Lumbar degenerative disease is a progressive process of disk and joint deterioration. As this pathology continues, it can lead to deformity of the lumbar spine. As a result of the multiplanar forces applied to the lumbar spine, this degeneration can cause multiplanar deformity in the axial, coronal, and sagittal planes. Patients are consistently noted to have facet joint degeneration, loss of lumbar lordosis, and sclerotic end plate changes, which progressively worsen, likely associated with the asymmetric nature of the degeneration. This progressive deformity can become symptomatic at any level of anatomical alteration, and the most common symptoms are back pain and radiculopathy. Back pain affects 80% of people at some point in their life and is a leading cause of disability in the United States and worldwide. Although back pain is multifactorial, it is the most common symptom encountered in patients with adult scoliosis or kyphosis and often improves after appropriate treatment. Radiculopathy can be caused by associated disk herniation or central stenosis. Most commonly, it is secondary to narrowing of the lateral recess or foramen resulting from the relative vertebral body rotations associated with multiplanar deformity ( ▶ Fig. 47.1).

Causes of spinal deformity include degenerative disease, adolescent idiopathic scoliosis, Scheuermann kyphosis, congenital syndromic scoliosis, neuromuscular scoliosis, post-traumatic deformity, postinfectious deformity, and iatrogenic deformity. Idiopathic scoliosis arises in childhood or adolescence and more commonly relates to the thoracic spine. Idiopathic scoliosis can have late progression to a degenerative, previously compensatory, lumbar curve. Symptomatic deformity in adults arises from degeneration, typically limited to thoracolumbar spine, leading to scoliosis and kyphosis. Adult scoliosis, which is a broad term referring to a coronal plane curve of 10 degrees or more, has a reported prevalence as high as 68% ( ▶ Fig. 47.2). Previous studies have demonstrated that more than one-third of volunteers aged 50 to 84 years without any scoliosis developed de novo scoliosis during an average follow-up period of 12 years. Risk factors for the development of scoliosis include asymmetric intervertebral disk degeneration, rotatory subluxation, and lateral spondylolisthesis of the L3 vertebra. This chapter is restricted to discussion of de novo degenerative multiplanar deformity of the lumbar spine.

Sagittal plane deformity (i.e., kyphosis) is the most important and symptomatic consideration when addressing degenerative lumbar deformity. Along with rotational subluxation, sagittal imbalance frequently compromises quality of life in patients with degenerative spinal deformity. To stand and walk effectively, the body center of mass must lie over the femoral axis. This typically means that the C7 plumb line must fall over the sacrum. When patients develop degenerative disease of the lumbar spine leading to uncompensated hyperkyphosis, the upright relation of their heads to their pelvis and feet drifts forward, causing sagittal imbalance, initially from the loss of disk height as a part of the degenerative cascade. To compensate, patients will extend their lumbar spine to re-establish balance, which results in facet impaction with more pain and spondylotic changes, also causing further foraminal narrowing, and this can increase neurogenic claudication symptoms.

Hyperextension also results in muscle strain with associated pain and fatigue. As the patient’s condition worsens, back extension may not be sufficient to accomplish balance. When this occurs, the pelvis rotates to achieve balance, and the knees and hips may flex. Severe pain can result, limiting the patient’s ability to stand and ambulate. Understanding the role of sagittal balance in lumbar deformity and its correction is the single most vital step in treating patients with this condition.

In addition to the curve and its absolute magnitude, listhesis plays an important role in lumbar degeneration and deformity. Listhesis commonly occurs in the sagittal plane. It also occurs in the coronal plane. Coronal lateral listhesis can lead to progression of the coronal deformity. This can also result in foraminal compression and radiculopathy. The goal of correction in this plane is to stabilize the painful segments as well as decompress the neural elements. In doing this, the spine should remain balanced in the coronal plane. In this way, the hips and shoulders remain level when the center sacral line falls through C7. Thus, even after surgery, a curve may remain with partial or limited correction to avoid iatrogenic coronal decompensation.

Axial rotation results in foraminal stenosis and increased shear forces on the facets and disks. Correction of axial rotation is of the most limited benefit. This is fortunate as it is the more difficult correction to achieve, especially in degenerative deformity, which commonly occurs in older patients with poor bone quality. The poor bone quality limits the force that can be applied through a spinal implant to the bone–metal interface.

