Impact of spinopelvic alignment on decision making in deformity surgery in adults

A review

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Sagittal spinal misalignment (SSM) is an established cause of pain and disability. Treating physicians must be familiar with the radiographic findings consistent with SSM. Additionally, the restoration or maintenance of physiological sagittal spinal alignment after reconstructive spinal procedures is imperative to achieve good clinical outcomes. The C-7 plumb line (sagittal vertical axis) has traditionally been used to evaluate sagittal spinal alignment; however, recent data indicate that the measurement of spinopelvic parameters provides a more comprehensive assessment of sagittal spinal alignment. In this review the authors describe the proper analysis of spinopelvic alignment for surgical planning. Online videos supplement the text to better illustrate the key concepts.

Abbreviations used in this paper:CA = coronal alignment; CSVL = central sacral vertical line; HRQOL = health-related quality of life; LL = lumbar lordosis; PI = pelvic incidence; PSO = pedicle subtraction osteotomy; PT = pelvic tilt; SA = sagittal alignment; SPI = spinopelvic inclination; SS = sacral slope; SSM = sagittal spinal misalignment; SVA = sagittal vertical axis; TK = thoracic kyphosis; TLK = thoracolumbar kyphosis.

Article Information

Address correspondence to: Christopher P. Ames, M.D., Department of Neurosurgery, University of California, Medical Center, 400 Parnassus Avenue, A850, San Francisco, California 94143. email: amesc@neurosurg.ucsf.edu.

Please include this information when citing this paper: published online March 23, 2012; DOI: 10.3171/2012.2.SPINE11320.

© AANS, except where prohibited by US copyright law.

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Figures

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    Illustration depicting the Dubousset cone of economy. Normally when humans assume an erect posture, they stand within a certain zone of balance in which their torso remains within a certain distance from their pelvis. By doing this, energy expended by postural muscles is minimized. Beyond this zone, the cone of economy, energy expenditure rapidly increases and eventually spinal misalignment results. Printed with the permission of K. X. Probst/Xavier Studio, 2012. Also see online Videos 1 and 2.

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    Illustration showing the distance between the C-7 plumb line (C7PL) and the CSVL, which defines the amount of coronal plane decompensation in centimeters (indicated as –X). Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Drawings showing measurement parameters for spinal SA. Left: The SVA is measured as the distance from the posterior superior corner of the sacrum to a vertical plumb line dropped from the C-7 centroid, here shown as +X°. Right: Spinopelvic inclination is a global angular measurement of SA. It is the angle formed by a line from the femoral heads to the T-1 or T-9 centroid and the vertical plumb line. Since this is an angle rather than a length measurement, it is not subject to magnification variability on radiographs. C7Pl = C-7 plumb line. Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Left: Diagram showing the method for measuring TK. Typically, TK is measured from T-5 to T-12 given that the T-2 endplate is often difficult to visualize. Right: Diagram showing the method for measuring LL. Lumbar lordosis is generally measured from T-12 to S-1 (−X°) and thoracolumbar alignment from T-10 to L-2 (+X°). Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Diagram showing the measurements of PI. Printed with the permission of K. X. Probst/Xavier Studio, 2012. Also see online Videos 3 and 4. a = center of sacral endplate; b = anterior superior point of sacral endplate.

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    Diagram showing the measurements of PT. Printed with the permission of K. X. Probst/Xavier Studio, 2012. Also see online Videos 3 and 4. VRL = vertical reference line.

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    Diagram showing the measurements of SS. Printed with the permission of K. X. Probst/Xavier Studio, 2012. Also see online Videos 3 and 4. HRL = horizontal reference line.

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    Diagrams depicting how an increase in PT (pelvic retroversion) contributes to the restoration of spinal SA. A: High SVA and low PT. B: Partial compensation of SVA with moderate PT. C: Full compensation of SVA with high PT. Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Diagrams showing the relative location of the gravity line (GL), heel line, pelvis, and femoral head (FH) for 3 age groups of patients. As patients age, the GL remains fixed with respect to the heels and lies anterior to the spine. Pelvic retroversion adjusts the GL–heel relationship as the plumb line shifts with age due to lumbar flattening and increased TK. Pelvic tilt and SVA normative values increase with age. Older patients may not require as low an SVA as younger patients. Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Smith-Peterson osteotomies over multiple levels combined with lordotic cages can be used to produce excellent sagittal realignment and correction of PT. Preoperative (A) and postoperative (B and C) radiographs demonstrating a change in PT. Arrow indicates C-7 plumb line.

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    Using vertebral column resection and PSO to correct fixed multiplanar deformity. Preoperative anteroposterior (A) and lateral (B) radiographs showing high PT and fixed sagittal and coronal misalignment. Drawings showing coronal misalignment corrected with vertebral column resection (C) and sagittal misalignment corrected with PSO (D). Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Postoperative anteroposterior (A) and lateral (B) radiographs from the case represented in Fig. 11 showing excellent SA and CA. Postoperative clinical photograph (C) showing the patient's standing posture.

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    Case representative of a patient with good correction for SVA and PT. Preoperative lateral radiograph (left) showing an SVA of 119.73 mm, LL of 28°, SS of 30°, PT of 22°, and PI of 52°. Postoperative lateral radiograph (right) showing an SVA of 30.14 mm, LL of 60°, SS of 38°, PT of 9°, and PI of 47°.

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    Case representative of high postoperative PT and poor correction of the SVA. Preoperative lateral radiograph (left) showing an SVA of 254.13 mm, LL of 32°, SS of 38°, PT of 40°, and PI of 78°. Postoperative lateral radiograph (right) showing an SVA of 150.42 mm, LL of 57°, SS of 40°, PT of 36°, and PI of 76°.

