X-ray Classification and Treatment of Hypotrophic Distraction Osteogenesis in Tibial Bone Transport

This study aims to investigate the X-ray manifestations of hypotrophic new bone formation in tibial bone transport, propose a classification system, and establish standard treatment protocols. A retrospective analysis was conducted on 53 out of 378 cases of hypotrophic distraction osteogenesis in tibial bone transport, performed from January 2012 to December 2023. The cohort included 34 males and 19 females, aged 18 to 71 years (mean age: 37.8 years). Distraction sites comprised 31 cases in the proximal tibia, 7 in the tibial shaft, and 15 in the distal tibia, with defect lengths ranging from 3.3 cm to 22.4 cm (average: 6.3 cm). X-ray imaging categorized hypotrophic bone formation into four types: longitudinal shape (Type A), transverse shape (Type B), worm-bitten shape (Type C), and complete shape (Type D). The treatment protocol included assessment and management of the general condition, callus stimulation through adjustments in transport rate or direction, and surgical interventions. The external fixation index (EFI) assessed healing and mineralization, while limb function was evaluated using the Paley method. Follow-up data over an average of 33.71 ± 11.7 months indicated that 2 cases required amputation, while 51 achieved bone union, restoring mobility in the transported leg. The EFI ranged from 1.47 to 2.73 months/cm, averaging 1.78 ± 0.32 months/cm. Outcomes were classified as excellent in 34 cases, good in 11, fair in 3, and poor in 3, resulting in an overall excellent and good rate of 84.9%. The X-ray characteristics of hypotrophic bone formation in tibial transport can be effectively categorized. A systematic evaluation followed by tailored interventions leads to favorable treatment outcomes. • Introduces a novel and systematic radiographic classification for hypotrophic distraction osteogenesis, a key challenge in Ilizarov bone transport. The system delineates four distinct types (Longitudinal, Transverse, Worm-bitten, Complete) based on specific morphological patterns observed on standard X-rays. • Links specific radiographic patterns to their probable etiologies, providing radiologists with a framework for actionable reporting. For instance, a Transverse pattern (Type B) suggests an excessive distraction rate, while a Worm-bitten pattern (Type C) indicates multifactorial causes like infection or instability. • Demonstrates that radiographic assessment is critical for staging (distraction vs. maturation phase) and selecting appropriate interventions. The study validates that imaging findings directly inform the treatment pathway, from non-invasive callus stimulation techniques to the timing of surgical intervention. • The classification system shows substantial inter- and intra-observer reliability (Kappa = 0.702 and 0.782), establishing it as a reproducible tool for radiologists to communicate findings consistently and guide clinical management in complex cases of bone defect reconstruction.