CHAPTER SYNOPSIS:
The number of patients with spinal deformities and sagittal and/or coronal imbalance is steadily increasing. Because these deformities and imbalances are often complex and multifactorial, treatment options must be weighed carefully and designed to correct each individual case. This chapter reviews the various types and roles of osteotomies for correction of deformities of the lumbar spine.
IMPORTANT POINTS:
Indications
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Fixed spinal global sagittal or coronal imbalance, or both
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Pseudoarthrosis in association with sagittal imbalance
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Rigid, scoliotic deformity especially with planned posterior approach
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Any of the above with disabling pain or progressive neurologic decline
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The most common osteotomies for these patients are:
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Smith–Petersen osteotomies (SPOs)
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Pedicle subtraction osteotomies (PSOs)
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CLINICAL/SURGICAL PEARLS:
SPOs
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In an SPO, the posterior column is shortened through resection of the posterior elements.
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The posterior column is closed while lengthening the anterior column through the disc spaces anteriorly.
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The average correction obtained with this technique is thought to be 10 to 15 degrees (1 degree for each millimeter of posterior bone resected).
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PSOs
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PSOs begin with a laminectomy in the area of the planned correction, identifying the exiting nerve room and then performing a wide foraminotomy.
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The final step involves removal of the posterior vertebral cortex.
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On average, 30 to 35 degrees of sagittal correction can be obtained through a single-level PSO.
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CLINICAL/SURGICAL PITFALLS:
SPOs:
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SPOs have the potential for destabilizing the spine through lengthening of the anterior column.
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Some authors recommend anterior column structural grafting to avoid this.
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This author believes that this is necessary only at the lumbosacral junction to avoid pseudoarthrosis.
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Complications include superior mesenteric artery syndrome and rare traction injuries to the vessels.
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PSOs
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The exiting nerve root must be carefully identified and protected while the pedicle is being resected.
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Using a preliminary rod bridging the osteotomy site during the final part of the resection will prevent the site from collapsing prematurely, which might endanger neural structures.
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SCOPE OF THE PROBLEM
Thoracic, thoracolumbar, and lumbar alignments are important to the overall sagittal and coronal balance. It is important to understand how these individual segments contribute to the global balance. Normal sagittal balance implies that the head is centered over the pelvis so that a plumb line dropped from the center of the C7 vertebral body falls over the posterior superior corner of the first sacral vertebra. If the C7 plumb line is anterior to the posterior-superior corner of S1, the individual is pitched forward, this is said to be a “positive sagittal balance.” When the C7 plumb line falls posterior to the posterior superior corner of the first sacral vertebra, the patient is said to have a “negative sagittal balance” ( Fig. 29-1 ). These parameters can be altered by change in the alignment of any individual spinal segment. Normal coronal alignment implies that, in frontal plane, the head should be positioned over the pelvis so that a plumb line dropped from the middle of the C7 vertebra falls over the center of the sacrum. These parameters still apply in the older patients.
Patients with de novo, or degenerative, or idiopathic scoliosis tend to have associated loss of normal lumbar lordosis or may even have a kyphotic alignment in the lumbar spine, which may lead to a positive global sagittal balance ( Fig. 29-2 ). Curve progression in adults may be quite variable as patients with idiopathic scoliosis may progress at a rate of one degree per year ; however, patients with de novo degenerative scoliosis are more likely to have a rapidly progressive curve, which may be as high as 3.3 degrees per year. Furthermore, without compensatory changes, an increase in the thoracolumbar or lumbar kyphotic alignment, or both, may lead to greater positive global sagittal balance; however, many patients with kyphotic lumbar spine deformity may actually have a normal global sagittal balance because of the compensatory changes in alignment at the levels above and/or below the deformity ( Fig. 29-3 ).
The classic causative factors for sagittal imbalance include conditions such as ankylosing spondylitis and Harrington distraction instrumentation, which lengthens the posterior column, especially when performed in the lumbar spine. Other traditional causative factors include Zielke and Dwyer anterior instrumentation, which shortens the anterior column. However, with advancement of surgical techniques and improvement of spinal instrumentation, these causative factors are becoming less and less common. Alternatively, postlaminectomy deformities, iatrogenic after fusion kyphosis, pseudoarthrosis, fusion, and intervertebral disc “breakdown,” and fractures above or below long spinal fusions continue to be common causes for sagittal plane imbalance ( Fig. 29-4 ).
INDICATIONS AND CONTRAINDICATIONS
Indications for thoracolumbar osteotomies include fixed spinal global sagittal and (less commonly) coronal imbalance, especially in association with pain and impairment. Poor cosmesis, although frequently dismissed or minimized by the patient and treating surgeon, is not an uncommon reason for patients to seek treatment. The presence of pseudoarthrosis in association with sagittal imbalance makes a strong case for deformity correction, which may aid the fusion by improving spinal biomechanics at the nonunion site. Other indications include rigid scoliotic deformity, especially when there is a contraindication to performing anterior release or if the surgeon chooses to correct the deformity through an all-posterior approach.
