Background

Chiropractic treatment is a form of manual therapy that is characterized by the use of high-velocity, low-amplitude thrusts typically applied to regions of stiffness, pain or muscle hypertonicity within the axial skeleton.¹ In humans, chiropractic care has primarily demonstrated clinical efficacy in treating acute and chronic neck and back pain.^2–4 Due to human applications and perceived therapeutic efficacy in treating musculoskeletal issues, chiropractic techniques have subsequently been applied to horses.⁵ Equine chiropractic techniques within the United States were primarily developed and taught by Dr. Sharon Willoughby beginning in 1985. Since then, numerous veterinary chiropractic certification programs have been established worldwide. Currently, chiropractic evaluation and treatment techniques have been applied to sport horses for issues mostly related to poor performance and overt signs of back pain.^6,7

Mechanism of action

The goal of chiropractic treatment is to restore normal joint motion, stimulate neurologic reflexes, and to reduce pain and muscle hypertonicity.⁵ Multiple theories have been proposed and tested over the years to explain the pathophysiology of vertebral segment dysfunction and its interactions and influences on the neuromusculoskeletal system.^8,9 Chiropractic treatment is thought to affect mechanoreceptors (i.e., Golgi tendon organ and muscle spindles) to induce reflex inhibition of pain, reflex muscle relaxation, and to correct abnormal movement patterns.^10,11 The literature suggests that any stimulus that activates high-threshold receptors within the periarticular tissues has the potential to initiate unique neurologic reflexes associated with joint manipulation.¹² Alterations in articular neurophysiology from mechanical or chemical injuries can affect both mechanoreceptor and nociceptor function via increased joint capsule tension and nerve ending hypersensitivity.¹³ Mechanoreceptor stimulation induces reflex paraspinal musculature hypertonicity and altered local and systemic neurologic reflexes. Nociceptor stimulation results in a lowered pain threshold, sustained afferent stimulation (i.e., facilitation), reflex paraspinal musculature hypertonicity, and abnormal neurologic reflexes.

It is likely that specific manual therapy techniques are inherently more effective than others in addressing each of these local, regional or systemic components.¹⁴ The challenge is in choosing the most appropriate form of manual therapy or combination of techniques that will be efficacious for an individual patient with specific musculoskeletal disabilities. If soft tissue restriction and pain are identified as the primary components of a musculoskeletal injury, then massage, stretching and soft tissue mobilization techniques are indicated for increasing tissue extensibility.^15,16 However, if the musculoskeletal dysfunction is localized to articular structures, then stretching, joint mobilization and manipulation are the most indicated manual therapy techniques for restoring joint range of motion and reducing pain.^17,18

Palpatory changes in osseous symmetry after manipulation often are associated with soft tissue alterations and not due to actual reductions of an articular misalignment or a ‘bone out of place’.¹⁹ The static position of the vertebral or sacroiliac joints in humans has been studied pre and post-manipulation by roentgen stereophotogrammetric analysis, which allows precise measurements of three-dimensional articular movement.²⁰ Static palpation changes have been noted pre and post-manipulation, however no changes have been reported with the roentgen stereophotogrammetric analysis. Therefore, soft tissue responses such as joint capsules, muscles, ligaments, tendons and postural neuromuscular reflex patterns should be the focus of future spinal manipulative studies and not articular malpositioning (i.e., bone out of place).²⁰

Indications

Back pain is a common cause of poor performance in sport horses (see Chapter 21). Unfortunately, medical and surgical treatment options are often limited for affected horses. Manual therapy has the potential to provide important diagnostic and therapeutic approaches for addressing equine axial skeleton problems that are not currently available in veterinary medicine. Most of the current knowledge about equine manual therapies has been borrowed from human techniques, theories, and research and applied to horses. Therapeutic trials of joint mobilization or manipulation are often used because of limited knowledge about the effects of manual therapy in horses. The indications for joint mobilization and manipulation are similar and include restricted joint range of motion, muscle spasms, pain, fibrosis, or contracted soft tissues.²¹ The principal indications for spinal manipulation are neck or back pain, localized or regional joint stiffness, poor performance, and altered gait that is not associated with overt lameness. Anecdotal evidence and clinical experience suggest that chiropractic is an effective adjunctive modality for the diagnosis and conservative treatment of select musculoskeletal-related disorders in performance horses. However, therapeutic trials of chiropractic manipulations are often used since we currently have limited formal research available about the effectiveness of chiropractic procedures in equine practice.

