Can hip-knee line angle distinguish the size of pelvic incidence? -Development of quick non-invasive assessment tool for pelvic incidence classification

概要

Objective
Pelvic Incidence (PI), which is measured by lateral spine radiography, has been attracting attention as a determinant of low back pain. PI has some features representing an angle that define the physiological lordosis of lumbar spine and constant independent of posture changes. In addition, providing a theoretical interpretation of PI, changing PI visually reflects the waist-line and buttocks due to increasing pelvic overhang with increasing sacroiliac joint angulation. Therefore, this study aimed to explore effective measurement angles for pelvic incidence (PI) classification and to develop a quick, non-invasive assessment tool for PI classification.

Methods
Study1: We defined five variation types of hip-knee line (HKL) angles and tested their discrimination ability of the receiver operating characteristic (ROC) analysis using 125 photographs of upright standing posture from the right lateral side.

Study2: We devised a quick non-invasive assessment tool for PI classification using the cut-offs of the HKL angle with a view to practical application.

Results
Study1: ROC analysis revealed an applicable HKL angle defined by the line connecting the most raised part of the buttock and the central point of the knee and the mid-thigh line. The acceptable cut-off points for discriminating small or large PIs in terms of HKL angle were 18.5° for small PI (sensitivity, 0.91; specificity, 0.79) and 21.5° for large PI discrimination (sensitivity, 0.74; specificity, 0.72).

Study2: The results of intra-and inter-rater reliability ensured a substantial/moderate level of the tool (Cohen’s kappa coefficient, 0.79; Fleiss's kappa coefficient, 0.50-0.54).

Conclusions
These results revealed that the HKL angle can distinguish the size of the PI with a high/moderate discrimination ability. Furthermore, the tool indicated acceptable inter- /intra-rater reliability for practical applications.