Understanding the susceptibility to lateral condyle fracture by analyzing unaffected Baumann's angle in children with distal humeral fracture.

Background: Previous studies have shown that posttraumatic cubitus varus deformity in children is somehow related to subsequent humeral lateral condyle fracture. Moreover, we had previously encountered an exactly similar case. In this study, we aim to understand whether there is a morphological difference between pediatric supracondylar and lateral condyle fracture of the humerus by comparing Baumann's angle of the unaffected elbow.

Methods: We conducted a retrospective evaluation of 40 cases of supracondylar fractures (36 boys, 4 girls) and 20 cases of lateral condyle fractures (16 boys, 4 girls) at a single facility between January 2014 and December 2018. The unaffected Baumann's angles and lateral capitellohumeral angles of both groups were measured by two orthopedic surgeons and analyzed using Welch's t-test. The effect size was also calculated using Cohen's d, and intraclass correlation coefficients were applied for intra-rater and inter-rater reliability.

Results: The average age of patients in the supracondylar fracture group was 6.78 years and that in the lateral condyle fracture group was 5.70 years. No significant differences were observed between gender and fracture type, between laterality and fracture type, and in the lateral capitellohumeral angles between the groups. Baumann's angle was significantly less in the lateral condyle fracture group (17.27° ± 4.68°) than in the supracondylar fracture group (20.28° ± 3.10°) as analyzed by Welch's t-test (p = 0.015). The effect size was 0.76. Each of the intra-rater reliabilities were 0.97 and 0.96, whereas the inter-rater reliability was 0.75.

Conclusions: A significant morphological difference was found between the supracondylar fracture group and the lateral condyle fracture group. The loss of Baumann's angle which tends to occur after the healing of supracondylar fracture may increase the susceptibility to lateral condyle fracture. Orthopedic surgeons should repair and fix supracondylar fractures appropriately to avoid an ipsilateral second fracture, such as lateral condyle fracture.