The “Degenerative Cascade”

The spine is dynamic and is constantly modeling and remodeling, a process greatly influenced by the physical stresses placed upon it. These changes can positively or negatively impact neurological status and spinal biomechanics. There are a certain set of conditions associated with degeneration of the aging spine. Most commonly seen disorders include degenerative disc disease, segmental dysfunction or instability, zygapophyseal arthropathy, spinal stenosis, cervical spondylotic myelopathy, and radiculopathy. To better understand these conditions and which therapeutic approach would be most appropriate, we need to understand the pathophysiology of the degenerating spine.

Currently, the most widely accepted theory of intervertebral disc degeneration pathophysiology is a three-stage approach described by Kirkaldy-Willis.¹ Stage I describes the acute pain of an initial insult occurring in the early 20 to 30 years of life. This is the beginning of what Kirkaldy-Willis described as the “degenerative cascade.” Repetitive microtrauma to the vertebral endplates results in ischemic events that can compromise the nutritional and metabolic transport to the disc. This microtrauma may also be responsible for an alteration in proteoglycan content resulting in decreased disc hydration and subsequent load-bearing capacity. Clinically, the patient will present with intermittent and self-limiting pain. However, the pain experienced may be extremely debilitating because of the innervation of the outer third of the annulus by the sinuvertebral nerve.

Stage II, or the instability stage, represents continued disc dehydration and loss of disc height. Increased force transfer to the annulus occurs with the subsequent loss of disc height.¹ This stage occurs later in life, between 30 and 50 years of age, and the patient presents with periods of low back pain which is usually more intense and protracted in duration.

Stage III, known as the stabilization stage, usually occurs in the 60 and older population. There is continued end-stage tissue damage and attempts at repair. Disc resorption leads to disc collapse, endplate destruction, fibrosis, and osteophyte formation. The patient usually presents with symptoms of neurogenic claudication or radiculopathy from central, lateral recess, and/or foraminal stenosis.¹

The Focus of Rehabilitation

Aging is a normal process, and understanding the anatomic and physiological changes that occur with normal aging will allow for optimal rehabilitation. Some age-related bodily changes may be misunderstood and can unnecessarily limit daily activities; however, when designing an exercise program for older adults, the possibility of a latent or active disease process must be taken into consideration. The exercise prescription must be individualized based on the health status and the goals of the individual.

The focus of rehabilitation in the aging population should consist of the following: (1) increasing, restoring, or maintaining range of motion, physical strength, flexibility, coordination, balance, and endurance; (2) recommending adaptations to make the home accessible and safe; (3) teaching positioning, transfers, and walking skills to promote maximum function and independence within an individual’s capability; (4) increasing overall fitness through exercise programs; (5) preventing further decline in functional abilities through education, energy conservation techniques, joint protection, and use of assistive devices to promote independence; and finally, (6) improving sensation, and joint proprioception, and reducing pain.

A conservative approach is usually warranted, considering the patient population’s comorbidities. Any form of aerobic activity should be structured to provide adequate rest and minimal imposition of joint stress.² Initiating resistance training under close supervision with the least amount of resistance can provide significant benefit in the aging population.³ As with younger individuals, functional range of motion is extremely important and all aspects of physical therapy should be preceded by appropriate stretching and warm-up to prevent further injury.

Much has been reported on the appropriate amount of rest a patient with acute back pain should adhere to. What has become clear is that excessive immobility will translate to decreased aerobic capacity, impaired flexibility, loss of muscle strength, and promotion of bone demineralization, all of which will exacerbate and promote further pain and disability.⁴ Ultimately limiting bed rest to a short period proves to be less detrimental than extended periods of bed rest, even in the population of patients who exhibit radiculopathic symptoms.⁵

Pathophysiologic Basis for Rehabilitation

The goal of exercise for the treatment of acute back pain is pain control. Therefore initiating exercises based on which direction of motion either increases or reduces pain will provide more positive outcomes.^6,7 Movement into flexion or extension will centralize low back pain and reduce the patient’s symptoms.

