Use of positron emission tomography and magnetic resonance imaging to identify central tarsal bone necrosis

Summary A 14‐year‐old Warmblood gelding presented for septic arthritis of the tarsocrural joint and tarsometatarsal joint post corticosteroid injection. Both joints were treated with arthroscopic and needle lavage, respectively. Additional treatments included systemic antimicrobials, intravenous regional limb perfusions and intra‐articular antimicrobials. Walking comfort significantly decreased 9 days post joint lavage. Persistent synovial infection was confirmed through repeat arthrocentesis, necessitating a second arthroscopic lavage. Progressive sclerosis of the central tarsal bone was observed on consecutive radiographs of the right tarsus. Given the clinical deterioration advanced diagnostic imaging using 18 F‐sodium fluoride (NaF) positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed. The images revealed loss of blood supply and severe sclerosis of part of the central tarsal bone, consistent with potential devitalized bone. The horse was humanely euthanised. Histopathology confirmed necrotic and sclerotic bone in the dorsomedial aspect of the central tarsal bone. It is hypothesised that the septic arthritis led to inflammation‐associated bone infarction and necrosis of the central tarsal bone. Clinicians should be aware of possible bone necrosis in the central tarsal bone of equine patients, presented for chronic septic arthritis. This report highlights the value in the use of 18 F‐NaF PET and MRI for early identification of osteonecrosis.