26.1 Introduction

Untreated adolescent idiopathic scoliosis (AIS) in the adult often presents to the surgeon with the patient experiencing many years of symptoms and/or progression of deformity. The purpose of surgery at a young age is to restore alignment, prevent curve progression and its later sequelae including pain and pulmonary dysfunction, and improve body image. In adults, surgery for scoliosis is more commonly driven by disability and a patient’s inability to function in daily activity, although body image is a common concern as well. ¹

26.2 Untreated Adolescent Idiopathic Scoliosis

Adolescent-onset idiopathic scoliosis may be previously untreated or treated nonoperatively and present in the adult. The delay in treatment may occur for a variety of reasons including a lack of symptoms such as pain and displeasure with a deformity, a fear of surgery by family members, or a lack of financial resources for an operative procedure. ^{2 , 3} Another reason for the delay is a conscious choice by the family to the delay surgery because of a perceived or real negative impact on spinal flexibility associated with spinal arthrodesis, particularly in patients in which fusion must extend into the lumbar spine. A family with an adolescent who is athletic, involved in a sport that requires full flexibility such as swimming, dance, or gymnastics, and who is interested in pursuing athletics beyond secondary school may make a decision to delay the procedure until later in life, especially if the patient is skeletally mature. These common scenarios may result in a later presentation of patients at various stages of their lives. The decision of the family to proceed with surgery for their skeletally mature adolescent now versus delaying to some future point in time is a discussion frequently conducted with the consulting surgeon. ⁴ Patients should be advised that, when delayed, future surgical options usually involve longer fusions with increasing loss of mobility.

Young adults in their 20s will often have a similar lack of symptoms as their adolescent counterparts but will have a deformity that may be progressive now or is anticipated to be so in the future based on natural history data; an individual may decide to undergo surgical correction. ^{5 , 6 , 7} Adults in their early 30s may have more pain and onset of occasional sciatica due to the development of degenerative disk disease most commonly associated with lumbar curvatures. At times, a mother with young children at home develops symptomatic curve progression. She is then faced with surgery and recovery while still needing to care for her young family. By the fourth through sixth decades of life, pain becomes the most prominent aspect of the patient’s day-to-day experience. Curve progression with increasing deformity, including waistline shifts and rotational prominences, is manifested. Symptomatic patients typically have diffused degenerative changes throughout the spine that often extend to the lumbosacral junction requiring arthrodesis to the sacrum (Fig. 26‑1).

Principles learned from the treatment of adolescents with idiopathic scoliosis can be applied, in part, to the young and middle-aged adult patient as well. As discussed in Chapter 6, the Lenke classification system is utilized to determine the curve type and which curvatures to include in the surgical construct in the adolescent and can inform treatment decisions in the young or middle-aged adult. ⁸ Curve and deformity correction and optimal global coronal and sagittal alignment, while minimizing fusion to the distal lumbar spine, are desired. Connolly et al showed a greater percentage of patients with a poor outcome if the fusion was extended to L4 as compared to L2 or L3. ⁹ Selective thoracic fusion can be considered in the setting of thoracic major curvature with flexible moderate lumbar curvature and the absence of symptomatic lumbar disk degeneration. However, curve progression and progressive lumbar disk disease and pain may require a subsequent extension of the fusion. The Adult Spinal Deformity Classification system incorporates curve type and sagittal measures in its assessment of adult scoliosis. This classification is a useful model for decision-making in the older adult where sagittal malalignment becomes a greater concern than the coronal plane deformity ^{10 , 11} . The classification includes coronal curve patterns as well as sagittal parameters including pelvic incidence–lumbar lordosis mismatch, global sagittal alignment, and pelvic tilt, with the sagittal modifiers all exhibiting clinically significant correlations with quality of life. ^{12 , 13 , 14} Later in life, patients are hampered by the sagittal plane deformity that supersedes the coronal plane and axial plane involvement and is the main driver of symptoms. ¹⁵ At some point in time, the thought of a surgical procedure becomes more appealing for these patients than living with the daily pain and disability. Global sagittal malalignment results from extensive degenerative disk disease leading to degenerative flatback deformity. The older patient (from the sixth decade of life on) often requires sagittal plane realignment and a reconstructive operation that extends to the sacrum and may include advanced osteotomies and/or combined anterior and posterior approaches to achieve the desired global alignment associated with improved health-related quality of life (HRQOL). ¹⁶ Extensive research of adult spinal deformity on HRQOL has been conducted using outcome instruments such as the Scoliosis Research Society-22 (SRS-22), the Oswestry Disability Index (ODI), 36-Item Short Form Health Survey (SF-36) and 12-Item Short Form Health Survey (SF-12), and EuroQOL Group Association (EQ-5D), and has facilitated our understanding of the severe impact of adult scoliosis on the individual. HRQOL assessments collected preoperatively in adult spinal deformity patients have shown that patients can be as debilitated by the deformity as patients suffering from chronic diseases such as arthritis, congestive heart failure, chronic lung disease, and diabetes. ^{17 , 18}

