While I was teaching an online course that reviews the history and development of manual medicine, one of the issues discussed in the course material caught my interest: the concept of subluxation as the central defining tenet of chiropractic1,2. Reading more on this topic, I came to believe that an understanding of this concept has implications for chiropractors and non-chiropractic manual medicine practitioners alike, especially where it relates to interprofessional cooperation and a manual medicine research agenda.
As reported by Terrett3, Hieronymus in 1764 was the first to characterize subluxation by the presence of lessened motion of the joints, slight changes in the position of the articulating bones, and pain. Hieronymus also noted that most displacements of vertebrae were not dislocations but rather subluxations3. The use of the term “subluxation” by D.D. Palmer as incomplete luxations with articular surfaces slightly displaced in the relative position they occupied towards each other4 differed from the allopathic definition of the time, but only in that the founder of chiropractic attributed vast and comprehensive disease-generating capacities to the vertebral subluxation1. Not that he was the first to do so; around 1820, a medical physician by the name of Harrison postulated a pathophysiological connection between spinal subluxations and visceral disease. He even adjusted vertebrae by pressing on the spinous and transverse processes3. At about the same time, another physician named Brown popularized the concept of “spinal irritation.” He noted how a shared nerve supply could implicate the spine in visceral disease and nervous conditions, which led him to target the spine with non- manipulative interventions3,5. However, by the time Palmer discovered chiropractic, these theories had fallen out of favor with the allopathic community.
Palmer’s original theory held that all disease was the result of inflammation that was caused by arteries, veins, nerves, muscles, bones, ligaments, joints, or any other anatomical structure displaced from its normal position6. This theory was later reduced (possibly to make chiropractic more distinct from osteopathy and prevent legal prosecution for practicing osteopathic medicine without a license) from any displaced anatomical part to exclusively joints of the body. Palmer especially emphasized vertebral subluxations hypothesized to pinch nerve roots in vertebral foramina, thus affecting neural impulses to the target organs6. Palmer later further refined his theory by stating that vertebral subluxations did not pinch nerves in the spinal foramina but rather that they altered the tension of the nerves, affecting what he called the “vibrational impulse” carried along the nerves, thereby affecting end organs4,6. However, it was the second theory of nerve impingement due to subluxation that Palmer’s son B.J. Palmer adopted and promoted using the appealing “foot-on-the-hose” analogy2. The younger Palmer later stated that subluxation only occurred between the atlas and either the occiput or the axis and that all other vertebrae were only malaligned2. His upper cervical “hole-in-one” adjustments were the logical consequence of this shift in subluxation theory6.
Both Palmers were proponents of the segmental approach to subluxation, supporting the “bone-
out-of-place” hypothesis1,6,7. Carver was the first to promote a structural approach with multi-level subluxations in spinal distortion patterns7. The structural approach is still emphasized today in those schools of chiropractic thought that emphasize levelling the pelvis by adjusting the sacroiliac joints6. The older Palmer detected subluxations by way of static palpation looking for misalignment8. Gillet developed the theory of spinal fixation; its identification by way of motion palpation added yet another dimension to the concept of subluxation7,9.