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    Case representative of high postoperative PT with good correction of the SVA. Preoperative lateral radiograph (left) showing an SVA of 142.38 mm, LL of 20°, SS of 16°, PT of 40°, and PI of 56°. Postoperative lateral radiograph (right) showing an SVA of 24.79 mm, LL of 54°, SS of 26°, PT of 30°, and PI of 56°.

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    Case representative of unfavorable thoracic reciprocal change; there was an increase in TK after fusion to T-10. Preoperative lateral radiograph (left) showing an SVA of 158.02 mm, LL of 14°, SS of 32°, PT of 27°, and PI of 59°. Postoperative lateral radiograph (right) showing an SVA of 128.59 mm, LL of 39°, SS of 35°, PT of 26°, and PI of 61°. Lumbar correction in this patient was insufficient.

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    Case representative of significant sagittal balance, degenerative flat back with primary extensor muscle weakness, and low preoperative PT. Despite improved postoperative lordosis of 37°, the patient had similar persistent stooping. The patient did not have hip flexion contracture. Low preoperative PT despite sagittal imbalance is a significant finding, as patients should retrovert the pelvis to partially rebalance. This finding can be indicative of poor extensor muscle strength or hip flexion contracture. Both hip flexion contracture and primary extensor muscle weakness will impair surgical correction and outcome. Preoperative lateral radiograph (left) displaying marked sagittal imbalance, flat-back deformity with 5° of lordosis, and 11° of PT. Postoperative radiograph (right) displaying continued sagittal imbalance despite 37° of lumbar correction, 42° of LL, 15° of PT, and 56° of PI.

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    The lower an osteotomy of a given size is placed in the spine, the greater the theoretical sagittal correction achieved. Stated a different way, for the same amount of angular correction, an osteotomy placed more superiorly in the spine would need to be larger. In practice, this additional angular correction achieved by more inferiorly placed osteotomies (for example, L-5 PSO vs L-3 PSO) may manifest as better PT correction. Preoperative radiograph (left) showing assessment of location for PSO. Blue line represents the C-7 plumb line; white vertical line, approximate corrected location of C-7 plumb line; and thick angled white line, the patient's spine. The angle subtended between the patient's spine and the planned C-7 plumb line (thinner white lines) represents the angle of correction needed given that the PSO was at that level. Thus, as the PSO moves more caudal, the angles become smaller. Postoperative radiograph (right) showing an L-3 PSO and adequate correction of the C-7 plumb line.

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    Photograph showing hip flexion contracture that will prevent successful sagittal realignment surgery and should be identified preoperatively.

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    Drawings showing the method for measuring pelvic obliquity. Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Preoperative (A) and postoperative (B) radiographs demonstrating that a failure to note a leg length discrepancy can lead to further coronal decompensation with correction of the scoliosis. Further decompensation to the right was noted after curve correction. Postoperative radiograph (C) obtained following a second surgery, showing that some of the curve correction was removed and the instrumentation was extended to the pelvis. Note that the pelvic obliquity due to leg length discrepancy was not significantly changed.

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    Pelvic obliquity may also be compensatory in severe curves, resulting from an attempt to maintain balance. In these cases, correction of the scoliosis results in rebalancing of the spine and spontaneous reciprocal decrease in the pelvic obliquity. Preoperative radiograph (left) displaying severe scoliosis and high pelvic obliquity. Postoperative radiograph (right) showing coronal correction and a decrease in pelvic obliquity.

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    Patients with pelvic obliquity on standing radiography should be assessed for leg length discrepancy, and the radiography studies should be repeated with a shoe lift approximating the leg discrepancy to assess the effect on the spinal curve. Photograph (A) obtained during clinical assessment, showing leg length discrepancy. Standing anteroposterior radiograph (B) showing spinal misalignment without the shoe lift. Standing anteroposterior radiograph (C) obtained after the addition of a shoe lift to the side with the short leg, showing partial correction of the scoliosis. Coronal alignment shifted back slightly to the left of neutral. Despite the curve correction with the shoe lift, the patient's back pain continued and she elected to undergo surgery for her symptoms.

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    Drawing of general algorithm for the treatment of patients with scoliosis, coronal misalignment, and pelvic obliquity. In patients with pelvic obliquity in which the spine is flexible and aligned, full correction of the curve may lead to significant coronal decompensation, as the scoliotic curve may be compensatory. In some of these patients, the addition of a shoe lift will allow the flexible spine to relax and may improve alignment and deformity-related symptoms. If the spine is rigid, as is more common in adults, a shoe lift may be poorly tolerated and may not be effective in rebalancing the spine. Patients in such cases may require incomplete curve corrections and sometimes a shoe lift as well depending on the final standing alignment. PO = pelvic obliquity. Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Drawings of complex curve patterns in which the coronal correction strategy must take into account the patients probable alignment shift when standing to determine how much curve correction is possible in each direction. Often this may involve shifting the patient's coronal plumb slightly off to the side opposite the short leg. Printed with the permission of K. X. Probst/Xavier Studio, 2012.

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    Preoperative standing anteroposterior radiograph (A) showing the C-7 plumb line initially off to the left, which was the side of the short leg. Radiograph (B) showing an intraoperative correction strategy designed to shift the intraoperative plumb line a few centimeters to the right. Radiograph (C) showing the return of pelvic obliquity upon standing, resulting in a well-aligned spine in the coronal plane. White line indicates the C-7 plumb line; black line, the CSVL.

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