Extent of the low-density line is associated with time to fracture in children with congenital anterolateral bowing of the tibia: a retrospective survival analysis.

Introduction: Congenital anterolateral bowing of the tibia (ALBT) represents a critical pre-fracture stage in the progression toward congenital pseudarthrosis of the tibia. The low-density line (LDL) is a characteristic radiographic feature, but its temporal relationship with fracture risk remains unclear. This study aimed to evaluate the association between LDL extent and time to fracture and to identify clinically relevant temporal risk patterns. Methods: In this retrospective cohort study, eligible participants were children diagnosed with ALBT and radiographically confirmed LDL who were treated at Hunan Children's Hospital between January 2015 and December 2020. LDL extent was quantified as the proportion of the LDL area ( Results: A total of 40 children were included. Fractures occurred in 31 (77.5%), with 61.3% of fracture events occurring within 6 months after LDL detection. The Kaplan-Meier-estimated cumulative fracture probability at 6 months was 47.5%. Kaplan-Meier analysis showed significant differences in fracture-free survival among LDL proportion groups (log-rank Conclusion: In this LDL-positive pediatric ALBT cohort, LDL proportion may be associated with earlier fracture timing. The clustering of fracture events within the first 6 months after LDL detection may indicate a potential period for closer monitoring. These findings provide preliminary evidence supporting LDL as an imaging marker for time-based risk stratification. Further validation in larger prospective studies is required.