Fixed sagittal plane imbalance

Abstract

Study Design Literature review. Objective To discuss the evaluation and management of fixed sagittal plane imbalance. Methods A comprehensive literature review was performed on the preoperative evaluation of patients with sagittal plane malalignment, as well as the surgical strategies to address sagittal plane deformity. Results Sagittal plane imbalance is often caused by de novo scoliosis or iatrogenic flat back deformity. Understanding the etiology and magnitude of sagittal malalignment is crucial in realignment planning. Objective parameters have been developed to guide surgeons in determining how much correction is needed to achieve favorable outcomes. Currently, the goals of surgery are to restore a sagittal vertical axis < 5 cm, pelvic tilt < 20 degrees, and lumbar lordosis equal to pelvic incidence ± 9 degrees. Conclusion Sagittal plane malalignment is an increasingly recognized cause of pain and disability. Treatment of sagittal plane imbalance varies according to the etiology, location, and severity of the deformity. Fixed sagittal malalignment often requires complex reconstructive procedures that include osteotomy correction. Reestablishing harmonious spinopelvic alignment is associated with significant improvement in health-related quality-of-life outcome measures and patient satisfaction.

Keywords: adult spinal deformity; pedicle subtraction osteotomy; sagittal plane imbalance.

Fig. 1

Cone of economy. The figure outlines the “stable” zone surrounding the individual that is conical in shape from the feet to the head. Deviation from the center within the zone results in greater muscular effort and energy expenditure to maintain an upright posture. Deviation of the body outside the cone results in falling or requiring support. Abbreviations: H, head; P-L, pelvic level; P-S, polygon of sustentation. (Reprinted with permission from Schwab F, Patel A, Ungar B, Farcy JP, Lafage V. Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery. Spine (Phila Pa 1976) 2010;35(25):2224–2231.5)

Fig. 2

(A) Pelvic incidence (PI) is defined as an angle subtended by line oa, which is drawn from the center of the femoral head to the midpoint of the sacral end plate and a line perpendicular to the center of the sacral end plate. (B) Sacral slope (SS) is defined as the angle subtended by a horizontal reference line (HRL) and the sacral end plate line (bc). (C) Pelvic tilt is defined as the angle subtended by a vertical reference line (VRL) originating from the center of the femoral head (o) and the pelvic radius (oa). It is positive when the hip axis lies in front of the middle of the sacral end plate. (Reprinted with permission from Labelle H, Roussouly P, Berthonnaud E, Dimnet J, O'Brien M. The importance of spino-pelvic balance in L5-S1 developmental spondylolisthesis: a review of pertinent radiologic measurements. Spine (Phila Pa 1976) 2005;30(6, Suppl):S27–S34.7)

Fig. 3

Lateral scoliosis X-ray of a 72-year-old man after a T10–S1 posterior spinal fusion. The sagittal vertical axis (SVA) is defined as the horizontal offset from the posterosuperior corner of S1 to the vertebral midbody of C7 (C7 plumb line).

Fig. 4

Sagittal spinal radiographic parameters. Thoracic kyphosis measures from the superior end plate of T4 to the inferior end plate of T12. Lumbar lordosis measured from the superior end plate of L1 to the superior end plate of S1.

Fig. 5

For a given structural deformity, how pelvic retroversion compensates for spinal deformity. Left: No pelvic retroversion and high sagittal vertical axis (SVA). Middle: Moderate pelvic retroversion and SVA. Right: High pelvic retroversion and no SVA. (Reprinted with permission from Schwab F, Patel A, Ungar B, Farcy JP, Lafage V. Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery. Spine (Phila Pa 1976) 2010;35(25):2224–2231.5)

Fig. 6

Realignment objectives in the sagittal plane. Sagittal vertical axis (SVA) < 50 mm, pelvic tilt (PT) < 20 degrees, and lumbar lordosis (LL) = pelvic incidence (PI) ± 9 degrees. (Reprinted with permission from Schwab F, Patel A, Ungar B, Farcy JP, Lafage V. Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery. Spine (Phila Pa 1976) 2010;35(25):2224–2231.5)

Fig. 7

(A–E) A case example. A 68-year-old woman after a T4–L4 posterior spinal fusion with multilevel interbody fusions for adult idiopathic scoliosis. She has adjacent segment degeneration at L4–L5 and sagittal plane imbalance. (B) The magnitude of the deformity (sagittal vertical axis [SVA] = 13 cm, pelvic incidence [PI] = 75 degrees, pelvic tilt [PT] = 40 degrees, and lumbar lordosis [LL] = 35 degrees). There is an L4–L5 degenerative spondylolisthesis with 15 degrees of focal kyphosis. (C) An “open disk space” at L4–L5 with advanced degenerative changes in the facet joints without ankylosis. An L4–L5 posterior column osteotomy and revision L4–sacrum with iliac fixation was performed. (E) Degree of correction and restoration of sagittal balance (SVA = 4 cm, PI = 75 degrees, PT = 25 degrees, and LL = 65 deg). The mobility of the L4–L5 disk space allowed for significant correction with the posterior column osteotomy (15 degrees of kyphosis to 25 degrees of lordosis = 40 degrees of correction).

Fig. 8

(A–D) A case example. A 72-year-old man after a T10–S1 posterior spinal fusion with multilevel interbody fusions. He has iatrogenic flat back with sagittal plane deformity and disability. A computed tomography scan revealed a pseudarthrosis at L5–S1. (B) Sagittal malalignment pelvic incidence (PI) and lumbar lordosis (LL) mismatch and compensatory pelvic retroversion (sagittal vertical axis [SVA] 18 cm, PI = 60 degrees, pelvic tilt = 35 degrees, and LL = 17 degrees). An L3 pedicle subtraction osteotomy and revision T10-S1 posterior spinal fusion with iliac fixation was performed and 33 degrees of correction was obtained. (D) Improvement in lumbar lordosis (50 degrees) and overall sagittal alignment (SVA < 5 cm). The pelvic tilt remains elevated (25 degrees), indicating slight undercorrection.