title: Femoroacetabular impingement predisposes to traumatic posterior hip dislocation.
abstract: BACKGROUND
  Traumatic posterior hip dislocation in adults is generally understood to be the result of a high-energy trauma. Aside from reduced femoral antetorsion, morphologic risk factors for dislocation are unknown. We previously noticed that some hips with traumatic posterior dislocations had evidence of morphologic features of femoroacetabular impingement (FAI), therefore, we sought to evaluate that possibility more formally.
  
  
  OBJECTIVE
  We asked whether hips with a traumatic posterior hip dislocation present with (1) a cam-type deformity and/or (2) a retroverted acetabulum.
  
  
  METHODS
  We retrospectively compared the morphologic features of 53 consecutive hips (53 patients) after traumatic posterior hip dislocation with 85 normal hips (44 patients) based on AP pelvic and crosstable axial radiographs. We measured the axial and the lateral alpha angle for detection of a cam deformity and the crossover sign, ischial spine sign, posterior wall sign, retroversion index, and ratio of anterior to posterior acetabular coverage to describe the acetabular orientation.
  
  
  RESULTS
  Hips with traumatic posterior traumatic dislocation were more likely to have cam deformities than were normal hips, in that the hips with dislocation had increased axial and lateral alpha angles. Hips with posterior dislocation also were more likely to be retroverted; dislocated hips had a higher prevalence of a positive crossover sign, ischial spine sign, and posterior wall sign, and they had a higher retroversion index and increased ratio of anterior to posterior acetabular coverage.
  
  
  CONCLUSIONS
  Hips with posterior traumatic dislocation typically present with morphologic features of anterior FAI, including a cam-type deformity and retroverted acetabulum. An explanation for these findings could be that the early interaction between the aspherical femoral head and the prominent acetabular rim acts as a fulcrum, perhaps making these hips more susceptible to traumatic dislocation.
authors: Department of Orthopaedic Surgery, Inselspital, University of Bern, Freiburgstrasse, 3010, Bern, Switzerland.
authors: Simon D
authors: SD
authors: Steppacher
authors: Christoph E
authors: CE
authors: Albers
authors: Klaus A
authors: KA
authors: Siebenrock
authors: Moritz
authors: M
authors: Tannast
authors: Reinhold
authors: R
authors: Ganz
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D060751:Bone Retroversion / Q000175:diagnosis / Q000453:epidemiology*; D015984:Causality; D002648:Child; D015897:Comorbidity; D005260:Female; D057925:Femoracetabular Impingement / Q000175:diagnosis / Q000453:epidemiology*; D006617:Hip Dislocation / Q000175:diagnosis / Q000453:epidemiology*; D025981:Hip Injuries / Q000175:diagnosis / Q000453:epidemiology*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies; D013557:Switzerland / Q000453:epidemiology; D015599:Trauma Severity Indices; D055815:Young Adult