Correlations Analysis of Different Pelvic Tilt Definitions: A Preliminary Study

Area of Science:

• Radiographic analysis of pelvic orientation.
• Biomechanical assessment of pelvic parameters.

Background:

• Pelvic tilt (PT) describes pelvic orientation on the transverse axis.
• Four radiographic definitions exist: anterior pelvic plane (PTa), center of femoral heads to sacral plate (PTm), pelvic outlet (PTh), and sacral slope (SS).
• Understanding the relationships and differences between these PT definitions is limited.

Purpose of the Study:

• To investigate the correlations and differences among four established pelvic tilt (PT) definitions.
• To provide clarity for educational and research applications of PT measurements.

Main Methods:

• Analysis of 105 sagittal pelvic radiographs from patients undergoing hip surgery.
• Two observers annotated four PT definitions (PTa, PTm, PTh, SS) with inter-observer reliability checks.
• Subgroup analysis included patients with hip hardware and spinal pathologies.
• Statistical analysis employed linear regression and intraclass correlation coefficient (ICC).

Main Results:

• Sacral slope (SS) showed no significant correlation with PTa, PTm, or PTh, except in females with hip hardware.
• Pelvic tilt measurement (PTm) and pelvic outlet (PTh) exhibited a very strong linear correlation (r > 0.9).
• A linear regression model was established: PTm = 0.951 × PTh - 68.284.
• Anterior pelvic plane (PTa) comparisons revealed significant anatomical variations.

Conclusions:

• Pelvic tilt measurement (PTm) and pelvic outlet (PTh) are interchangeable and can be calculated using a linear regression equation.
• Sacral slope (SS) demonstrates poor correlation with other PT parameters, warranting further investigation in specific subgroups.
• High anatomical variability in PTa necessitates careful consideration during comparative analyses.