Del Inspector Fiscal

Several key aspects of spinal mechanics are discussed in the section on anatomy of the trunk, but to better illustrate the function of the spinal components, this section briefly summarizes several biomechanical aspects to consider when devel- oping exercise and functional progression programs related to the spine.

The sacroiliac joint is designed to attenuate the forces of compression, torsion, and shear. Many injuries seen in sport or in activities of daily living are combi- nations of torque and shear at the joint. Torque is a rotary force of the ilium on the sacrum or the sacrum within the ilia, while shear is a force that is parallel to the joint surfaces. When someone steps into a small hole while running or slips and lands on the ischial tuberosity, an excessive torsional and shear force occurs, potentially resulting in injury to the support ligaments. When this is the injury mechanism, the clinician must carefully monitor exercises, especially those exercises that move the hip joint to end-range positions. When that happen, the resultant tightening of the hip’s capsular and muscle tissues results in a transfer- ence of the force to the sacroiliac joint—often resulting in further torsional and shear stress to the already injured joint.

The lumbar apophyseal joints are oriented primarily in the sagittal plane and thus primarily resist lumbar rotation. In contrast, this joint plane allows more freedom of motion in flexion and extension. Consequently, the design of exercise and functional progression programs must be such that the rate and amplitude of lumbar torsion are controlled. Unchecked rotary stresses increase the com- pressive load to the facet joint contralateral to the side rotated, resulting in a potential compression injury to these joints. When guiding an athlete or patient through exercise from the standing position, the clinician must be sure that the primary rotary movement is via the pelvis over the femurs rather than between the lumbar vertebrae or between the fifth lumbar vertebrae and the sacrum. One of the functions of the oblique muscles is to help control the rate and amplitude of lumbar torsion.

Extension of the lumbar spine also increases facet joint compression; as noted earlier in the discussion about fracture of the pars interarticularis, this can result in lumbar spondylolisthesis. Extension and rotation compound the loading to the lumbar facets, with the rotated facet joint on the contralateral side having the greatest compressive load. While the bone–disc interface is built to withstand compressive loads, the facet joints are not. Care must be taken in exercise posi- tions or movements that adversely load these facet joints in compression.

The review of the intervertebral disc in the first section of the chapter delineates the role of the annulus fibrosus and the nucleus pulposus. The biomechanics of the disc are such that the annulus is particularly vulnerable to excessive tensile loads. Therefore, flexion and rotation of the lumbar spine place an increased tensile load on the annular rings, potentially exceeding their viscoelastic capacity. Like any other ligament of the body that is subject to a tensile load it cannot attenuate, the result can be tearing or overstretching of the collagen framework.

In the case of the annulus fibrosus, the resultant problem is twofold. First, there is a loss of stability between adjacent vertebral bodies because of the damage to the annulus. Second, and perhaps slightly more critical, the altered annulus cannot exert an equal and opposite force against the pressure of the nucleus pulposus.

188 Effective Functional Progressions in Sport Rehabilitation

As a result, the nucleus pulposus may “leak” through defects in the annulus and into the spinal canal, irritating the thecal sac and nerve root complex and resulting in signs and symptoms of nerve root irritation. The nucleus pulposus material can also exert pressure against the annulus, causing it to bulge into the spinal canal and mechanically distort structures such as the posterior longitudinal ligament, thecal sac, or lumbosacral nerve roots. These cases can then present with signs and symptoms of either nerve root irritation or nerve root compression. Intradis- cal pressure is typically higher when in the sitting position, lower when standing, and even lower when lying down. Since the erector spinae group and the psoas major span the lumbar column, contraction of these muscles further increases intradiscal pressure.

