Motion palpation works so well because it is based upon sound biomechanical facts. It represents a functional analysis of the joints of the body. But, like any evolving body of knowledge, refinements and changes are in order when we expand or re-think our basic concepts. It is to chiropractic's advantage that no one man is seen as the ultimate authority on a given topic, including motion palpation.
In considering segmental motion, it is necessary to define the movements involved. This paper is not intended to be a biomechanical treatise, so we will consider only flexion and extension of the lumbar spine.
I. A. Kapandji tells us that during flexion of a motor unit, the body of the upper vertebra tilts and slides anteriorly, reducing the thickness of the intervertebral disc anteriorly and increasing it posteriorly. At the same time, the inferior articular processes of the upper vertebra slide superiorly and move away from the superior articular processes of the lower vertebra. Similarly, during extension of the motor unit, the body of the upper vertebra tilts and moves posteriorly, flattening the disc posteriorly and expanding it anteriorly. Meanwhile, the articular processes of the lower and upper vertebra become slightly more tightly interlocked. From this description, it can be said that flexion at the facet level is defined as the gliding of the articular processes of the uppermost vertebra superiorly. Likewise, extension at the facet level may be defined as the gliding of the articular processes of the uppermost vertebra inferiorly.
Figures 1 & 2
Drs. Richard C. Schafer and Leonard J. Faye describe palpation of extension in the lumbar spine as contacting the inferior articular process of the superior vertebra of the motor unit, and applying force such that it moves anteriorly. The motion elicited would involve gliding of the articular process superiorly as the joint is closed. From the biomechanical standpoint that was previously established, this would not be extension. This motion would have to be defined as flexion at the facet level, even though the superior vertebra is moving posteriorly on the inferior vertebra. It is, after all, the facet joints we are checking and not the gross range of motion. It should also be pointed out that if the palpatory force were producing apposition of the articular processes (closing of the joint space), any springy movement detected would be this gliding or translation of the joint surfaces. If the articular process of the uppermost vertebra was gliding inferiorly (true extension), the joint would be in an interlocked and closed position. No springy end-feel would be possible.
When Drs. Schafer and Faye discuss the adjustment of an extension fixation in the lumbar spine, they describe it as a contact on the articular process and an impulse directed anteriorly and superiorly. Thus, conceptually, the adjustive force reproduces the motion checked with palpation. The joint space would be closed by the adjustment and the articular process of the upper vertebra would glide superiorly.
I submit to you the following points to consider: When extension is palpated in the lumbar spine, a digital contact on the articular processes is not possible. The thickness of the soft tissue in the area dissipates the pressure exerted with the palpating thumb and keeps it more than an inch away from the intended contact. The palpatory force exerted is spread out and will be taken up by the most prominent bony landmark beneath the thumb, the mamillary process of the inferior vertebra. As the patient is leaned backwards and force is exerted anteriorly, extension is being palpated but in a way that differs from what has been conceptualized in the past. As the patient is leaned backwards, the superior vertebra of the motor unit moves posteriorly on the inferior vertebra and the articular processes are brought into apposition. When palpatory force is exerted upon the mamillary process of the inferior vertebra, the vertebra moves anteriorly, relative to the one above it, and the joint space opens. The springing sensation detected is the opening or gapping of the facet joint.
Figure 3
When adjusting an extension fixation, the contact is on the mamillary process of the inferior vertebra of the motor unit. An impulse delivered anteriorly and superiorly moves the inferior vertebra anteriorly, relative to the vertebra above it, and the facet joint is opened with an audible release. This last point is an important one. A joint makes an audible noise when the joint surfaces are separated and the joint space is gapped open. An audible release is not produced by forcing the joint surfaces together. Any adjustive force that produces a "crack" has opened a joint.
By now you have realized that none of this changes the way you palpate or adjust an extension fixation. What I am striving for is a clearer explanation of the mechanics involved. If, however, you accept the idea that the therapeutic effect of an adjustment is closely associated with an audible release, some procedural changes may be in order when palpating other ranges of motion.
A joint "clicks" or "cracks" when it gaps open or separates. Given that the adjustment is intended to correct the dysfunction detected by palpation, and that the effect of the adjustment is to gap open a joint, should we not be checking for the ability of the joint to open or separate with our palpation? Rather than define the movements that we are palpating as strictly a translation or gliding of the facet surfaces through the range of motion represented by the gross movements of the patient's trunk, we should view them as the gapping open of the facet joint which stretches the joint capsule and surrounding tissues in a specific direction. The movement of the patient's trunk may or may not coincide with the motion induced in the joint. This is due to the fact that the joint does not need to be taken to the end of its passive range of motion to be gapped open. In fact, some slack should be left in the joint capsule in order for separation of the joint surfaces to occur.
These concepts will change the way in which a motion restriction is listed or described. The convention from static palpation and x-ray analysis has always been to compare a vertebra to the one directly below it. When we began to consider joint function, rather than vertebral position, this convention was adhered to without question. The contact for both the palpation and adjustment of the dysfunctioning joint has always been described as the superior vertebra of the motor unit. If you accept the idea that the dysfunction palpated represents the failure of a joint to gap open or separate normally, and that the effect of the adjustment is to open the dysfunctional joint, then it must be acknowledged that the contact for both the palpation and adjustment of the joint is often the inferior vertebra of the motor unit. Thus, an extension restriction listed at T5/T6 in which palpating contact was on T5, should actually be listed at T5/T4. Likewise, an adjustment aimed at releasing an extension restriction at T5/T6 in which contact is on T5 has actually produced an audible release by gapping the joint at T4/T5.
Remember, a joint clicks when a joint separates. If we are thinking in terms of palpating and adjusting translation or gliding at the facet level, rather than separation or opening of the joint space, we may be conceptually inaccurate, even though the clinical application is the same. A similar problem was encountered at the inception of motion palpation concepts in general. Generations of chiropractors had delivered adjustments based on vertebral malposition, with good results. They were conceptually inaccurate, while being clinically correct. Motion palpation was proposed as a more conceptually correct way to explain what we do. I offer my ideas as a further refinement of the motion palpation concepts. Your responses are welcome.
Part II will examine, in more detail, the concept of joint play and the separation of facet joints in more detail.
References
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