53 Assessment and Avoiding Complications in the Scoliotic Elderly Patient

Introduction

Scoliosis — defined as a curvature of the spine in the coronal plane measuring over 10 degrees — can be found in the adult population and can be a significant source of disability, especially in the elderly.^1,² There are three principal forms of scoliotic spinal deformity that can be described: idiopathic, i.e., that whose development can be found during the juvenile or adolescent growing years of life and which persists into adulthood; de novo, which involves the development of a new scoliosis later in life as a result of degenerative changes in the lumbar spine; and osteoporotic scoliosis, a less common form of spine curvature secondary to osteopenic collapse of vertebral bodies.

In the adolescent with scoliosis, the primary focus of treatment is the deformity and concerns of curve progression. In the older patient, it is much more common that pain is the primary complaint.^3,⁴ In the later decades of life, curve progression becomes less and less of a concern, primarily because of the restraint provided by the degenerating and ossifying disc spaces and the arthritic facet joints. Being out of balance, especially in the sagittal plane, adds an element of posturally related fatiguing pain that limits patients’ ability to perform upright activities.⁵ Older adults are most commonly symptomatic in the lower thoracolumbar or lumbar region, due to the age-related disc degeneration and osteoarthritis associated with the deformity.

Patient Evaluation

Clinically, the evaluation of the elderly patient with scoliosis begins with an appreciation of the overall coronal and sagittal balance. There are many reasons other than spinal deformity for the patient to have difficulty standing upright: hip and knee degeneration, spinal stenosis, lumbosacral or thoracolumbar kyphosis, trunk muscle weakness, or flatback pathology. The last entity — flatback syndrome — typically due to some form of loss of the normal lumbar lordosis, can result in a loss of trunk strength and difficulty fully extending the hips. All patients should thus have a careful examination of the hip range of motion, including assessment of their ability to extend completely when in the supine examining position. Hips that have become locked into contracture may well require some form of release before considering any corrective surgery on the spine. On occasion, degenerative arthritis of the hips can be treated with arthroplasty first before proceeding with spinal surgery.

Routine radiographs are obtained in the upright position and should include standing, full-length, anterior-posterior, and lateral films to assess not only the dimensions of the curve, but the overall alignment in both the coronal and sagittal planes. It is important to obtain the images with the patient’s hips and knees as extended as possible in order to appreciate the true sagittal profile. In addition, side-bending or hyperextension lateral films are quite helpful in determining the flexibility of the curve, and, if considering surgery, whether some form of anterior release or posterior osteotomy is necessary.

Because the majority of patients present with pain, magnetic resonance imaging is often obtained. MRI can assess the quality of the distal intervertebral discs, and as many patients will complain of varying degrees of leg pain from stenosis, axial MRI imaging is useful to study the spinal canal and foramen and determine levels of decompression if necessary. MRI can also be used to study the most caudal intervertebral discs of the spine, as a fusion may on occasion stop short of the sacrum if distal painful pathology does not appear to exist, although this is somewhat less common in the elderly compared with younger patients. MRI is also very helpful in ruling out malignancies or infections.

Computerized tomography is helpful during the planning stages for studying the bony anatomy; in the setting of previous fusions, the quality and extent of the previous arthrodesis can be best obtained with CT imaging. CT is also quite helpful in analyzing the size of the pedicles, the width of the ilium, and the morphology of the vertebrae themselves.

Treatment

Elderly patients with painful scoliosis can be considered candidates for nonoperative treatment modalities, just as their younger counterparts are. As the majority of the patients present with symptomatic curves in the lumbar or thoracolumbar region, simple education and an understanding that the curvature does not present an immediate threat to their cardiac or pulmonary systems (as did primary thoracic curves left untreated) may be reassuring enough to many. Combinations of the judicious use of nonsteroidal antiinflammatory medications, activity modifications, and physical therapy are often helpful. Physical therapy will tend to be more successful when it is low-impact and focused on aerobic conditioning rather than vigorous activity. Water-based conditioning is also quite helpful in many. Use of orthotics is not typically well tolerated by the elderly, but an occasional patient may find the use of a brace supportive and helpful in his or her daily activities.

