title: Risk factors for the development of heterotopic ossification after acetabular fracture fixation.
abstract: BACKGROUND
  Heterotopic ossification (HO) is a common complication of the operative treatment of acetabular fractures. Although the surgical approach has been shown to correlate with the development of ectopic bone, specific risk factors have not been elucidated.
  
  
  OBJECTIVE
  The purposes of this study were to determine specific risk factors associated with the development of severe HO and the frequency with which patients develop severe HO after acetabular fracture fixation through an isolated Kocher-Langenbeck approach.
  
  
  METHODS
  Using an institutional orthopaedic trauma database at a regional Level I trauma center, patients undergoing open treatment of acetabular fractures during the study period (January 2000 to January 2010) were identified. A review of medical records and imaging studies was performed on 508 patients who were treated by the senior author (MR) through an isolated Kocher-Langenbeck approach. During the study period, the senior author used indomethacin for HO prophylaxis in patients who had ipsilateral femur fracture treated with antegrade reamed medullary nailing or severe local soft tissue injury; 49 (10%) of the patients he treated with the Kocher-Langenbeck approach received prophylaxis, and they were excluded from this study, leaving a total of 459 patients who met inclusion criteria. Of those, 147 (29%) were lost to followup or did not have radiographs both before and at a minimum of 6 weeks (median, 1 week; range, 0-3 weeks), leaving 312 (61% of the patients treated with the Kocher-Langenbeck approach during this time) available for this analysis. Demographic data as well as information related to cause of injury, associated periacetabular findings, other system injuries, and treatment were gathered. Final followup radiographs were assessed for the presence of ectopic bone by two of the authors (TJO, AS) using the modified Brooker classification. Logistic regression was performed to identify possible predictors of development of severe ectopic bone.
  
  
  RESULTS
  The only predictor we identified for the development of severe HO was the need for prolonged mechanical ventilation (odds ratio, 7.1; 95% confidence interval, 2.9-17.3; p=0.001). Injury Severity Score, sex, presence of comminution, femoral head impaction, dislocation, degloving injury, debris in the joint, number of other fractures, and head and chest Abbreviated Injury Score>2 did not correlate with severe HO. Severe HO (Brooker Class III or IV) developed in 38 of 312 patients (12%).
  
  
  CONCLUSIONS
  Patients with prolonged mechanical ventilation might benefit from HO prophylaxis given the increased risk of developing severe HO in this patient population. However, future prospective studies need to be performed to verify this finding given the fact that a considerable number of patients were prophylactically treated in this study.
  
  
  METHODS
  Level IV, prognosticstudy. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery and Sports Medicine, Harborview Medical Center, 325 Ninth Avenue, Box 359798, Seattle, WA, 98104, USA, Rezaf2@uw.edu.
authors.forename: Reza
authors.initials: R
authors.lastname: Firoozabadi
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: O'Mara
authors.forename: Alan
authors.initials: A
authors.lastname: Swenson
authors.forename: Julie
authors.initials: J
authors.lastname: Agel
authors.forename: John D
authors.initials: JD
authors.lastname: Beck
authors.forename: Milton
authors.initials: M
authors.lastname: Routt
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000293:injuries* / Q000601:surgery*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015984:Causality; D002648:Child; D015897:Comorbidity; D005260:Female; D005500:Follow-Up Studies; D005593:Fracture Fixation, Internal / Q000009:adverse effects; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000601:surgery*; D006801:Humans; D007213:Indomethacin / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009999:Ossification, Heterotopic / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000517:prevention & control*; D011859:Radiography; D012121:Respiration, Artificial / Q000706:statistics & numerical data*; D012307:Risk Factors; D055815:Young Adult
chemical_list: D007213:Indomethacin