Pelvic Incidence: Computed Tomography Study Evaluating Correlation with Sagittal Sacropelvic Parameters

Area of Science:

• Spinal Anatomy and Biomechanics
• Radiographic Measurement Techniques

Background:

• Normal spinal alignment is often assessed using pelvic incidence (PI), a critical angle whose determinants are not fully understood.
• Accurate assessment of PI is vital for diagnosing and managing spinal deformities.

Purpose of the Study:

• To investigate the correlation between various sacropelvic parameters and pelvic incidence (PI) using computed tomography (CT).
• To identify key anatomical factors that determine PI.

Main Methods:

• Retrospective analysis of 177 CT scans from patients over 16 years old.
• Measurement of PI, sacral table angle (STA), sacral kyphosis (SK), pelvic thickness (PTH), crest-to-sacrum distance (CSD), and inlet-outlet angle.
• Correlation and multivariate regression analyses were performed to establish relationships between parameters and develop a predictive equation for PI.

Main Results:

• Pelvic incidence (PI) showed significant correlations with sacral kyphosis (SK) (r=0.769), inlet-outlet angle (r=-0.533), pelvic thickness (PTH) (r=-0.370), crest-to-sacrum distance (CSD) (r=0.290), and sacral table angle (STA) (r=-0.276).
• A predictive equation for PI was developed: PI = 101.45 - (0.52 × STA) + (0.67 × SK) - (0.34 × inlet-outlet angle), with an adjusted R² of 0.734 (P < 0.001).
• Sacral morphology (SK) and the sacrum's spatial orientation were identified as strong contributors to PI.

Conclusions:

• Sacral morphology and spatial orientation are significant determinants of pelvic incidence (PI).
• The established predictive equation highlights the importance of SK and inlet-outlet angle in determining PI.
• These findings provide a basis for further research into the factors influencing PI and potential modification strategies.