Within the diagnostic triad of asymmetry, range-of-motion abnormality, and tissue texture abnormality, perhaps the most significant is the alteration in the range of joint and tissue movement. Loss of normal motion within the tissues of the musculoskeletal system, or one of its component parts, responds most favorably to appropriate manual medicine therapeutic intervention. To achieve the goal of manual medicine intervention and restore maximal, pain-free movement to a musculoskeletal system in postural balance, we must be able to identify both normal and abnormal movements. In the presence of altered movement of the hypomobility type, an appropriate manual medicine intervention might be the treatment of choice. We must strive to improve the mobility of all of the tissues of the musculoskeletal system, bone, joint, muscle, ligament, fascia, and fluid, with the anticipated outcome of restoring normal physiologic movement and maximum functional physiology as well.

In the musculoskeletal system, there are inherent movements, voluntary movements, and involuntary movements. The inherent movement has been described by some authors as relating to the recurrent coiling and uncoiling of the brain and longitudinal movement of the spinal cord, together with a fluctuation of the cerebral spinal fluid. Inherent motion is also the movement of the musculoskeletal system in relation to respiration. It has been observed that during inhalation, the curves within the vertebral column straighten and with exhalation, the curves are increased. With inhalation, the extremities rotate externally and with exhalation, internally. The voluntary movements of the musculoskeletal system are active movements resulting from contraction of muscle from voluntary conscious control. The involuntary movements of the musculoskeletal system are described as passive movements. An external force moving a part of the musculoskeletal system through an arc of motion induces passive movement. The joint play movements described by Mennell are also involuntary movements. They are not a component of the normal active or passive range of movement but are essential for the accomplishment of normal active and passive movement.

In structural diagnosis, we speak of normal and abnormal barriers to joint and tissue motion. The examiner must be able to identify and characterize normal and abnormal range of movement and normal and abnormal barrier to movement in order to make an accurate diagnosis. Most joints have motion in multiple planes, but for descriptive purposes, we describe barriers to movement within one plane of motion for one joint. The total range of motion (Fig. 3.1) from one extreme to the other is limited by the anatomic integrity of the joint and its supporting ligaments, muscles, and fascia. Exceeding the anatomic barrier causes fracture, dislocation, or violation of tissue such as ligamentous tear. Somewhere within the total range of movement is found a midline neutral point.

Within the total range of motion, there is a range of passive movement available that the examiner can extraneously introduce (Fig. 3.1). The limit of this passive range of motion has been described as the “elastic barrier.” At this point, all tension has been taken within the joint and its surrounding tissues. There is a small amount of potential space between the elastic barrier and the anatomic barrier described by Sandoz as the paraphysiologic space. It is within this area that the high-velocity, low-amplitude thrust appears to generate the popping sound that results from the maneuver.

The range of active movement (Fig. 3.1) is somewhat less than that available with passive movement, and the end point of the range is called the “physiologic barrier.” The normal end feel is due to resilience and tension within the muscle and fascial elements.

Frequently, there is reduction in available active motion due primarily to myofascial shortening. This is often seen with aging, but it can occur at all ages. It is the stretching of this myofascial shortening that all individuals, particularly athletes, should do as part of physical exercise. Stretching exercise to the muscles and fascia enhances the active motion range available and the efficiency of myofascial function.

When motion is lost within the range, it can be described as major (Fig. 3.2) or minimal (Fig. 3.3). The barrier that prevents movement in the direction of motion loss is defined as the “restrictive barrier.” The amount of active motion available is limited on one side by the normal physiologic barrier and on the opposite side by the restrictive barrier. The goal of a manual medicine intervention is to move the restrictive barrier as far into the direction of motion loss as possible. Another clinically describable phenomenon associated with motion loss is the shifting of the neutral point from midline to the middle of the available active range. This is described as the “pathologic” neutral and is usually, but not always, in the midrange of active motion available.