Paraspinal muscle contraction is essential for spinal stabilization except in the supine position. When bending, the trunk paraspinal muscles must contract to stabilize the multisegmented linkages of the spinal column. If we rapidly change position while bending, we tear these contracted muscles by stretching some of the stabilizing muscles. The diagnosis of paravertebral muscle injury is made by the patient history and physical examination. As with the paravertebral muscles, the appendicular muscle-tendon complexes rupture under similar circumstances, that is, when contracted muscles are suddenly stretched. The concept that the primary function of ligaments is to restrain the extremes of joint motion is inconsistent with good engineering design principles. Chronic subluxation is defined as the momentary displacement of the normal configuration of the two parts of a joint with spontaneous relocation.