Pelvic ring ratio: a novel indicator of comprehensive pelvic alignment assessment

Abstract

Study design: A cross-sectional study.

Purpose: To determine the effectiveness of the pelvic ring ratio as an indicator for assessing pelvic tilt (PT) from the frontal view and explore its correlation with various whole-body sagittal alignment (WBSA) parameters using EOS imaging technology.

Overview of literature: Traditional indicators of PT often rely on sagittal plane measurements, which can be challenging in cases of pelvic rotation or obesity. A new indicator such as the pelvic ring ratio could address these challenges and aid in the comprehensive assessment of pelvic alignment.

Methods: In total, 104 healthy participants (28 men, 76 women; mean age, 52.8±12.3 years) with no spinal disorders were recruited. Whole-body radiography using the EOS imaging system was performed to obtain sagittal and coronal parameters, including the pelvic ring ratio. Intra- and interobserver variability were assessed using intraclass correlation coefficients (ICCs) based on measurements by three spine surgery specialists. Correlation analyses among the pelvic ring ratio, age, body mass index, and WBSA parameters were conducted, and a multiple linear regression model was developed to predict PT.

Results: The mean pelvic ring ratio was 53.3%±11.5%. The intra- and interobserver ICCs were 0.89 and 0.87, respectively, indicating good reliability. The pelvic ring ratio was negatively correlated with age (r =-0.387, p <0.05) and PT (r =-0.598, p <0.05). The regression model revealed that the pelvic ring ratio and sex significantly predicted PT (p <0.05). Women had higher pelvic ring ratio (55.0%±11.3%) than men (48.6%±10.8%).

Conclusions: The pelvic ring ratio is a reliable and valuable indicator for PT assessment from the frontal view. It exhibits significant correlations with age and certain WBSA parameters, showing potential to improving the diagnostic accuracy and treatment planning for patients with spinal and hip disorders.

Keywords: Adult spinal deformity; Lower limb alignment; Pelvic ring ratio; Pelvic tilt; Sagittal alignment.

Fig. 1

Diagram showing the measurement of the pelvic ring ratio. The pelvic ring ratio was determined by measuring the vertical distance from the line connecting the lower ends of the sacroiliac joints to the cranial edge of the pubic symphysis, along with the horizontal diameter of the pelvic ring, on a frontal radiograph and then calculating the ratio of these measurements.

Fig. 2

A 71-year-old female with a pelvic ring ratio of 53.3%. Pelvic parameters: pelvic incidence, 61.7°; pelvic tilt, 25.4°; and lumbar lordosis, 46.8°. Additionally, the patient exhibited knee flexion of 5.9° and an ankle angle of 6.6°.

Fig. 3

A 45-year-old female with a pelvic ring ratio of 71.7%. Pelvic parameters: pelvic incidence, 45.8°; pelvic tilt, 6.2°; and lumbar lordosis, 62.7°. Additionally, the patient exhibited knee flexion of 4.8° and an ankle angle of 6.1°.

Fig. 4

Histogram of the pelvic ring ratio. The mean pelvic ring ratio was 53.3%±11.5%, showing a normal distribution.