INCLUSION OF CERVICAL RADIOGRAPHS IN PRE PURCHASE EXAMINATIONS
with clinical signs, in all studies there was a high incidence of radiographic abnormalities in clinically normal horses (Crijns & Broeckx, 2021 ; Espinosa- Mur et al., 2021 ; Haussler et al., 2019 ; Koenig et al., 2020 ), with 100% (372/372) of control horses dem- onstrating enlargement of the C6- C7 articular process joints in one study (Crijns & Broeckx, 2021 ) and 97% (29/30) in another (Koenig et al., 2020 ). Interobserver agreement for radiographic abnormalities of the articular process joints has been shown to be fair to moderate, with a kappa of 0.29–0.6 depending on lo- cation in one study (Koenig et al., 2020 ), and a kappa of 0.62 for C5- T1 in another (Donati et al., 2022 ). Modest agreement in this instance is likely due to the high level of superimposition that is inherent to cervical radiographs and as a result, computed tomography (CT) of this region for clinical cases has become in- creasingly common (Gough et al., 2020 ; Lindgren et al., 2021 ; Rovel, Zimmerman, Duchateau, Adriaensen, et al., 2021 ; Rovel, Zimmerman, Duchateau, Delesalle, et al., 2021 ). A combination of these factors means that these radiographic findings are dif- ficult to interpret on PPE radiographs. Muscle atrophy has been shown to be associated with clinical signs of neck pain, and neck stiffness is a commonly reported observation in horses that are clinically affected but osteoarthritis (Kernot et al., 2022 ; Koenig et al., 2020 ). These findings could be detected on a physical exam and should highlight to clinicians the importance of testing neck mobility and palpating the neck during a PPE. In the majority of clinical cases, medication of the articular process joints with cor- ticosteroid is shown to be effective, with 64% of horses returning to their intended use (Koenig et al., 2020 ).
Osteochondral fragmentation Osteochondral
fragmentation
| 369
cases (Tucker et al., 2022 ). Therefore, although these fragments certainly present some risk in the pre- purchase setting, they are not always clinically significant. There is a paucity of research investigating whether cervical osteochondral fragments found in a clinically normal horse will become clinically significant later in life, or with an increase in athletic performance. Osteochondrosis has also been described at the occipital condyles in a Belgian horse (Muirhead et al., 2003 ) and the cranial articular surface of C2 in a Thoroughbred (Beck et al., 2002 ), however these are rare occurrences. In foals, radiographically apparent defects can be present in the occipital condyles and are considered a normal finding in animals up to 156 days of age (Sage et al., 2021 ).
Cervical vertebral malformation
Cervical vertebral malformation (CVM) is a developmental disease with a mean age at presentation of 2 years, and clinical signs usually develop in horses under 10 years of age (Levine et al., 2008 , 2010 ; Szklarz et al., 2018 ). It is the most common cause of ataxia in horses and two times more likely to be diagnosed in geldings and intact males, compared to females (Levine et al., 2008 ). Radiographic abnormalities of the vertebra consistent with CVM include flaring of the caudal epiphysis of the vertebral body, caudal extension of the dorsal lamina, stenosis and/or a funnel shape of the vertebral canal, step formation between vertebra, subluxation or malalignment of
the inter- central joint, and enlargement associated with the cervical
articular process joints has been confirmed by histopathology to be caused by osteochondrosis dissecans in a small number of horses (Beck et al., 2002 ; Tucker et al., 2018 ) (Figure 1c ). However other differentials include synovial osteochondromatosis and traumatic fragmentation (Moore et al., 1992 ). These fragments are most frequently present at C4- C5 followed by C7- T1 and are most commonly located in the ventromedial aspect of the joint, followed by the dorsolateral aspect (Tucker et al., 2022 ). They also preferentially affect the cranial articular process of the cervical vertebra (Bergmann et
al., 2020 ). There is limited evidence
about the sensitivity of radiographs for the detection of these fragments, however, radiographs have been shown to detect 40% of fragments later seen on CT (Tucker et al., 2022 ). Lateroventral- laterodorsal oblique radiographic projections can help visualise the articular processes with less superimposition, and lateralise pathology but are rarely acquired during a PPE (Withers et
al., 2009 ). CT examination of horses with osteochondral
fragmentation yielded additional findings such as remote causes of spinal cord compression in 11/13 cases, and fragmentation was considered to be the primary cause of the clinical signs in only 6/13
of the articular process joints (Butler et al., 2017 ) (Figure 2 ). Accurate diagnosis of clinical cases can be difficult with only moderate agreement between radiography and necropsy (Levine et al., 2010 ). A clinically normal horse is unlikely to demonstrate severe radiographic abnormalities (Hahn et al., 2008 ). Therefore, only subtle manifestations of the disease are likely to be present during a PPE, making interpretation even more challenging. There is a scarcity of knowledge in the literature on the predictive value of
radiographs in developmental disease. Unfortunately,
the
main question the purchaser will have is whether these findings will progress to clinical disease. Inter- and intravertebral sagittal diameter ratios could be utilised in this scenario. There is evidence to suggest a horse with a ratio of ≤0.485 is likely to have histological evidence of spinal cord compression (Hahn et al., 2008 ) and using this cut- off value will result in greater specificity than if <0.5 or <0.52 are used. However, given the inter and intra- observer variability of 5%–10% when performing these measurements, they should be interpreted with caution (Hughes et al., 2014 ; Scrivani et al., 2011 ). We do not know how these measurements will impact a clinically normal horse in later life. In a clinically normal horse, if a ratio is outside the reported reference range you may be cautious in suggesting the horse is suitable for a certain career, but this may also lead to wastage of a clinically normal animal. This situation may warrant a second opinion from a colleague or specialist, however, a final decision about the suitability of a horse may require a complete neurological examination.
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