Temporohyoid osteoarthropathy: Recurrence of clinical signs following standing partial ceratohyoidectomy in a Swiss Warmblood mare

Summary A 17‐year‐old Swiss Warmblood mare presented with signs of left‐sided facial nerve paralysis and was diagnosed with left‐sided temporohyoid osteoarthropathy (THO). A partial ceratohyoidectomy was performed in the standing, sedated mare to treat this condition. Despite surgery and an initial improvement of clinical signs, the horse showed a sudden worsening of facial nerve paresis and additional ataxia grade 4/5 (modified Mayhew scale) 7 months after surgery. Cone‐beam computed tomography revealed new bone formation and partial fusion of the left basihyoid and ceratohyoid bone, and this was considered responsible for the clinical deterioration. Therefore, a total ceratohyoidectomy was performed under general anaesthesia. Intraoperatively, pseudoankylosis of the basihyoid–ceratohyoid joint was confirmed. After the second surgery, the horse showed clinical improvement within 2 days after surgery. The remaining grade 1/5 ataxia and facial paresis showed further progressive improvement during the 8 months follow‐up after the second surgery.