Degenerative Scoliosis: Surgical Treatment

Fig. 46.1

PA view of patient with degenerative scoliosis showing severe spondylitic changes from L1 to the sacrum with L2–L3 and L3–L4 being the worst. There is significant lateral listhesis at L4–L5 and obliquity at the L5–S1 disk space typical of the fractional curve. The patient complained of left lower extremity pain extending to the dorsum of her foot. Radicular symptoms from the concavity of either the major curve or fractional curve is typical with this type of deformity

It is important to inquire about increasing clinical deformity. Rapidly progressing deformity can be a sign of neurogenic scoliosis, although rare in this adult population. This type of scoliosis results from a central nervous system condition with altered signaling to the spinal musculature and merits complete neural axis imaging [11]. Besides timing of deformity, patients often relate increasing deformity as an increasing rib or paraspinal hump, decreased height, or even the feeling of falling forward as the day progresses. The rotational deformity should be evaluated and documented with a scoliometer at each visit along with height recording. Any shoulder or pelvic asymmetry should be noted. Several subtleties on physical exam can help illuminate increasing sagittal or coronal imbalance. As the day progresses, these patients have to utilize more and more compensatory mechanisms to keep them upright with minimal energy expenditure and may complain of spinal extensor fatigue. The pelvis retroverts and hips extend while the knees flex. Hyperextension of the neck along with shoulder extension can all be seen in patients with a sagittal imbalance, as they are trying to center their head over their pelvis. These exam findings are reflected on long-cassette 36″ standing radiographs as well. Overall, it is very important to pay attention to the sagittal profile when deciding which surgery and instrumentation construct as extending the upper instrumented vertebra (UIV) more proximally is likely necessary for significant sagittal imbalance.

Adult deformity patients pose a more challenging medical scenario compared to adolescent patients. And the role of comorbidities has been well documented as an important determinant of postoperative clinical outcome improvement [12]. Surgical interventions, especially long instrumented fusions, tend to be lengthy and maximally invasive and require diligent presurgical screening. Cardiopulmonary status and general medical condition should be evaluated and approved by the patients’ general medical physician and/or cardiologist. Nutritional status assessment and bone quality analysis are important for the treatment algorithm as well [13]. A preoperative dual-energy x-ray absorptiometry (DEXA) scan is helpful. If patients are osteoporotic and have yet to be treated, one should consider provisional treatment.

Full-length (36-in.) standing anterior-posterior and lateral radiographs are required for preoperative planning. The addition of “spot” films (lumbosacral or thoracolumbar junction) in the correct profile, as rotation can be significant, can be useful for pedicle assessment. Supine long-cassette radiographs (gravity removed) are utilized to assess flexibility. Push-prone or bending radiographs can aid in the assessment of flexibility although these are typically rigid deformities. Cobb angle measurements, coronal and sagittal balance (sagittal- and coronal-vertical axis), and spinopelvic parameters (lumbar lordosis, pelvic incidence, pelvic tilt) are all determined. Advanced imaging with computed tomography (CT) scan (± myelogram) and/or MRI can be useful to help evaluate the degree of central, lateral recess, or foraminal stenosis. CT myelograms in this population are particularly useful as a significant percentage of these patients will have a contraindication (pacemaker, stent, coil, implanted stimulator) to an MRI. Additionally, a CT myelogram allows for the best appraisal of the bony architecture.

46.3 Surgical Options and Navigating a Surgical Algorithm

Patients that fail nonoperative modalities and have symptoms that correlate with radiographic findings should be considered for operative treatment.Specific radiographic parameters that tend to correlate with postoperative clinical improvement include lumbar curves >30–40, ≥6 mm of lateral listhesis, >3 mm increase in listhesis with flexion/extension, L3 and L4 endplate angulations, thoracolumbar kyphosis, and progressive curves (>10°) [1, 2, 8]. Lenke and Silva et al. describe six levels of operative treatment: I, decompression alone; II, decompression and limited instrumented posterior spinal fusion; III, decompression and lumbar curve instrumented fusion; IV, decompression with anterior and posterior spinal instrumented fusion; V, thoracic instrumentation and fusion extension; and VI, utilization of osteotomies for deformity correction [2].

