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the images from a bone scan be evaluated in light of the physical examination of the horse. When evaluating scintigraphic scans for pathology, it is


important to understand what is within ‘normal’ limits. Nelson (2009) has produced an extensive table describing the scintigraphic appearance of the back and pelvis of normal horses. When pathology exists and more radiopharmaceutical is detected at a particular place on the horse, it is identified as increased uptake of radiopharmaceuticals, or IRU. The appearance of IRU on the scintigraphy images usually indicates a site of increased bone activity. These sites are then evaluated based on the horse’s age, anatomical location and other diagnostic parameters, such as the physical examination and radiography. A young horse, with open growth plates, will have uptake of the radiopharmaceutical in areas of bone growth and these must be recognised as normal artefact. Areas of thicker soft tissue, such as the pelvis, will result in lighter images than those of the lumbar spine (Dyson 2014). A limited amount of work has been done on evaluating


bone scans of the TL spine. Studies of DSPs of the TL spine have shown that up to 73% of clinically normal horses showed mild radiographic or scintigraphic changes on examination (Erichsen et al. 2003, 2004). It has also been found that there might be mild IRU present in the summits of the DSPs in nonpainful horses (Zimmerman et al. 2014). For this reason, it is important to acknowledge that mild scintigraphic changes may be present in both painful and asymptomatic horses and the clinical examination must form the basis of any evaluation of TL pain in horses. When the scintigraphic image and radiographic lesions of the painful back agree with the clinical examination, there can be a reasonably reliable indication of significant bony pathology (Gillen et al. 2009).


Ultrasonographic assessment


It is the ability to ultrasound the anatomical structures of the equine TL spine that is likely to put the diagnosis of back pathology into the hands of the general practitioner. While there is an advantage to having a large powerful machine with multiple transducers, most TL ultrasonography can be performed with a portable ultrasound machine and linear, curvilinear or sector scanners using frequencies between 2.5 and 7.5 MHZ (Lamas and Head 2009). The DSPs of the thoracic and lumbar vertebrae can easily


be examined with ultrasonography. Variations occur on the dorsal surface of the thoracic DSPs, with T3–6 showing roughening while T7–18 are smooth (Lamas and Head 2009). It is also possible to identify the spaces between the DSPs of the vertebra as an aid in diagnosing overriding dorsal spinous processes and associated remodelling on the bone (Fonseca et al. 2006). In some cases, even fractures can be identified with ultrasonography. Through the work undertaken by Denoix, it has become


possible to ultrasound the articular facets of the TL vertebrae. The technique used for this type of imaging has been described (Denoix 1999; Lamas and Head 2009). When performing ultrasonography of the articular facets, it is useful to place the images of the left and right sides of each vertebra together. This allows a comparison of both joints from each vertebra, making bony changes easier to detect. Ultrasonography is the main way to evaluate the supra-


and intraspinous ligaments (SSL and ISL). Ultrasonography of the SSL must be done in both the longitudinal and transverse


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plane. The ISL lies between the DSPs of the vertebrae and can also be examined by ultrasound (Fonseca et al. 2006; Lamas and Head 2009). In a painful TL spine, damage to the supraspinous ligament (SSL) is a possibility and ultrasound has been used to identify lesions in the SSL of the TL spine. It must be noted, however, that abnormalities of the SSL detected by ultrasound also occur in normal, nonpainful horses (Henson et al. 2007). In human medicine, ultrasonography is used to measure


the cross sectional area (CSA) of the multifidus muscle on both sides of the spine. Asymmetric atrophy of this muscle has been identified as a reliable marker of associated spinal pathology. Stubbs et al. (2010) studied 22 Thoroughbred racehorses presented for euthanasia for reasons other than back pain. They identified an asymmetrical reduction in the CSA of the multifidus muscle occurring in the area of, or adjacent to, the site of bony pathology of the spine.


Thermographic assessment


Thermography has been used to examine the horse’s back in association with other techniques (Fonseca et al. 2006). Several types of thermographic cameras exist and it is important to obtain a camera within the spectral range of 8– 14 lm, which is the range for medical evaluations in man (Turner 2009). The camera measures the heat generated by the body


and released through the skin. The heat from blood vessels affects skin temperature, so any evaluation of thermographic images must be undertaken with knowledge of blood flow patterns in the area under investigation. Like other imaging modalities, thermography is affected by motion, artefact and extraneous radiation. Infrared thermography has been reported to represent the regulation of vasomotor tone by the sympathetic nervous system (Von Schweinitz 1999). Areas of acute inflammation appear as ‘hot spots’ on examination while areas of chronic pain and pathology appear as ‘cold spots’. While many veterinarians have tried thermography on their cases, it remains an infrequently used tool. As with any of the other modalities, results from thermography must be considered in light of the clinical examination.


Algometry as a potential aid to pain assessment


The algometer is a small, hand-held tool initially introduced into equine back evaluations by Haussler (Haussler and Erb 2006a). It is an instrument used by human therapists to assess the level of pressure a patient can tolerate in a particular area, which is termed the mechanical nociceptive threshold (MNT) or pressure pain threshold (PPT) of that area. The algometer has been tested in several research studies in man as a method of objectively measuring musculoskeletal pain (Persson et al. 2004; Potter et al. 2006). The algometer has also been used in studies on the


equine back and sacroiliac areas (Varcoe-Cocks et al. 2006; De Heus et al. 2010). The repeatability of the algometric measurements in horses has been tested with positive results (Haussler and Erb 2006a,b) and median MNTs were established (Table 3). Palpation of the back by a clinician has been identified as one of the most important tests to determine if a horse is suffering from TL pain (Fonseca et al. 2006). As previously mentioned, however, manual palpation by a veterinarian or other therapist is highly subjective. A


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