Chiropractic is a manual therapy, which strongly relies on a sound understanding of body mechanics, and biological tissues. Like other health professions, chiropractic has its own dialect and vocabulary, which also has great variation within the practice (1). One of the professions’ well-known words is “subluxation” (1). The term subluxation has many interpretations, from the earlier Palmerian concept of subluxations as a cause of disease, to the newer concept of subluxation as an impairment to a joint segment (4). Despite the change in meaning of the term over time, it has proven to be very difficult to detach the word subluxation from its previous meaning and stigma. Along with this, chiropractic’s buzzword has been responsible for some of the professions greatest advancements in biomechanics, pathology, as well as clinical effects of therapy.
The biomechanics of a subluxation has been ever evolving since the term first appeared. In the past, chiropractic adopted the term to define a segment that was the cause of disease (2). This laid down a foundation for the philosophy of chiropractic, as well as a scientific theory to build from. Mechanical models developed to study these “subluxations” lead to motion palpation, concepts of joint play and “end-feel”, as well as the interest in studying locomotion and gait (2). From this it is evident that the establishment of subluxation-based techniques has led to discovering the importance of unity, and the dynamic nature of the musculoskeletal system (2). By no longer focusing on single segments lesions, it is possible to gain a better appreciation of biomechanics of the human body as a whole (2).
Within the profession of chiropractic, there are many pathophysiological models of subluxation, all of which have lead to hypothesize others through time. In common, these models all originate from the Palmerian theory that states subluxation is caused by the misalignment of a vertebra, ultimately leading to nerve impingement and disease (4). Newer models of pathophysiology have taken a more holistic approach, focusing on the dynamic nature of spinal motion segments (2). Here then, subluxation does not only apply to the static vertebra, but also to the mechanics of the soft tissues that surround and make the joint (2). It follows that new views of subluxation manifest profession changing theory such as central sensitization and inflammation of the facet joint, all of which are no longer cause and effect of a segmental dysfunction but rather result of many biological factors (4).
As health care professionals, it is important to be able to deliver an effective therapy with the correct intent. In order for this to successfully occur, one must understand the effects of chiropractic manipulation and all the possible theories that encompass it. We will explore some of these theories here.
To begin, the muscle spindle theory is one in which adjustments reset the spindles, allowing the musculature around the joint to relax, in turn decreasing the protective muscle spasm effect of a irritated joint (3). Moreover, there are several theories that relate to the joint being adjusted. These are the mechanoreceptor, scar tissue, joint locking, and synovial joint theories. The mechanoreceptor theory is based on a premise that an adjustment affects the three different types of mechanoreceptors within a joint, producing three different effects (3). The beneficial effects of stimulating mechanoreceptors are reflexogenic, perceptual, and suppression of pain through the restoration of motion (3). These are associated with the afferent decrease in muscle tone around the affected area, an increased postural awareness by removing bombarding inflammatory products, and decreased pain sensation by stimulating the inhibitory neuron in the gate control theory, respectively (3).
Furthermore, joints that are restricted may form adhesions when mobility is limited. Gapping and mobilizing a joint with an adjustment can break down this scar tissue (3). This gapping property of adjustments also applies to the joint locking theory, in which the joint surface mensicoid becomes trapped, creating a feeling of a “locked joint” (3). Here, adjustments would allow the trapped tissue to escape and assume its normal position. As joints are vascular, they require motion to obtain nutrients and to maximize joint health. Therefore, a restricted joint may lack adequate nutrients and manipulation can restore joint health by re-establishing segmental motion (3). It has also been suggested that adjustments cause endorphins to be released by the brain, enhancing overall feelings of wellbeing and decreasing pain, a lot like the effects of exercise and motion (3).
Lastly, ADIO is the seventh theory, which relates to the central nervous system and nerve outflow. It supports that optimal nerve flow can be hindered when a “bone is out of place” (a subluxation), resulting in nerve compression (3). Adjusting then in this case would reposition the bone, and restore proper nerve flow.
The clinical syndrome of subluxation ultimately depends on how you define subluxation, however if one used the Palmerian definition, symptoms would include: vertebra misalignment, nerve impingement, and loss of function (4). For this specific syndrome then, it is clear to see that the Above Down Inside Out model for adjusting would be appealing; supporting the subluxation based practice.