Movement of the trunk is tightly integrated with movement of the extremities. In fact, there is evidence that contraction of trunk muscles occurs even before movement of the extremities begins (Hodges and Richardson 1997a, 1997b; Mose- ley, Hodges, and Gandevia 2002). This certainly results in a unique perspective regarding the spine when the subject of functional movement patterns is consid- ered. There is often no observable movement pattern of the trunk; instead there is a coordinated contraction of trunk muscles, allowing the axial skeleton to serve as the stable platform from which the upper and lower extremities can act. The central nervous system programs trunk muscle activity, resulting in anticipatory postural adjustments allowing the body to counter the perturbations encountered with throwing, running, jumping, kicking, and so on.

Conversely, there are functional movement patterns in which the trunk moves powerfully in order to allow the distal segment to move effectively. A proximal (from the trunk) to distal development of force occurs, much like the speed and force felt when standing on the peripheral edge of a merry-go-round while it is spinning rapidly as compared with standing closer to the center. Torque generated through the trunk is passed through the proximal bony levers to the distal bony levers of the extremities in much the same manner.

Thus the functional movement patterns of the trunk can be arbitrarily divided into two broad patterns: (1) those patterns that are focused on coordination and precision of trunk muscle activity in order to optimally position the spine and pelvis and (2) those patterns in which the strength, endurance, and power of the trunk muscles are used to generate torque in order to allow for optimal torques and forces to be applied though the extremity levers. Each is trained in a different way, but often both elements are combined when teaching functional movement patterns.

The first pattern—muscle activity designed to optimally position the spine and pelvis—is often a first step in managing the person who has spine pain or is returning to activity after injury to the spine. The key aspects of determining the optimal position of the spine for exercise is described in the section on functional progressions. This aspect of functional movement patterns is largely a motor control phenomenon. Feedforward and feedback information to the central ner- vous system readies the spinal system to attenuate loads. The normal functional movement pattern of the spine is smooth, coordinated, and sequential. A forward bending motion, for example, involves controlled eccentric muscle activity to allow the pelvis to rotate over the femurs, the last lumbar vertebra to rotate over the sacrum, and the lumbar and thoracic spine to rotate over their subjacent segments. Ultimately, control and balance of the forward bending position are passed from active muscle activity to the connective tissues that support end-range positions of the spinal segments.

Figure 5.18 illustrates this orientation of the muscles from the shoulder girdle, through the trunk, and down to the pelvis. The clinician can appreciate from this perspective the spiral-diagonal muscle fiber orientation. Furthermore, it is easy to recognize that the total spine is geared to multiplanar dynamic movement (i.e., movement simultaneously through the sagittal, frontal, and horizontal planes). In functional training, such combined planar movement must be incorporated instead of uniplanar movement. Throwing is an excellent example of the multiplanar motion of the trunk, as it simultaneously moves from a position of extension, side bending, and lateral flexion to a completed throw position of flexion, rotation to the opposite direction, and lateral flexion to the opposite direction. This winding up and then unwinding via the lengthening and subsequent shortening of the musculature allow the muscles to serve as prime movers over several spinal joints simultaneously, ultimately producing force at the trunk and transfering the force and motion to the distal terminal segment (in this case, the upper extremity).

injuRies

In most injuries to the spine, the precise anatomical structure involved cannot be identified. Nerve root conditions, however, do have a much greater chance of being identified because the signs and symptoms of nerve root irritation and nerve root compression are fairly well understood. When a person has leg pain greater than spine pain, when a straight-leg raise reproduces leg pain, when the pain pattern is clearly demarcated over lower extremity dermatomes, and when pain results in excessive radiation into the lower extremities with gentle spinal motion, the clin- cian can reasonably assume that a radicular disorder—inflammation of the nerve root—is the problem. When there is even greater compromise of the nerve root, signs such as muscle weakness in the related myotome, sensory loss in the related dermatome, reflex changes, or muscle atrophy are all strong indicators of nerve root injury. Thus, one of the first issues to clarify in the examination is whether the case is presenting as a radicular disorder or a nonradicular disorder.

Nerve root injuries are typically caused by chemical or mechanical irritation of the root complex within the spinal canal. There are several mechanisms. Perhaps the most common is intervertebral disc injury. As noted already, the intervertebral disc is often injured by excessive flexion and rotation of the spine. This poten- tially damages the posterior annulus, allowing the nucleus pulposus to cause an inflammatory response in the nerve root.

