Back pain and metaphor.

Last February I completed a class on the lumbar spine. One exciting epiphany for me was the thought that pain relief obtained through spinal manipulations are mediated not through mechanical "release" of joints, but rather through neurophysiological inhibition of pain neurons. Chiropractors and therapists in the past explained the efficacy of manipulations referring to poor spinal alignment due to capsular restrictions in the small spinal joints. Manipulations were purported to "adjust" the spine by "freeing" certain capsular restrictions. The idea of manipulations freeing restricted capsules has become decreasingly popular (although I would say at this time not decreasingly tenable) with a paradigm shift toward neurophysiologically decreased spinal pain via manipulations.

In particular two research studies with which I became familiar advanced my own understanding of spinal pain. One study was performed by chiropractors on cats. These cats had force transmitters surgically attached to their 6th lumbar spines. Additionally electrophysiologic readings were obtained from afferent mechanoreceptors (aka: nerves that sense muscle length) of spinal muscles. Oscillations were transmitted to the 6th lumbar spine and as the force on the lumbar bone approached that of a spinal manipulation an abrupt increase was sensed in electrical activity in the afferent mechanoreceptors. Doubtless this increased sensory input to the spianl cord has an effect on regulating the back. I would propose that stimulation of mechanoreceptors could be an initial step of a pathway of spinal reflexes to neurologically block the conduction of local pain sensations. In short, the vibrations from manipulations stimulate sensory nerves in spinal muscles which could in turn block pain conduction and recalibrate muscle resting tone. This theory (commonly referred to as the "gait theory" of pain inhibition) has been well developed in the medical field and there exist substantial scientific data which can be used to validate it.

A second study looked at the use of lumbar spinal manipulations for patients who satisfied a clinical prediction rule. This rule was developed to help clinicians predict which patients would benefit from manipulations. One interesting side note in this study was that each patient was manipulated at the same spinal level regardless of the location of "reduced capsular tightness". The location of the manipulation was not the determining factor in the success of the manipulation. One could conclude that it doesn't mater at which lumbar joint the manipulation was performed. This does not bode well for the older idea of "freeing" capsular restrictions at specific joints to relive pain. It does, however, fit well with the idea of neurophysiological reductions in pain sensation via a mechanically stimulated reduction of resting muscle tone and a lowering of resting membrane potentials in pain neurons.

My parting thoughts relates to truth and metaphor. As mentioned above, chiropractors and therapists used the idea of "freeing" capsular restrictions when performing manipulations. This is a prime example of the use of metaphor to convey powerful meaning to a patient about returning to health. The patient feels that something is "stuck" in her back and the therapist says he is "freeing" that which is "stuck." Regardless of whether or not this metaphor has been a true description of the biomechanical and neurophysiological reality or not, it has been helpful in conveying a sense of efficacy. During my career as a therapist I regularly am asked for explanations about function of the human body. "Why does my leg hurt when I walk?" "Why is my arm muscle weak some days but not others?" The questions are always personal and always difficult to answer in a meaningful and helpful way. Often times I employ metaphor for the purposes of encouraging the patient's understand of procedures and increase motivation towards compliance in therapy. The ethical qualm for me has become, how do I speak in metaphor while honestly tipping my hat to the ambiguity present in human understanding. Currently I am beginning to steer away from answers to 'how' questions and focusing on 'what' questions. I'll give anecdotes of what others have done to successfully overcome spinal pain and just skip over the how altogether. Intellectually these are dull answers but they are more true than any metaphor I can dream up to describe the latest theory. I do not deem the linguistic tool of metaphor to be intrinsically misguiding; rather I deem metaphor that construes fiction as fact to be false in the worst way--deception.