Side posture lumbar spinal manipulative therapy (SPLM) is one of many conservative interventions argued to remedy such maladies as sciatica and mechanical low back pain. Its notoriety and frequency of use have increased substantially over the years as chiropractors and other related health practitioners that employ SPLM have increased in numbers in conjunction with the greater acceptance of spinal manipulation. Although there is an entire body of literature regarding spinal manipulation, in-depth studies of the applied kinetics of SPLM are sparse. This knowledge is critical in teaching/evaluating the application of such a modality and in understanding its potential therapeutic mechanisms.

This thesis is a compilation of cascading experiments starting with preliminary work in chapters 1 and 2 to set groundwork by exploring various assumptions. From these chapters, the remainder of this thesis was then positioned to quantify the external mechanical parameters of SPLM, eventually manipulating these parameters themselves to increase the chance and affect the site of lumbar cavitation.

Chapter 1 of this thesis addressed the issue of using a uniaxial force transducer to quantify the applied forces during SPLM. Large pressure mats were used in Chapter 3 to measure applied forces at and distant from subjects’ spines during SPLM. It has been argued that a triaxial force transducer mounted on the skin is required to measure all forces to the underlying skeleton. The results of chapter I established that the thoracic skin-fascia interface has negligible friction and thus only the normal component of the external force is transmitted to the underlying skeleton at the contact location leaving the shear forces transmitted to the overlying skin. From the results of this chapter, it was argued that a triaxial force transducer is no more beneficial in understanding the overall forces transmitted to the skeleton than measuring the normal forces alone. The advantage however, of using large pressure mats are far reaching with the ability to quantify potentially all applied forces during SPLM, something that the literature has not, as yet, addressed. This chapter also examined the ability of a contacting hand to “hook” onto a bony prominence of a thoracic vertebra to directly transmit shear forces through the skin-fascia interface to a vertebral segment.

Chapter 2 of this thesis addressed the controversy regarding the source of the audible “crack” during SPLM. It has been postulated that this sound originates from an engineering phenomenon known as cavitation within the lumbar zygapophysial joints. The results of this study established that there is a refractory period for the audible crack following SPLM supporting this phenomenon of cavitation that can be recorded by accelerometers. The number of audible cracks during each SPLM further supported the zygapophysial joint as being the location of cavitation.

Chapter 3 of this thesis mapped the location and quantified the magnitude of applied forces to individual’s posterior pelvis, upside lateral thigh and spine at the time of peak thrust during SPLM. Assumptions were then made to estimate the lumbar axial moment. The results of this study showed that SPLM successful in generating cavitation requires emphasizing sufficient forces to areas on a recipient of SPLM remote from their spine such as the pelvis and/or lateral thigh. Failing to do so meant failing to achieve cavitation. Using distant locations to apply the forces would produce a sufficient lumbar axial moment speculated to be paramount in generating lumbar cavitation during SPLM.

Chapter 4 of this thesis was of two parts. In part I, lumbar kinematics (i.e. measured as degrees within the 3 orthopaedic planes) and site of cavitation during SPLM were determined over several trials of SPLM at the point of each cavitation. Lumbar axial twist was observed to be unique and potentially responsible for the presence and site of lumbar cavitation when compared to the remaining orthopaedic rotations during SPLM. In part II, subjects were exposed to two variations of axial twist during SPLM thought to differ in their ability to direct the site of cavitation. Emphazing the thrust to the upper torso while stabilizing the lower torso caused the first cavitation to originate superior in the lumbar spine. The opposite was observed when the upper torso was stabilized and the thrust was imposed to the subject’s pelvis. This study is a first step in developing manipulative techniques to cavitate desired vertebral segments.