Biological activation of prolonged delayed fracture healing following abaloparatide under stable circular external fixation: successful limb salvage of a Gustilo type III-C pilon fracture in severe immune thrombocytopenia—a case report

BACKGROUND: Delayed fracture healing may persist despite adequate mechanical stability, reflecting biological insufficiency rather than mechanical failure. Although abaloparatide has osteoanabolic effects, its role in prolonged delayed fracture healing remains unclear. CASE PRESENTATION: A 59-year-old Japanese man with severe immune thrombocytopenia (platelet count approximately 5000/microL) sustained a Gustilo type III-C open pilon fracture after a crush injury. Emergency management included aggressive debridement, posterior tibial artery and vein repair, and circular external fixation. Because of the high bleeding risk, a minimally invasive limb-salvage strategy was selected in collaboration with hematologists, with strict perioperative bleeding control and platelet transfusion support. A medial soft-tissue defect was managed using negative-pressure wound therapy only after hemostasis had been confirmed; a lower pressure setting of -75 mmHg was selected to reduce bleeding risk, and complete epithelialization was achieved at 2 months without clinically significant bleeding. Despite stable fixation, early full weight bearing, and low-intensity pulsed ultrasound therapy, serial radiographs showed minimal progression and absence of bridging callus for more than 8 months. At 9 months after injury, abaloparatide was initiated for a sacral insufficiency fracture associated with severe osteoporosis. Within 6 weeks, abundant bridging callus appeared at the tibial fracture site, followed by cortical bridging at 12 weeks without additional intervention. Sustained union and full functional recovery were confirmed at 24 months. CONCLUSIONS: This case demonstrates that limb salvage may be feasible in a patient with a Gustilo type III-C pilon fracture and severe immune thrombocytopenia when a minimally invasive circular external fixation strategy is combined with meticulous multidisciplinary bleeding control. The case also documents a temporal association between abaloparatide initiation and rapid progression of fracture healing after prolonged biological inactivity. Because this is a single case, causality cannot be established, and the findings should not be generalized.