Anterior Pelvic Plane: A Potentially Useful Pelvic Anatomical Reference Plane in Assessing the Patients' Ideal Pelvic Parameters Without the Influence of Spinal Sagittal Deformity

Abstract

Study design: Observational study.

Objective: This study was aimed at investigating the reliability of anterior pelvic plane (APP) as an anatomical reference plane for assessing the patients' pelvic incidence in patients with ankylosing spondylitis kyphosis deformity.

Methods: The globe kyphosis (GK), lumber lordosis (LL), thoracolumbar kyphosis (TLK), thoracic kyphosis (TK), anatomical cervical 7 sacrum angle (aC7SA), and cervical 7 sacrum angle (C7SA) were measured on full-length spine radiography imagines. The pelvic incidence (PI), anatomical pelvic tilt (aPT), and anatomical sacral slope (aSS) were measured on the pelvic synthesized 2D lateral radiography imagines. Because the angle between APP and vertical line was about 4°, Angle1 and tPT were calculated using the following formulas: Angle1 = aC7SA - 4; PT = aPT + 4. According to the study conducted by Vialle, traditional PT (tPT) was calculated using the following widely accepted formula: tPT = PI * 0.37 - 7. Measured PT (mPT) was also measured on the full-length spine radiography imagines.

Results: The data analysis showed that PI, mPT, aSS, aPT, and APPA were 50.83 ± 13.44°, 32.52 ± 4.64°, 41.36 ± 9.46°, 8.56 ± 6.80°, and 23.95 ± 5.17°, respectively. There was no significant difference between the PT and tPT (12.56 ± 6.80, 11.49 ± 4.73; P = .152). So, the results demonstrated that the PT could play the equivalent effect as tPT did for making surgical plans in patients with kyphosis deformity.

Conclusion: The pelvic anatomical reference plane had potential to be used in assessing the patients' ideal pelvic incident without the influence of spinal sagittal deformity. The aPT+4 may represent patients' postoperative ideal PT.

Keywords: anterior pelvic plane; pelvic incident.

Figure 1.

PI was measured as the angle between the line perpendicular to the sacral plate and the line through the middle point of the sacral plate and the center of the femoral head. aSS was the angle between the superior plate of S1 and the line perpendicular to the APP. aPT was the angle between the line connecting the sacral plate middle point and the center of the femoral head and the APP. Abbreviations: APP, pelvic anterior plane; aPT, anatomical PT; aSS, anatomical SS.

Figure 2.

The anatomical cervical 7 sacrum angle (aC7SA) is measured as the angle formed by APP and the line through the seventh cervical vertebra center and the superior-posterior corner of the first sacrum vertebra. The C7SA was the angle formed by the C7 plumb line and the line through C7 center and superior-posterior corner of the first sacrum vertebra. APPA is defined as the angle between the line connecting the midpoint of both anterior superior iliac spines to the pubic symphysis and the vertical line of the lateral radiograph of the pelvis in patient’s standing position.