INCLUSION OF CERVICAL RADIOGRAPHS IN PRE PURCHASE EXAMINATIONS
performance cases, it seems prudent for veterinary surgeons to in- clude some tests of neck mobility and palpate the neck in their ex- amination. These tests should be sufficient to detect neck pain and overt ataxia given that elements of the examination mirror parts of a standard neurological examination of gait. As such, a horse which has undergone a PPE and is deemed fit for its intended purpose is unlikely to have clinical signs attributable to the cervical spine. Therefore, we must consider the radiographic findings that may be present in a clinically normal horse, the reliability of interpretation of such findings, and the risk of future clinical disease. Certain dis- ease processes such as fractures, scoliosis, severe cervical vertebral malformation (CVM), neoplasia and osteomyelitis rarely occur in horses without clinical signs and will not be the focus of this review (Biervliet et al., 2004 ; Hahn et al., 2008 ; Raes et al., 2014 ; Rossignol et al., 2016 ; Wong et al., 2006 ). Pre- purchase examinations are often performed in an ambu-
latory setting where certain facilities, equipment and professional horse handlers may not be available. These factors can affect di- agnostic radiographic acquisition. A position statement from the Federation of European Equine Veterinary Associations (FEEVA) in 2018 stated that in asymptomatic horses there is no evidence of an association between the radiographic appearance of the thoraco- lumbar spinous processes and future risk of disease. As such, they do not recommend that this region be included in a standard pre- purchase radiographic protocol. In this review, we summarise the significance of radiographic findings in the cervical spine and con- sider other factors which may influence the decision to acquire these radiographs as part of a PPE.
RADIOGRAPHIC CHANGES OF THE CERVICAL SPINE
Morphological variations of the cervical vertebrae
The most common anatomical variation of the cervical spine is a variably sized spinous process on the dorsal aspect of C7, which is considered to be an incidental
finding (Butler et al., 2017 ).
Radiographically this is seen in 76% of horses (Santinelli et al., 2016 ) and on cross- sectional imaging, it has been reported to be present in all adult horses (Veraa et al., 2016 ). On laterolateral projections this process can be misinterpreted as bone formation associated with the C6- C7 articular process joints, or if a separate centre of ossification is present, osteochondral fragmentation. Transposition of the ventral lamina of C6 to C7 is seen in approximately 13%–33% of horses (DeRouen et al., 2016 ; Santinelli et al., 2016 ; Veraa et al., 2016 ) (Figure 1a ). This is more frequently unilateral and more common in Thoroughbreds and Warmblood horses (DeRouen et al., 2016 ; May- Davis, 2014 ; Spoormakers et al., 2021 ). Some studies have shown this variation to be associated with an intravertebral sagittal ratio of less than 50%, a greater likelihood of ataxia and neck pain, and arthropathy of the C6- C7 articular process joints (Beccati et al., 2020 ; DeRouen et al., 2016 ). The proposed mechanism for this
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is related to the insertion of the Longus coli muscle on the ventral lamina, and variation to this structure may destabilise the neck (Beccati et al., 2020 ). However, there is also evidence to suggest that there is no significant association between this variation and the presence of clinical signs (Crijns & Broeckx, 2021 ; Veraa et al., 2016 ), or even that this variation is less common in horses with clinical signs (Veraa et al., 2020 ). Therefore, further research is needed to establish the significance of this finding. Transitional vertebra can be seen at the cervicothoracic junction with rudimentary ribs on C7 in approximately 3% of horses and transverse processes on T1 in 1% (Veraa et al., 2016 ). This finding is rare and alone not proven to be associated with clinical signs in horses. However, in people, cervical ribs are associated with thoracic outlet syndrome (Kuhn et al., 2015 ) and in horses, synostosis of the first and second rib is associated with forelimbs lameness (Rovel et al., 2018 ). Separate centres of ossification can form at the ventral process of C6 and occasionally other vertebra (Dyson, 2011 ). These should not be confused with fractures and are an incidental finding.
Congenital malformations The most
common vertebrae is
congenital occipitoatlantoaxial
abnormality of the cervical malformation,
with Arabians
being overrepresented (Gilsenan, 2019 ; Mayhew et al., 1978 ). Radiographically this appears as an abnormal shape or fusion of the vertebra and/or occipital condyles (Butler et al., 2017 ). Atlantoaxial subluxation is a frequent concurrent finding (Mayhew et al., 1978 ). These abnormalities are rare, with the literature limited to an older case series (Mayhew et al., 1978 ) and a few case reports (Brünisholz et al., 2019 ; Cole et al., 2017 ; Puangthong et al., 2020 ). They can be found in foals that are dead at birth, tetraparetic, tetraplegic or exhibit progressive ataxia (Mayhew et al., 1978 ). However, there are case reports of horses which develop clinical signs in later life (Brünisholz et al., 2019 ; Puangthong et al., 2020 ). At the time of examination by a veterinary surgeon, these horses demonstrated signs of ataxia or marked neck stiffness and palpable abnormalities. Block vertebra can also occur in the cervical spine and may not be of clinical significance but can be found alongside other malformations such as stenosis of the vertebral canal (Perris et al., 1994 ) (Figure 1b ). Given the rarity of these diseases and the likelihood of an affected horse showing clinical signs appreciable by a veterinarian, these are unlikely findings on PPE radiographs.
Osteoarthritis of the cervical articular process joints
Osteoarthritis of the cervical articular process joints is a common radiographic finding, with 68% of healthy competing Warmblood horses in one study having radiographic evidence of the disease (Espinosa- Mur et al., 2021 ). Radiographic abnormalities consist- ent with osteoarthritis include enlargement of the articular pro- cesses, regions of increased opacity or radiolucency within the
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