Pelvic Compensation in Sagittal Malalignment: How Much Retroversion Can the Pelvis Accommodate?

Area of Science:

• Spine surgery
• Radiographic analysis
• Biomechanical assessment

Background:

• Sagittal malalignment, measured by T1-Pelvic Angle (TPA), is a common spinal deformity.
• Pelvic tilt (PT) is a key compensatory mechanism for sagittal malalignment.
• Individual variations in pelvic incidence (PI) may affect PT recruitment.

Purpose of the Study:

• To investigate the relationship between varying degrees of pelvic incidence (PI) and pelvic tilt (PT) recruitment.
• To determine if PI modulates the compensatory response to sagittal malalignment (TPA).

Main Methods:

• Retrospective analysis of 2077 patients with TPA > 10°.
• Patients categorized into five PI groups (Very Low, Low, Average, High, Very High).
• Linear regression used to assess TPA-PT correlation within each PI group; multivariate regression compared group differences.

Main Results:

• Mean PT increased with higher PI levels (P < 0.05).
• Significant differences in TPA-PT linear relationships observed across PI groups.
• Very Low PI group showed 3.4° less PT than Average PI for constant TPA (P < 0.001); Very High PI group showed 1.9° more PT (P = 0.01).

Conclusions:

• Pelvic incidence is associated with variable recruitment of pelvic tilt in response to sagittal malalignment.
• This study provides a basis for surgeons to estimate compensatory PT based on a patient's PI.
• Findings aid in personalized surgical planning for spinal alignment.