47.2 Patient Selection

As in any surgical procedure, a significant factor in successful surgery for lumbar multiplanar deformity is patient selection and evaluation. The surgical indications for patients with degenerative lumbar deformity include back pain, radiculopathy, functional limitations from spinal imbalance, and progressively worsening neurologic function. As previously mentioned, this is secondary to degenerative disk disease and facet joint deterioration. Facet capsule and ligament strain, as well as muscle fatigue and imbalance, also contribute. To become a surgical candidate, the patient continues to have an unacceptable quality of life secondary to pain despite extensive nonsurgical treatment. The goals of surgery for such patients are to stabilize all involved degenerative joints and disks and to return spinal balance in the sagittal and coronal planes.

Patients who are candidates for lumbar degenerative deformity surgery should have completed comprehensive programs of nonsurgical treatment. Conservative management of sagittal and coronal imbalance can be performed in patients with good functional status and with mild pain. Physical therapy, core strengthening, and nonsteroidal anti-inflammatory drugs are the primary conservative treatment options. Fluoroscopic-guided epidural steroid injections, facet joint injections, and selective nerve root blocks may benefit some patients with radicular pain. Operative treatment should be contemplated in patients with moderate to severe symptoms for whom conservative management fails, patients with neurologic deficits, and patients with disabling pain causing a profound impact on quality of life. Extensive counseling is required because of the magnitude of the surgical procedures. Both the surgeon and the patient should have realistic goals for surgery and outcome. One of the biggest pitfalls in the surgical management of adult scoliosis or kyphosis is unrealistic patient expectations. During presurgical discussions, patients should be counseled that they will likely have postoperative back pain from the surgery itself and that it may take some time for the pain to improve as the patient heals. Furthermore, neurologic deficits (e.g., motor weakness and sensory disturbances) may or may not improve. One of the goals of surgery is to prevent progressive worsening of neurologic deficits, however, actual improvement of preexisting neurologic deficits may be unlikely following surgery.

A detailed history, including an understanding of the most disabling and distressing symptoms, is important. The physical examination helps to localize the pathology as well. Disabling pain may be immediately evident given a patient’s antalgic gait on presentation to the clinic. Patients with kyphosis may have an obviously stooped posture. Patients with scoliosis may have an asymmetric tilt to their shoulders or hips. Patients with kyphoscoliosis may have a combination of these features. Patients with cervical involvement of their kyphosis or scoliosis may have weakness in any or all muscle groups in the upper and lower extremities, in addition to loss of proprioception or hyperesthesia in their upper extremities. Patients whose kyphosis or scoliosis is thoracic or lumbar in location may have weakness in any or all muscle groups in their lower extremities only, in addition to loss of proprioception or sensation to light touch or pinprick in their lower extremities. Hyperreflexia is indicative of cervical or thoracic myelopathy, whereas hypoactive reflexes are a sign of nerve root involvement.

The best single tool to evaluate the structural areas that must be stabilized is the standing anterior–posterior and lateral 36-inch cassette radiographs. The patient should be standing with hips and knees in extension to minimize sagittal imbalance compensation, and the view should include the occiput superiorly, shoulders laterally, and femoral heads inferiorly. This study allows for measurement of Cobb angles, sagittal balance, and other spinopelvic parameters to give the most critical information on overall alignment, areas of disk and foraminal height loss due to degeneration, and listhesis. Dynamic instability should be evaluated by comparison of standing, upright and supine films, flexion and extension films, and lateral bending films of the lumbar spine. Computed tomography (CT) provides the best visualization of bony anatomy. Magnetic resonance imaging (MRI) is also helpful in diagnosing areas of stenosis and disk degeneration. Its value is primarily to confirm the clinical evaluation of nerve compression and the areas of stenosis that require decompression.

Electrodiagnostic testing can be useful when clinical presentation and radiographic evaluation do not clearly define the compressed nerve root or roots as the one causing symptoms. Isolation of the nerve root (s) allows the surgeon to tailor the approach for adequate decompression. At times, it is possible to limit the surgical procedure to the symptomatic level rather than addressing the entire deformity.

