Relationship Between Blurred Boundary and Neurological Deficits in Extension-Type Pediatric Supracondylar Humeral Fractures.

Background: Supracondylar humeral fractures are common in children and are associated with nerve damage. However, the primary complaint may be unclear due to pain, and examination can be difficult in young children. This study aimed to introduce and validate the blurred boundary (BB) as a new radiographic measure. Methods: This retrospective study analyzed extension-type pediatric supracondylar humeral fractures treated surgically at Mizoguchi Hospital between January 2017 and October 2023, with a minimum postoperative follow-up of 60 days. Data collected included age, sex, height, weight, body mass index, fracture type (Wilkins-modified Gartland classification), surgical method, neurological injury status, and recovery period. BB positivity was defined as the absence or blurring of a clear line between the muscle and subcutaneous fat on lateral elbow x-rays. Type IIB and Type III cases, which are at high risk of nerve injury, were included in the statistical analysis of this study and were classified into 2 groups based on the presence or absence of nerve injury. Univariate and multivariate logistic regression analyses were performed to identify risk factors. Results: Neurological injuries were observed in 30 patients (16.0%), of which 18 cases (60%) were diagnosed preoperatively and 12 cases (40%) were not diagnosed before surgery. The fracture distribution included 43 cases of Type IIB (37.7%) and 71 cases of Type III (62.3%). BB was positive in 52.6% of these cases, with a higher prevalence in the nerve injury group (76.7% vs. 44.0%, p = 0.003). Multivariate analysis identified BB positivity (odds ratio [OR]: 4.15, 95% confidence interval [CI]: 1.52 to 11.30, p = 0.005) as an independent risk factor for nerve injury. BB demonstrated a sensitivity of 76.7%, which was higher than the proportion of cases diagnosed preoperatively. The specificity, positive predictive value, and negative predictive value were 56.0%, 38.3%, and 87.0%, respectively, with an overall accuracy of 61.4%. Conclusions: BB was closely associated with the presence of nerve injury, suggesting that BB may be a useful adjunct in identifying patients at higher risk of neurological injury, particularly to augment the limited sensitivity of clinical examination in pediatric cases.