Kevin K. Haussler
Managing Back Pain
As the field of equine sports medicine has continued to grow, optimal function of the axial portion of the skeleton has become an important clinical issue in athletic horses in all disciplines, including those engaged in both ridden and nonridden exercise. Poor performance is the most common chief complaint of owners with affected horses. Unfortunately, this is a nonspecific sign of back problems, and a long list of differential diagnoses must be considered in horses presented with signs of poor performance. As with any disease, the treatment is only as good as the diagnosis. I consider the term back problems a syndrome or a prerequisite collection of clinical signs that, if present, are indicative of a structural or functional disorder of the axial skeleton. The primary indicators of spinal dysfunction include heat, swelling, pain, muscle hypertonicity, and stiffness. However, horses with chronic back problems often do not have any evidence of localized heat or swelling; treatment is therefore often directed at reducing pain and muscle hypertonicity and improving spinal flexibility. Over the years, a multitude of different medical, surgical, physical medicine, nutritional, and equitation approaches have been applied to horses with back problems. Unfortunately, few medical treatments have any evidence of proven clinical efficacy in managing chronic back pain in horses, beyond anecdotal reports; however, there is a growing body of evidence on the use of manual therapy, acupuncture, and physical therapy approaches (Table 22-1). Treatment methods are often diverse and are typically based on an individual practitioner’s clinical bias or postgraduate training in adjunctive therapies that have been extrapolated from human medicine and applied to horses. The pathophysiology of equine back pain also continues to be poorly understood; however, advances in human medicine have helped veterinarians develop rational treatment and management measures for affected horses. The focus of this chapter is to review the current evidence on treatment of the most common causes of spinal dysfunction in horses, which include ligamentous, muscular, bony, articular, and neurologic disorders.
TABLE 22-1
Review of the Current Equine Literature on Effective Treatment or Rehabilitation Methods for Managing Back Pain
| Treatment Options | Literature Sources |
| Spinal mobilization and manipulation | Haussler KK: Equine Vet J Suppl 2010; Nov(38):695-702 |
| Haussler KK: Vet Clin North Am Equine Pract 2010; 26:579-601 | |
| Sullivan KA: Equine Vet J 2008; 40(1):14-20 | |
| Gómez Alvarez CB: Equine Vet J 2008; 40(2):153-159 | |
| Haussler KK: Am J Vet Res 2007; 68(5):508-516 | |
| Wakeling JM: Equine Comp Exer Physio 2006; 3:153-160 | |
| Faber MJ: J Vet Med A Physiol Pathol Clin Med 2003; 50:241-245 | |
| Surgery | Coomer RP: Vet Surg 2012; 41:890-897 |
| Desbrosse FG: Vet Surg 2007; 36:149-155 | |
| Perkins JD: Vet Surg 2005; 34:625-629 | |
| Walmsley JP: Equine Vet J 2002; 34:23-28 | |
| Acupuncture | Rungsri PK: Am J Traditional Chinese Vet Med 2009; 4:22-26 |
| Xie H: J Am Vet Med Assoc 2005; 227:281-286 | |
| Skarda RT: Am J Vet Res 2002; 63:1435-1442 | |
| Massage therapy | Sullivan KA: Equine Vet J 2008; 40:14-20 |
| McBride S: J Equine Vet Sci 2004; 24:76-81 | |
| Stretching exercises | Stubbs NC: Equine Vet J 2011; 43:522-529 |
| Local anesthetic | Roethlisberger Holm K: Equine Vet J 2006; 38:65-69 |
| Tiludronate | Coudry V: Am J Vet Res 2007; 68:329-337 |
Epaxial Myopathies
Epaxial muscle atrophy can be localized or generalized, unilateral or bilateral, and symmetric or asymmetric. The distribution and severity of spinal or gluteal muscle atrophy may provide insights into the etiology and prognosis. Generalized and bilaterally symmetric epaxial muscle atrophy suggests generalized disuse or systemic diseases that influence overall body conditioning and weight loss, which include starvation, severe gastrointestinal parasite infestation, and poor dentition. Disuse muscle atrophy occurs in horses that are poorly conditioned or have not been in active work or exercise for long periods of time. Localized or asymmetric muscle atrophy suggests local disease processes as possible etiologies, which include local trauma or neurogenic atrophy, if evidenced by a myotomal pattern or within a region of known spinal pathology or chronic back pain. Neurogenic muscle atrophy can also be caused by equine protozoal myelitis, which causes localized pronounced epaxial or, more commonly gluteal, muscle atrophy. Osseous spinal pathologic change, such as impinged spinous processes or articular facet osteoarthritis, can cause significant local or regional back pain and subsequent disuse or neurogenic atrophy. Spinal nerve compression at an intervertebral foramen could be caused by adjacent osseous proliferation related to osteoarthritis; however, antemortem diagnosis is difficult for abnormalities arising in the thoracolumbar portion of the spine.
