Introduction

Adult scoliosis is a common and sometimes disabling degenerative condition of the spine, with an overall prevalence reported in up to 60% of the elderly population.¹ Adult scoliosis has a marked impact on patients’ general medical health and well-being; it has been shown that scoliotic patients have a significantly depressed perception of their mental and physical health in comparison with the general U.S. population. Even when individuals are compared with those having additional comorbidities, the adult scoliosis patients rate lower in clinical health assessment. In addition to the subjective considerations of this progressive disease, severe pain and disability occur in this population.²

The management of patients with symptomatic spinal deformity and spinal stenosis is controversial. The greatest challenge confronting contemporary spine surgeons in management of the aging patient population is patient selection; the surgeon must balance benefits, risks, complicatios, and the durability of various interventions. Analysis and application of these is difficult because of the limited number of prospective outcome studies and because there is a wide array of different interventions used in this patient population. The spine surgeon is increasingly confronted with the older patient and must decide on a suitable yet realistic treatment plan while considering the social and psychological factors affecting this unique patient population.

Pathoanatomic Changes

Aging of the spine is similar to the degenerative process throughout the body. The physiologic aging cascade affects the anatomic structures and creates progressive changes that are biomechanical, biochemical, and physiologic. Changing pathophysiology affects the structure and function of the spine, which becomes relatively important because of the spine’s role as the central foundation for the human upright posture.

Degenerative adult scoliosis occurs as result of both macroinstability and microinstability. There is segmental instability and translation of adjacent vertebral aligment in the lumbar spine, acquired secondary to years of chronic disc disease and progressive facet incompetence. Disc degeneration leads to disc collapse and bulging of the annulus fibrosus and posterior longitudinal ligament, thus triggering subperiosteal osteophyte formation. Additionally, articulating facets undergo degenerative changes that result in hypertrophy, calcification, and thickening of the ligamentum flavum. These changes eventually result in forward and translational displacement of the posterior elements that, in combination with degenerative disc changes, result in severe narrowing of the spinal canal and neural foramen (spinal stenosis) to cause symptoms of neurogenic claudication and radiculopathy.

Definition of Stenotic Degenerative Disease in Deformity

Lumbar spinal stenosis is defined as a narrowing of the spinal canal that produces compression of the neural elements before their exit from the neural foramen. The narrowing may be limited to a single motion segment (two adjacent vertebrae and the intervening intervertebral disc, facet joints, and supporting ligaments) or it may be more diffuse, spanning two motion segments or more.

Adult deformity of the spine with degenerative disease can be a major contributing factor in the narrowing of the spinal canal. Adult degenerative scoliosis occurs on the right and left sides with equal frequency. Adult degenerative scoliosis develops as a result of asymmetrical narrowing of the disc space and vertebral rotation secondary to the instability caused by degeneration of the disc.

Neural compression associated with adult lumbar scoliosis is commonly manifested as a radicular pain that may be related to physical activity. As the apex of a curve rotates, there is associated hypertrophy and subluxation of the facet joints in the concavity of the curve. Additionally, collapse in the concavity results in narrowing of a neural foramen between adjacent pedicles. As a result, symptoms occur in the anterior portion of the thigh and leg (resulting from compression of the cephalic and middle lumbar nerve roots). Radiating pain in the posterior portion of the lower extremity is more common on the side of the convexity of the lumbar curve; such pain is due to compression of the caudal lumbar nerve roots and the sacral nerve roots, well caudad to the apex, as the spine curves back to meet the pelvis. ²

Clinical Complex of Symptom Presentation

The degenerative aging spine with deformity creates the complex of four major categories of clinical symptom presentation:

• Neurologic pain (both peripheral and radicular)

• Back pain

• Deformity-related issues

Neurologic pain occurs with activity-related claudication caused by diminished blood flow to the nerves. It is incumbent upon the healthcare provider to rule out common causes of leg pain such as peripheral vascular disease, cardiac disease, arteriosclerotic vascular disease, and/or primary neurologic disease. Compressive radicular pain occurs on the concave collapsing side of a degenerative scoliosis, from direct compression of the nerve at the exiting foramen or subarticular space. Nerve stretch radicular pain occurs on the convex nerve roots that are exiting from the stenotic collapsing scoliotic spine. Therefore, a patient may present with either convex radicular pain or concave nerve root pain, or both.

Back pain may be caused by arthrosis and normal aging body changes of the discs, facets, or other structures. Another cause of back pain may occur from abnormal restricted segmental spine motion, as referred to by the term “mechanical pain.” Also, back pain may occur secondary to nerve root compressive pain, which is secondary to decreased circulation and/or nerve compression.

Adult Scoliosis Classification

Adult Scoliosis is classified by Aebi ³ using an AO system based on a pathoanatomic etiology and on a temporal onset of deformity. His classification defines adult scoliosis as spinal deformity in a skeletally mature patient with a Cobb angle of more than 10 degrees in the coronal plane. Aebi separates adult scoliosis into four types:

• Type I: Primary Degenerative Scoliosis (“de novo” form), mostly located in the thoracolumbar or lumbar spine. This occurs on basis of a disc and/or facet joint arthritis, affecting structures asymmetrically, and presents with back pain symptoms, often with or without signs of spinal stenosis (central and/or lateral stenosis) (Figures 51-1 and 51-2).

• Type II: Idiopathic Adolescent Scoliosis of the thoracic and/or lumbar spine, which progresses in adult life and is usually combined with secondary degeneration and/or imbalance.

• Type III: Secondary Adult Curves:

a) In the context of an oblique pelvis (i.e., due to a leg length discrepancy or hip pathology), or as a secondary curve in idiopathic, neuromuscular, and congenital scoliosis or asymmetrical anomalies at the lumbosacral junction.

b) In the context of metabolic bone disease (mostly osteoporosis combined with symmetric arthritic disease and/or vertebral fractures). ³

FIGURE 51-1 A 66-year-old woman with an AO type 1 de novo scoliosis curve pattern. Myelogram and intrathecal CT scan demonstrate typical pathoanatomic changes consistent with severe spinal stenosis at the L4 vertebral level. Note the facet hypertrophy, facet malalignment, ligament flavum hypertrophy, thecal sac compression, disc degeneration, and vertebral olisthesis.

FIGURE 51-2 A 66-year-old woman with an AO type 1 de novo scoliosis curve pattern. Sagittal view shows postoperative fusion from T10 to L5 with maintenance of lumbar lordosis for standing balance.

Schwab et al.⁴ proposed a three-tier classification system for adult scoliosis based on parameters of coronal and sagittal plane. These radiographic criteria include lumbar lordosis, location of coronal curve apex, olisthesis of vertebra segments relative to each other, and sagittal balance on x-ray (Figures 51-3 through 51-6). The classification system has accurately correlated radiographs with clinical significance, in an attempt at suggesting the most appropriate successful treatment in the adult patient. The rate of disease progression is influenced by the magnitude of the curve, the degree of lateral listhesis, the quality of the bone and the severity of associated spondylotic disease. Table 51-1 shows two classification schemes.