Medical evaluation should include the normal evaluation for patients undergoing major surgical procedures. This includes cardiac and pulmonary evaluations as well as general medical workup. Many patients with adult degenerative deformity are elderly. They are often deconditioned and have a component of malnutrition. Routine laboratory tests should include complete blood count, basic metabolic panel, and coagulation profile. Patients at risk should be evaluated and optimized nutritionally before surgery. Serum proteins—including albumin, transferrin, prealbumin, and retinol-binding protein—are the most widely used blood tests for assessment of nutritional status. Optimization of nutritional status can improve the speed of recovery and rate of fusion and can decrease perioperative risks such as infection. Deconditioned patients should also undergo physical therapy before surgery to cultivate physical stamina. Particular attention should be given to releasing contractures of the hip flexors. This is commonly seen in patients with a positive sagittal balance. When patients have too much pain to undergo land-based conditioning, consideration should be given to aquatic therapy to decrease the strain of gravity and postural support on the spine, and to allow for gainful exercise, stretching, and conditioning. Dual-energy X-ray absorptiometry (DEXA) scans should be obtained on all patients with or suspicion of osteoporosis, as the presence of this condition drastically affects surgical management. Bone health can be optimized by vitamin D and calcium supplementation. Smoking cessation is necessary given its strong association with pseudoarthrosis and fusion revision.

47.3 Preoperative Preparation

The complexity of lumbar degenerative deformity necessitates comprehensive surgical preplanning. Multiple considerations must be given to the biomechanics of the pathology and reconstruction as well as the decompressive needs. The goals of the surgery and the mechanical needs are analyzed with an eye to the short- and long-term consequences of treatment, which is the focus of this section.

Radiculopathy that fails to respond to nonsurgical treatment may need surgical decompression. When symptoms are secondary to nerve root compression and there is minimal axial pain, the patient may benefit from a limited surgical procedure. Decompression without fusion can be considered in patients without evident instability and without severe sagittal imbalance. Minimally invasive decompressive techniques are particularly advantageous in older patients to decrease blood loss and hospital stay. The main limitations of decompressive techniques are the inabilities to restore sagittal balance and improve axial back pain. There is also a small risk of later instability secondary to decompression. Thus, the area of decompression must not destroy the joint at that level, the deformity must be rigid on dynamic imaging with radial osteophytes providing some stability, and the decompression must not be at a junction or curve apex. When surgery may destabilize a segment, a limited fusion is possible if the primary curve will not be destabilized. This is again possible if the curve is rigid, there is no listhesis above or below the limited fusion, and the surgery does not occur at a primary transition site or curve apex. To understand curve flexibility, flexion and extension X-rays are useful. Equally valuable are side-bending 36-inch scoliosis films. MRI is also helpful in localizing a precise area of decompression. Combining this information results in a clear understanding of the biomechanical implications of both disease and treatment.

Coronal deformity is defined as thoracic, thoracolumbar, or lumbar by the location of the curve apex. Thoracic deformities have a curve apex between T2 and the T11–12 disk, thoracolumbar deformities have a curve apex between T12 and L1, and lumbar deformities have a curve apex distal to the L1–2 disk space. Coronal deformity is defined by the convexity location (i.e., dextroscoliosis and levoscoliosis) and the largest or main structural curve. These patients typically develop compensatory curves to maintain balance, which may or may not correct on bending radiographs. The Cobb angle is a measurement of the maximal curve degree between vertebrae and can be used to characterize coronal and sagittal deformity. Parallel lines are drawn from the cephalad involved vertebral superior end plate and caudal involved vertebral inferior end plate. Perpendicular lines drawn from each end plate line bisect to define the Cobb angle. To define the most appropriate levels for fusion, one must identify vertebrae not axially rotated and vertebrae centered on the sacrum. Coronal balance is quantified by the distance between the central sacral vertical line and the C7 plumb line (vertical line from the midportion of C7 on an anterior–posterior radiograph). Sagittal balance is quantified by the distance between the dorsal rostral corner of the sacrum and the C7 plumb line (vertical line from the midportion of C7 on a lateral radiograph). Axial rotation is best characterized on CT scan with three dimensional reconstruction.