Epaxial muscle disorders can generally be categorized as localized injuries or generalized myopathies. Local longissimus muscle injuries are associated with tissue trauma secondary to either intrinsic factors (e.g., overloading or abscesses) or extrinsic causes (e.g., bites or lacerations). Acute muscle injuries are characterized by localized pain, tissue disruption, heat, and swelling of the affected tissues or structures. Diagnostic ultrasound is useful for identifying the affected tissues and the extent and severity of the injury. Occasionally, radiopharmaceutical uptake may be localized to a specific region of inflammation or an individual muscle with nuclear scintigraphy. In most horses that express pain during superficial palpation of the axial muscles, there is no obvious etiology; however, improper saddle fitting or training, unbalanced riders, and compensatory gait changes secondary to chronic lameness need to be ruled out. Approximately 30% of horses with lameness have concurrent back pain.
Treatment
Acute exertional rhabdomyolysis can be managed with a reduction in the intensity, duration, or frequency of exercise to limit continued muscle strain and to allow for soft tissue healing. Nonsteroidal antiinflammatory drugs (NSAIDs) are indicated to help reduce soft tissue pain and inflammation. Treatment of severe rhabdomyolysis may necessitate hospitalization, intravenous fluids, and more aggressive pain management strategies. Acute medical management may include administration of methocarbamol, dantrolene, and phenytoin. Methocarbamol (4 to 25 mg/kg, slow IV infusion) is a potent skeletal muscle relaxant that acts specifically on the internuncial neurons of the spinal cord to reduce acute skeletal muscle spasms without a concomitant alteration in muscle tone. Methocarbamol is usually given orally to effect for moderate (1 to 4 mg/kg) or severe (4 to 11 mg/kg) muscle hypertonicity. Dantrolene is a ryanodine R1 receptor antagonist that decreases release of calcium from the calcium channels in the sarcoplasmic reticulum, the process required for normal muscle contraction. Optimal administration of this drug (1 to 4 mg/kg PO q 24 hr) involves giving it on an empty stomach 2 to 3 hours before strenuous exercise in at-risk horses. Phenytoin (6 to 8 mg/kg PO q 24 hr) affects the sodium and calcium channels in muscles and nerves, but therapeutic levels need to be adjusted to achieve a plasma concentration of 8 to 12 µg/mL. Additional medications for acute exertional rhabdomyolysis may include sedatives, such as acepromazine or xylazine, and dimethylsulfoxide.
Treatment of localized epaxial muscle pain or traumatic injury requires identification and removal of the etiology, if possible. A general treatment plan for local muscle pain includes rest, cryotherapy, NSAIDs, and compression, if feasible. Strict stall rest is likely contraindicated for most muscle injuries; however, controlled hand walking, small paddock turnout, and reduced intensity, duration, or frequency of training will help to decrease local tissue strain and provide a low level of muscle activity required for maintenance of muscle function and minimized fibrosis. Cryotherapy is best provided by the application of large crushed ice packs mixed with water to maximize conduction at the site of injury and covered with several layers of towels to insulate the ice packs from rapid melting. The optimal treatment of acute muscle injuries with cryotherapy involves application of ice packs for 20 to 30 minutes at hourly intervals until local heat and pain are abated, a regimen that may extend for 2 to 4 days. Ice massage is also an effective method of reducing pain and inflammation. Water frozen within a paper or Styrofoam cup provides a good means of applying tissue cooling while protecting the fingers of the person applying the treatment. The NSAIDs are effective for addressing acute inflammatory pain; the most commonly used agents include phenylbutazone (4.4 mg/kg, PO, q 12 hr for 1 to 3 days, followed by 2.2 mg/kg, PO, q 12 hr, as needed) and flunixin meglumine (0.5 to 1.1 mg/kg, IV or PO, q 12-24 hr, as needed). Compression is recommended for all acute musculoskeletal injuries, although it is not typically practical for application in trunk regions. Abdominal compression wraps or weighted sandbags may be applied to the dorsal aspect of the trunk, either alone or in combination with ice packs. Needle aspiration or surgical drainage may be indicated for treatment of large hematomas or abscesses. Acupuncture, massage, and gentle, individualized stretching exercises aimed at reducing pain and mobilizing adjacent soft tissues are indicated in the subacute phase of muscle injury and healing. Additional intermediate goals include restoring neurophysiologic functions related to proprioception, muscle spindles, and motor control. Therapeutic exercises at this stage include navigating obstacles, ground pole exercises, underwater treadmill, and core stability training. Longer term goals are focused on restoring overall muscle endurance and strength.
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