Extension-based exercises, or McKenzie exercises, may be effective in reducing discogenic pain⁸ by alleviating pressure on the posterior annular fibers and thereby altering intradisk pressure,⁹ which will concurrently allow anterior migration of the nucleus pulposus¹⁰ and subsequent decreased tension on the nerve root.¹¹ Contraindications to extension-based exercises include segmental instability, bilateral sensory or motor deficits, large or uncontained herniations, or an increase in radiculopathic symptoms. If the patient responds well to extension exercises and demonstrates centralization of his or her pain, repeated extension posturing while standing and use after sitting or forward bending is stressed. If the patient does indeed have segmental instability, manual blocking of extension at that level can be achieved by the therapist, and the patient can be educated on preventing segmental mobility.

Flexion-based exercises, or Williams exercises, may be effective in decreasing zygapophyseal joint compressive forces, thus alleviating the compressive load to the posterior disc, decompressing the intervertebral foramen, stretching hip flexors and paraspinal musculature, and strengthening core stabilizers, such as the abdominals.¹² Included in flexion-based exercises are pelvic tilts, which can be performed either with bent knees, straight legs, or standing, depending on the comfort level of the patient. These exercises will help decompress the zygapophyseal joint and help mobilize the pelvis for sacroiliac joint dysfunction.

When dealing with patients with idiopathic scoliosis it is widely understood that therapeutic exercises cannot prevent the progression of the curvature; however, there is a clear role for rehabilitation in this setting. The fundamental goal is to prevent the progression of secondary morbidities. Exercises to restore range of motion and strength should begin early. The patient will benefit from exercises that focus on improving trunk posture and alignment, which may prevent the development of a pathological curve. Abdominal and gluteal strengthening helps prevent deconditioning and atrophy, whereas lower extremity hip flexor stretching works well to prevent contractures.¹³

Comorbidity Influence on Rehabilitation

The key to a successful rehabilitation approach in any patient population is conservatism and understanding the patient’s limitations. Interaction between exercise and the medical condition is essential to grasp so that deleterious exercise effects can be avoided, particularly when dealing with patients that may have cardiac disease, diabetes mellitus, obesity, osteoarthritis, peripheral vascular disease, or cancer.

In patients who have cardiac comorbidities, a typical rehabilitation approach would include isotonic, aerobic, and rhythmic exercises involving large muscle groups, as well as isometric and resistive exercises, particularly for patients with left ventricular dysfunction. Instituting heart rate and systolic and diastolic blood pressure parameters varies depending on the pathology.

Patients that have pulmonary comorbidities such as chronic obstructive pulmonary disease (COPD) respond to controlled breathing techniques to improve pulmonary function parameters with diaphragmatic breathing exercises. The need to monitor for hypercapnia is an essential indicator for the need for muscle rest periods to be added to the exercise program. As with cardiac precautions, pulmonary precautions are instituted with regard to respiratory rate and oxygenation.

Osteoporosis must be considered when therapeutic exercises are instituted. Physical therapy should be tailored to individual fitness level and anticipated propensity to fracture or current fractures. Precautions include avoiding spine flexion exercises, which may predispose to vertebral compression fracture.

Physiologic Factors of Spinal Stabilization

Stability of the lumbar spine requires both passive stiffness, through the osseous and ligamentous structures, and active stiffness, through musculature. Any injury to the passive supporting network of the spine will result in instability.¹⁴ That is why optimal muscle strength can protect the damaged spine from repetitive shear forces or nonphysiologic weight bearing. The thoracolumbar fascia acts as a physiologic corset, in essence providing a link between the lower limb and the upper limb, supporting the spinal segments and providing proprioceptive feedback to the individual. Therefore a comprehensive stabilization or facilitation of the abdominal, pelvic, and trunk muscles, which attach to the thoracolumbar fascia and provide for flexion, extension, and rotation of the spine, is a key component to improving trunk strength and preventing future exacerbation of pain.

