Bit & Bridle

Equine Zygomatic Arch Disease

Other Names

  • Zygomatic Arch Fracture
  • Zygomatic Arch Periostitis
  • Facial Crest Disease
  • Temporal Fossa Disease

What is Equine Zygomatic Arch Disease?

Equine Zygomatic Arch Disease encompasses a range of conditions affecting the zygomatic arch — the bony ridge that forms the prominent facial crest running along the side of a horse’s head, roughly from beneath the eye toward the ear. The zygomatic arch is formed by the joining of the zygomatic process of the temporal bone and the temporal process of the zygomatic bone, and in horses it is a palpable, prominent landmark.

Conditions affecting this structure include fractures (from trauma or ill-fitting equipment), periostitis (inflammation of the periosteum, the fibrous covering of the bone), and more rarely, neoplastic changes. Zygomatic arch problems are not commonly discussed in equine health literature but are a genuine source of pain and dysfunction in affected horses — particularly those in work where browbands, bridles, or headcollars put direct pressure on the facial crest.

Causes of Equine Zygomatic Arch Disease

The most common causes include:

  • Trauma: Direct blows to the side of the head — from a fall, a kick from another horse, striking a fixed object, or a road traffic accident — can fracture or bruise the zygomatic arch. Because the arch is prominent and relatively unprotected, it is vulnerable to contact injuries.
  • Poorly fitted tack: Browbands, bridles, and headcollars that sit too tightly or are incorrectly positioned can place chronic pressure on the zygomatic arch, leading to periostitis (bone inflammation) and pain. Horses worked extensively in ill-fitting headgear are at particular risk.
  • Repeated microtrauma: Horses in high-contact sports or those that habitually rub their heads may develop cumulative injury to the arch.
  • Dental disease: The roots of the upper cheek teeth (premolars and molars) lie in close proximity to the zygomatic arch. Severe dental pathology can occasionally extend into the surrounding bony structures.
  • Neoplasia: Tumours of the soft tissue or bone in the zygomatic region are rare but do occur. Sarcoids and fibrosarcomas have been reported in this location.

Symptoms and Signs

Signs of zygomatic arch disease can range from subtle to obvious:

  • Visible swelling, deformity, or asymmetry of the facial crest
  • Heat or pain on palpation of the zygomatic arch
  • Reluctance to accept bridling or headcollar application
  • Head shaking, tossing, or resistance to bit contact
  • Unexplained behavioural changes under saddle, particularly head carriage issues
  • Discharge or sinus tracts in the zygomatic region (in cases of fracture with infection)
  • Muscle wasting of the temporal region (in chronic cases or those with local nerve involvement)
  • Asymmetric chewing or quidding (dropping partially chewed food) if dental involvement is present

Diagnosis

Zygomatic arch disease can be missed if it is not specifically looked for, particularly in horses presenting primarily with ridden behavioural problems. Diagnosis includes:

  • Clinical examination: Systematic palpation of the facial crest for swelling, heat, crepitus (grinding sensation), and pain response. Comparison with the contralateral side is helpful.
  • Radiography: Skull radiographs can confirm fractures, bony proliferation, or abnormal densities. Multiple projections may be needed to fully characterise the pathology.
  • Ultrasonography: Useful for evaluating soft tissue swelling, haematomas, and the integrity of the periosteal covering.
  • CT scanning: Where available, CT provides the most detailed imaging of complex bony architecture and is particularly valuable if dental or sinus involvement is suspected.
  • Tack assessment: It is important to evaluate the fit of all headgear the horse wears and identify whether any item is placing pressure over the arch.

Treatment

Treatment depends on the underlying cause and severity:

  • Tack modification: In cases caused by ill-fitting equipment, modifying or replacing the offending tack is essential and often dramatically improves the situation. A wider browband, differently positioned cheekpieces, or a correctly fitted headcollar may be all that is needed for mild periostitis.
  • Rest and anti-inflammatory medication: NSAIDs (phenylbutazone or flunixin) to reduce pain and inflammation during the acute phase, combined with rest from work.
  • Corticosteroid injections: Periosteal injections of corticosteroids may be used in cases of persistent periostitis to reduce localised inflammation.
  • Fracture management: Simple, non-displaced fractures typically heal with conservative management (box rest, anti-inflammatory medication). Displaced fractures or those involving sinus cavities may require surgical repair.
  • Wound management: Open wounds over the arch require appropriate wound care and may need antibiotic coverage to prevent infection of the underlying bone.
  • Neoplasia: Treatment of tumours depends on type — sarcoids in this location may be treated with intralesional chemotherapy, topical agents, or surgery. Early referral to a specialist is advisable.

Prevention

  • Ensure all bridles, browbands, and headcollars are correctly fitted and checked regularly — the browband should not pull the headpiece against the ears, and cheekpieces should not exert pressure on the facial crest
  • Have a qualified saddle fitter or bridle fitter assess headgear fit, especially for horses in intensive work
  • Promptly address any head trauma, even if the initial reaction seems mild
  • Check the zygomatic arch region during routine grooming — run your hand along the facial crest to detect any new swellings or asymmetry early
  • Provide appropriate fencing and stable environments to reduce the risk of head trauma

Prognosis

Prognosis depends on the underlying cause. Periostitis from tack pressure, caught early and managed with tack modification and anti-inflammatory treatment, typically resolves well. Simple, undisplaced fractures generally heal uneventfully with conservative management. Complex fractures, infected fractures, or those with sinus involvement carry a more guarded prognosis and may require prolonged treatment.

Cases involving neoplasia are managed on a case-by-case basis, with prognosis dependent on the tumour type and extent of local infiltration.

When to Call the Vet

Consult your vet if:

  • You notice swelling, asymmetry, or deformity of the facial crest
  • The horse is in pain when the area is touched or when bridling
  • There is any discharge or wound overlying the zygomatic region
  • The horse has suffered a significant head trauma
  • Ridden behavioural problems do not resolve after tack fitting assessment
  • Any mass in the zygomatic region is growing or not resolving

Frequently Asked Questions

Can a poorly fitting browband really cause zygomatic arch disease?

Yes — this is one of the most common causes of zygomatic periostitis in working horses. A browband that is too tight pulls the headpiece down and forward onto the base of the ears, and simultaneously causes the cheekpieces to press against the facial crest. Over time, this chronic pressure causes periosteal irritation. Bridle fit is frequently overlooked in favour of saddle fit, but it is equally important for comfort and soundness.

How do I check if my horse’s bridle is pressing on the zygomatic arch?

With the bridle correctly fitted and on the horse, check that the browband is not pulling the headpiece down or creating any tension. You should be able to slide a finger easily under the browband at the centre. The cheekpieces should lie smoothly along the face without pressing into the facial crest. If the horse’s facial crest area is sore to touch, or if the horse shows resistance specifically when the bridle is applied or removed (rather than when the bit is introduced), tack pressure is a strong possibility.

Is zygomatic arch fracture an emergency?

It depends on severity. A simple, undisplaced fracture from a blow to the head may be managed conservatively without emergency surgery. However, any fracture accompanied by significant swelling, open wound, suspected sinus involvement, or neurological signs should be assessed urgently. When in doubt, call your vet for same-day assessment rather than waiting.

Can zygomatic arch disease affect a horse’s performance?

Yes, significantly. Pain in the zygomatic arch region causes horses to resist bit contact, evade the bridle, and show altered head carriage. These signs are frequently misinterpreted as training problems or bit issues. Any horse presenting with new or persistent ridden head carriage problems, particularly alongside reluctance to accept the bridle, should have this area evaluated as part of a broader veterinary workup.