Patients with a degenerative sagittal imbalance in whom fusions have initially been performed in the distal lumbar spine in a hypolordotic or kyphotic position with subsequent degeneration of segments above the fusion may require a combination of extension of the fusion to include the degenerated segments and osteotomies through the fusion mass. Most of the correction should be accomplished through the osteotomies with additional correction achieved by including the degenerated segments. In patients with ankylosing spondylitis, the correction can be achieved either using either a single or multiple osteotomies.
The usual goal is to restore the regional segmental spinal alignment and to achieve global balance. Global balance is confirmed when the C7 plumb falls over the lumbosacral disc on a standing long-cassette lateral radiograph taken with the patient standing with the knees fully extended in a natural and comfortable position. Most patients should have at least 10 to 20 degrees more lumbar lordosis than thoracic kyphosis.
Surgery may be considered for the following reasons: (1) persistent, severe, disabling pain that may be axial or radicular in nature; (2) global sagittal imbalance; and (3) progressive neurologic deficit or neurogenic claudication symptoms.
PAIN
Pain is one of the most common presentations in adults with spinal imbalance. It is thought to be caused by abnormal spine biomechanics at the level of the deformity that alters the forces being placed on the soft tissues and the surrounding structures. The pain is usually constant, aching in quality, and at the level of the deformity or higher. Patients with an angular kyphotic deformity of 30 degrees or greater appear to be at an increased risk for chronic pain. Patients may also experience radicular-type pain, which is often related to degenerative changes above or below the deformed segment, leading to central or foraminal spinal stenosis, or both.
IMBALANCE
Patients with global sagittal imbalance often present with a chief complaint of a stooped forward posture, though this is rarely an isolated presentation and is often associated with pain and decreased walking tolerance. This is more commonly noticed by family members or friends and is usually attributed to poor posture. Sagittal imbalance can have significant cosmetic effect, and most patients believe they are made to look much older. Sagittal imbalance has been associated with greater disability. Coronal balance, although better tolerated, can sometimes be partially corrected by a shoe lift. It may be associated with unilateral upper back or periscapular pain, or even a proximal coronal spinal curvature as the patient attempts to compensate (see Fig. 29-4 ).
NEUROLOGIC DEFICIT
Neurologic deficit is a rare presentation but can be seen in patients with the fusion extending into the thoracic spine. It can be an acute event secondary to a fracture at the junctional levels that usually occurs early (within the first 2–3 months) after long fusions, especially in patients with osteoporosis. It can also be seen as a gradual progression secondary to degeneration above the fusion leading to progressive stenosis of the spinal canal. The latter presentation is more common in the thoracic spine, probably secondary to the relatively narrow canal diameter. The presenting symptom is usually of a myelopathic picture, which may be subtle.
SURGICAL TECHNIQUE
Presurgical Evaluation
General assessment for co-morbidities must include cardiac evaluation, especially for patients older than 50 years. Nutritional assessment is important, because some patients may need perioperative enteral or even parenteral hyperalimentation. Pulmonary function testing should be considered in patients with history of respiratory compromise and especially in patients with a large thoracic/thoracolumbar curve or if anterior approach is required. Radiographic evaluation should include long-cassette erect posteroanterior and lateral views in addition to the routine lumbar radiographs. Flexibility films will help in assessing the correctability of the curves.
Magnetic resonance imaging is usually adequate for assessing the spinal canal and the neural elements; however, computed tomographic myelography may be preferred in patients with large curves and in patients who already have instrumentation in place. In women older than 40 years, a baseline dual-energy radiograph absorptiometry scan on the hips should also be obtained because this may aid in deciding whether pedicle screw augmentation or prophylactic vertebroplasty at the junctional levels may be required.
Surgical Approach
Surgical approaches vary depending on the nature and the cause of the deformity, its location, as well the presence or absence of solid fusion in the area of intended correction.
It is also important to plan the corrective procedure so that the final correction ensures that the patient’s spine alignment is at least neutral or negative sagittal balance.
Surgical options include: (1) an all-posterior approach, (2) an all-anterior approach, or (3) a combined anterior and posterior approach. When considering which approach is the most appropriate, many factors need to be considered; for example, if significant spinal canal stenosis is present, a posterior approach will allow decompression of the neural structures. If pseudoarthrosis with poor bone quality and extensive laminectomy associated with a rigid deformity is present, then a combined approach may be necessary. In severe cases, a three-stage surgery may be necessary: posterior, anterior, then posterior. However, I would resort to such an approach only in patients with compromised posterior column, when associated with a rigid deformity and multilevel nonunion and poor posterior bone stock ( Fig. 29-5 ).
Related posts:
Rheumatoid Arthritis of the Cervical Spine
Instrumentation of the Lumbar Spine for Degenerative Disorders
Management of Postoperative Lumbar Wound Infections
Postlaminectomy Kyphosis: Anterior, Posterior, and Combined Approaches
Failure of Lumbar Spine Instrumentation
Facet Joint Replacement for the Treatment of Degenerative Disorders of the Spine
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