Inter-observer Reliability of Sacral Slope Measurements in Healthy Individuals: Implications for Hip-Spine Syndrome

Hip-spine syndrome is a complex condition characterized by concurrent degenerative pathologies of the hip and lumbar spine, often leading to significant morbidity. Accurate radiographic measurements are critical for diagnosing and managing this syndrome, particularly in the context of total hip arthroplasty. This study aimed to evaluate the interobserver reliability of sacral slope measurements on pelvic radiographs in healthy individuals to enhance diagnostic accuracy and treatment strategies.

This cross-sectional study included 30 healthy volunteers (15 male, 15 female) aged 25 to 50 years, with no history of spinal, hip, or pelvic pathology. Lateral pelvic radiographs were taken in both standing and sitting positions. Sacral slope was measured by four independent observers, including radiologists and orthopaedic surgeons. Intraclass correlation coefficients with 95% confidence intervals (CIs) were calculated using linear mixed-effects models to assess interobserver reliability. Data analysis was performed using SAS and SPSS software.

The mean sacral slope measurements for standing and sitting positions were as follows: observer 1 (standing: 39.59° ± 6.67°, sitting: 26.83° ± 10.84°), observer 2 (standing: 38.02° ± 6.76°, sitting: 22.11° ± 10.71°), observer 3 (standing: 41.15° ± 6.63°, sitting: 26.04° ± 12.48°), and observer 4 (standing: 39.53° ± 6.93°, sitting: 24.80° ± 12.00°). The intraclass correlation coefficient for standing sacral slope was 0.956 (95% CI, 0.916 to 0.978) and for sitting sacral slope was 0.974 (95% CI, 0.944 to 0.988), both indicating excellent interobserver reliability.

Sacral slope measurements on lateral pelvic radiographs exhibit excellent interobserver reliability, making them reliable indicators of pelvic orientation. This reliability is crucial for the clinical utility of sacral slope as a metric for assessing spinopelvic alignment, particularly in the management of hip-spine syndrome and in patients undergoing total hip arthroplasty.