, USA.
authors: Josef K
authors: JK
authors: Eichinger
authors: Shoulder Biomotion Laboratory, Massachusetts General Hospital, Boston, Massachusetts, USA.|Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors: Daniel F
authors: DF
authors: Massimini
authors: Department of Orthopaedic Surgery, CHA Bundang Medical Center, CHA University, Seongnam, South Korea.|Department of Orthopedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors: Jungryul
authors: J
authors: Kim
authors: Department of Orthopedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA ldhiggins@partners.org.
authors: Laurence D
authors: LD
authors: Higgins
mesh_terms: D000368:Aged; D000070896:Bankart Lesions / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D061165:Glenoid Cavity / Q000503:physiopathology*; D006801:Humans; D058430:Humeral Head / Q000503:physiopathology; D007593:Joint Instability / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D012399:Rotation; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery
keywords: anatomy; glenohumeral; mechanism; morphology; subluxation