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the saddle should not be too wide or too narrow for the horse (Meschan et al. 2007). A narrow saddle will sit too close to the spine on both sides and impinge upon the horse’s movements, while a saddle that is too wide will often come into contact with the dorsal spinous processes, potentially causing pain. Having saddles fitted and regularly refitted professionally is important, as the horse’s shape changes often throughout its life (Greve and Dyson 2015a,b). There is also the rider to consider. A rider with stiffness in
one side of the body can create uneven pressure loading on one side of the saddle, potentially exacerbating TL pain in the horse (Belock et al. 2013; Greve and Dyson 2015a). Instrumentation is now available to aid riders in becoming aware of their weight distribution on the horse (McGreevy et al. 2004) and physiotherapy for equestrians has become a popular practice. Saddle slip, uneven flocking and shims or pads under the saddle all contribute to the possibility of epaxial muscle pain and asymmetry, especially in the region of the wither (Von Peinen et al. 2010). Once the clinical examination at rest and exercise has
been completed, the veterinarian must decide if further diagnostic testing is required. Radiology, nuclear scintigraphy, ultrasonography and thermography are all available to evaluate the horse with back pain. Infusion of local anaesthesia has been evaluated, as has algometry to assess their usefulness as diagnostic aids to evaluate back pain in the horse.
Infiltration of local anaesthesia as an aid to diagnosis
It is tempting to use infiltration of local anaesthesia into the painful muscles of the horse’s back as a diagnostic aid. However, Holm et al. (2006) found that local infiltration of an anaesthetic solution in and around T16 to L2 results in a change in the function of the back in asymptomatic horses. Horses without perceived back pain showed increases in dorsoventral flexibility as well as lateral bending following infusion of mepivicaine along the spine. In fact, the local anaesthesia is thought to be blocking the stabilising effect of the multifidus muscles, allowing laxity in the TL joints (Stubbs et al. 2011). Research on horses’ backs has shown that infiltration of
local anaesthesia into the sites of impingement can relieve pain in cases of overriding DSPs (Jeffcott and Hickman 1975; Cauvin 1997). It can also aid in identifying which DSPs are affected. Walmsley et al. (2002) describe the technique as part of the clinical work-up prior to surgery for resection of the DSPs. Radiography is also important in these cases.
Radiographic assessment
Radiography of the equine back used to be quite a challenge, often requiring general anaesthesia with all its accompanying difficulties. However, since 1979, imaging techniques have improved, as has our ability to understand the pathology depicted on radiographs. Today, wireless plates and digital images have made radiography of the equine TL spine important in the diagnosis of pathology. While sedation of the horse for radiology is common, general anaesthesia is usually only required when taking ventrodorsal views of the TL spine or sacroiliac joints (Jeffcott 1979b,c; Cauvin 1997; Haussler and Jeffcott 2014).
Diagnostic images of the equine back require equipment
with an output of >150 kV and mA of 250–500 (Henson 2009). This generally means that most portable radiographic generators are not powerful enough for use on the back. This limits TL radiography to referral centres. The only part of the back that can be radiographed with a portable machine are the DSPs to allow examination for overriding. Adequate knowledge of the anatomy of the horse’s back
is essential to correctly evaluate spinal radiographs (Henson 2009). It must also be recognised that the immature horse will have different radiographic findings from a mature horse due to open growth plates and ossification centres (Haussler and Jeffcott 2014). One of the important conditions that can be seen radiographically is overriding of the DSPs, particularly from T10–L3. This will be seen as a reduction of the interspinous spaces, local periostitis, sclerosis and areas of radiolucency in the DSPs. A grading system for overriding of the DSPs was developed by Jeffcott (1979c) (Table 2). There is, however, poor correlation between the grade of overriding DSPs and clinical signs (Jeffcott 1980b). The position of the head and neck also influences the apparent distance between the thoracic DSPs, confounding the issue (Berner et al. 2012). Radiographs can be taken of the vertebral bodies and
intervertebral discs of T11 to L3 in the standing horse. In the thoracic area (T6–T18), the lungs provide excellent contrast to the spine. The vertebrae can be evaluated for spondylosis, a condition that may contribute to equine back pain (Meehan et al. 2009). To visualise the articular facets of the vertebral bodies, several oblique views can be taken (Girodroux et al. 2009). Articular facet changes can often be visualised on radiographs. The usual radiographic signs are loss of joint space, bony proliferation around the joints and sclerosis of the joint margins (Henson 2009), although the clinical significance of these lesions can vary. When combined with a positive pain reaction, these lesions can be recognised as a source of discomfort for the horse and should be further evaluated with nuclear scintigraphy.
Nuclear scintigraphic assessment
Ueltschi first described orthopaedic nuclear scintigraphy, or ‘bone scanning’, in 1977 as a new diagnostic tool for equine lameness evaluation. Since then, it has become an established part of the clinical work-up for back and pelvic issues in the horse. Unfortunately, due to expense, the use of nuclear scintigraphy is currently limited to large equine practices. As with any imaging modality, it is essential that
TABLE 2: System for grading radiographic evidence of overriding dorsal spinous processes (Jeffcott 1979c)
Grade 0
1 2
3 4 5 Radiographic evidence
No impingement of the spinous processes Impingement of the summits only
Impingement with signs of mild overriding, i.e. crowding
Overriding of spinous processes associated with periosteal reaction at sites of impingement
Severe overriding with periosteal reaction, pseudoarthrosis and misshapen dorsal summits Fusion of adjacent dorsal spinous processes
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