Background <p>Infected nonunion after severe pilon fracture remains a major challenge in limb reconstruction, particularly when chronic infection and repeated debridement result in severe metaphyseal bone loss and compromised distal tibial morphology. In such cases, conventional resection to create a flat arthrodesis surface may enlarge the defect and substantially prolong bone transport duration. We report a bone-preserving reconstructive strategy using tapered distal docking and fibular-assisted ankle arthrodesis during bone transport for infected pilon fracture nonunion.</p> Case presentation <p>A 25-year-old man developed chronic infected nonunion after a severe AO/OTA type 43–C3 pilon fracture treated with multiple operations at another institution. Methicillin-sensitive Staphylococcus aureus infection, repeated debridement procedures, and implant removal resulted in persistent nonunion with progressive tapering of the distal tibia. Computed tomography demonstrated a markedly cone-shaped distal tibial morphology with an extremely limited anticipated tibiotalar contact area, while the residual cortex retained structural continuity. Conventional resection to obtain a flat docking surface would have required approximately 40&#xa0;mm of additional tibial shortening, substantially prolonging the planned bone transport phase. Because the residual tapered cortex appeared biologically viable and mechanically reconstructable with planned augmentation, we intentionally preserved the native distal tibial morphology rather than sacrificing additional bone for geometric simplification. Limb salvage using bone transport and ankle arthrodesis with circular external fixation was performed. To compensate for the limited docking area, fibular osteotomy and fibular-assisted ankle arthrodesis were incorporated as a lateral load-sharing support. After staged debridement, antibiotic spacer placement, proximal tibial corticotomy, gradual bone transport, and fibular-supported docking, successful union and ankle arthrodesis were achieved without recurrent infection. At final follow-up 6&#xa0;years postoperatively, durable union and maintained alignment were confirmed radiographically without adjacent joint degeneration or recurrent infection. The patient reported no pain (VAS 0), achieved an AOFAS ankle–hindfoot score of 92, and returned to physically demanding construction work without orthotic support.</p> Conclusions <p>This report highlights an important educational principle in limb-salvage reconstruction after infected pilon fracture nonunion. In highly selected patients with controlled infection, viable residual cortex, favorable computed tomography morphology, and feasible mechanical augmentation, severely tapered distal tibial cortex may be preserved and incorporated into ankle arthrodesis rather than routinely resected for geometric simplification. This strategy should not be regarded as broadly applicable, but as a selected bone-preserving option within individualized limb-salvage reconstruction.</p>