Abstract
OBJECTIVE: To quantify the effect of different hip positions on lumbar lordosis (LL) and spinopelvic parameters in the right lateral decubitus position (RLDP) and identify the configuration that most closely replicates physiologic standing alignment during lateral lumbar interbody fusion in minimally invasive spinal surgery. METHODS: Thirty healthy volunteers (15 males, 15 females; mean age, 27.8±8.6 years) underwent lateral lumbar radiographs in standing position and 5 RLDP configurations: neutral hips (NN), 30° flexion of both hips (30FF), 30° flexion of the right hip with left hip neutral (30FN), 60° flexion of both hips (60FF), and 60° flexion of the right hip with left hip neutral (60FN). LL, pelvic tilt (PT), sacral slope (SS), and pelvic incidence (PI) were measured. Each position was compared to standing using paired t-tests. Intra- and interobserver reliability were evaluated using intraclass correlation coefficients (ICCs). RESULTS: LL decreased significantly in all RLDP positions compared with standing (51.1°±3.8°). The 30FN position showed the smallest change (ΔLL=-4.9°, p<0.001), whereas 60FF showed the greatest (ΔLL=-15.0°, p<0.001). In 30FN, PT decreased (p=0.013) and SS increased (p=0.003), indicating mild anterior pelvic rotation. PI showed minimal variation across positions. Intra- and interobserver ICCs ranged from 0.92 to 0.99, confirming high measurement reliability. CONCLUSION: Hip position significantly influences lumbar and pelvic alignment in RLDP. Among tested configurations, the 30FN position (right hip flexed 30°, left neutral) showed the smallest numerical deviation from standing alignment and spinopelvic harmony relative to standing in RLDP.