Level I treatment includes decompression alone. This treatment is typically utilized best in the setting of neurogenic claudication secondary to central stenosis requiring only a limited decompression. The potential for deformity progression has been well documented and must be considered. To minimize this risk, patients with radiographic evidence of deformity stability should be selected. The presence of anterior osteophytes, collapsed disk space, and no more than 2 mm of subluxation can be helpful signs of inherent stability. Additionally, the curve should be <30^° without hyperkyphosis and/or sagittal or coronal imbalance. Lastly, these patients should have minimal to no mechanical back pain or deformity complaints as these symptoms will not improve and likely worsen [2].

Level II treatment is level I + limited instrumentation involving only the area of decompression. Patients requiring a more extensive decompression (lateral recess) or evidence of instability prior to decompression are good candidates for this option. Radiographic clues are similar to above, and patients without anterior osteophytes, a well-preserved disk space, and/or more than 2 mm of subluxation may be better served with the addition of instrumented fusion. The curve should still be <30^° without hyperkyphosis and/or sagittal or coronal imbalance as only a limited fusion outside of these parameters could promote deformity progression or accelerated adjacent segment breakdown [2, 11]. Daubs et al. present a series of 55 consecutive patients with ADS treated either with decompression alone (level I, 16 patients) or decompression with limited instrumented fusion (level II, 39 patients). Although the level II patients were younger and had larger curves, at a minimum 2-year follow-up, 62 % of the level I versus 82 % of the level II patients reported a good-excellent result (p < 0.05). At 5-year follow-up, 75 % of the decompression-only patients had recurrent stenosis, while 36 % of the decompression/limited fusion patients had adjacent level stenosis (p = 0.008) [14].

Level III treatment encompasses fusion of the entire lumbar curve and any necessary decompressions. As to not stop the upper instrumented vertebra (UIV) at a physiologic apex, this level of treatment typically involves T10 or T11 instrumentation down to the sacrum/pelvis. Clinically, these patients commonly complain of axial or mechanical pain associated with their deformity. The curves are typically >45^°, having >2 mm of subluxation, lack anterior osteophytes, but still have reasonable balance in both coronal and sagittal planes (Fig. 46.1) [2]. Although there is no clear literature that ascertains a critical construct length that pelvis fixation should definitely be included (versus just sacrum), it is common practice to consider pelvic fixation at our center when the UIV is L2 or proximal [15–19]. Additionally, anterior column support with interbody fixation (via TLIF) should be considered with this surgical option. The combination of anterior column support and sacropelvic fixation may reduce pseudarthrosis rates, screw pullout, and instrumentation failure [20].

Level IV treatment includes both anterior and posterior fusion of the lumbar spine. Traditionally, anterior spinal fusion has played a significant role in the correction of lumbar hyperkyphosis and sagittal imbalance. The load sharing and increased fusion surface area are obvious biomechanical advantages that will help decrease pseudarthrosis rates and instrumentation failure [2]. Additionally, this adds indirect decompression via foraminal distraction. At our center, the refinement of posterior-only techniques has significantly decreased the need for formal anterior exposures and fusions. The current trend and increased utilization of lateral-based procedures will likely further decrease the use of formal anterior lumbar fusion procedures.

Level V treatment includes the extension of the instrumented fusion into the upper thoracic region. This is needed in patients with thoracic hyperkyphosis, thoracic decompensation, thoracolumbar junctional kyphosis, and/or sagittal or coronal imbalance (Fig. 46.2) [2]. O’Shaughnessy et al. evaluated a series of 58 patients from a single center with an average 3-year follow-up and compared outcomes of patients with lower thoracic (LT) versus upper thoracic (UT) primary instrumented fusions in patients with adult scoliosis. The UT group had a greater preoperative thoracic kyphosis and coronal Cobb and increased blood loss. The UT group experienced more perioperative complications (30 % vs 16 %), a higher pseudarthrosis rate (20 % vs 5 %), and a higher prevalence of revision surgery (20 % vs 11 %). The LT cohort developed more proximal junctional kyphosis (18 % vs 10 %) but rarely requiring revision surgery [21].