e challenging.
Following the physical examination the horse should be assessed dynamically, ideally both on the lunge and under the saddle. Any asymmetry of the gait should be investigated, as back pain and concurrent lameness is common (Zimmermann et al, 2011). Horses deemed to be unsafe to ride, due to exhibiting dangerous behaviours, can be assessed with tack on the lunge or with a weighted surcingle. The majority of clinical signs associated with back pain have not been measured yet and, therefore, the investigation is primarily subjective.
The ‘gold standard’ for the objective assessment of back movement is 'optical motion capture'. This technique is highly accurate but restricted to the gait laboratory or treadmills and is not applicable for the use in the field. Alternatively, wireless inertial sensors can be used to collect kinematic data. This technique can also be used to assess for gait asymmetries and evaluate interactions between horse and rider (Pfau et al, 2007, 2009). When compared to optical motion capture, inertial sensor data showed a good level of consistency and an acceptable accuracy for back movement (Warner et al. 2010).
Back pain and lameness
Horses compensate hindlimb lameness by adapting spinal movement, which becomes evident as a reduction of range of motion at the lumbosacral junction and extension of the thoracolumbar region (Buchner et al 1996; Alvarez et al 2008). By abolishing the hindlimb lameness with diagnostic local anaesthesia, these asymmetries and reduced range of motion can be reversed (Greve et al 2017).
Saddle slip was observed in a large proportion of horses with hindlimb lameness, probably partly due to asymmetrical epaxial muscling (Greve et al 2013). Furthermore, saddle slip could be corrected by abolishing hindlimb lameness, suggesting that asymmetrical thoracolumbar movement in lame horses is the cause. A study assessing back dimensions of sport horses over time showed that lame horses had a reduced ability to develop normal epaxial musculature (Greve et al 2015).
Due to the close association of lameness, spinal movement and back pain, gait asymmetries should not be overlooked and both should be investigated and treated accordingly.
Diagnostic imaging modalities for the back include radiography, ultrasonography and scintigraphy (bone scan). Standard imaging modalities allow the assessment of the most relevant areas of the back. Gamma scintigraphy might be useful to further assess radiographic and ultrasonographic suspicions or findings. Furthermore, bone scan allows the assessment of bigger breeds, where standard imaging modalities are insufficient due to poor or non-diagnostic image quality. Ultrasonography of the articular process joints of the back is frequently compromised in horses with significant soft tissue coverage. It is important to carefully interpret imaging findings and confirm their clinical significance with diagnostic local anaesthesia or trial medications, where possible.
• Radiography allows the visualisation of the vertebral column, intervertebral articulations (IVAs/’facet joints’) and vertebral bodies to a varying degree, depending on location, equipment and patient size. Latero-lateral views as well as oblique projections can be obtained. Standard radiographs ideally include three to five overlapping latero-lateral radiographs using radiopaque markers, such as coins, for orientation. Collimated views of specific regions of interest can help to increase image quality by reducing scatter. Main limitations of the technique include attenuation and inability to visualise lumbar vertebral bodies. Care should be taken when interpreting or measuring interspinous spaces (ISS). Geometric distortion markedly affects the appearance of the spaces, depending on the shape and the distance of the dorsal spinous processes to the focal spot emitting X-ray beams (Djernæs et al 2017). Furthermore, the head position influences the distance between thoracic dorsal spinous processes and it is therefore advised to acquire back radiographs in a neutral position with the muzz