Prevalence of hip fractures in emergency department patients with blunt trauma and negative initial plain-film radiographs

Abstract

Study objectives: The purpose of this study is to determine the prevalence of hip fractures in emergency department (ED) patients with blunt trauma and negative initial plain-film radiographs. Methods: This was a retrospective cohort study. The study was conducted in an academic, community-based ED with an annual patient census of 27,000. Patients presenting to the ED during a 1-year period with blunt trauma to the hip, for whom a plain-film radiograph was obtained and for whom follow-up was subsequently available, composed the study group. Eligible patients were identified by query of a searchable electronic radiographic log and medical record. Clinical data were recorded on a standardized form. Plain film hip radiographs and magnetic resonance imaging (MRI) were ordered at the discretion of the treating physician. Initial plain film radiographic readings were provided at point of care by a board-certified radiologist. All MRIs were reviewed by a radiologist with fellowship training in musculoskeletal imaging. These MRIs were subsequently reviewed by a second similarly trained radiologist to determine interobserver agreement for the diagnosis of fracture. A study author (physician) conducted structured telephone follow-up more than 1 month postvisit or electronic medical record review to determine whether a diagnosis of hip fracture was made after the ED visit. Hip fracture was defined as fracture evident on initial plain film radiograph, fracture evident on MRI of hip performed at ED care, or subsequent diagnosis of hip fracture as determined through follow-up. Ninety-five percent confidence intervals (CIs) were calculated as appropriate. κ Was also calculated to determine interobserver agreement for presence of hip fracture on MRI. Results: Eight hundred ninety-five patients had plain film hip radiographs during the study period. Seven hundred sixty-four (85.3%) patients had follow-up completed and composed the study group. Of the study group, 85.4% were injured in a fall and 2% in motor vehicle crashes. Two hundred nineteen (29%) patients had evidence of fracture on initial plain-film radiographs. Follow-up was subsequently performed for the 545 (71%) patients who did not have evidence of hip fracture on plain-film radiographs. Of these patients, 62 (11.4%) patients had hip MRI performed during the ED visit. MRI identified 24 additional patients with hip fractures. Interobserver agreement for the presence of fracture on MRI was good (κ=.847). For patients with initial plain-film radiographs (–) who did not have a hip MRI, follow-up did not identify any of these patients as having a subsequent diagnosis of fracture. Thus, 24 of 545 (4.4%; 95% CI 3.0% to 6.5%) of patients with (–) initial plain-film radiographs had a hip fracture identified by MRI. The most common fracture not identified by plain-film radiograph was a femoral neck fracture (5/24). Conclusion: In our cohort of ED patients with blunt hip trauma who had negative plain-film radiograph results, we found that 4.4% were subsequently diagnosed with fracture. Further studies are warranted to identify characteristics of patients requiring advanced hip imaging studies.