In a recent study by Lonner et al, ⁴ adult idiopathic surgical patients, despite having larger progressive curves, had equal curve correction but greater improvement in SRS scores compared to matched AIS surgical patients. Adult patients compared to adolescent scoliosis patients had longer operative times, more levels fused, and fusion to the sacrum/pelvis (36%) compared to 0% in the AIS cohort and a fivefold higher major complication rate compared to AIS counterparts (25 vs. 5%; Fig. 26‑1). ⁴ Decision-making in the adult patient goes beyond the presence of structural curvature and deformity. Surgical decision-making also must include a detailed assessment of frequently present comorbidities. The presence of incapacitating back pain associated with disk degeneration, facet arthrosis, and radiculopathy often dictates a longer fusion, frequently including the sacrum/pelvis as documented in the previous study.

26.3 Preoperative Assessment and Nonoperative Treatment

History and physical examination inform further workup of the adult scoliosis patient. Patients are queried about back and/or radicular leg pain, numbness, tingling, or weakness, which suggest the presence of a radiculopathy due to nerve root compression or spinal stenosis. Effect of the back condition on activities of daily living and ability to walk determines the level of impact on the function of the individual. History of prior interventions delineates the extent of prior treatment that the patient has undergone and the role for further nonoperative care or escalation to an operative approach. History of height loss, waistline changes, and change in the fitting of clothing all indicate progressive deformity. Physical examination includes a thorough neurologic examination to assess for radiculopathy, evaluation of gait, hip range of motion, and presence of contractures. A painful hip with a restricted range of motion may indicate underlying osteoarthritis of the joint, which might be the primary driver of disability in the individual and should be the focus of treatment in that case. A hip flexion contracture will result in an inability of the patient to stand erect following surgery and should be addressed with physical therapy and, if ineffective, surgery. In addition, the strength of the hip extensor muscles will gauge the ability of the patient to compensate postoperatively for incomplete restoration of global sagittal alignment through pelvic retroversion. The spinal deformity is assessed through evaluation of shoulder and waistline symmetry or lack thereof and the Adams forward bend test with an inclinometer to measure rotational deformities.

Radiographic assessment with standing full-length X-rays of the spine and measurement of regional, global sagittal, and coronal alignment is performed. Adjacent segments are evaluated for junctional deformities or disk degeneration in previously operated patients. Assessment of structural curvatures and radiographic evidence of disk degeneration (including sclerosis, endplate irregularities, osteophytes, and lateral listhesis) is performed. ¹⁹ The primary measurements of interest in the sagittal plane are the lumbar lordosis, pelvic incidence, pelvic tilt, the L4–S1 lordosis, C7 sagittal vertical axis (C7 SVA) the T1 pelvic angle (TPA), and global tilt. For more details on primary measurements of interest, refer to Chapter 4. Postoperatively, these parameters can be utilized to calculate a global alignment and proportion (GAP) score. As the gap score increases, so does the risk of mechanical complications and proximal junctional kyphosis (PJK), according to one study. ²⁰

Magnetic resonance imaging (MRI) is utilized to identify central and foraminal stenosis as well as the disk and facet health of caudal motion segments and the potential need to include degenerated segments in a fusion. Decisions on the need to decompress either directly or indirectly are made with this modality.

Finally, computed tomography (CT) scan evaluation is important to assess fusion status in previously operated patients or for patients with a rod fracture and to assess the accuracy of previously placed pedicle screws, which may require revision in the presence of neurologic symptoms. The CT also assesses the health of the facet joints and can be combined with myelography, especially in the patient with an MRI-incompatible pacemaker or another metallic implant. Dual-energy X-ray absorptiometry (DEXA) scan evaluation of bone mineral density is imperative in determining the adequacy of bone to accept fixation and may indicate perioperative pharmacologic treatment and intraoperative strategies to improve fixation and avoid failure at the bone–implant interface.

Physical examination findings and radiographic image evaluation, along with a patient’s health status, are critical components of decision-making on behalf of the patient. HRQOL is assessed with patient-reported outcome measures to assess the quality-of-life impact of their disease state. Improvement in the SRS-22 score, ODI, visual analog scale (VAS), and SF-36 or SF-12 after surgery has been shown. ^{17 , 21}

Adult spinal deformity is a progressive disease that takes years before it significantly impacts a patient’s quality of life. Nonoperative treatment may be beneficial early on and includes low-impact aerobic conditioning and core strengthening, the use of nonsteroidal anti-inflammatory medication, and the judicious use of braces or corsets for pain control. Facet block and epidural steroid injections may play a role, but for those with a significant decline in HRQOL, surgical treatment is associated with improved outcomes at 2 years, whereas nonoperative treatment shows no improvement or even progressive decline overall. ²²

26.4 Complications and Mitigation of Complications in Adult Scoliosis Surgery

Most degenerative spinal conditions are managed by a single surgeon. In adult spinal deformity care, there is a growing trend to utilize multidisciplinary spine conferences to identify patients most likely to benefit from surgical treatment and to mitigate complications. Shared decision-making with physiatrists, anesthesia pain specialists, and other nonsurgical providers has demonstrated benefits in the literature while decreasing the number of unnecessary surgeries. ²³ That same study showed that when 100 degenerative spinal patients were referred to a multidisciplinary spine center for surgery, 58 of them were instead recommended nonoperative management. Interventions in addition to the ones listed earlier include weight loss, smoking cessation, and spinal cord stimulation. Two-surgeon approaches for adult spinal deformity result in reduced operative time, blood loss, and overall complication rate. ^{24 , 25}

Several modifiable risk factors have been shown to correlate with worse surgical outcomes following spinal deformity surgery. These risk factors include an elevated body mass index (BMI), smoking, narcotics use, and anxiety/depression. ²⁶ Another recent study shows that elderly patients (age 65–85) undergoing spinal deformity surgery have up to 70% incidence of complications. The European Spine Study Group investigated the GAP score. In a recent study, patients were randomly assigned to derivation (n = 148 [66.7%]) and validation (n = 74 [33.3%]) cohorts. GAP score parameters were relative pelvic version (the measured minus the ideal sacral slope), relative lumbar lordosis (the measured minus the ideal lumbar lordosis), lordosis distribution index (the L4–S1 lordosis divided by the L1–S1 lordosis multiplied by 100), relative spinopelvic alignment (the measured minus the ideal global tilt), and an age factor. The study showed that patients with a proportioned spinopelvic state postoperatively according to the GAP score had a mechanical complication rate of 6%, whereas those with a moderately or severely disproportioned spinopelvic state had rates of 47 and 95%, respectively. ²⁰

26.5 Proximal and Distal Junctional Kyphosis

Patients with AIS who undergo spinal fusion have a relatively high rate of radiographic PJK. The definition of PJK in the literature has been variable, with no agreed-upon definition. ²⁷ However, Helgeson et al proposed that the PJK angle was defined from the inferior endplate of the upper instrumented vertebra (UIV) to the superior endplate of one, instead of two, vertebra above the UIV. In addition, the PJK rate may be higher with the utilization of all pedicle screw constructs, loss of kyphosis, larger preoperative kyphosis, Lenke curve type, and decreased rod contour angle. ^{28 , 29 , 30} Kim et al showed that the SRS-22 outcomes for patients with AIS were no different for the PJK group as compared to controls. ³² Although this radiographic finding is rarely symptomatic in the adolescent, it can present later in the adult patient as a painful condition requiring revision (Fig. 26‑2).

In adult patients, one of the most recognized complications in patients undergoing instrumented posterior fusion for spinal deformity is PJK. ^{31 , 32 , 33} Although there are variable definitions of PJK in the literature, radiographic kyphosis that is asymptomatic is fundamentally different from symptomatic PJK or catastrophic failure. Proximal junctional failure includes loss of fixation and potentially neurologic injury requiring revision surgery entailing proximal fusion extension and decompression of the neural elements. Causes of PJK are multifactorial, including age, the magnitude of sagittal plane correction, disruption of the posterior ligamentous complex and musculotendinous dynamic tension band, and a biomechanical construct difference between the unfused spine and the rigid fusion. ³⁴ There are several measures utilized to prevent the onset of PJK following fusion. Vertebroplasty, hook fixation, terminal rod contouring, percutaneous fixation, and ligament augmentation can all be used in appropriately selected patients individually or in combination. These techniques warrant further investigation but have some supporting data and compelling biomechanical rationale, especially in elderly high-risk patients. Age-adjusted modifications in alignment goals, which reduce the degree of sagittal correction for elderly patients, have the potential to reduce implant-related complications and PJK. ³¹ Finally, as suggested earlier, utilization of the GAP score can help minimize all implant-related complications.

In adults, the incidence of distal junction breakdown is high, especially for long fusion constructs ending at L4 or L5. In a study by Kuhns et al, advanced lumbar degenerative disk disease developed in 69% of patients after long fusions to L5. In that study, 31 patients were followed for 5 to 15 years. ³⁵ In another study, Edwards et al reported that 61% of patients with fusion to L5 developed loss of sagittal alignment, worsening SRS-22 score, loss of L5 implant fixation, and significant loss of sagittal alignment. These patients had an increased likelihood of revision surgery as shown in Fig. 26‑3. ³⁶

26.6 Revision Surgery, Alignment, and HRQOL

As adolescent patients transition to adulthood, the principles of adult deformity surgery with a reliance on the sagittal plane become increasingly important to consider, especially due to the fact that fusion tends to be extensive and eliminates compensatory motion segments that are available to the adolescent patient with shorter fusion and little or no disk degeneration. ³⁷ In an ideally balanced spine, a plumb line drawn from C7 should bisect the L5–S1 disk space and is referred to as the SVA. ³⁸ In a young, healthy person, the SVA can be several centimeters negative. With age, progressive kyphosis is expected, and the SVA gradually becomes increasingly positive. ³¹ The young adult spine behaves more like the adolescent spine, but the aging process changes the considerations in decision-making on behalf of the patient as stated earlier. Glassman et al have shown that as the SVA becomes increasingly positive, there is a strong correlation with increasing disability. ³⁹

Glassman et al have also reported on the impact of complications in adult deformity surgery. ⁴⁰ In that study, clinical outcome questionnaires in the form of the SRS-22, SF-12, and ODI were included and compared for patients who had either major or minor complications. Whereas minor complications had no bearing on outcomes, major complications adversely affected clinical outcomes at 1 year postoperatively. In the setting of revision, Cho et al showed that the complication rate is significantly higher than for primary operations (58 vs. 45%). ⁴¹ Despite a higher complication rate, however, surgery conferred equivalent benefits as compared to primary cases. Older age (age > 60) continued to be an independent risk factor for complications but had no bearing on clinical outcome measures in the long term. This study was in contrast to a previous study by Linville et al that showed an equivalent complication profile for primary versus revision cases. In that study, short-term complications (<6 months) were similar for primary versus revision procedures. ⁴²

26.7 FlatBack

Harrington instrumentation for the surgical management of scoliosis was revolutionary at the time that it was developed. Utilizing a single hook at both the rostral and caudal ends of the construct, curve correction was achieved purely through distraction. At the time, correction of the coronal plane and stabilization of curve progression was the primary goal, which was reasonable for younger patients. However, this distraction into the lumbar spine with a straight rod resulted in a loss of lordosis. Initially, the patient is able to compensate through hyperlordosis of remaining caudal motion segments and pelvic retroversion. Eventually, as disk degeneration distal to the instrumentation occurs, a symptomatic loss of lumbar lordosis and ability to stand upright with back pain develops, the so-called flatback syndrome. ⁴³ Even at 21 years of follow-up, most patients treated with Harrington fusion were functioning well in one study. ⁴⁴ However, older patients or patients with lumbar curve involvement inevitably had progressive back pain and distal junctional breakdown related to lumbar flatback deformity. Up to 47% of adult patients developed sagittal plane deformity requiring revision in adulthood for the adjacent segment or for lumbar flatback following Harrington instrumentation in a landmark publication by Lagrone et al. ⁴³ Improved understanding of the sagittal plane has improved curve correction goals to include the coronal and sagittal planes. Modern surgical techniques including anterior column support, segmental posterior fixation, and rod contouring have helped mitigate this complication but not to eliminate it.

In the aging spine, correction of spinal deformity, especially when rigid, often requires varying degrees of bony resection or osteotomies. With various options for osteotomies depending on the individual case, it has proven difficult to compare clinical outcomes. The Comprehensive Anatomical Spinal Osteotomy Classification (CASOC) system is a grading system that quantifies the extent of the osteotomy and can be used as a common language to compare different techniques for correction of deformity including their complication profiles, which tend to increase with higher-grade osteotomies such as the pedicle subtraction or grade 3 to 4 osteotomy. ⁴⁵

Restoration of lordosis can be accomplished by a posterior shortening osteotomy. These osteotomies include removal of the facet joints (grade 1 vs. grade 2, which includes complete removal of both facets of the facet joint), removal of the pedicle (grade 3 or grade 4, which includes the disk above), or removal of the vertebral body (grade 5 vs. grade 6, more than one vertebrae resected). Fig. 26‑4 illustrates a grade 4 resection osteotomy for flatback. An alternative to posterior shortening is a procedure that lengthens the anterior column from a lateral or anterior approach. Numerous methods exist to provide anterior column support including lateral interbody fusion (LIF) and oblique lateral interbody fusion (OLIF). Both of these techniques vary slightly in their approach being either transpsoas or anterior to the psoas. The advantage of the LIF or OLIF procedure is the ability to place a large lordotic graft through a relatively small exposure window.

Anterior lumbar interbody fusion (ALIF) offers perhaps the best opportunity to restore lordosis, with the placement of a lordotic cage, and is performed from a direct anterior access to the disk (Fig. 26‑5). Anterior column realignment (ACR), alternatively, involves the release of the anterior longitudinal ligament (ALL) via a lateral minimally invasive approach. In a recent review, 12 manuscripts were identified describing the procedure. ALL release combined with 30-degree cage placement led to a mean of 11.6 degrees of segmental lordosis correction. In contrast, a 20-degree cage placement led to 9.5 degrees of lordosis, and a 10-degree cage placement led to 4.1 degrees of lordosis. ⁴⁶

A classification system has been developed recently. The six grades of ACR are as follows:

• 
  

  Grade A: ALL release with hyperlordotic cage, intact posterior elements.

  
  
• 
  

  Grade 1 (ACR + Schwab grade 1): additional resection of the inferior facet and joint capsule.

  
  
• 
  

  Grade 2 (ACR + Schwab grade 2): additional resection of both superior and inferior facets, interspinous ligament, ligamentum flavum, lamina, and spinous process.

  
  
• 
  

  Grade 3 (ACR + Schwab grade 3): additional adjacent-level three-column osteotomy including pedicle subtraction osteotomy.

  
  
• 
  

  Grade 4 (ACR + Schwab grade 4): two-level distal three-column osteotomy including pedicle subtraction osteotomy and disk space resection.

  
  
• 
  

  Grade 5 (ACR + Schwab grade 5): complete or partial removal of a vertebral body and both adjacent disks with or without posterior element resection. ⁴⁷

Fig. 26‑6 illustrates a multilevel LIF with posterior instrumented fusion for degenerative lumbar scoliosis.

When patients with previous scoliosis fusions require a revision, it is frequently related to a sagittal plane problem requiring additional lordosis. The LIF, OLIF, and ALIF-ACR procedures offer a means to provide anterior column support and restore lordosis. Revision surgery often necessitates a fusion to the sacrum, which must include pelvic fixation in order to protect against screw pullout from the sacrum and loss of alignment, particularly for elderly patients. Instrumentation to the pelvis offers a more definitive base for the construct but will sacrifice mobility. Fixation options to the pelvis include the more traditional transiliac screw with an offset connector or sacral alar iliac (SAI) fixation popularized by Kebaish et al. ⁴⁸ The SAI fixation allows for a lower-profile iliac fixation and a screw that remains in line with the pedicle screws of the lower lumbar spine. Long fusions to the sacrum are at significant risk for pseudarthrosis, particularly in the absence of anterior column support. For this reason, the authors recommend either an ALIF or a transforaminal lumbar interbody fusion (TLIF) fusion at the lumbosacral junction.