Degenerative Spine Disease

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Chapter 30 Degenerative Spine Disease

James K.C. Liu, Edward C. Benzel

Clinical Pearls

• Degeneration in the spine is a naturally occurring process that can be understood through the “three-joint complex,” which is composed of the intervertebral disk and the two dorsal articulating joints. Degeneration of any one joint leads to degeneration of the other two, initiating a cascade that leads to spinal degenerative disease.

• A detailed history and neurological examination can be used to isolate the level at which the underlying disease originate. Understanding the presenting symptoms can help to understand the degree of degeneration present and then start to formulate the most efficient treatment plan.

• Conservative treatment is a feasible first course of action to treat the clinical manifestations of first-onset degenerative spine disease. The most commonly accepted modalities range from anti-inflammatory therapy to exercises designed to increase muscle strength and relieve joint loading.

• Surgical intervention to treat symptoms that result from degenerative spine disease include diskectomy, laminectomy, and fusion procedures. Despite continuing controversy surrounding which procedure is most effective in providing long-term relief, the authors believe that the best course is to understand the underlying disease and select the least invasive procedure to target that pathological area.

• Fusion remains a heavily debated topic. Multiple studies have been performed to evaluate the benefits of fusion in the spine, none of which have provided definitive class I evidence to indicate a clear benefit. However, in addition to the class II and III evidence showing some benefit in selected patients, spine fusions may be indicated based on the need to create stability in an unstable region of the spine.

Back pain is the one of the most common reasons for primary care physician outpatient visits in the United States. A survey performed in 2002 reported that approximately 26% of Americans had low back pain and 14% had neck pain.¹ In 2002, 890 million office visits were due to back pain. As may be expected from these statistics, the cost associated with the diagnosis and treatment of spine-related problems is astronomical. The Journal of the American Medical Association reported $86 billion in health expenditures in 2005 devoted to spine-related problems. This amount was an increase of 65% from 1997.²

The process that leads to the development of neck and back pain can be segmented and categorized into acquired and congenital/developmental processes. This chapter focuses on the naturally occurring events that lead to degeneration of the spine.

Anatomy and Physiology of Spine Degeneration

Three-Joint Complex

An understanding of the process of spinal aging involves an understanding of the relevant anatomy of the affected spine. In order to understand the sequence of events that leads to degeneration of the spine, efforts have been made to deconstruct the spine in order to demonstrate the nature of the degenerative process, for such a process begins in one segment of the spine and then spreads to adjacent segments.

The Kirkaldy-Willis three-joint complex theory deconstructs the spine into three joints that are affected in the degenerative process. At each level of the spine there exists the “three-joint complex,” composed of the intervertebral disk and two dorsal zygapophyseal joints.³ Kirkaldy-Willis proposed that the three joints are linked, in that degeneration of one joint leads to degeneration of the other two joints, and ultimately results in the global manifestations of degenerative spine disease (Fig. 30.1).

FIGURE 30-1 Three-joint complex. Each motion segment is composed of a three-joint complex, which consists of one intervertebral disk space and two dorsal zygapophyseal joints. Degeneration in one of these joints often leads to accelerated degeneration in the adjacent joints. This results in a relatively predictable progression of degeneration.

Degeneration, as stated, typically begins in one joint. This, in and of itself, may lead to clinical manifestations. It, however, is the interplay of the three-joint complex as a whole that leads to degenerative disease, as it typically presents in the clinical setting. The three-joint complex is first examined individually here, and then a discussion of the interaction of pathological changes that lead to spinal stenosis follows.

The intervertebral disk has three components: the nucleus pulposus, which is surrounded by the annulus fibrosis, and the cartilaginous end plates.⁴ The nucleus pulposus is a semigelatinous structure situated near the center of the disk complex. It is a remnant of the notochord and is composed mainly of mucopolysaccharides with salt and water. The surrounding annulus fibrosis is a multilayered circular structure that surrounds the nucleus pulposus. It is composed of fibrocartilaginous lamellae and is stiffer than the nucleus. It is usually thicker ventrally than dorsally.⁴

The process of disk degeneration is a part of the natural aging process. Repetitive loading results in forces that foster degeneration. As part of the normal aging process, the intervertebral disk becomes desiccated as collagen and proteoglycans are replaced with fibrous tissue. As axial pressure continues to be repetitively applied to the disk, the less compliant annulus fibrosis develops circumferential tears that are most frequently observed in the dorsolateral aspect of the annulus.⁵ These tears can enlarge and eventually develop into radial tears. These tears are areas through which the nucleus pulposus may herniate. Since the nucleus pulposus is situated relatively dorsal in the disk space, herniation typically occurs dorsally into the spinal canal. The presence of the posterior longitudinal ligament forces disk herniations laterally. The aforementioned anatomical and biomechanical factors often lead to the common classical dorsolateral disk herniation.