Surgery

Patients are considered candidates for surgical intervention if their symptoms have remained significant despite attempts at nonoperative care or, less commonly, if there is problematic curve progression.

Elderly patients undergoing surgery for scoliosis face the prospect of increased morbidity and mortality compared with their younger counterparts, primarily because they enter into the surgery much more disabled and with worse health status.⁶^–⁸ In the preoperative assessment, careful attention should be paid to their cardiac and pulmonary systems, as many patients have become quite sedentary and the stress of surgery may thus become problematic. If patients smoke, they should be encouraged to quit at least a number of weeks before the operation, not only to improve the chances of bone healing but to lessen the likelihood of pulmonary and wound complications, which are already elevated in the elderly population. If there is a suspicion of respiratory compromise, a history of smoking, or planned procedures about the diaphragm, preoperative pulmonary function should be assessed.

Elderly patients may have become relatively malnourished and the associated risks of sepsis, wound breakdown, etc., are well established.⁹ Total parenteral nutrition should be considered in staged surgical treatments, as it has been shown to diminish the rate of nutritional depletion and postoperative infections.

Surgical Techniques

A multitude of issues need to be assessed in each elderly surgical patient, including sagittal balance, coronal alignment, any complicating spinal or nerve root stenosis, disc degeneration, listhesis either anterior or lateral, osteoporosis, and any complicating medical comorbidities.

Unlike in the adolescent, where maximal safe correction of the coronal plane curvature is sought, in the elderly, aside from obtaining a solid arthrodesis, much more critical than Cobb angle correction is the obtaining and maintenance of appropriate balance in both the coronal and sagittal planes. A stable and balanced spine is the principal goal of deformity surgery in the elderly, and this often involves accepting less curvature correction. Numerous studies have emphasized that the component of postoperative radiography most closely tied to overall clinical success is the achievement of adequate balance, especially in the sagittal plane. Glassman and other members of the Spine Deformity Study Group, in a review of nearly 300 patients, have suggested that restoration of the normal sagittal balance is the most critical goal for any reconstructive spine surgery.⁵ A plumbline dropped from C7 should fall in the middle of the sacrum in the coronal plane and within the disc space of the lumbosacral articulation in the lateral view. Older adults have typically developed pronounced disc degeneration and narrowing, which leads to a loss of the normal lumbar lordosis and a forward drift of the sagittal plumbline. Osteopenic compression-type fractures can worsen the sagittal alignment, as can any thoracolumbar kyphosis.¹⁰ For these reasons, fusions of primarily lumbar pathology may well need to be extended proximally into the upper thoracic spine.

With the increased use of pedicle-screw fixation and advancing techniques such as vertebral resections, the majority of surgery in the elderly is performed through the posterior approach.¹¹ This would even include access to the anterior column, e.g., the intervertebral discs via posterior or transforaminal lumbar interbody fusion (PLIF or TLIF, respectively). Interbody support at the lumbosacral junction within at least the lower two spaces, L4-5 and L5-S1, is biomechanically mandatory for successful fusion rates.¹²^–¹⁴ Support here lessens the strain seen on the posterior instrumentation and protects to a certain degree against pull-out failure. As a general rule, but especially in the elderly, instrumentation should be used to maintain correction, not obtain correction.

In the case of previous decompressive surgery, scarring within the spinal canal may, however, make these PLIF and TLIF approaches somewhat more difficult. Direct anterior access to the lumbosacral junction can be successfully accomplished via a midline or paramedian incision, retraction of the peritoneal contents, and direct visualization via the retroperitoneum of the disc spaces from L3 to the sacrum with little morbidity and low risk of complications. Through this approach, more extensive removal of disc material and direct placement of femoral rings or specialized cages packed with bone fusion material can be realized.

