Methods: A total of 209 patients with osteoporosis and 54 with adult spinal deformities were included. Patients were divided into two groups based on pelvic incidence–lumbar lordosis (PI–LL): <20° and ≥20° groups. The sagittal vertical axis (SVA), thoracic kyphosis, PI, pelvic tilt (PT), LL, sacral slope, and pelvic femoral angle (PFA) were measured. Health-related quality of life (HRQOL) was assessed in 86 patients using the Japanese Orthopedic Association Back Pain Evaluation Questionnaire (JOABPEQ). A new index, PFA–(PI–LL), was defined as spinopelvic–hip mismatch. Correlation coefficients were calculated for each radiographic parameter, and the coefficient of determination (R2) for the relationship of each parameter with SVA was evaluated in both groups. The correlations between SVA, PT, PI–LL, PFA–(PI–LL), and JOABPEQ domain scores were also analyzed. Results: PI–LL correlated with PFA in the PI–LL <20° group (r=0.56, p<0.001) but not in the PI–LL ≥20° group. Among all parameters, PFA–(PI–LL) demonstrated the strongest association with SVA, indicating its superior ability to explain variations in sagittal alignment in both groups and across all patients (all patients, R2=0.77). Significant correlations were observed between the radiographic parameters and JOABPEQ scores across all domains. Conclusions PFA–(PI–LL), which represented spinopelvic–hip mismatch, was a reliable indicator of hip compensatory function in terms of anterior trunk inclination and HRQOL.