A thorough diagnostic workup is required to identify soft tissue and osseous pathology, neurologic disorders, or other lameness conditions that may not be responsive to manual therapy. Clinical signs indicative of a primary spinal disorder include localized musculoskeletal pain, muscle hypertonicity and restricted joint motion. This triad of clinical signs can also be found in a variety of lower limb disorders; however, they are most evident in horses with neck or back problems. Clinical signs indicative of chronic or secondary spinal disorders include regional or diffuse pain, generalized stiffness, and widespread muscle hypertonicity. In these cases, further diagnostic evaluation or imaging should be done to identify the primary cause of lameness or poor performance. Chiropractic treatment may help in the management of muscular, articular and neurologic components of select musculoskeletal injuries in performance horses. Musculoskeletal conditions that are chronic or recurring, not readily diagnosed, or are not responding to conventional veterinary care may be indicators that manual therapy evaluation and treatment is needed. Chiropractic treatment is usually more effective in the early clinical stages of disease processes versus end-stage disease where reparative processes have been exhausted. Joint manipulation is usually contraindicated in the acute stages of soft tissue injury; however, mobilization is safer than manipulation and has been shown to have short-term benefits for acute neck or back pain in humans.²² Manipulation is probably more effective than mobilization for chronic neck or back pain and has the potential to help restore normal joint motion, thus limiting the risk of reinjury.¹⁹

Contraindications

Chiropractic treatment is not a ‘cure all’ for all joint or back problems and is generally contraindicated in the presence of fractures, acute inflammatory or infectious joint disease, osteomyelitis, joint ankylosis, bleeding disorders, progressive neurological signs, and primary or metastatic tumors.²¹ Contraindications are often based on clinical judgment and are related to the technique applied and skill or experience of the practitioner.²¹ Acute episodes of osteoarthritis, impinged dorsal spinous processes, and severe articular instability are often contraindications for manipulation. Inadequate physical or spinal examination and poorly developed manipulative skills are also contraindications for applying manual therapy.²³ All horses with neurologic diseases should be evaluated fully to assess the potential risks or benefits of joint mobilization or manipulation. Cervical vertebral myelopathy occurs because of both structural and functional disorders.²⁴ Static compression caused by vertebral malformation and dynamic lesions caused by vertebral segment hypermobility are contraindications for cervical manipulation; however, adjacent regions of hypomobile vertebrae may benefit from mobilization or manipulation to help restore joint motion and reduce biomechanical stresses in the affected vertebral segments. Serious diseases requiring immediate medical or surgical care need to be ruled out and treated by conventional veterinary medicine before any routine manual therapy is initiated, although manual techniques may contribute to the rehabilitation of most post-surgical cases or severe musculoskeletal injuries by helping to restore normal joint motion and function. Horses that have concurrent hock pain (e.g., osteoarthritis) and a stiff, painful thoracolumbar or lumbosacral vertebral region are best managed by addressing all areas of musculoskeletal dysfunction. A multidisciplinary approach entails combined medical treatment of the hock osteoarthritis and manual therapy evaluation and treatment of the back problem.

In humans, most adverse events associated with spinal manipulation are benign and self-limiting.²⁵ Mild adverse effects include transient stiffness or worsening of the condition that usually last less than one to two days and resolve without concurrent medical intervention. Severe complications following spinal manipulation are typically uncommon. Estimates of the incidence range from one in 200 000 to one per 100 million manipulations in humans.^22,26,27 The most common serious adverse events in humans are vertebrobasilar accidents, disk herniation and cauda equina syndrome.²⁸ Even though the complication rate of spinal manipulation is small, the potential for adverse outcomes must be considered because of the possibility of permanent impairment or death.²² The benefits of chiropractic care in humans seem to outweigh the potential risks.²⁹

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