Another sequelae of disc injury is instability. Just as the loss of the capsular restraints of the glenohumeral joint result in excessive translation of the humerus and glenoid, so too can damage to the annulus fibrosus result in excessive transla- tion of the adjacent vertebral segments. When instability of the spine results, the architecture of the spinal canal and intervertebral foramen change, potentially resulting in nerve root compromise.

The apophyseal joints can also be sources of pain in the low back as well as referred pain into the lower extremities. As noted earlier in the chapter, the apsophyseal joints can be involved with pain syndromes such as overloading of the subchondral bone trabeculae, microfractures of bone trabeculae, mechanical deformation or chemical irritation of joint capsule nociceptors, internal derange- ments from joint loose bodies, vascular disturbances in the bone or soft tissues, and joint inflammation. Referred pain such as that from involvement of the apopshyseal joints is different from radicular pain in that it is characterized by spine pain being worse than leg pain, while radicular pain is characterized by

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leg pain being greater than spine pain. Apophyseal joint injury can occur with extension rotary stresses or end-range flexion and rotary stresses. These joints are quite small, and they cannot tolerate large compression loads. Injury can result in subchondral bone fracture or articular cartilage fissuring. This typically results in a decreased capability of the joints to tolerate loading—a condition resulting in early-onset degenerative joint changes. Besides being a source of pain themselves, degenerative changes of the joint can result in altered architecture of the interver- tebral foramen and the lateral recess of the spinal canal. Both these conditions can result in compromise to the nerve root complex or the vasculature supplying the nerve root complex.

Trauma directly to the spine or trauma resulting in excessive motion of the spine can result in bony fracture. Particularly susceptible areas of fracture include the vertebral body, pars interarticularis, facet, and pedicle. Since the pars, facet, and pedicle are all part of the posterior neural arch, and the major muscles acting to stabilize the spine are attached to the neural arch, spinal mechanics are compromised with any fracture. Most important, however, fracture of the spine can result in compromise of the neural tissues within the spinal canal and the intervertebral foramen.

Spondylolisthesis, one of the most common injuries to the spine in athletics, has already been detailed in preceding sections. This injury to the pars interar- ticularis potentially results in an instability between adjacent spinal segments. Spondylolisthesis alters the shape and volume of the intervertebral foramen, thus potentially compromising the thecal sac, the nerve root, or the dorsal root ganglion at that segmental level.

The disc itself can also be a source of pain and should be suspected when pain is primarily centrally located but has a history of shifting to left of center and right of center. Facet joint pain and muscle pain will typically present as unilateral pain, which makes their presentations subtly different from discogenic pain. The disc is a central structure of the spine, and its pain is typically related as such. Imag- ing studies and invasive disc testing such as discography, however, are typically needed to confirm disc involvement.

Muscles can also be a source of pain and can also refer pain into the lower extremities. Unfortunately, the diagnosis of muscle strain is often given when the clinical presentation is unclear. Advances in imaging technology will no doubt increase the accuracy of muscle strain diagnoses in spinal conditions. Muscle spasm and muscle guarding are very common sequelae with many back injuries, and it is difficult to discern true muscle injury from the protective muscle guard- ing that often occurs with joint, disc, or nerve root injury.

funcTionAl TesTing of The TRunk

This section considers how to assess trunk function in order to develop exercise progressions, keeping the previous detail of the specialized lumbopelvic connective tissues, muscle anatomy, and biomechanics in mind. Many factors come into play when considering testing of the trunk. To develop a training program as specific as possible for the required need, the clinician must not only consider the activity to be performed but also understand and account for the biological factors.

The normal attenuation of loads through the lumbar spine must be such that the load does not exceed the physiological capacity of the tissues. If the load exceeds the physiological capacity of any of the specialized connective tissue elements, such as the articular cartilage of the facet or the collagenous framework of the annulus