What is the evidence to support intra- / peri-articular facet joint injections of the neck and back

Osteoarthritis is one of the more common conditions affecting the facet (articular process joints / APJ) of the neck and back, with the caudal aspect of the neck, the thoracolumbar and lumbar regions of the back being most affected. There are many anecdotal reports on the significance of these two conditions but fewer evidence based papers. The more common clinical signs of osteoarthritis of the caudal APJs of the neck include neck pain and stiffness, abnormal neck / head carriage, reduced performance, poor action under saddle, a forelimb lameness, subtle hind limb gait abnormalities, ataxia, patchy sweating and hyposensitivity. Ataxia and forelimb lameness have been shown to be due to compression of the spinal cord or the spinal nerve roots at the level of the intervertebral foramen respectively^{8, 21, 23, 26}. The clinical signs of osteoarthritis of the facet joints of the thoracolumbar / lumbar region of the back mostly include back pain, poor performance, hind limb lameness and gait abnormalities, bucking, kicking out and reduced jumping ability^{5, 6, 7, 8, 17} . Osteoarthritis of the facet joints has been detected at post-mortem in the caudal aspect of the neck in up to 50% of normal horses^{10, 30} and in the thoracolumbar region of the back in up to 93% of Thoroughbreds^{19, 20}. An association between increasing age of the horse and increasing severity of the radiographic changes of the caudal APJs, C5-C6 has also been demonstrated¹⁰. There does not appear to be any association between the severity of radiographic changes and the breed, sex, use or clinical signs of the horse¹⁰ . The clinical significance of osteoarthritis of one or more facet joint in the neck or back can therefore be difficult to determine by clinical and radiographic examinations alone. Radiographic abnormalities of osteoarthritic facet joints include enlargement, alteration in the joint space, partial or complete obliteration of the intervertebral foramina, pitted lucent zones, scerlosis and extension of the dorsal laminae^{2 3 11 28}. The use of nuclear scintigraphy and ultrasonography are additional imaging modalities that are readily available. Computed tomography is less readily available but has been shown to be highly sensitive in detecting osteoarthritis of the APJ of the neck²⁸. There is no evidence describing the association between ultrasonographic findings and a confirmed diagnosis of osteoarthritis of the facet joints in either the neck or the back. Expected ultrasonographic changes include irregularity of the articular processes and bone modelling at the joint margins. Joint effusion is difficult to determine. The size and breed of the horse has a significant influence on the diagnostic quality of ultrasonographic images obtained of the facet joints in the caudal aspect of the back. The evidence to support the use of nuclear scintigraphy in the diagnosis of osteoarthritis of the facet joint within the neck is also lacking. In normal horses, the radiopharmaceutical uptake by the articular processes in the caudal aspect of the neck and the vertebral symphyses should be similar^{9 12}and the left and right side of the neck should also be comparable. An increased uptake of the radiopharmaceutical (IRU) by the facet joints above that of the corresponding vertebral bodies would therefore appear to be suggestive of facet joint pathology. Nuclear scintigraphy is also useful for ruling out other conditions, particularly when the horse presents with a fore limb lameness. In the thoracolumbar region of the back, a moderate or intense IRU is more  [...]