Temporohyoid joint osteoarthropathy (THO)

ISSN 2398-2977

Contributor(s) :

Introduction
Pathogenesis
Diagnosis
Treatment
Prevention
Outcomes
Further Reading

Introduction

Cause: infection, inflammation or age-related degeneration → osteitis and bony swelling of the joint. Compression on adjacent structures including cranial nerves.
Signs: head shaking/tossing, ear rubbing; dysphagia; acute onset vestibular signs and facial nerve paralysis; sudden death.
Diagnosis: physical examination, ear examination, gait evaluation, radiography, endoscopy, head CT.
Treatment: antibacterials, anti-inflammatories, surgery.
Prognosis: guarded to fair.

Presenting signs

Early osteoarthritis

Headshaking Behavior: headshaking.
Pain or discomfort at the base of the ear or in the throatlatch area.
Reluctance to perform under saddle in specific head positions.

Late osteoarthritis and temporal fracture

Head tilt, nystagmus.
Drooping lip.
Dysphagia.
Corneal ulceration.
Aural discharge.
Difficulty in eating and chewing.

Acute presentation

Facial nerve Facial nerve: trauma or vestibular dysfunction Neurology: vestibular disease.

Age predisposition

Adult horses only and usually middle-aged to older individuals.

Cost considerations

Costs of diagnostic techniques and treatment, which may include long-term antibacterial therapy Therapeutics: antimicrobials and surgery.
Costs of loss of use of animal for long periods or loss of animal if euthanasia Euthanasia.

Special risks

Extension of infection → meningoencephalitis.
If horse is ataxic, then recovery from general anesthesia Anesthesia: general - overview may be more difficult.

Pathogenesis

Etiology

Hematogenous infection.
Otitis externa Ear: otitis externa / otitis media.
Guttural pouch infection Guttural pouch: empyema.
Trauma to hyoid apparatus.
Age-related degeneration of joint Musculoskeletal: osteoarthritis - joint disease.

Predisposing factors

General

Significant association between increasing age and severity of temporohyoid joint degeneration.

Specific

Crib-biting behavior Behavior: crib-biting and wind-sucking has been associated with an increased risk of THO in Japan.

Pathophysiology

The hyoid apparatus is a collection of bones that suspend the tongue and larynx from the skull. The paired stylohyoid bone of the apparatus connects to the temporal bone of the skull via the temporohyoid joints.
Osteoarthropathy of the temporohyoid joint is a well-recognized disease of the joint and is usually characterized by bone proliferation surrounding the joint and, in chronic cases, joint fusion.
The exact cause of THO is not completely understood but possible causes include:
- Infection (septic) or inflammation (non-septic) of guttural pouch Guttural pouch: mycosis or internal ear → osteitis Bone: osteitis - septic of the tympanic bulla, proximal stylohyoid bone and the temporohyoid joint at articulation with the petrous temporal bone.
- Trauma of the temporohyoid joint which may be associated with stylohyoid bone fracture.
- Degenerative (possibly age-related) arthritic changes of the joint.
Arthritis Musculoskeletal: osteoarthritis - joint disease from whatever source → decreases movement of joint → surrounding bony proliferation → potential fusion of stylohyoid bone to petrous temporal bone (temporohyoid articulation).
Loss of joint movement → stress on thin-walled petrous temporal bone during swallowing, prolonged vocalization, sudden movement of the head, neck or jaw → fracture of the temporal bone or rarely, basilar bone → sudden worsening of the clinical signs and in some cases compression on the internal acoustic meatus (contains cranial nerves facial (7) and vestibulocochlear (8) → neurologic signs such as changes in facial expression, eye lubrication, and balance. Cranial nerves IX and X may also be affected.