The mineralisation of a particular ligament in the upper neck of horses is not related to the problematic issue of head shaking, researchers at the University of Liverpool have concluded.
The longitudinal odontoid ligament is a single, robust, fan‐shaped, bi‐lobed ligament that extends from the cranial part of the C2 vertebrae and attaches cranially to the floor of the body of the C1 vertebrae.
A study published in 2020 identified mineralisation of this ligament during CT scans of three horses being examined for head shaking and poor performance.
Head shaking in horses is largely a diagnosis of exclusion, with assumed or confirmed trigeminal neuralgia as the underlying cause. Others have suggested that musculoskeletal pain may be a factor in some horses.
“It is often a frustrating and debilitating condition to treat and as such the suggestion that mineralisation of the longitudinal odontoid ligament may be involved in this syndrome requires further investigation,” Alison Talbot and her fellow researchers wrote in the journal, Veterinary Radiology & Ultrasound.
Talbot, together with Miguel Rodrigues and Thomas Maddox, noted that imaging of the cervical spine in horses has historically been difficult largely because of the size of the animals. However, recent improvements in equipment have allowed imaging of this region in equines to be more widely available.
For their study, the trio re-examined images from CT scans of 96 horses that underwent head and cranial cervical spine imaging for a variety of clinical reasons at the Philip Leverhulme Equine Hospital, part of the University of Liverpool.
They examined the clinical records to find any relationship between the presence of mineralisation of the ligament and the primary presenting problem, as well as age, breed, use, and sex of the patient. They also looked for any association with head shaking, neck pain or restricted range of neck motion.
The researchers found that 25 of the 96 horses (26%) had some degree of mineralisation of the ligament. Eight of the 25 horses (32%) were categorised as having marked mineralisation, five of the 25 (20%) as moderate, and 12 of the 25 (48%) as mild.
They found no association between mineralisation of the ligament with either idiopathic head shaking or any other clinical signs investigated in this group of horses.
They did, however, find that increasing severity of mineralisation was linked with increasing age, and with being female.
The study team, discussing their findings, said the results indicate that mineralisation of the ligament can be a common finding in CT studies of the equine head, being present in nearly a quarter of all horses in the sample.
“Perhaps unsurprisingly, mineralisation was also more commonly found in older horses and ponies; however, the finding of an effect of sex and association with being female was not expected.”
The findings, they said, refuted the hypothesis that mineralisation would be associated with head shaking or neck pain.
“Findings from the current study indicated that veterinary radiologists should be aware that mineralisation within the longitudinal odontoid ligament is a reasonably common finding in horses undergoing CT examination of the cranial cervical region,” they concluded.
It should be considered age‐related and is more likely to be seen in female horses. However, the presence of marked mineralisation in younger animals is unusual and may be a reflection of inflammation of this ligament.
“Further investigations are warranted to fully investigate the clinical relevance of CT image findings in this structure.”
They said the clinical significance of mineralisation of the ligament should be interpreted cautiously in equine CT studies.
Computed tomography‐identified mineralisation of the longitudinal odontoid ligament of the horse is associated with age and sex but not with the clinical sign of head shaking
Alison M. Talbot, Miguel Rodrigues, Thomas W. Maddox
Veterinary Radiology & Ultrasound, January 1, 2021, https://doi.org/10.1111/vru.12947