Equine Temporohyoid Osteoarthropathy Study Guide

Overview and Clinical Importance

Temporohyoid osteoarthropathy (THO), also known as middle ear disease or stylohyoid osteoarthropathy, is a progressive condition affecting the temporohyoid joint and surrounding structures in horses. This disease is characterized by proliferative bone changes at the articulation between the stylohyoid bone and the petrous temporal bone, potentially leading to joint fusion, nerve damage, and fractures. THO represents an important differential diagnosis for horses presenting with facial nerve paralysis, vestibular dysfunction, or head-shaking and is a recognized cause of neurological disease on the NAVLE.

THO can affect horses of any age, breed, or gender, though it most commonly presents in adult horses. The condition may be unilateral or bilateral, with bilateral disease reported in a significant proportion of cases. Early recognition and appropriate treatment are essential for optimal outcomes.

Anatomy of the Hyoid Apparatus

The hyoid apparatus is a complex arrangement of bones that suspends the tongue, pharynx, and larynx from the skull. Understanding this anatomy is fundamental to comprehending the pathophysiology and clinical signs of THO.