title: An analysis of the rotator interval in patients with anterior, posterior, and multidirectional shoulder instability.
abstract: OBJECTIVE
  To describe anatomic measurements of the rotator interval (RI) on magnetic resonance arthrogram (MRA) images and to assess the relationship between increased dimensions of the RI and instability conditions of the shoulder.
  
  
  METHODS
  Three groups of patients with clinical instability were treated arthroscopically (anterior [A = 19 patients], posterior [P = 14 patients], and multidirectional [M = 13 patients]), and a group of 10 control patients without clinical instability were also identified. The MRAs of all groups were randomized, and 5 blinded reviewers recorded RI anatomic measurements of: (1) sagittal measures of the distance between the subscapularis (SSc) and supraspinatus (SS) tendons at 3 anatomic landmarks across the RI, and (2) the sagittal position of the long head of the biceps (LHB) relative to the most anterior aspect of the SS.
  
  
  RESULTS
  The rotator interval distance between the SS and SSc tendons was nearly identical for all groups of instability, and was also not different from control groups. On the sagittal oblique sequences, the distance from the LHB tendon to the anterior edge of the SS tendon was significantly increased in posterior (7.4 mm) instability versus both the control group (2.4 mm; P = .025) and those with anterior instability (4.5 mm; P = .041), with the LHB in a consistent anterior position. The remainder of the measures was not statistically different between the groups.
  
  
  CONCLUSIONS
  The distance between the SS and SSc and the overall size of the RI was well preserved in all instability patterns and control conditions. The LHB tendon assumes a more anterior position relative to the supraspinatus tendon in patients with posterior instability versus those patients with anterior instability or those without clinical instability. Additional work is necessary to further define objective radiographic evidence of RI insufficiency in patients with shoulder instability.
  
  
  METHODS
  Level III, prognostic case-control study.
authors.affiliation: Department of Orthopaedic Surgery, Division of Sports Surgery, Naval Medical Center San Diego, San Diego, California 92134-1112, USA. matthew.provencher@med.navy.mil
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Provencher
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Dewing
authors.forename: S Josh
authors.initials: SJ
authors.lastname: Bell
authors.forename: Frank
authors.initials: F
authors.lastname: McCormick
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Solomon
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Rooney
authors.forename: Mark
authors.initials: M
authors.lastname: Stanley
mesh_terms: D000328:Adult; D001182:Arthroscopy; D016022:Case-Control Studies; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis* / Q000601:surgery; D008023:Ligaments, Articular / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D017006:Rotator Cuff / Q000473:pathology*; D012785:Shoulder Joint / Q000473:pathology*; D016037:Single-Blind Method