J Korean Orthop Assoc.  2016 Feb;51(1):9-29. 10.4055/jkoa.2016.51.1.9.

Spino-Pelvic Parameters in Adult Spinal Deformities

• Lee CS
• Kang SS

• KMID: 2154345
• DOI: http://doi.org/10.4055/jkoa.2016.51.1.9

Abstract

In the recent 10 to 15 years, the most popular issue in the spine field is evaluation and treatment of the sagittal alignment and sagittal balance of the spine. Adult spine deformity (ASD) includes not only coronal deformity, such as degenerative scoliosis, but also sagittal deformity. Degenerative scoliosis is also associated with sagittal deformity of the spine. Even in degenerative scoliosis, accompanying sagittal deformity is more important to clinical symptoms than coronal deformity. Sagittal deformity of the spine is significantly correlated with health-related quality of life score, such as visual analogue scale and Oswestry disability index, short form-36 health survey. For the appropriate evaluation and treatment of ASD, understanding the normal and abnormal sagittal alignment and sagittal balance of the spine is very important. Various compensatory mechanisms should be applied in order to maintain the balanced upright posture. Assessment of the compensatory mechanism is also mandatory for proper surgical planning. Some spinopelvic parameters show particularly high correlation with clinical symptoms in case of sagittal imbalance. Therefore, assessment of these parameters is necessary for evaluation of surgical outcomes.

Keyword

adult spinal deformity; sagittal balance of the spine; spino-pelvic parameter

MeSH Terms

Adult*
Congenital Abnormalities*
Health Surveys
Humans
Posture
Quality of Life
Scoliosis
Spine

Figure

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  Figure 1 SRS-Schwab classification system. An individual's coronal curve pattern is categorized, and, most importantly, each of 3 sagittal modifiers (PI-LL, SVA, and PT) is classified as 'nonpathological (0),' 'moderate deformity (+),' or 'marked deformity (++).' SRS, Scoliosis Research Society; PI, pelvic incidence; LL, lumbar lordosis; SVA, sagittal vertical axis; PT, pelvic tilt.

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  Figure 2 Segmental angles. Lower most two segments, L4 and L5 comprised of approximately 70% of maximum lumbar lordosis. Restoration of these two segmental angles is very important for restoration of adequate sagittal balance.

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  Figure 3 Jackson's pelvic radius technique for measurement of pelvic morphology and pelvic balance around both hips. HASP, the distance between hip axis and sacral promontory; HAS1, the distance between hip axis and posterior superior corner of S1; pelvic radius (PR), distance between the center of the hip axis and the S1 reference point; pelvic angle (PA), angle of rotational pelvic balance around the hip joint; PR-S1, pelvic morphology which does not change regardless of pelvic rotation; Ant., anterior; Post., posterior; SS, sacral slope; PI, pelvic incidence.

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  Figure 4 Pelvic parameters. Positional parameters; pelvic tilt, sacral slope and overhang, morphologic parameters; pelvic incidence and pelvic thickness.

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  Figure 5 Demonstration of relationship between pelvic incidence and pelvic tilt in compensatory adjustment for kyphosis. Smaller pelvic incidence indicates less compensatory ability. PI, pelvic incidence; SS, sacral slope; PT, pelvic tilt.

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  Figure 6 (A) Model and lateral X-ray of a low-grade pelvic incidence pelvis (vertical pelvis). Note the high position of the L5 S1 disc with respect to the top of the iliac crest. (B) High grade pelvic incidence pelvis (horizontal pelvis). L5 S1 disc and L5 are totally below the top of the iliac crest.

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  Figure 7 (A) Left maximum pelvis anterior rotation: which is the same as a complete hip flexion and can facilitate hip dislocation. (B) Right maximum pelvis posterior rotation: which shows the limit of pelvis backtilt (the extension reserve).

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  Figure 8 Parameters of the sagittal balance of the spine and pelvis. The spinal balance is defined as the horizontal offset between the midsacral point and C7 plumb line; spinopelvic balance, between hip axis and C7 plumb line; and sacropelvic balance, between hip axis and midsacral point.

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  Figure 9 Preoperative planning using the full balance integrated technique. C7 translation angle: C7TA. Midpoint of the C7 inferior plateau (a) is translated on the plumb line ascending from the mid part of the S1 plateau (b). Point c is on the anterior cortex of the selected vertebra for osteotomy, which is mainly L4 vertebra. Femur obliquity angle: FOA. Femur flexion is measured as the angle between the femoral axis and the plumb line (d). Pelvis compensation angle: PTA. Pelvic tilt is measured as usual: line between center femoral head to mid part of S1 plateau and vertical line. If PT between 15° and 25°: add 5°. If PT superior 25°: add 10°. PT, pelvic tilt.

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  Figure 10 Measurement of global spinal balance. (A) Spinosacral angle; (B) spinal tilt; and (C) C7 translation ratio.

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  Figure 11 Spinopelvic angle (SPA) formed by the line between the center of the C7 body and the center of the S1 upper endplate and the line between the center of the S1 upper endplate and hip axis. SPA combines the spinosacral angle (SSA) and pelvisacral angle, the pelvic morphologic angle. Therefore, SPA consider not only positional parameter but also anatomical parameter.

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  Figure 12 T1 pelvic angle (TPA), a novel radiographic parameter that accounts for both global malalignment and compensation through pelvic retroversion. The TPA is defined as the angle between the line from the femoral head axis to the centroid of T1 and the line from the femoral head axis to the middle of the S1 superior end plate. The TPA is the sum of the T1 spinopelvic inclination (T1SPi) and the pelvic tilt (PT).

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  Figure 13 Incliniation of spine over the hip joint. T1 Spinopelvic inclination and T9 spinopelvic inclination defined as the angle between the vertical plumbline and the line drawn from the vertebral body center of T1 or T9 and the center of the bicoxofemoral axis.

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  Figure 14 Mechanism for acquisition of upright posture. Two main mechanisms, first, hip extension with verticalization of the sacrum by contraction of the gluteal muscle and hamstring muscle and relaxation of the anterior tension band to make hip extension easier and second, making lordosis with horizontalization of the sacrum by the erector spinae muscle and tightening of the anterior tension band to prevent or limit hip overextension. This mechanism is also applied as a compensatory mechanism for maintaining sagittal balance.

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  Figure 15 New pelvic parameters; femoropelvic angle (FPA) and femoral tilt angle (FTA) (asterisks). Note that pelvic tilt (PT) is equal to the sum of FPA and FTA. Cited from the article of Lee et al. (Eur Spine J. 2013;22:1059-65).84)

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  Figure 16 Two different responses according to the knee flexion. (A) Standing without knee and hip flexion. The angle of femoropelvic angle (FPA) (asterisks) is equal to pelvic tilt (PT). (B) No pelvic compensation. Note that FPA does not change and PT increases with knee flexion. (C) Pelvic compensation. Note that PT does not change and FPA decreases with knee flexion Cited from the article of Lee et al. (Eur Spine J. 2013;22:1059-65).84) FTA, femoral tilt angle.

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  Figure 17 Realignment objectives in the sagittal plane. Sagittal vertical axis (SVA)<50 mm, pelvic tilt (PT)<20°, and lumbar lordosis (LL)=pelvic incidence (PI)±9° sets the stage for achievement of a successful harmonious spinopelvic realignment.

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