Elderly Adults

The aging baby boom generation is leading a shift in demographics toward a “gray society,” and over the next 25 years, a significant proportion of the population in industrialized societies will be older than 65 years. Because both symptomatic spinal stenosis and DDS typically appear between the fifth and seventh decade of life (40–60 years), these conditions frequently coexist, and many patients with these conditions will become surgical candidates. Although decompression of disabling lumbar spinal stenosis may lead to a significant improvement in quality of life, concerns about potential medical complications in this sometimes fragile population and uncertainty about the expected outcome of operative treatment make many surgeons apprehensive about big surgeries, such as decompression with arthrodesis.

Some controversy exists whether age should be considered an independent risk factor for surgery. Many authors report no difference in outcome or rate of complications between elderly and younger patients of comparable health. Therefore, advanced age alone should not be a contraindication for surgery. Some studies, in contrast, have demonstrated that increasing age can be an independent risk factor for surgery, especially if the patient is older than 60. One such study notes a 41% complication rate (14% major and 27% minor) for patients 41 to 60 years of age and a 64% complication rate (24% major and 40% minor) for those 61 to 85 years of age. Pulmonary complications were the most common major complications, and genitourinary problems were the most common minor complications. Age older than 60 years, therefore, was found to be a significant risk factor for perioperative complication.

It has also been reported that decompressive surgery in the elderly population can be effective without the need for supplemental fusion, and many authors therefore do not recommend fusion in patients older than 70 years. This is partly because the risk for development of postoperative instability in this age-group appears to be small because of some intrinsic stability afforded by the spondylosis and spondylarthrosis that occur as the spine ages, as well as the decreased activity level of this population.

If decompression without supplemental fusion is performed in this population, care should be taken to limit the number of levels decompressed. It has been shown that the probability of postoperative spondylolisthesis developing increases with the number of levels decompressed (6% for 2 levels progressing to 15% for 3 or more levels).

Multiple Co-morbidities

Patients who have multiple co-morbidities, such as cardiac disease, vascular disease, or diabetes, have an increased risk for postoperative complications. The preoperative evaluation and optimization of patients with these conditions is critical. The addition of an arthrodesis increases the length of anesthesia, as well as the amount of blood loss. Both of these factors can delay recovery time, and patients with multiple co-morbidities are therefore more likely to require an extended rehabilitation period. These factors should all be considered when deciding on the advisability of supplemental fusion with decompression. Finally, for patients with a limited life expectancy, treatment should be focused on obtaining an immediate improvement in quality of life without subjecting the patient to a prolonged and painful recovery period.

Osteoporosis

Bone quality is a major determinant of success in all fusion procedures, especially those involving instrumentation. The curvature of patients with mild DDS can progress and become more symptomatic as osteoporosis worsens, as commonly occurs in postmenopausal women. As the vertebrae weaken, the asymmetric load from the curve can cause increasing deformity and curve progression, which can increase the patient’s symptoms.

Osteoporotic bone is a relative contraindication to instrumented fusion because of the difficulty in obtaining and maintaining adequate fixation at the bone-screw interface. Although variations in technique such as the use of larger diameter screws, screw threads with more aggressive pitch to improve pullout strength, and augmentation of the bone-screw interface with methylmethacrylate have been advocated, failures of fixation are still likely.

A conundrum thus exists with respect to treatment of symptomatic stenosis in a patient with DDS: The structural integrity of a potentially progressive curve can be compromised by laminectomy, and it can be difficult to reliably achieve fixation with instrumentation. Therefore, an already challenging situation can be made more difficult, and care should be taken to minimize disruption of posterior supporting structures during the procedure. If the decision is made to proceed with decompression, the patient should be optimally treated for the osteoporosis. This can be accomplished with nutritional supplementation and medications to reduce bone resorption (bisphosphonates calcitonin raloxifene estrogen), as well as promote bone growth (teriparatide).

Lateral Spondylolisthesis

Several forms of degenerative spondylolisthesis commonly occur in association with DDS. The deformity may occur in any of three axes: axial rotation on the vertical axis, lateral translation toward the convexity of the curve, and anterior translation in the sagittal plane. The types of spondylolisthesis that can occur are, therefore, rotatory olisthesis (rotational subluxation of one vertebral body on another), lateral subluxation, and translatory shift. These deformities are common in DDS, coexist in 13% to 34% of adults with scoliosis, most commonly occur at the L3-4 level, and become more common with increasing age and with larger curves.

The clinical significance of these abnormalities in DDS is that their presence increases the likelihood of postoperative instability after decompression. Of particular concern is the lateral subluxation of one vertebral body on another. This requires both minimizing structural disruption during decompression and also close follow-up for curve progression if instrumented fusion is not performed.

Significant Curve/Progressing Curve

Consideration must be given to both the magnitude of the DDS curve and whether it is progressive. Although slow curve progression may occur without surgery, more significant and rapid progression is likely after decompression without instrumented fusion.

Literature on the association between curve magnitude and risk for progression after laminectomy is sparse. In general, patients who present with symptoms of spinal stenosis and have degenerative scoliosis of less than 20 degrees without instability can be safely and effectively treated with spinal decompression alone. This approach is more likely to be successful in male patients with large vertebral bodies and stabilizing osteophytes. Conversely, once a curve becomes greater than 20 degrees, it is more likely to progress because of excessive stress on the facet joints or structural failure of osteoporotic vertebral bodies, or both. Larger curves such as these often require instrumentation.

Axial and Radicular Pain

Although the progression of DDS is usually slow, it commonly results in significant axial and radicular pain. One of the most frequent indications for the surgical treatment of DDS is intractable pain. As is generally true in spinal surgery, success is more likely with radicular pain than with axial pain. The treatment of axial pain often involves correction or stabilization of the deformity. Thus, fusion with instrumentation is usually required.

Radicular pain accompanying axial back pain is commonly the result of nerve root compression in the concavity of the curve as a result of foraminal narrowing. It may also result from traction of the nerve root in the convexity of the curve. Although this type of radicular pain may be treated with decompressive procedures, such as laminectomy or foraminotomy, it can be difficult to ensure adequate foraminal decompression within the concavity without distraction via instrumentation.