SPORTS MEDICINE AND REHABILITATION


affected spinous processes. One study found that corticosteroid infiltration resolved the pain in 89% of 38 horses with kissing spines, although 56% of those had recurrence of pain in  1 year7 and repeating this treatment once or twice a year is often neces- sary.8 In cases of thoracolumbar osteoarthritis, corticosteroid injection of the articular facet joints can be performed using ultrasound guidance.9 The author prefers triamcinolone (3 mg/ joint, up to 18 mg total body dose) diluted to 2 mL volume with sterile saline or hyaluronic acid. A less specific al- ternative, and one that does not require ultrasound guidance yet is still clinically effective, is to perform an intramuscular corticosteroid injection (of the multifidus or longissimus muscle) in the region of the affected facet joints. The author has only per- formed this in a small proportion of horses using triamcinolone though others may use methylpred- nisolone or isoflupredone. While theoretically methylprednisolone could lead to mineralization of the soft tissues, the author has not appreciated this clinically. In humans, injection of methylpred- nisolone into the multifidus muscle was more effec- tive in treating lower back pain than a 10-week physiotherapy program.10 Horses with clinical evidence of SI pain typically


benefit greatly from corticosteroid injections of that region. Interestingly, response to treatment is not correlated with the presence or absence of pathologic changes of the SI joint identified with diagnostic imaginga. There are multiple published techniques for injecting the SI joints.11,12 Regardless of tech- nique, it should be noted that the SI joint contains a very small volume of synovial fluid (1mL)13 and an SI “joint” injection is a bit of a misnomer as the injection is almost exclusively periarticular.11 For SI region injections, the author prefers to inject a fairly large volume using the cranial ultrasound- guided approach (typically 100 mg methylpred- nisolone diluted to 15–20 mL in sterile saline per side); the cranial approach avoids the risk of pene- trating the rectum as is possible using the caudal approach12 and the higher volume ensures diffusion to the cranial and caudal aspects of the joint as well as the surrounding structures. In cases in which corticosteroid therapy is contraindicated, injection of autologous conditioned serum has yielded good clinical effects, anecdotally, in a handful of horses. Generally speaking, adverse reactions are uncom-


mon, but a minority of horses will have some in- crease in muscle pain and spasm following intra- articular facet joint injection or SI region injections at the site of needle placement. In these cases, the author prescribes hot packing (apply a warm com- press, 20 minutes, q12h) and NSAIDs (1 mg/kg flu- nixin meglumine q24h) for 2–3 days following injection.


Methocarbamol


Methocarbamol is a centrally acting muscle relaxer used to decrease muscle spasms and excessive mus-


cle tone (hypertonicity). One of the first reports of such use dates back to 1958 when a human physi- cian reported “often prompt and striking” results in patients with acute orthopedic conditions, including herniated lumbar and cervical disks.14 In a double blinded, placebo-controlled study, treatment with methocarbamol was effective in 70% of 98 people with acute lower back pain and spasm.15 Like the 30% of people in the aforementioned study who were “non-responders,” so too in horses there seems to be variable efficacy (from negligible to quite effec- tive). In the majority of cases, the author appreci- ates a good clinical result from administration of 25 mg/kg q12h PO for 2 weeks followed by 25 mg/kg once daily for an additional 2 weeks. In cases with underlying back pathology, it is most effective when administered in conjunction with an initial cortico- steroid treatment of the back and/or SI region. However, in more mild cases of thoracolumbar epaxial muscle pain, it can be used effectively in isolation, as a sole treatment. Methocarbamol is generally safe but rarely can cause drowsiness. It is important to note that the above dose is not legal under United State Equestrian Federation (USEF) drug regulations, which restricts its use to 5 mg/lb (11 mg/kg) every 24 hours for no more than 5 consecutive days.


Bisphosphonates


Despite the widespread clinical use of bisphospho- nates to treat horses with osseous pathology of the thoracolumbar spine, the supporting research is extremely limited. A single study reports on the outcome of 29 horses with osteoarthritis of the tho- racolumbar vertebrae, with or without concurrent osseous changes of the spinous processes.16 The treatment group (consisting of 15 horses, each ad- ministered a single treatment of 1 mg/kg tiludro- nate in 1 L saline via slow IV infusion) had significantly better dorsal flexion of the back in canter compared with the control group 60 days following treatment. At 120 days, treated horses showed improvement over the control horses, but the difference between the groups was not statis- tically significant. Another clinical study demon- strated decreased lameness scores in horses with distal hock joint osteoarthritis 60 days after treat- ment with tiludronate (same dosing protocol as above).17 These reports, in combination with the FDA-approved use for the treatment of navic- ular syndrome in adult horses, make the use of bisphosphonates for other osseous pathologic con- ditions a reasonable choice. Thus, in cases of osteoarthritis of the axial skeleton and/or kissing spine, judicious use of bisphosphonates could be considered. Currently, treating thoracolumbar conditions with


either FDA-approved bisphosphonate, clodronate, or tiludronate constitutes off-label use. Bisphospho- nates are not approved for use in young ( 4 years old), pregnant, or lactating mares and can cause


AAEP PROCEEDINGS  Vol. 66  2020 233


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