out the potential clinical significance is limited (Henson et al 2007). The clinical significance of heterogenous regions in the SSL should therefore be questioned and further tests, such as diagnostic local anaesthesia, should be applied.
Deep to the ligament the fibrocartilaginous cap, visualised as a hypoechogenic line of approximately 1mm, is visible and runs parallel to the hyperechoic line of the DSP bone surface. The ISS cannot be assessed fully and a statement about potential iminging DSPs should not be made based on ultrasonography alone. The intervertebral articulations can be examined ultrasonographically, both in sagittal and frontal planes, using a convex transducer (Denoix 1999a; Reisinger and Stanek 2005).
The anatomy and ultrasonographic appearance of the joints change slightly from cranial to caudal. The mammillary process is more prominent in the thoracic spine and the joint is positioned further axial and closer to the DSP compared to the lumbar region. Signs of pathology in the intervertebral articulations (see Figure 4) include new bone formation and an enlarged outline of the facet (Denoix and Dyson 2003).
Muscle asymmetries are common in horses with back pain. Measuring the multifidus muscles may add objective information during back investigations and is easily applied. Furthermore, progress made following treatment and training can be measured by re-assessing m. multifidus symmetry (Halsberghe et al 2017).
• Scintigraphy is commonly applied to further image the back in cases where the standard modalities were inconclusive or specific findings require advanced diagnostic imaging. Mild increased radionuclide uptake (IRU) associated with the DSPs is a common finding in horses without clinical signs of back pain (Erichsen et al 2003, 2004). A study of Zimmermann et al (2011) looking primarily at the spinous processes of the thoracolumbar spine showed that the severity of radiographic lesions was associated with scintigraphic abnormalities. DSPs at T14-T17 were most commonly affected. Horses with severe DSP lesions were more likely to have osteoarthritis in the IVAs. But there were also horses with radiographic evidence of ‘kissing spines’ that had no IRU associated with DSPs on bone scan images. Moderate or severe IRU associated with the IVAs was more likely seen in horses with clinical signs of back pain than in normal horses in a study from Gillen et al (2009).
The advantage of applying scintigraphy is the ability to identify dynamic processes of bone modeling and remodeling associated with the entire spine. These processes are either adaptive or pathologic and require careful interpretation, as findings are not necessarily associated with pain. Bone scan is a useful diagnostic tool to help ruling out other regions possibly mimicking back pain, such as the sacroiliac joint region.
Diagnostic local anaesthesia is considered the most important test to confirm that clinical signs of back dysfunction are associated with impingement of DSPs (Walmsley et al 2002). Horses that tolerate injections, are safe to ride and show a consistent, repeatable problem or behaviour are most suitable candidates. The effect of diagnostic local anaesthesia is usually assessed by performing a ridden examination (or other exercise test) before and 10-20 minutes after infiltration of the local anaesthetic solution (Marks 1999; Walmsley et al 2002; Denoix and Dyson 2003). The test is considered positive, if a marked improvement of performance can be recognised by both the rider and the veterinary surgeon. Interpretation difficulties without objective measurements such as interpretation bias should be borne in mind.
In a study of Roethlisberger Holm et al (2006) the back of horses without clinical signs of back pain or lameness was infiltrated with local anaesthetic solution. Kinematics of the back were measured showing an affect on the function of the back. An increased range of motion for dorsoventral flexion-extension resulting in improved flexibility was possibly due to an altered neuromuscular activity by injections made 