title: Low early and late dislocation rates with 36- and 40-mm heads in patients at high risk for dislocation.
abstract: BACKGROUND
  Large (36- and 40-mm) femoral heads with highly crosslinked polyethylene liners were introduced to reduce the risk of dislocation after primary total hip arthroplasty (THA), but it is unclear whether the risk is reduced and whether there is osteolysis or liner fracture.
  
  
  OBJECTIVE
  We therefore determined (1) the incidence of early and late (> 5 years) dislocation; (2) the rate of femoral and acetabular component loosening and revision; and (3) the rate of liner fracture and pelvic osteolysis.
  
  
  METHODS
  We retrospectively reviewed 112 patients presumed at high risk for dislocation who had 122 primary THAs: 108 with 36-mm and 14 with 40-mm femoral heads. The risk factors were: age > 75 years (80 hips); proximal femur fracture (18); history of contralateral dislocation (two); history of alcohol abuse (two); large acetabulum > 60 mm (six); and other (14). Patients were evaluated for early (< 1 year) and late (> 5 years) dislocation; rate of reoperation; clinical result with Harris hip score; and standard radiographic analysis for radiolucent lines and osteolysis.
  
  
  RESULTS
  The rate of early dislocation was 4% (five of 122 hips), all with a 36-mm head. There were no late dislocations in 74 hips followed for 5 to 10 years, no revision for acetabular or femoral loosening, and no liner fractured. There were no hips with pelvic osteolysis and seven hips with an acetabular radiolucent line.
  
  
  CONCLUSIONS
  The 36- and 40-mm femoral heads were associated with a low risk of dislocation in high-risk patients undergoing primary THA with no osteolysis or liner fracture.
  
  
  METHODS
  Level IV, therapeutic study. See the Guidelines for Authors for a complete description of level of evidence.
authors.affiliation: Chapel Hill Orthopedics Surgery and Sports Medicine, 101 Conner Drive, Suite 200, Chapel Hill, NC 27514, USA. paul.lachiewicz@gmail.com
authors.forename: Paul F
authors.initials: PF
authors.lastname: Lachiewicz
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Soileau
mesh_terms: D000077:Acetabulum / Q000601:surgery; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D005260:Female; D006617:Hip Dislocation / Q000453:epidemiology* / Q000209:etiology; D006621:Hip Joint / Q000601:surgery; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010014:Osteolysis / Q000453:epidemiology* / Q000209:etiology; D011446:Prospective Studies; D011475:Prosthesis Failure; D012189:Retrospective Studies; D012306:Risk; D016896:Treatment Outcome