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.