Magnetic resonance imaging identifies occult hip fractures missed by 64-slice computed tomography

Background: Citing the enhanced resolution of 64-slice computed tomography (CT), some clinicians now use CT instead of magnetic resonance imaging (MRI) to detect occult hip fracture.

Objective: Our objective was to determine the incidence of occult hip fractures missed by 64-slice CT but detected by MRI.

Methods: We reviewed the medical records and radiology reports of patients over age 60 years with a hip fracture (acetabular, intertrochanteric, trochanteric, femoral neck, and femoral head) during a 3-year period, January 1, 2007 through December 31, 2009. We also reviewed all hip CT and MRI scans ordered during that period. Occult fractures were those visualized on CT or MRI but with negative plain films. We compared CT and MRI findings, and calculated percentages and 95% confidence intervals (CIs).

Results: Of 235 hip fractures, 211 were visible on initial plain films (90%, 95% CI 85-93%) and 24 (10%, 95% CI 6-15%) were occult. Eighteen occult fractures (7.6%, 95% CI 4.6-11.8%) were identified by CT (MRI not done), one (0.4%, 95% CI 0-2%) by MRI (CT not done), one (0.4%, 95% CI 0-2%) by both CT and MRI, and 4 patients (1.7%, 95% CI 0.5-4.3%) had a positive MRI but negative CT scan.

Conclusion: Although 64-slice CT detected the majority of occult fractures, it missed four (2%) significant fractures detected by MRI. CT scan is helpful in the diagnosis of occult hip fracture, but one should not completely exclude the diagnosis based on a negative 64-slice CT scan in a patient with persistent, localized hip pain who cannot bear weight.