title: Defect Characteristics of Reverse Hill-Sachs Lesions.
abstract: BACKGROUND
  Little scientific evidence regarding reverse Hill-Sachs lesions (RHSLs) in posterior shoulder instability exists. Recently, standardized measurement methods of the size and localization were introduced, and the biomechanical effect of the extent and position of the defects on the risk of re-engagement was determined.
  
  
  OBJECTIVE
  To analyze the characteristics and patterns of RHSLs in a large case series using standardized measurements and to interpret the results based on the newly available biomechanical findings.
  
  
  METHODS
  Case series; Level of evidence, 4.
  
  
  METHODS
  In this multicenter study, 102 cases of RHSLs in 99 patients were collected from 7 different shoulder centers between 2004 and 2013. Patient- as well as injury-specific information was gathered, and defect characteristics in terms of the size, localization, and depth index were determined on computed tomography or magnetic resonance imaging scans by means of standardized measurements. Additionally, the position (gamma angle) of the posterior defect margin as a predictor of re-engagement was analyzed.
  
  
  RESULTS
  Three types of an RHSL were distinguished based on the pathogenesis and chronicity of the lesion: dislocation (D), locked dislocation (LD), and chronic locked dislocation (CLD). While the localization of the defects did not vary significantly between the subgroups (P = .072), their mean size differed signficantly (D: 32.6° ± 11.7°, LD: 49.4° ± 17.2°, CLD: 64.1° ± 20.7°; P < .001). The mean gamma angle as a predictor of re-engagement was similarly significantly different between groups (D: 83.8° ± 14.5°, LD: 96.5° ± 17.9°, CLD: 108.7° ± 18.4°; P < .001). The orientation of the posterior defect margin was consistently quite parallel to the humeral shaft axis, with a mean difference of 0.3° ± 8.1°.
  
  
  CONCLUSIONS
  The distinction between the 3 different RHSL types based on the pathogenesis and chronicity of the defect helps identify defects prone to re-engagement. The gamma angle as a measurement of the position of the posterior defect margin and therefore a predictor of re-engagement varies significantly between the defect types.
authors.affiliation: Department of Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria philipp.moroder@pmu.ac.at.
authors.forename: Philipp
authors.initials: P
authors.lastname: Moroder
authors.affiliation: Department of Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria Department of Shoulder and Elbow Surgery, ATOS Clinic Munich, Munich, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Tauber
authors.affiliation: Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Scheibel
authors.affiliation: Department of Shoulder and Elbow Surgery, ATOS Clinic Munich, Munich, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Habermeyer
authors.affiliation: Department for Orthopaedic Sports Medicine, Technical University Munich, Munich, Germany.
authors.forename: Andreas B
authors.initials: AB
authors.lastname: Imhoff
authors.affiliation: Department of Orthopedics and Tumor Orthopedics, University Hospital Muenster, Muenster, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Liem
authors.affiliation: Department of Trauma and Reconstructive Surgery, Friederikenstift Hospital Hanover, Hanover, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Lill
authors.affiliation: Department for Orthopaedic Sports Medicine, Technical University Munich, Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Buchmann
authors.affiliation: Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Wolke
authors.affiliation: Department for Orthopaedic Sports Medicine, Technical University Munich, Munich, Germany.
authors.forename: Alberto
authors.initials: A
authors.lastname: Guevara-Alvarez
authors.affiliation: Department of Trauma and Reconstructive Surgery, Friederikenstift Hospital Hanover, Hanover, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Salmoukas
authors.affiliation: Department of Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Herbert
authors.initials: H
authors.lastname: Resch
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging* / Q000473:pathology; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000209:etiology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D012008:Recurrence; D012782:Shoulder / Q000000981:diagnostic imaging; D012783:Shoulder Dislocation / Q000150:complications / Q000000981:diagnostic imaging* / Q000473:pathology; D012784:Shoulder Fractures / Q000150:complications / Q000000981:diagnostic imaging* / Q000473:pathology; D012785:Shoulder Joint / Q000000981:diagnostic imaging* / Q000473:pathology; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: chronic locked dislocation; gamma angle; locked dislocation; posterior shoulder dislocation; posterior shoulder instability; reverse Hill-Sachs lesion