Abstract: BACKGROUND: Bone transfer operation has gradually become the “gold standard” for the treatment of tibial bone defects. During bone regeneration and mineralization, the morphology of the callus in the extension area of the tibia was significantly different. The study of the relationship of the morphology of the callus in the extension area with bone healing and limb function can provide clinical guidance.  
OBJECTIVE: To explore the relationship of the morphology of three types of callus in the extension area after tibial bone transfer with bone healing and limb function.
METHODS: A retrospective analysis was performed in 86 patients with large segmental tibial bone defect who were admitted from May 2014 to June 2022. According to the three types of callus in the extension area, it could be divided into concave type, uniform type and bulging type. There were 14 cases of concave type, 60 cases of uniform type, and 12 cases of bulging type. All patients were treated with single-plane bone transport for the treatment of large segmental tibial bone defects. During the period, the central transverse diameter of the bone regeneration area, the transverse diameter of both ends of the osteotomy, the length of extension, the bone transport time, the mineralization time of the bone regeneration area, the healing index and related complications were recorded. Bone healing and limb function were assessed according to the Association for the Study and Application of Ilizarov's Methods score.  
RESULTS AND CONCLUSION: (1) All 86 patients were followed up after operation for 21 to 37 months, with a mean of (29.0±6.7) months. No internal fixation infection occurred during the treatment of the three types of callus in the extension area, and all of them achieved bony union. (2) There was no statistical significance in the preoperative general data of patients of the three groups (P > 0.05), and they were comparable. (3) The healing indices of concave type, uniform type and bulging type were (73.5±25.4), (51.1±18.8), and (39.6±7.9) d/cm, respectively, and the comparison between groups was statistically significant (P < 0.05). (4) According to Association for the Study and Application of Ilizarov's Methods bone healing score, there were excellent in 11 cases and poor in 3 cases in the concave group, excellent in 53 cases and poor in 7 cases in the uniform group, and excellent in 12 cases and poor in 0 cases in the bulging group; there was no significant difference between the groups (P > 0.05). (5) According to the Association for the Study and Application of Ilizarov's Methods limb function results, there were excellent in 3 cases and good in 11 cases in the concave group, excellent in 17 cases and good in 43 cases in the uniform group, and excellent in 4 cases and good in 8 cases in the bulging group; there was no significant difference between the groups (P > 0.05). (6) The results showed that there was no significant difference among the concave type, the uniform type and the bulging type in the Association for the Study and Application of Ilizarov's Methods bone healing and affected limb function scoring standards. However, there was a significant difference in the comparison of the healing index, the concave type > the uniform type > the bulging type, namely, the bulging type had the shortest healing time, followed by the uniform type, and the concave type was slowest.

Key words: tibial bone defect, callus morphology, bone transport, healing index, distraction osteogenesis