title: Dislocation of bipolar hip hemiarthroplasty through a postero-lateral approach for femoral neck fractures: A cohort study.
abstract: OBJECTIVE
  To analyze postoperative global femoral offset (FO), leg length discrepancy (LLD) and Wiberg angle as risk factors for prosthetic dislocation after treatment with bipolar hemiarthoplasty (HA) through a postero-lateral approach for femoral neck fracture (FNF).
  
  
  METHODS
  Three hundred and seventy three patients treated with a cemented bipolar HA through a postero-lateral approach between January 2006 and December 2013 were included in a cohort study with a follow-up time ranging from 6 months to 7 years. Radiographs and all surgical records were reviewed regarding Global FO, LLD and Wiberg angle. We compared stable hips without dislocation to those with either a single dislocation and those with recurrent instability.
  
  
  RESULTS
  Three hundred and twenty eight hips fulfilled the inclusion criteria and were analyzed in the study. The incidence of prosthetic dislocation was 10.7% (36/373). The mean time from surgery to first dislocation was 3.9 months (0-47) and 62.5% had recurrent dislocations. Patients with dislocation had a statistically significantly decreased postoperative global FO (-6.4 mm vs. -2.8 mm, p = 0.04), LLD (-2 vs. 1.5 mm, p = 0.03) and smaller Wiberg angle (40° vs. 46°, p = 0.01) on the operated side compared with the rest of cohort. In comparison to age and sex-matched control groups from the cohort, the difference in the radiographic parameters were significant in patients with recurrent dislocations but not in patients with a single dislocation.
  
  
  CONCLUSIONS
  Patients with recurrent dislocations had a decreased postoperative global FO, shorter leg and shallower acetabulum on the operated side compared with their controls. These factors might decrease the soft-tissue tension around the operated hip and predispose to dislocation.
  
  
  METHODS
  Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Surgical and Perioperative Sciences (Orthopaedics), Sundsvall Hospital, Umeå University, 85186, Sundsvall, Sweden, sebastian.mukka@gmail.com.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Mukka
authors.forename: Jenny
authors.initials: J
authors.lastname: Lindqvist
authors.forename: Sara
authors.initials: S
authors.lastname: Peyda
authors.forename: Cyrus
authors.initials: C
authors.lastname: Brodén
authors.forename: Sarwar
authors.initials: S
authors.lastname: Mahmood
authors.forename: Hamid
authors.initials: H
authors.lastname: Hassany
authors.forename: Arkan
authors.initials: A
authors.lastname: Sayed-Noor
mesh_terms: D000328:Adult; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D015331:Cohort Studies; D005260:Female; D005265:Femoral Neck Fractures / Q000601:surgery*; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery*; D062785:Hemiarthroplasty / Q000009:adverse effects*; D006617:Hip Dislocation / Q000209:etiology / Q000601:surgery*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D015994:Incidence; D007870:Leg Length Inequality / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012307:Risk Factors; D013548:Sweden