Diagnosis of femoral neck fracture associated with femoral shaft fracture: blinded comparison of computed tomography and plain radiography.

OBJECTIVE

Femoral neck fractures that are associated with femoral shaft fractures have historically been associated with high rates of missed diagnosis. Despite the potentially serious consequences of a missed femoral neck fracture, little work has been conducted to rigorously evaluate the ability of commonly used imaging studies to detect such fractures. Our hypothesis was that axial-view computed tomography is superior to plain radiography at detecting femoral neck fractures.

DESIGN

Blinded assessment of a randomized image set that included axial-view computed tomographic scans of the pelvis, anteroposterior-view radiographs of the pelvis, and anteroposterior-view radiographs of the femur.

SETTING

Academic trauma center.

PATIENTS

Twenty-eight patients who had femoral shaft fractures with femoral neck fractures and 60 patients who had femoral shaft fractures without femoral neck fractures.

INTERVENTION

Images that were stripped of demographic data were independently viewed in random order on computer workstations by 5 trauma fellowship-trained orthopaedic surgeons who were blinded to treatment and diagnosis.

MAIN OUTCOME MEASUREMENTS

Sensitivity, specificity, positive post-test probability, and 1 minus negative post-test probability were calculated for diagnosing femoral neck fracture based on each image type.

RESULTS

Interobserver reliability showed "substantial agreement" (kappa > 0.65) for all imaging modalities, indicating that the surgeons had a high level of agreement. All 3 imaging sets had high specificity (>94%) and 1 minus negative post-test probability (>95%) but had poor sensitivity (<65%) and positive post-test probability (<58%). False positives and false negatives were equally likely for all imaging modalities (P > 0.2).

CONCLUSIONS

Plain radiography and computed tomography have rates of missed femoral neck fractures that are similar and substantial, with a sensitivity of only 56%-64%. Our data emphasize the importance of intraoperative and postoperative imaging in detecting nondisplaced femoral neck fractures in association with femoral shaft fractures.