Stabilization of the spine progresses through a sequence of events that begins with strengthening of the smaller intersegmental local muscles of the lumbar spine, such as the multifidi and transversus abdominis. The multifidi usually span a few segments and thereby have a poor mechanical advantage as a significant mover of the spine, but they do play a role in rotational movement and balancing of the shear forces of the spine.^15,16 Initial exercises focus on obtaining isolated control of these muscles without substitution.

The next phase of stability training focuses on neutral spine stabilization exercises, regarded as the “safe,” pain-free position.¹⁷ A neutral spine position decreases tension on ligaments and joints, appropriate segmental forces with respect to the disc, and the zygapophyseal joint provides optimal stability with axial loading and gives the patient the greatest level of comfort. The neutral spine is located through various body positions, which is followed by lower extremity exercises initially without resistance, then with resistance while maintaining a neutral spine. This approach will help facilitate coordination, endurance, and strength.

Finally, the prime movers, including the rectus abdominis, erector spinae, and latissimus dorsi, are strengthened. Traditionally abdominal exercises have been emphasized as part of a low back exercise program, as well as lower extremity strengthening because of their integral association with the trunk. This is particularly important during lifting, where education in proper bending and lifting techniques is stressed to prevent new-onset low back pain. Lower extremity muscular flexibility is extremely important for optimal physiologic lumbar motion. Hip flexors and extensors attach to the pelvis and will essentially dictate lumbar positioning, which can result in excessive stress on lumbar segments and the sacroiliac joint. If a patient has tight hip flexors, this will result in extension of the lumbar spine and subsequent shear forces on the intervertebral disc. A slight alteration in the kinetic chain biomechanics will promote pain and disability. Self-stretching techniques should be initiated as early as possible in the neutral pelvic position.

Core Stabilization Exercises

The most common stabilization exercises incorporated in a routine rehabilitation program include (1) finding the neutral position, (2) sitting stabilization, (3) prone gluteal squeezing exercises, (4) pelvic bridging progression, (5) kneeling stabilization, (6) wall slide quadriceps strengthening, (7) position transition with postural control, (8) curl-ups, (9) diagonal curl-ups, (10) side bridging, and (11) straight leg lowering. Fitness programs that follow core-strengthening principles include Pilates, yoga, and taichi—all of which must first be determined appropriate in the aging population with certain limitations.

Figures 17-1 and 17-2 demonstrate abdominal strengthening exercises, showing proper activation of the muscles around the abdominal area to support the low back in static and dynamic positions. Daily dynamic load bearing causes the muscles to contract around the viscera to form a stable core region against which the forces are balanced, in coordination with posture.

FIGURE 17-1 Abdominal exercises: single leg curl.

FIGURE 17-2 Abdominal exercises: lying trunk twist.

Figures 17-3 to 17-5 demonstrate back and buttock exercises, which along with abdominal training help control movement, transfer energy, shift body weight, and move in any direction. Weak core muscles result in loss of lumbar lordosis and postural deficiency. Stronger, more balanced core musculature helps maintain appropriate posture and reduce strain on the spine.

FIGURE 17-3 Buttock and back exercises: floor bridging.

FIGURE 17-4 Buttock and back exercises: single-leg bridging.

FIGURE 17-5 Buttock, back, and abdominal exercises: horse stance.

Figures 17-6 to 17-8 demonstrate trunk and full body exercises, which are important for proper coordination patterns and abdominal and low back endurance.

FIGURE 17-6 Trunk and full body exercises: modified weighted lunges.

FIGURE 17-7 Trunk and full body exercises: standing weighted obliques.

FIGURE 17-8 Trunk and full body exercises: standing weighted obliques.

The ultimate goal of core stabilization is to achieve optimal task performance while maintaining appropriate trunk position and control, which will help ensure the prevention of recurrent injury. As always, consideration must be given to individual musculoskeletal response to the exercise and the overall metabolic demands.