Pelvico-Sacro-L1 Angle: An Index for Rapid Evaluation of Spinopelvic Sagittal Balance

This study aimed to evaluate the Pelvico-Sacro-L1 angle (PSLA) as a direct parameter for assessing PI-LL mismatch as a key determinant of sagittal balance.

In this retrospective study, adult patients scheduled for total hip arthroplasty (THA) underwent spinopelvic lateral radiography. The pelvic sagittal line angle (PSLA) was defined as the angle between a line drawn from the center of the femoral head to the center of the superior endplate of S1 and the superior endplate of L1. The deviation from 90° was termed the modified PSLA, proposed as an alternative to the pelvic incidence-lumbar lordosis (PI-LL) mismatch. Two independent orthopaedic surgeons measured the spinopelvic parameters and repeated the assessments four weeks later to evaluate intraobserver reliability.

A total of 92 patients (average age: 57.4 ± 9.9 years, 50 females) were included. The Bland-Altman plot indicated no significant systematic difference between the two measurement sets, suggesting good agreement between methods. The intraclass correlation coefficient (ICC) for PSLA in both inter- and intraobserver reliability was greater than 0.9, indicating excellent agreement.

The PSLA demonstrated a strong agreement with the PI-LL mismatch, confirming the reliability of this approach, which provides a more straightforward and easily interpretable measurement.