title: The effect of defect orientation and size on glenohumeral instability: a biomechanical analysis.
abstract: OBJECTIVE
  The purpose of this study was to determine the relationship between bony stability and percentage of anterior glenoid bone loss and the effect of bone loss orientation.
  
  
  METHODS
  Twelve cadaveric shoulders were studied. Glenoid bone defects were simulated in two different osteotomy angles: 0° and 45° to the superoinferior (SI) axis of the glenoid. The force and displacement required for dislocation were measured under two compressive forces of 40 and 60N. Testing was performed for the intact glenoid and glenoid defects of 2, 4, 6, 8, and 10 mm from the anterior margin.
  
  
  RESULTS
  The maximum force for dislocation with the 2-mm glenoid defect was significantly decreased compared with intact glenoid (p = 0.01), and this force also significantly decreased with each increase in defect size (p < 0.05). The dislocation force for 45° osteotomy was significantly higher than that for 0° osteotomy for all defect widths up to 8 mm with 40N compression and 6 mm with 60N compression (p < 0.001). The displacement at dislocation did not significantly decrease until the 8-mm defect with the 45° osteotomy but significantly decreased with the 4-mm defect with the 0° osteotomy. The required force for dislocation with 60N compression was significantly higher than that with 40N compression for all osteotomy sizes and orientations.
  
  
  CONCLUSIONS
  The decrease in stability even with glenoid bone loss as small as 2 mm or 7.5 % of the glenoid width suggests that bony restoration is recommended whenever any bone loss exists. Bone defects parallel to SI axis may be more susceptible to recurrent instability, and shoulder muscle strengthening exercises may increase glenohumeral compressive force and thus improve glenohumeral stability. Bony restoration is recommended whenever bone loss exists even with small bone fragments particularly those in line with the superior-inferior axis of the glenoid.
authors.affiliation: Department of Orthopaedic Surgery, Ewha Womans University, Seoul, Korea.
authors.forename: Sang-Jin
authors.initials: SJ
authors.lastname: Shin
authors.affiliation: Department of Orthopaedic Surgery, Ewha Womans University, Seoul, Korea.
authors.forename: Young Won
authors.initials: YW
authors.lastname: Ko
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, 5901 East 7th, Street (09/151), Long Beach, CA, 90822, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Scott
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, 5901 East 7th, Street (09/151), Long Beach, CA, 90822, USA.
authors.forename: Michelle H
authors.initials: MH
authors.lastname: McGarry
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, 5901 East 7th, Street (09/151), Long Beach, CA, 90822, USA. tqlee@va.gov.|Department of Orthopaedic Surgery, University of California, Irvine, CA, USA. tqlee@va.gov.|Department of Biomedical Engineering, University of California, Irvine, CA, USA. tqlee@va.gov.
authors.forename: Thay Q
authors.initials: TQ
authors.lastname: Lee
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000473:pathology* / Q000503:physiopathology* / Q000601:surgery; D008875:Middle Aged; D010027:Osteotomy; D012540:Scapula / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D012783:Shoulder Dislocation / Q000209:etiology / Q000601:surgery; D012785:Shoulder Joint / Q000473:pathology* / Q000503:physiopathology* / Q000601:surgery
keywords: Anterior shoulder instability; Bony restoration procedure; Glenoid bone loss; Glenoid defect orientation; Glenoid defect size; Rehabilitation; Shoulder muscle strengthening