Specific callus patterns in intermediate stage of distraction osteogenesis bring negative impact on consolidation.

Abstract

Distraction osteogenesis (DO) enables gradual bone elongation through controlled osteotomy and distraction. Existing radiographic and index-based assessments face limitations. Callus pattern classification offers predictive value, but its early applicability across age groups and gap lengths remains unclear. We retrospectively reviewed 129 patients (155 bone segments) who underwent lower limb DO between 2003 and 2023. Patients had a mean age of 37.3 years (5.6-77). The mean distraction length was 53.2 mm (11-174). Radiographs were graded monthly using modified Li classification, depicting two callus consolidation routes: Route 1 (no presence of type 5/8) and Route 2 (presence of type 5/8). Patients were stratified by age (younger: < 25 years; middle: 25-49 years; older: ≥ 50 years) and distraction length (shorter: < 5 cm; longer: ≥ 5 cm). Outcome measures included parameters such as distraction-consolidation time (DCT), healing index (HI), etc., compared by Mann-Whitney test and analysis of variance. Trends of radiographic progress were analyzed by Loess regression. Route 1 demonstrated favorable healing with significantly lower DCT (300.4 vs 381.6 days; p = 0.002) and HI (70.1 vs 89.1 days/cm; p = 0.021). Younger age patients showed negligible differences between two routes. However, middle and older age groups showed delayed consolidation in Route 2, particularly from the high-intermediate callus density grades, Li classification type 6 and 7, onward (p < 0.05). Long distraction gaps further amplified route-based divergence in the trajectory of consolidation. Evolution of callus patterns closely correlate with outcomes of DO. Negative patterns (types 5/8) are associated with delayed healing, particularly in older patients and those with longer distraction lengths. These findings support their use as a timely marker for risk stratification and suggest heightened surveillance or protocol adjustment, such as slowdown of distraction, cyclic distraction-compression dynamization, or additional fixation methods, to optimize outcomes. Level III, retrospective cohort study.