title: What factors affect posterior dislocation distance in THA?
abstract: BACKGROUND
  Dislocation remains common after total hip arthroplasty. Efforts have been made to identify and minimize risk factors. One such factor, jump distance, or the distance the femoral head must travel before dislocating, has been poorly characterized with respect to three-dimensional kinematics.
  
  
  OBJECTIVE
  We therefore determined: (1) the three-dimensional stability of four different component designs; (2) whether the degree of abduction and anteversion affects the stability; (3) whether pelvic inclination angles affected stability; and (4) which combination of these three factors had the greatest stability.
  
  
  METHODS
  We created a positionable three-dimensional model of a THA. Acetabular components were modeled in various abduction and anteversion angles and in two different pelvic inclinations which simulate standing and chair-rising activities.
  
  
  RESULTS
  The posterior horizontal dislocation distance increased as inclination angle and femoral head size increased. The 48-mm resurfacing typically had lower jump distances and was at risk of posterior edge loading at 30° inclination. The highest jump distance for all positions and activities occurred with the dual-mobility bearing.
  
  
  CONCLUSIONS
  These findings suggest that monoblock cups require extremely accurate positioning for low dislocation risk and that pelvic orientation may increase dislocation risks.
  
  
  CONCLUSIONS
  As a result of the dual-mobility designs having the greatest resistance to dislocation, these cups may be appropriate for patients who are at risk for dislocation in difficult primary situations and in revision hip arthroplasty procedures in which proper component orientation may be less likely to be achieved.
authors.affiliation: Stryker Orthopaedics, Mahwah, NJ, USA.
authors.forename: Jim
authors.initials: J
authors.lastname: Nevelos
authors.forename: Aaron
authors.initials: A
authors.lastname: Johnson
authors.forename: Christopher
authors.initials: C
authors.lastname: Heffernan
authors.forename: James
authors.initials: J
authors.lastname: Macintyre
authors.forename: David C
authors.initials: DC
authors.lastname: Markel
authors.forename: Michael A
authors.initials: MA
authors.lastname: Mont
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D006617:Hip Dislocation / Q000209:etiology*; D006622:Hip Prosthesis; D006801:Humans; D008953:Models, Anatomic; D011187:Posture; D011475:Prosthesis Failure; D016059:Range of Motion, Articular; D012307:Risk Factors