Compensation for sagittal imbalance is frequently accomplished via changing the spinopelvic relationship. Patients with loss of lumbar lordosis frequently will retrovert their pelvis and extend their hips to bring their head into alignment with the center of their pelvis. As such, when fusions extend to the sacrum or pelvis, spinopelvic parameters must be determined and accounted for so as not to undercorrect sagittal imbalance by not taking compensation into consideration. Pelvic tilt or pelvic retroversion is measured using the angle between a vertical line through the femoral head axis (i.e., center of femoral heads) and a line from the femoral head axis to the sacral endplate midpoint. Sacral slope is measured using the angle between a line drawn along the sacral endplate and a horizontal line. Pelvic incidence is measured using the angle between a line perpendicular to the sacral endplate midpoint and a line from the femoral head axis to the sacral end plate midpoint. The addition of pelvic tilt and sacral slope is equal to pelvic incidence. Ideal lumbar lordosis can be approximated by adding 9 degrees to pelvic incidence, which is useful for determining the amount of correction needed in patients with flat-back deformity.

Correction of spinal balance is a key to success in the treatment of adult multiplanar deformity. Coronal balance must be re-established to place the C7 plumb line over the center sacral line and at a minimum within the zone of the sacroiliac joint. Failure to do so results in the body center of mass falling outside a stable zone and putting increased strain on the hip and knee, which can lead to long-term joint deterioration and more immediate functional difficulty. It is necessary to examine how coronal deviation correction will affect the shoulders and hips. These structures should remain level to optimize function and cosmesis. The longer the fusion, the more valuable these considerations because of the increasing inability of the patient to compensate for any imbalance (iatrogenic or residual) as more motion segments are immobilized. When a fusion includes both the thoracolumbar and lumbosacral joints, the patient has extremely limited compensatory ability.

Sagittal correction is the most important aspect of adult degenerative deformity correction. Failure to achieve adequate sagittal correction results in continued pain and functional disability. This positive balance can become symptomatic when the C7 plumb line falls more than 5 cm from the dorsal rostral corner of the sacrum. Again, the longer the fusion, the more vital it is the patient achieves balance; long fusions mean limited compensation ability.

An important aspect of patient selection is determination of levels for fusion and correction. To do this, the surgeon must first understand the surgical requirements to address the patient’s symptoms, including the areas that require decompression due to symptomatic radiculopathy. There is little benefit in decompressing asymptomatic stenotic areas, and the history and physical examination will direct this. MRI confirms these findings and further refines the evaluation. After decompressive needs are known, the areas of degeneration to be stabilized must be planned. Again, the 36-inch standing scoliosis X-ray is the most important tool to decide the levels of fusion. This film will show coronal and sagittal alignment and balance, disk height maintenance, foraminal stenosis, and areas of listhesis. Flexion and extension X-rays and side-bending X-rays also delineate curve flexibility. If the patient’s problem seems limited to a specific area of degeneration, consideration can be given to a limited fusion and decompression if the curve is stable. The specificity of a limited segment as the cause of pain can be determined by nerve blocks and facet blocks. The entire degenerative deformity should be addressed if a limited area cannot be found, the area of pain is at a curve apex, the curve is not rigid, or there is a significant spinal alignment issue.

If the whole degenerative deformity must be addressed, evaluation of the cephalad and caudad fusion limits must be considered. In general, the entire deformity should include the Cobb levels, and the construct should end at a stable vertebra (centered over the center sacral line). When possible, the construct’s cephalad end should stop at an area with intact facet joints and minimal degeneration. Ideally, the posterior tension band remains intact to avoid undue adjacent segment strain and topping off with a junctional deformity. The disk height above the construct should also be well preserved and show minimal signs of degeneration on X-ray and MRI. If the deformity extends to L1, consideration should be given to extension into the structural thoracic spine. There should also be no junctional kyphosis and minimal osteoporosis. When the fusion must be extended into the structural thoracic spine, the issue becomes whether to stop in the lower thoracic spine, below the physiological kyphotic apex, or whether the construct needs to be taken into the upper thoracic spine. This is determined by looking at the bone quality, the thoracic curvature, and the requirements of sagittal correction. In patients with thoracic hyperkyphosis, osteoporosis, or neurologic disorders, it has been our experience that transitional syndromes (i.e., topping off) result from ending in the lower thoracic spine. These fusions should generally extend to the upper thoracic spine as should patients with an expected residual sagittal imbalance. This structural benefit must be weighed against the added surgical risk of the fusion extension. Patients with good bone quality, restoration of sagittal balance, and a normal thoracic spine can have a construct stop in the lower thoracic spine.

