title: An analysis of capsular area in patients with anterior, posterior, and multidirectional shoulder instability.
abstract: BACKGROUND
  Although increased capsular volume has been implicated in shoulder instability, there is a paucity of clinical evidence to quantify the size of the capsule with specific instability conditions of the shoulder.
  
  
  OBJECTIVE
  Shoulder capsular area, as measured by magnetic resonance arthrography, is increased with specific patterns of shoulder instability.
  
  
  METHODS
  Cross-sectional study; Level of evidence, 4.
  
  
  METHODS
  During an 8-month period, all patients with a diagnosis of anterior (n = 19), posterior (n = 14), or multidirectional (n = 13) instability of the shoulder and who were assessed with a magnetic resonance arthrogram were reviewed. A group of 10 control patients without clinical instability were also identified. The magnetic resonance arthrograms of all groups were randomly mixed, and 5 reviewers recorded measures of capsular length and area and determined labral abnormalities. The magnetic resonance arthrogram measurements were compared between groups, and interobserver agreement was determined.
  
  
  RESULTS
  The cross-sectional area of the capsule was increased in patients with posterior (P = .017) or multidirectional instability (P = .021) versus controls, but not in patients with anterior instability. Additionally, the posteroinferior cross-sectional area was increased in patients with posterior (P = .001), multidirectional (P = .003), and anterior (P = .008) instability. In patients with a posterior labral tear, the mean axial (P = .043) and mean posteroinferior sagittal cross-sectional area (P = .011) was increased, but there were no differences in cross-sectional area for those with an anterior labral tear. The overall interobserver reliability was very good (correlation coefficient range, 0.68-0.94).
  
  
  CONCLUSIONS
  Our results reinforce the concept that capsular elongation and laxity, either preexisting or acquired, play a role in certain instability conditions of the shoulder. Additional work is needed to determine how to correlate surgical decision making with the cross-sectional area measurements demonstrated in this study.
authors.affiliation: Department of Orthopaedic Surgery, Division of Sports Surgery, Naval Medical Center San Diego, San Diego, California 92134-1112, USA.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Dewing
authors.forename: Frank
authors.initials: F
authors.lastname: McCormick
authors.forename: S Josh
authors.initials: SJ
authors.lastname: Bell
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Solomon
authors.forename: Mark
authors.initials: M
authors.lastname: Stanley
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Rooney
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Provencher
mesh_terms: D000328:Adult; D006801:Humans; D017746:Joint Capsule / Q000473:pathology*; D007593:Joint Instability / Q000473:pathology*; D008875:Middle Aged; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000473:pathology*