Many theories have been proposed to explain the clinically observed phenomenon of hypomobility.³ One theory proposes that there is entrapment of synovial material or a synovial meniscoid between the two opposing joint surfaces. There is some anatomic evidence that meniscoids do occur, but whether they actually cause joint restriction has not been demonstrated. The joint meniscoid has innervation by C fibers that suggest nociception function.

A second theory suggests that there is a lack of congruence in the point-to-point contact of the opposing joint surfaces. This theory postulates alteration in the normal tracking mechanism between the joint surfaces and that the role of manual medicine is to restore the joint to the “right track.”

A third theory suggests an alteration in the physical and chemical properties of the synovial fluid and synovial surfaces. In essence, the smooth gliding capacity has been lost because the opposing surfaces have become “sticky.” Following a mobilization with impulse (high-velocity, low-amplitude thrust) procedure, in both vertebral and extremity joints in which separation of the joint surfaces has occurred, the “cavitation” phenomenon has been demonstrated. In addition to the audible popping sound, there has been the observation of a negative density within the joint on x-ray. This “vacuum phenomenon” appears to have the density of nitrogen, and this gaseous shadow is present for a variable period before it is no longer observable. This observation suggests a change from liquid to gaseous state as a result of the thrusting procedure.

A fourth theory regards the restriction of motion as a result of altered length and tone of muscle. Some muscles can become hypertonic and shortened in position, whereas others become lengthened and weaker. Of greatest significance is the loss of muscle control. Physiologic control of muscle is highly complex and includes the behavior of mechanoreceptors in joints and related soft tissue, muscle spindle and Golgi tendon apparatus, cord level and propriospinal pathway reflexes, pathways to the motor cortex, corticobulbar and corticospinal pathways modulated by the cerebellum, and the final common pathway of the alpha motor neuron to muscle fiber. Any alteration in afferent stimulus to this complex mechanism or alteration of function within the system can result in dysfunctional muscle activity and ultimately affect joint mechanics and dynamic stability. Any alteration in muscle tone then restricts normal motion and serves as a perpetuating factor in altered joint movement. Whether the abnormal muscle activity is primary or secondary to the vertebral dysfunction is purely conjectural. However, altered muscle component of a vertebral dysfunction should always be dealt with in some fashion by the treatment provided. Using the analogy of a computer, the nervous system can be viewed as the software and the musculoskeletal system as the hardware. Altered function of the nervous system (the software) does not allow the musculoskeletal system (hardware) to function appropriately. Some manual medicine practitioners view the effectiveness of manual medicine treatment as being the reprogramming of the software through the alteration of mechanoreceptor behavior at the joint and soft-tissue levels.

A fifth theory considers changes in the biomechanical and biochemical properties of the myofascial elements of the musculoskeletal system, the capsule, the ligamentous structures, and fasciae. When these structures are altered through traumatic, inflammatory, degenerative, or other changes, reduction of normal vertebral mobility can result.

Regardless of the theory to which one might subscribe, the clinical phenomenon of restricted vertebral motion can be viewed as the influence on the paired zygapophysial joints of the segment. We speak of the capacity of facets to open and
close and refer primarily to the accordion-type movement, not separation-type movement. In forward bending, the facets should normally open, and in backward bending, they should close. If something interferes with the capacity of both facets to open, forward-bending restriction will occur. Conversely, if something interferes with both facets’ capacity to close, backward-bending restriction will occur. It is also possible for one facet to move normally and the other to become restricted. If, for example, the right facet does not open, but the left functions normally, right-side bending is possible, but left-side bending is restricted. Since side bending and rotation are coupled movements in the typical vertebral segments, rotation can also be affected by alteration in facet joint movement.

Dysfunctions in the vertebral column can be described as single-segment dysfunctions involving one vertebral motion segment and group dysfunctions involving three or more vertebrae. After one completes a screening-and-scanning examination and fine-tunes the diagnostic process to segmental definition, one is particularly interested in the motion(s) lost by the vertebra(e) involved. There are many methods to accomplish the process. The most commonly used one is palpating the same bony prominence of two or more vertebrae (e.g., spinous processes or transverse processes) and actively and/or passively putting the segment(s) through successive ranges of movement into forward bending, backward bending, side bending right, side bending left, rotation right, and rotation left, comparing the motion of one segment with another. These procedures are most frequently done passively as the operator attempts to define restriction and quality of restriction of movement in one or more directions. Although this method is frequently effective, it does have two serious drawbacks. First, every time you introduce multipleplane motion in a dysfunctional segment diagnostically, there is a therapeutic effect since you are accomplishing a mobilization without impulse (articulatory) procedure. This results in your finding being constantly under change. A second disadvantage is the difficulty in making an assessment following a treatment procedure, that is, knowing whether you have modified the amount of range present before the procedure. It is difficult to accurately remember all of the nuances of motion restriction that were present prior to the therapeutic intervention.

A second method, preferred by this author, is to follow a pair of transverse processes through an arc of forward bending and backward bending and interpret the findings on the basis of the phenomena of facets opening and closing. Regardless of the method used, one can describe vertebral motion from the perspective of the motion available, the position in which the segment is restricted, or the motion of the segment that is restricted.

A simple and accurate method used to consistently appreciate and interpret motion of a vertebral segment is to place and maintain your thumbs over a pair of transverse processes, sight down your thumbs along the coronal plane, and observe them through an arc of forward bending and backward bending. This method is excellent for beginners who are gaining confidence in their palpatory discrimination. Capitalizing on depth perception, it also allows one to appreciate subtle motion differences.

In Table 6.1, a suffix is used in each term, either a static suffix representing the position of the segment or a motion suffix, which describes the motion available or the motion lost. The current convention of describing vertebral dysfunction is either the position of the restricted segment or the motion that is lost in the restricted segment. Therefore, a segment that is backward bent (extended), right rotated, and right-side bent has forward bending (flexion), left-side bending, and left rotation restrictions. A plea is made for the use of appropriate terminology to describe either position or motion restriction. One should learn to translate between the two systems of positional and motion restriction diagnosis, but clearly, a statement of terms is necessary for accurate communication between examiners.

Single vertebral motion segment dysfunctions in all areas of the spine can be easily identified by the finding of hypertonicity of fourth-layer vertebral muscle in the medial grove adjacent to the spinous processes. In the cervical spine, this hypertonicity is best appreciated with the patient in the supine position, and in the lumbar spine with the patient in the prone position, in each instance when paravertebral musculature is quiet. Palpable fourth-layer muscle hypertonicity is not present in normal vertebral motion segments. When fourth-layer hypertonicity is palpable at a vertebral level, the practitioner should identify the motion characteristics of that vertebra in relation to the one above and the one below.