Annular tears also lead to a weakening of the annulus fibrosus and to circumferential bulging of the annulus, which in turn results in a loss of disk height. Disk bulging can lead to osteophyte formation at the attachment of the annulus to the vertebral body. This contributes to narrowing of the central canal, as well as the neural foramen.

Dorsal Joint Degeneration

The dorsal aspect of the intervertebral joint is composed of articulating facets from the superior and inferior vertebral segments. The joints are diarthrodial joints with articular cartilage, a synovial membrane, and a capsule.⁶ Studies have shown that natural aging of the dorsal joints passes through a progression that includes synovial reaction, fibrillation of the articular cartilage, osteophyte formation, and ultimately, laxity of the joint capsule. This inevitably results in instability of the joint complex and can lead to subluxation of the joint. Osteophytic formation from the joint protruding into the spinal canal can also contribute to stenosis, particularly in the lateral recesses of the spinal canal.

Combined Three-Joint Complex Degeneration

The three-joint complex degeneration concept implies that the individual aging process of the intervertebral disk and dorsal facet joints are interlaced to contribute to the clinical manifestation of spondylosis. As disk degeneration occurs, loss of disk height contributes to subluxation of the dorsal joints. The instability caused by the loss of disk height compounds the natural process of facet joint degeneration, which includes capsular laxity. Eventually, subluxation of the dorsal joints can occur. This results in subluxation of the rostral vertebral body ventrally with respect to the caudal vertebral body (spondylolisthesis). Such translation of the vertebral segments can result in further narrowing of the neural foramina, manifesting as lateral nerve root entrapment. Lateral nerve root entrapment can also result from loss of disk height. Disk resorption reduces the rostral-caudal dimension of the neural foramina, thus further contributing to this presentation.

Three Stages of Degenerative Spine Disease

Using the three-joint complex as a basis for degenerative spine disease, Kirkaldy-Willis categorized the degeneration of the spine into three stages to rationalize the natural history of spine degeneration, as well as to provide an algorithm to tailor treatment for each stage (Fig. 30.2).

FIGURE 30.2 The three stages of degenerative spine disease. The first stage is dysfunction, which results primarily in simple disk herniations, often necessitating a surgical diskectomy. Progression of the degenerative process results in destabilization and abnormal spinal motion. This may necessitate the performance of a fusion procedure to stabilize the spine. The most advanced stage of degeneration is that of restabilization. The spine become more stable due to osteophyte formation, but in doing so creates a central and lateral recess stenosis, which often necessitates decompression, with or without a supplemental fusion. Red arrows designate the most likely surgical strategy for each phase of the degenerative process.

Clinical Presentation

The manifestation of clinical symptoms depends upon the type and degree of ongoing degeneration. A careful history and clinical examination enables the examiner to determine the stage of degeneration and the underlying disease. Determining the fundamental disease process facilitates the formulation of a focused plan of treatment, without the performance of unnecessary surgical intervention, to prevent advanced symptomatic segmental degeneration.

The first stage of degeneration as described by Kirkaldy-Willis, dysfunction, is characterized in the disk joint by annular tears and herniation of the nucleus pulposus. This leads to intervertebral disk herniation, one of the most common reasons for back pain, leg pain, and spine surgery. Disk herniation typically occurs in the dorsolateral aspect of the disk interspace. The strength of the posterior longitudinal ligament causes a paramedian migration and herniation of the nuclear material, which may result in impingement of a single nerve root, causing pain known as radiculopathy. Compression of the nerve root typically manifests as pain, but can also result in numbness or weakness in the distribution of the affected nerve root.

With cervical spine involvement, the patient often complains of a shooting pain that travels from the shoulder to the fingers. The exact location of the shooting pain can help to isolate the level of the disk herniation. Cervical disk herniations most often occur at the C5-C6 and C6-C7 levels.⁷ In the lumbar spine disk herniations most commonly occur at the L4-L5 interspace⁸ and manifest as shooting pain that often begins in the buttock region and passes down the legs, with or without extension into the feet. Once again, the distribution can help to localize the level of herniation. Thoracic disk hernations are much less common than cervical or lumbar disk herniations. In a study of 82 patients with thoracic disk herniations, 76% of the presenting complaints consisted of pain. Of the patient who presented with pain, 41% presented with localized back pain, thus relegating surgical management to the “precarious” category in most clinical cases.⁹

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