Osteotomies have become increasingly popular and have become a part of the armamentarium of most adult deformity spine surgeons for effecting corrective change in the sagittal balance. Especially in the elderly, they have become vehicles for avoiding the time and morbidity of separate anterior approaches. Smith-Peterson osteotomy, a V-shaped resection of the posterior arch through the facets bilaterally, can effect moderate corrections per level; however, if multiple resections are combined, the overall effect on sagittal balance can be significant. The success for Smith-Peterson osteotomy, however, depends on the integrity of the anterior intervertebral disc, which must retain a certain degree of flexibility, as the correction hinges posteriorly. In other words, a disc space that is severely narrowed or even ankylosed, as can be seen in many older individuals, may not have enough residual motion and the ability to correct may be lost.

Pedicle subtraction osteotomies (PSOs) are very powerful tools for obtaining sagittal plane correction at single levels — up to 35 or more degrees per level. However, as the procedure involves a wedge-shaped resection of the laminae, the pedicles, and the posterior vertebral body itself, the blood loss can be significant, and may not be well tolerated by the aged patient . PSOs are also most efficient when performed in a previously fused spine, especially anteriorly, as the hinge is at the anterior vertebral body wall. It may be difficult to obtain the same degree of correction in spines without previous fusions. Also, as the success of maintaining the correction depends on a rigid anterior aspect of the vertebral body, significant osteoporosis, as seen in many elderly patients, can be a potential contraindication, for if the remaining vertebral body is not sufficiently strong, the bone may collapse, lessening the degree of correction.

Adequate fixation of the thoracolumbar spine with surgical implants can be problematic in the elderly patient for a number of reasons. Obviously, the quality of the bone of the spine is less than that in a younger age group, and the spine itself is typically much stiffer. In addition, many patients have had prior surgery including fusions and decompressions, which can obscure the typical landmarks for fixation and actually limit the number of possibilities for obtaining purchase, especially in the setting of previous decompressions. Use of fluoroscopy can aid in finding the pedicles, especially in the thoracic spine.

Pedicle screws have become the primary method of fixation in deformity surgery, including the elderly, although their bone quality still remains a concern. Pull-out strength of pedicle screws in patients with normal bone density is typically about 1400 N; however, in patients with osteoporosis, the strength can be as low as 200 N.¹⁵ Fixation strength of pedicle screws has been correlated with insertional torque. Hence, it is recommended that, in order to obtain some purchase with the inner cortical wall of the osteopenic pedicle, the largest-sized screw that can comfortably be placed be chosen. This is another reason for careful assessment of preoperative computed tomography with measurement of the inner diameters of the pedicles. In settings of reduced purchase quality, many surgeons treating the elderly may reinforce pedicle screws with adjacent laminar hooks or sublaminar wires. Of note, in the elderly spine, compared with younger adolescent patients treated for scoliosis, the transverse processes are typically quite brittle, and, with few exceptions, are not commonly recommended as points of principal fixation for instrumentation such as hooks.

In some setting of robust previous fusions, however, especially when extending down the ilium or sacrum, hooks can still be used when pedicle screws are not possible or practical. Hook site placement can be performed with small power burrs into the fusion mass — typically in multiple claw formations — and connected to the rods extending down to the more distal spine.

Fixation into the sacrum is a particular problem as the quality of the bone is probably the poorest here, and the risk of fusion failure (pseudarthrosis) may be one of the highest.^16,¹⁷ This is another reason why combined anterior and posterior surgery is recommended for long fusions down to the sacrum or the ilium: at a minimum, L4-5 and L5-S1 require strong structural support. In addition, because of the risk of osteopenic fracture of the sacrum when long fusions extend distally, supplemental iliac fixation is highly recommended (Figure 53-1).¹⁸