The caudal aspect of fusion should also include the Cobb levels of the curves and a stable vertebra. Again, it should end above a disk with normal height and at a level with minimal degenerative joint disease. There should be minimal tilt of the lower lumbar level and an intact posterior tension band at the end of the procedure. When these criteria are met, it is possible to stop at L5. This has the advantage of avoiding the need to extend to the sacrum, which will preserve the patient’s important sacral motion for function and compensation. It also diminishes the size of the procedure at the area of the spine with the greatest risk of nonunion, L5–S1. Unfortunately, most patients with degenerative lumbar deformity also have deterioration at L5–S1 and require fusion to the sacrum and pelvis.

When fusion to the sacrum is required, consideration must be given to stabilizing the area that is prone to pseudarthrosis and nonunion. Sacral screws should be tricortical and ideally purchase the anterior–superior aspect of the anterior cortex of S1 where the cortical bone is thickest. Unicortical sacral screws are very weak construction points and provide little cantilever resistance. Anterior interbody grafts also greatly reduce strain on the construct at L5–S1, and this graft under compression greatly enhances fusion. This can be achieved by either the anterior lumbar interbody fusion (ALIF) or posterior lumbar interbody fusion/transforaminal lumbar interbody fusion (PLIF/TLIF) techniques. Iliac fixation provides the most powerful resistance to strain and cantilever forces at L5–S1. Consideration should be given to its use when fusions extend from the sacrum to L2 or above. These long fusions for degenerative lumbar disease create great strain on the caudal end of the construct and the S1 screws, which can result in failure of the sacrum and fracture, loss of correction, and pseudarthrosis.

Anterior approaches may include the ALIF and lateral lumbar interbody fusion (LLIF) techniques. Potential advantages of these approaches may include indirect decompression via expanded foraminal height, as well as avoidance of posterior lumbar muscle trauma. The LLIF technique can also improve coronal spine alignment, especially from L1–4 levels (the L5–S1 level is limited by the iliac crest), but it may require a combined posterior approach. ALIF may have complications such as retrograde ejaculation or vascular injuries. LLIF has some risk of lumbar plexus injuries and rare vascular or bowel injury. In general, anterior spine techniques are useful to restore lumbar lordosis and to provide interbody fusion with indirect nerve root decompression, but usually will require a combined posterior approach to achieve normal or near-normal restoration of spinopelvic measurements.

Most spinal deformities are treated by a posterior approach with instrumentation and fusion, with or without an anterior approach. Posterior approaches allow for direct decompression of a stenotic spinal canal or neural foramina. Advantages of the posterior approach include direct decompression, the possibility to perform lumbar interbody fusion using PLIF or TLIF, and access to perform spinal osteotomies that can correct coronal and sagittal imbalance.

Once the levels of decompression and fusion and approach have been determined, further consideration must be given to how alignment and balance will be established, typically done through a series of releases and osteotomies. Neurophysiological monitoring is used throughout the case, and motor evoked potentials and somatosensory evoked potentials are checked at closure of the osteotomy.

Osteotomies are used to attain coronal and sagittal deformity correction, especially in rigid deformities ( ▶ Fig. 47.3). The chosen osteotomy technique may vary according to the degree of correction required to restore sagittal balance. Smith–Petersen osteotomy (SPO) includes resection of the adjacent facet joints, lamina, and ligaments of the involved level. It can be done at multiple levels, can decompress the foramen, and corrects 5 to 10 degrees of lordosis per level. The pedicle subtraction osteotomy (PSO) consists of resection of the facet joints, lamina, pedicles, and wedge-shaped portion of the vertebral body. Closure of the PSO can result in 30 to 40 degrees of lordosis correction and significant improvement of sagittal imbalance. This is particularly helpful in severe, fixed, or rigid deformities. The potential for complications, particularly blood loss and neurologic deficit, is higher for PSO compared with SPO.

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