title: Detecting cause of dislocation after total hip arthroplasty by patient-specific four-dimensional motion analysis.
abstract: BACKGROUND
  Dislocation is a major complication after total hip arthroplasty. Prosthesis impingement is considered to be an important cause of dislocation because impingement marks are more frequently found on retrieved cups or liners in patients who have undergone revision surgery because of dislocation (80%-94%) than in those who have undergone reoperation for other reasons (51%-56%). However, it remains a question whether impingement marks are the cause of dislocation or are instead its result. To clarify the issue, it is necessary to confirm noninvasively whether the point of impingement matches the patient's hip position when dislocation occurs.
  
  
  METHODS
  Using four-dimensional patient-specific analysis, we recorded prosthesis impingement in 10 hips with instability after primary total hip arthroplasty when the patients reproduced the dislocation-causing motion.
  
  
  RESULTS
  We found prosthesis impingement to be related to at least instability in 6 of 10 hips with dislocation after primary total hip arthroplasty and in 4 of 4 hips that underwent revision surgery for recurrent dislocation. All impingements occurred between the anterior wall of the liner and the stem neck in posterior dislocation and between the posterior wall of the liner and the stem neck in anterior dislocation. Revision surgery in 1 of those 4 hips revealed 2 impingement marks on the retrieved liner that closely matched the prosthesis impingement point and the dislocation pathway of the metal head on the liner that were detected earlier during motion analysis.
  
  
  CONCLUSIONS
  Prosthesis impingement is an important factor in dislocation after total hip arthroplasty.
authors.affiliation: Department of Orthopedic Surgery, Osaka National Hospital, Osaka, Japan. miki_osaka@nifty.com
authors.forename: Hidenobu
authors.initials: H
authors.lastname: Miki
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sugano
authors.forename: Kazuo
authors.initials: K
authors.lastname: Yonenobu
authors.forename: Kosuke
authors.initials: K
authors.lastname: Tsuda
authors.forename: Maki
authors.initials: M
authors.lastname: Hattori
authors.forename: Naoki
authors.initials: N
authors.lastname: Suzuki
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000379:methods; D005260:Female; D057925:Femoracetabular Impingement / Q000150:complications*; D006617:Hip Dislocation / Q000209:etiology*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods*; D007593:Joint Instability / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D011475:Prosthesis Failure / Q000209:etiology*; D012086:Reoperation