Sat., 10/16/10 Polytrauma & Femur, Paper #75, 11:26 am OTA-2010
CT Scans Have a High Rate of Missed Femoral Neck Fractures
Robert V. O’Toole, MD1; Lindsay Dancy, BS1; Adam R. Dietz, MD1;
Aaron J. Johnson, MD, MS1; Andrew N. Pollak, MD1; Gregory M. Osgood, MD1;
Jason W. Nascone, MD1; Marcus F. Sciadini, MD1; Renan C. Castillo, PhD2;
1R Adams Cowley Shock Trauma Center, Department of Orthopaedics, University of Maryland
Medical School, Baltimore, Maryland, USA;
2Center for Injury Research and Policy, Johns Hopkins Bloomberg School of Public Health,
Baltimore, Maryland, USA
Purpose: Femoral neck fractures occurring with ipsilateral femoral shaft fractures have been associated with high rates of missed diagnosis. Based on the results of our previously presented pilot study on displaced femoral neck fractures, our hypothesis was that axial CT would be superior to plain radiographs at detecting both displaced and nondisplaced femoral neck fractures.
Methods: Image sets, including axial CT, AP pelvis, and AP femur radiographs, were created for 28 patients with ipsilateral femoral neck and shaft fractures, and 60 patients with isolated femoral shaft fractures. Images were deidentified, randomized, and viewed on computer workstations by 5 trauma fellowship–trained orthopaedic surgeons who were blinded to treatment or diagnosis. Interobserver agreement, sensitivity, specificity, post-test positive probability, and post-test negative probability were all calculated, adjusting for the incidence of ipsilateral neck and shaft fractures in clinical practice (9%). To further validate our findings, we performed a retrospective review of all patients with ipsilateral femoral shaft and neck fractures between 2003 and 2008, when our center used a protocol of routine CT scan for all patients with femoral shaft fractures
Results: Interobserver reliability indicated “substantial agreement” (kappa >0.66) for all imaging modalities. Sensitivity was generally poor (AP femur film, 0.51; AP pelvis, 0.56; CT, 0.64), and specificity was better (AP femur film, 0.95; AP pelvis, 0.96; CT, 0.96) for all imaging modalities. Positive probability was low (AP femur, 0.48; AP pelvis, 0.58; CT, 0.52) but the negative predictive ability was high (AP femur, 0.95; AP pelvis, 0.96; CT, 0.96). For a subset of 10 neck fractures that were not discovered clinically until intraoperative imaging, only 1 CT scan was read as positive by the 5 attending physicians (1 of 50 true positives for this subset of the study). This result mirrored our clinical experience where 25% (15 of 59) of femoral neck fractures were missed preoperatively, despite routine use of CT scans.
Conclusions: Clinicians should be aware that in both our blinded study evaluation and in our clinical experience, a normal CT scan does not guarantee the absence of femoral neck fracture. These data contradict our pilot study that focused only on displaced femoral neck fractures and demonstrated better performance of the imaging studies. In clinical practice, both plain films and CT scans have a rate of missed femoral neck fractures on the order of >25%, emphasizing the importance of intraoperative and postoperative imaging in detecting minimally displaced femoral neck fractures in association with femoral shaft fractures.
Alphabetical Disclosure Listing (292K PDF)
• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant.