Over the past 3 decades the sagittal plane has received increasing attention from the scientific community and spine surgeons alike. There remains a lack of clear and concise methods for incorporating surgical techniques and radiographic parameters to achieve the best possible outcome on a patient-specific level. This article proposes a new method for a treatment approach to sagittal malalignment by incorporating new digital tools for surgical planning. This technique offers a consistent approach to adult spinal deformity with sagittal-plane components, and can permit optimization in consistently achieving proper postoperative spinopelvic alignment.
Key points
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Poor sagittal alignment has been shown to correlate highly with poor preoperative and postoperative patient-reported outcomes.
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Surgical techniques exist to correct sagittal alignment, including osteotomies; however, there is a lack of a clear standardized methodology for planning and executing surgical corrections.
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New digital tools can make surgical planning, in particular osteotomy planning, more effective and accurate.
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This article offers a logical and thoughtful process in surgical planning with regard to the use of corrective osteotomy in the adult patient with spinal deformity.
Introduction
Sagittal Plane Deformity: A Growing Problem
Over the past 3 decades the scientific community and spine surgeons have shown an increased interest in sagittal-plane deformity, ultimately acknowledging the complexity of this problem. The term, initially restricted to abnormalities such as “flat back syndrome” or “failed back,” is gaining applicability as it now refers to any condition with an abnormal spinopelvic alignment in the sagittal plane: from degenerative conditions, to pediatric abnormalities such as adolescent idiopathic scoliosis or spondylolisthesis, and including a broad range of deformity in the adult spine. The general principles of realignment procedures are well accepted, although the systematic analysis of patients remains challenging and poorly implemented. The lack of implementation can be easily explained by the limited availability of formal training in the relevance of sagittal parameters and by the historical emphasis given to the coronal Cobb angle. However, a shift in perspective is necessary, as coronal Cobb angle has been proved to poorly correlate with patient-reported outcomes in the adult population.
Why Should We Plan?
Identification of the sagittal plane as a major driver of poor clinical outcomes has given way for science to delve deeper into the concept and, ultimately, offer better clinical approaches to sagittal malalignment and associated methods of compensation. Acknowledging the influence of sagittal alignment on health-related quality of life (HRQoL) forces a clear change in surgeons’ perspectives; to improve clinical outcomes, we must correct sagittal malalignment. Several studies have proved that proper restoration of the sagittal profile is critical to postoperative patient-perceived improvement as quantified through HRQoL scores.
Acknowledging the impact of sagittal alignment on patient outcomes is critical; however, a systematic approach to quantifying sagittal parameters and planning optimal correction is lacking. Through multicenter studies it is emerging that a reasonably sizable number of patients are ultimately undercorrected after surgery. In one such study examining patients who underwent lumbar pedicle subtraction osteotomy (PSO), it was determined that 23% of realignment procedures failed. Similarly, 22% of thoracic PSO patients were found to have poor postoperative spinopelvic alignment. Realignment failure has been associated with not only poor functional outcome but also major complications, such as pseudarthrosis and rod breakage, which often ultimately result in addition surgical procedures. Smith and colleagues evaluated symptomatic rod fracture after posterior instrumented fusion for adult spinal deformity, and found rod breakage in up to 8.6% of adult patients with deformity and 15.6% of PSO patients. The investigators concluded that remaining sagittal malalignment may increase the risk for rod breakage. It is clear that this issue must be addressed, and a method for determining the ideal amount of sagittal correction on a patient-by-patient basis is essential to attaining favorable postoperative outcomes.
How Much Correction is Necessary to Achieve Good Postoperative Results?
The question of the required amount of correction in the setting of deformity is not simple. A proper response requires measuring key spinopelvic parameters, and classifying the extent of compensation. It is necessary to accept that surgical planning starts with measurement of the spinopelvic parameter. The objective of this article is to propose a systematic clinical approach for surgeons through a step-by-step analysis based on a patient presenting with sagittal-plane deformity. For each key radiographic parameter, the clinical relevance of the measurements are discussed in light of the recent literature, and a new method for surgical planning using Surgimap Spine software (Nemaris Inc, New York, NY) is offered as a tool. This case presentation aims to illustrate how a complex spinopelvic alignment can be broken down into simple key numbers to differentiate the primary drivers of the deformity from the compensatory mechanisms.
Introduction
Sagittal Plane Deformity: A Growing Problem
Over the past 3 decades the scientific community and spine surgeons have shown an increased interest in sagittal-plane deformity, ultimately acknowledging the complexity of this problem. The term, initially restricted to abnormalities such as “flat back syndrome” or “failed back,” is gaining applicability as it now refers to any condition with an abnormal spinopelvic alignment in the sagittal plane: from degenerative conditions, to pediatric abnormalities such as adolescent idiopathic scoliosis or spondylolisthesis, and including a broad range of deformity in the adult spine. The general principles of realignment procedures are well accepted, although the systematic analysis of patients remains challenging and poorly implemented. The lack of implementation can be easily explained by the limited availability of formal training in the relevance of sagittal parameters and by the historical emphasis given to the coronal Cobb angle. However, a shift in perspective is necessary, as coronal Cobb angle has been proved to poorly correlate with patient-reported outcomes in the adult population.
Why Should We Plan?
Identification of the sagittal plane as a major driver of poor clinical outcomes has given way for science to delve deeper into the concept and, ultimately, offer better clinical approaches to sagittal malalignment and associated methods of compensation. Acknowledging the influence of sagittal alignment on health-related quality of life (HRQoL) forces a clear change in surgeons’ perspectives; to improve clinical outcomes, we must correct sagittal malalignment. Several studies have proved that proper restoration of the sagittal profile is critical to postoperative patient-perceived improvement as quantified through HRQoL scores.
Acknowledging the impact of sagittal alignment on patient outcomes is critical; however, a systematic approach to quantifying sagittal parameters and planning optimal correction is lacking. Through multicenter studies it is emerging that a reasonably sizable number of patients are ultimately undercorrected after surgery. In one such study examining patients who underwent lumbar pedicle subtraction osteotomy (PSO), it was determined that 23% of realignment procedures failed. Similarly, 22% of thoracic PSO patients were found to have poor postoperative spinopelvic alignment. Realignment failure has been associated with not only poor functional outcome but also major complications, such as pseudarthrosis and rod breakage, which often ultimately result in addition surgical procedures. Smith and colleagues evaluated symptomatic rod fracture after posterior instrumented fusion for adult spinal deformity, and found rod breakage in up to 8.6% of adult patients with deformity and 15.6% of PSO patients. The investigators concluded that remaining sagittal malalignment may increase the risk for rod breakage. It is clear that this issue must be addressed, and a method for determining the ideal amount of sagittal correction on a patient-by-patient basis is essential to attaining favorable postoperative outcomes.
How Much Correction is Necessary to Achieve Good Postoperative Results?
The question of the required amount of correction in the setting of deformity is not simple. A proper response requires measuring key spinopelvic parameters, and classifying the extent of compensation. It is necessary to accept that surgical planning starts with measurement of the spinopelvic parameter. The objective of this article is to propose a systematic clinical approach for surgeons through a step-by-step analysis based on a patient presenting with sagittal-plane deformity. For each key radiographic parameter, the clinical relevance of the measurements are discussed in light of the recent literature, and a new method for surgical planning using Surgimap Spine software (Nemaris Inc, New York, NY) is offered as a tool. This case presentation aims to illustrate how a complex spinopelvic alignment can be broken down into simple key numbers to differentiate the primary drivers of the deformity from the compensatory mechanisms.
Step-by-step analysis
Case Presentation
The patient is a 73-year-old man complaining of low back pain for about 7 years. The patient feels he also has marked truncal shift anteriorly. He underwent spine surgery with an interspinous device in 2008 and experienced mild relief of some leg pain, but over time, particularly the last 4 years, he has noted increasing low back pain (7 out of 10 on a visual analog scale), with fatigue to the lower extremities and loss of standing and ambulatory endurance. The patient denies any neurologic deficits such as leg numbness, weakness, or paresthesias. Past treatment included pharmacologic management, physical therapy, and steroid injections.
On physical examination the patient’s standing posture is with marked positive truncal inclination and an ability to stand fully erect. The patient demonstrates paravertebral lumbar tenderness, and discomfort with range of motion of the lumbar spine. Neurologic examination of the lower extremities reveals no deficits.
Evaluation of the Coronal Plane
Historically, evaluation of the coronal plane has been extrapolated from the Lenke classification of adolescent idiopathic scoliosis (AIS) ; however, recent studies have demonstrated that adult spinal deformity should not be considered an “adult version” of AIS. One of the first studies to closely examine the clinical impact of coronal deformity demonstrated that the obliquity of lumbar vertebrae (but not Cobb angle) correlate with pain scores. Subsequently, multicenter studies have revealed that apical level of a scoliotic deformity, intervertebral subluxation, and coronal imbalance are also correlated with outcomes scores. In light of these findings, a systematic evaluation of the coronal plane in the setting of adult spinal deformity should include the quantification of local (ie, intervertebral subluxation), regional (ie, identification of the apex), and global deformities (ie, global coronal malalignment). It appears that coronal C7 to center of the sacrum (central sacral vertical line) offset up to 4 to 5 cm is well tolerated, and that rotatory subluxations become mostly significant above 7 mm.
As illustrated Fig. 1 (left), preoperatively the patient did not present any coronal deformity (local, regional, or global).
Evaluation of the Sagittal Plane
Global spinopelvic alignment
One of the most commonly used radiographic parameters in the setting of sagittal-plane evaluation is the sagittal vertical axis (SVA). This global parameter is defined as the linear offset between a plumb line dropped from C7 and the posterosuperior corner of S1. A possible substitution of the SVA is the T1 spinopelvic inclination (T1SPI), defined as the angle between a vertical and the line from T1 to the center of the bicoxofemoral axis. T1SPI demonstrates almost perfect correlation with SVA and carries the advantage of being an angular measurement, which avoids the error inherent in measuring offsets in noncalibrated radiographs. Global spinal realignment should attempt to obtain a postoperative SVA of less than 50 mm, or T1SPI of less than 0°. Restoration of global alignment facilitates level gaze and achievement of a physiologic standing posture. From a clinical point of view, both parameters correlate with HRQoL (pain and disability), and restoration of these parameters within normative values correlates with an increased likelihood of reaching a minimal clinically important difference.
As illustrated in Fig. 1 (right), preoperatively the patient had an SVA measured at 14.7 cm. According to the Scoliosis Research Society Schwab classification of adult spinal deformity, this level of SVA identifies the patient as “severe sagittal deformity” with an SVA grade of ++.
Compensatory mechanisms
In addition to the evaluation of global spinopelvic alignment, it is of primary importance to also identify and quantify the use of compensatory mechanisms used in an effort to maintain the trunk as vertical as possible. From a physiologic point of view several mechanisms have been reported in the literature, such as changes of spinal curvatures (eg, hyphokyphosis of the thoracic spine, flexion of the knee, or retroversion of the pelvis). Changes in spinal curvatures are very common across the spectrum of spinal pathology (eg, increase of segmental lumbar lordosis above spondylolisthesis); they require not only a flexible spine but also the muscular ability to maintain those changes. Because of the nature of standard scoliosis films, knee flexion is difficult to evaluate on radiographs; a surrogate measurement can be the quantification of the femoral angulation with the vertical.
Among the possible compensatory mechanisms to sagittal-plane malalignment, pelvic retroversion is probably the most commonly measured parameter. Pelvic retroversion is defined as a backward rotation of the pelvis; it is quantified by an elevated pelvic tilt (PT): the angle between the vertical and the line from the center of the bicoxofemoral axis to the middle of the superior endplate of S1. Jean Dubbouset introduced the concept of “pelvic vertebra,” considering the pelvis as the pedestal of the spine where pelvic retroversion aims at “bringing back” the spine into a vertical position. From a physiologic point of view, an increase in PT is not energy efficient, and correlates with increased pain and disability.
As illustrated in Fig. 2 A, preoperatively the patient had a PT of 31°, illustrating a pelvic retroversion in an effort to compensate for the sagittal deformity. From a hypothetical point of view, if the patient was able to further increase his pelvic retroversion (physiologic limit of pelvic retroversion = horizontal sacral endplate), the SVA would be within normative values ( Fig. 2 B; PT = 48°, SVA = 2.5 cm). From a pragmatic point of view, this illustrates that measurement of SVA alone does not permit accurate quantification of the sagittal plane, as it does not integrate how much of the “true SVA” is compensated for by increased retroversion. Using the same analogy, if the patient was not using any pelvic compensation (ie, PT = normative value [∼20°]), the projected SVA would be even more severe than the one measured on standing radiographs ( Fig. 2 C; PT = 20°, SVA = 22 cm).
Related posts:
Clinical and Radiographic Evaluation of the Adult Spinal Deformity Patient
Spinal Deformity Surgery
Coronal Realignment and Reduction Techniques and Complication Avoidance
Spinal Osteotomies for Rigid Deformities
Treatment Algorithms and Protocol Practice in High-Risk Spine Surgery
Management of High-Grade Spondylolisthesis
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