Veterinary Manipulative Therapy: Neurology, Biomechanics, and Available Evidence

Veterinary Manipulative Therapy: Neurology, Biomechanics, and Available Evidence

Marilyn Maler


Manipulative therapy of animals as a standardized modality is a fairly recent development compared to manipulative therapy of humans. While Danial David Palmar established the first chiropractic school in 1897, it would be nearly a century later before a recognized program of animal chiropractic arose. Sharon Willoughby Blake DVM, DC is considered the founder of modern animal chiropractic. While practicing as a veterinarian, Dr. Willoughby witnessed the positive effects of chiropractic therapy on both herself and her canine patients. She subsequently earned a Doctorate of Chiropractic and then sought to educate her colleagues on animal chiropractic. She founded the American Veterinary Chiropractic Association and the first postgraduate animal chiropractic training program which was the main training program from 1989 to 2001. The development of the manipulative modality of animal osteopathy took a similar path, but instead it arose in Europe initially. Despite originating in the United States, osteopathy of humans became more popular in Europe, followed by osteopathy practice on animals.

It should be noted that while modern animal manipulative therapy education in the United States was developed from established human chiropractic techniques, the widely used term “chiropractic” in reference to manipulative therapy on animals has been legally challenged as a term that is strictly in reference to humans. Thus, the terms “spinal manipulation” or simply “manipulation” are now used to describe the modality instead.

Manipulation in Practice

While the terms mobilization and manipulation are often used interchangeably, they are different manual techniques in practice. Mobilization techniques use repetitive graded passive movements and can be applied to musculoskeletal soft tissue or joints. The unique biomechanical characteristic of manipulation is the application of a nonrepetitive, high velocity, low amplitude (HVLA) thrust directed to an articular or axial joint. There is low to moderate evidence to support manipulation as a therapy to reduce local pain, address muscle hypertonicity, and increase joint range of motion (ROM) [1]. As the HVLA thrust cannot be resisted by the patient, manipulations are thought to be less safe than mobilizations. A thorough knowledge of anatomy and biomechanics, good palpation skills, and well developed “feel” of joint motion is essential to perform manipulations safely and effectively [2, 3].

While manipulations are typically associated with the chiropractic and osteopathic practice, physiotherapists sometimes also use manipulations as part of their therapy. Osteopathic treatment may also consist of cranial therapy and visceral mobilization. In the United States, the legalities of which practitioners are allowed to perform manipulations on animals and the education requirements are covered in each state’s veterinary practice act.

Joint Mechanics of Manipulative Therapy

Manipulation aims to correct a subluxation, a term which has caused confusion among medical practitioners. In manipulative therapy, subluxation refers to a hypomobility of a joint within the normal physiologic ROM. The term subluxation should not be confused with a luxation or dislocation which is characterized by hypermobility [4].

There are three zones of joint motion as described starting from the neutral position: physiologic, paraphysiologic, and pathologic. The physiologic zone is where mobilization occurs and includes the active ROM and passive ROM. In the active ROM, the patient can actively move the joint themselves. The passive ROM is outside the active ROM and requires an outside force to move into and within. The paraphysiologic zone is where the HVLA thrust of manipulation occurs. In between the physiologic and paraphysiologic zones is the elastic barrier and is where joint end-feel is evaluated. In the pathological zone, anatomical limits of the joint are exceeded, and injury occurs [2, 3]. (Figure 7.1)

Figure 7.1 The three zones of joint motion. (Courtesy of Ashley Reid).

To determine if any subluxation is present and before any HVLA is applied, the joint should be evaluated for ROM and end-feel in all potential directions. (Figure 7.2) The normal ROM of joints will vary between species, within species and even within a spinal region on an individual. Joint end-feel is palpated at the elastic barrier. It will start as soft and resilient and will become firmer and restrictive as end of motion is reached. An abnormally restrictive end-feel will occur earlier within the ROM or will have a more abrupt and hard feeling [2, 3].

Figure 7.2 Joint motion in all directions should be evaluated before manipulation. An example of mobilization within the passive range of motion. To the untrained eye, the amount of mobility seen in this picture may appear excessive, but it is in fact normal. (Courtesy of Ashley Reid).

Theoretical Mechanism of Subluxation Effects

Numerous theories have been put forth to explain how a subluxation can cause deleterious effects on the body. The theories can be broadly grouped into three mechanism-oriented classifications and are not mutually exclusive. The first classification is encroachment of the intervertebral canal or spinal canal. Structures such as hypertrophied facet joint capsules, bulging disks, or enlarged intra-foraminal ligaments may encroach on the pressure sensitive nervous and vascular tissues of the intervertebral foramen or spinal canal and compromise their function. The second classification is based on the subluxation causing altered afferent input to the central nervous system which in turn alters function. In this theory, spinal manipulation corrects the biomechanics of the spine which then restores normal afferent input to the central nervous system. The third classification is founded on theories that during subluxation or misalignment, dentate ligaments may put abnormal traction on the spinal cord, causing cord distortion and consequently dysfunction. Each of these mechanisms has some supporting research, but deficiencies in studies are also noted, thus no conclusions are made currently [4].

Neurology of Pain Relief

While spinal manipulative therapy is commonly used to treat back and neck pain in human and veterinary integrated medicine, the mechanism of action for pain relief is not yet fully understood. Studies have reported potential pain-relieving effects from peripheral nervous system changes, spinal cord mechanisms, and supraspinal processes [5, 6]. There is support for the segmental/spinal cord mechanisms as the main contributor of pain relief [7].

Peripheral Mechanisms

It has been proposed that manipulative therapy provides pain inhibition through release of the hormone cortisol, which is known to have an anti-inflammatory effect on the periphery [8]. However, studies of blood and plasma cortisol levels showed inconsistent results after spinal manipulation [8, 9]. The conflicting results prevent drawing any conclusions about the role of cortisol as a method of pain inhibition at the present and more research is needed to make any determination of cortisol’s role in spinal manipulation pain relief.

Another proposed peripheral mechanism of spinal manipulation pain relief is through an effect on sensitization of nociceptive fibers by reactive oxygen species. This is supported by animal studies that show spinal manipulation may provide pain relief by preventing an increase in the reactive oxygen species [10] or increasing serum antioxidant enzymes in humans [11]. While these studies are promising, more research is needed to determine if these mechanisms contribute specifically to pain relief through spinal manipulation.

A third potential peripheral mechanism of pain relief is through a reduction of pro-inflammatory and pro-nociceptive mediators (chemokines, TNF-α, and IL-1β) that are elevated during spine pain. These mediators are involved in peripheral sensitization of nociceptors. Research has suggested that spinal manipulation may decrease these pro-inflammatory responses, and this may in turn provide pain relief by altering peripheral inflammation and sensitization of nociceptors [10, 12

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Jul 30, 2023 | Posted by in ANIMAL RADIOLOGY | Comments Off on Veterinary Manipulative Therapy: Neurology, Biomechanics, and Available Evidence

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