Headshaking in horses is a frustrating and often debilitating condition that can significantly 
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impact welfare and performance. Most commonly, it presents as sudden, repetitive, and often violent vertical or horizontal movements of the head, sometimes accompanied by snorting, rubbing the muzzle, or signs of facial pain. In many cases, headshaking is considered idiopathic, but it is frequently associated with trigeminal-mediated neuropathic pain - meaning the horse perceives abnormal, often painful, sensations due to dysfunction of the trigeminal nerve.
Because clinical signs can mimic discomfort arising from other sources, diagnostic work-ups for headshaking often include advanced imaging techniques such as computed tomography (CT) of the skull. These scans aim to identify or rule out structural abnormalities that may be contributing to the signs.
One anatomical area of interest is the hyoid apparatus, a complex chain of small bones that supports the tongue and larynx and connects to the base of the skull via the temporo-hyoid joint. The hyoid plays a critical role in swallowing, vocalisation, and possibly in movement coordination between the head and neck. It is anatomically and functionally close to the ear and cranial nerves, including the trigeminal nerve, raising the question: could hyoid apparatus pathology contribute to headshaking?
To explore this possibility, Ralph Lloyd-Edwards and colleagues conducted a retrospective study to assess CT changes in the hyoid apparatus of horses.
All horses that were referred to the Diagnostic Imaging Division, Department of Clinical Sciences of the Veterinary Teaching Hospital, in the Faculty of Veterinary Medicine of Utrecht University with reported clinical signs consistent with headshaking between February 2015 and June 2022 were included in the study.
The researchers compared a group of horses showing clinical signs of headshaking to a control population with no history of headshaking. Additionally, a subgroup of headshakers with no other identifiable causes (e.g. sinus disease, dental issues, or ear pathology) was compared to controls, to evaluate whether hyoid changes might be more significant in otherwise unexplained cases.
Several anatomical changes were documented via CT, including:
- Temporohyoid joint sheath ossification – a thickening and bony change in the connective tissue surrounding the joint.
- Mineralisation of the tympanohyoid cartilage – hardening of the cartilage connecting the hyoid to the temporal bone.
- Joint space alterations – either narrowing or widening of the temporohyoid joint space.
- Structural abnormalities – such as deformation, fracture, or degenerative joint changes within the hyoid bones.
These changes were found to correlate significantly with age - older horses were more likely to show ossification and other degenerative features. Additionally, the degree of change in one area of the hyoid often correlated with changes in adjacent structures, suggesting a progressive or systemic pattern of bony adaptation.
Interestingly, centres of ossification were also described in smaller hyoid bones, including the epihyoid, thyrohyoid, and the lingual process of the basihyoid, highlighting the complex and variable anatomy of this region.
Despite some initial trends - especially in the subgroup of horses with no other obvious cause for headshaking- no consistent or statistically significant association was found between hyoid apparatus abnormalities and clinical signs of headshaking. While odds ratios for certain changes were elevated in headshakers, they did not reach levels that would support a causal link.
CT imaging of the hyoid apparatus reveals a wide range of anatomical variations and age-related changes, but these findings do not appear to be directly or consistently linked to headshaking in horses. While it remains possible that in certain cases hyoid abnormalities could contribute to or exacerbate discomfort, particularly in horses with concurrent trigeminal sensitivity, this study did not establish a clear diagnostic or therapeutic target in the hyoid region for managing headshaking.
For horse owners and equine professionals, this study underscores the complexity of diagnosing headshaking and highlights the importance of a comprehensive work-up. While CT can be valuable for ruling out other structural causes, hyoid changes should be interpreted cautiously and within the broader clinical context.
For more details, see:
Lloyd-Edwards, Ralph A., Eva Mulders, Marianne M. Sloet van Oldruitenborgh-Oosterbaan, and Stefanie Veraa. 2025.
Computed Tomography of the Hyoid Apparatus in Equine Headshaking Syndrome
Veterinary Sciences 12, no. 6: 511.
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