A Rare Case of Total Talar Replacement for Talar Osteonecrosis Due to Fragility Fracture Secondary to Transient Osteoporosis of the Talus.

We report the case of a 44-year-old male patient without a notable medical history who developed transient osteoporosis following surgery for a medial malleolus fracture, which led to a stress fracture and osteonecrosis, ultimately requiring total talar replacement. The patient sustained the fracture spraining his ankle while welding. Osteosynthesis was performed using two cannulated cancellous screws, whereas bone union was achieved 3.5 months postsurgery. Five months after surgery, ankle joint pain worsened without new trauma episodes. Magnetic resonance imaging (MRI) showed diffuse hyperintensity over the entire talus on short tau inversion recovery (STIR) sequences, whereas radiography and computed tomography (CT) revealed fracture lines in the posterior talus. The fracture was initially treated with a non-load-bearing period; however, compression progressed, thereby leading to a diagnosis of talar osteonecrosis and total talar replacement. One year postsurgery, the Japanese Society for Surgery of the Foot ankle-hindfoot scale score improved from 24 presurgery to 85. The patient is currently being followed up. The Hounsfield units (HU) of the talus at the time of the fragility fracture, retrospectively measured via CT, were lower in areas with fragility fractures than in those with medial malleolar fractures, which suggests osteoporotic changes in the talus. Pathology of the excised talus confirmed osteoporosis with thinning of the trabecular bone, which was consistent with the MRI findings and suggested that transient osteoporosis led to fragility fractures and talar necrosis. The findings suggest that the delayed diagnosis of transient osteoporosis led to fragility fractures and osteonecrosis. This case highlights the importance of considering transient talar osteoporosis as a differential diagnosis in cases of persistent pain after ankle fracture surgery and performing an MRI early to guide treatment.