Using The Fat Pad Sign In Pediatric Occult Elbow Fractures: Is It As Reliable As We Think?

Elbow fractures account for about 15% of pediatric fractures but are often occult. The radiographic fat pad sign (FPS) is frequently used to assist with this diagnosis. However, there is limited data regarding the accuracy of using the FPS to make such a diagnosis nor its ability to differentiate fracture location. PURPOSE: To evaluate the sensitivity, specificity, and predictive value of the FPS in diagnosing occult elbow fractures in children. METHODS: Single-center retrospective cohort study of patients 2-21 years-old with acute elbow injury who had an elbow x-ray from 2013-2023. We identified the anterior FPS (AFPS), posterior FPS (PFPS), presence of fracture, and fracture type on initial and follow-up x-rays. For occult fractures initially classified as a clinical diagnosis, bony healing on follow-up x-ray was used for confirmation of elbow fracture. RESULTS: Seven-hundred fifty-two patients met initial inclusion criteria. After randomization of cases via random number generator, 204 total cases were reviewed and 50 (24.51%) were excluded: loss-to-follow-up, non-applicable indications for x-ray, lack of mention of a fat pad. Of the 154 cases included in the final analysis, 88 patients (57.1%) had an elbow fracture. Ninety-nine patients (64.3%) had a positive FPS. The sensitivity of a positive FPS was 94.3% (95% confidence interval (CI), 87.2% to 98.1%) with a specificity of 75.8% (95% CI, 63.6% 85.5%) and a negative predictive value (NPV) of 91% (95% CI, 80.9% to 96%). The sensitivity of an AFPS was 83.9% (95% CI, 74.5% to 90.9%) with a specificity of 84.8% (95% CI, 73.9% to 92.5%) and a NPV of 80% (95% CI, 71% to 86.7%). The sensitivity of a PFPS was 62.1% (95% CI, 51.0% to 72.3%) with a specificity of 89.4% (95% CI, 79.4% to 95.6%), and a NPV of 64.1% (95% CI, 57.4% to 70.3%). CONCLUSION: The presence of an AFPS on elbow x-ray is a strong predictor of occult elbow fracture. The presence of a PFPS is less reliable, but its absence may help rule-out occult fracture. When combined, they are even more predictive of fracture. The location of fracture cannot be distinguished based on the FPS. Therefore, clinicians should rely on the history and physical exam to determine fracture type.