Abstract: BACKGROUND: The sagittal parameters of the spine and pelvis in patients with degenerative scoliosis are closely related to the clinical efficacy. Professor SCHWAB once proposed the standard of lumbar lordosis = pelvic incidence angle ±9°, but statistics showed that the pelvic incidence angle of the domestic population was smaller than that of the European and American population. The application of this formula to the correction of lumbar lordosis in domestic patients is controversial.  
OBJECTIVE: To evaluate the correlation between pelvic incidence-lumbar lordosis and clinical outcomes after posterior spinal pedicle screw internal fixation for degenerative lumbar scoliosis, and explore the appropriate matching of lumbar vertebrae and pelvis.
METHODS:  A retrospective analysis of the medical records of 32 patients with degenerative scoliosis who underwent posterior pedicle screw fixation at the General Hospital of Ningxia Medical University from January 2015 to August 2017 was performed. The follow-up time was all > 6 months. Cobb angle, lumbar lordosis, T1 pelvic angle, sagittal vertical axis, pelvic incidence, pelvic til, sacral slope, and pelvic incidence-lumbar lordosis were measured and calculated preoperatively and at final follow-up. Visual analogue scale score, Oswestry disability index, and Short-Form-12 Health survey score were recorded preoperatively and at final follow-up.  
RESULTS AND CONCLUSION: (1) Cobb angle, T1 pelvic angle, pelvic til, pelvic incidence-lumbar lordosis, Visual analogue scale score, and Oswestry disability index at final follow-up were significantly less than those before operation (P < 0.05-0.001). Lumbar lordosis, sacral slope, and Short-Form-12 Health survey score were significantly increased at final follow-up compared with those before operation (P < 0.05-0.001). Sagittal vertical axis was not significantly different before and after operation (P > 0.05). Symptoms were significantly relieved at the final follow-up postoperatively, and the efficacy was satisfied. (2) Pelvic incidence-lumbar lordosis was associated with sagittal vertical axis, T1 pelvic angle, pelvic incidence, pelvic til, sacral slope, visual analogue scale score, Oswestry disability index, and Short-Form-12 Health survey score at the final follow-up (r=0.387, 0.433, 0.660, 0.575, 0.313, 0.400, 0.378, -0.352, P < 0.05). (3) The scatter diagrams and fitting curve results suggested that the patients could get a better clinical match when the pelvic incidence-lumbar lordosis of final follow-up was in the -10°-7° interval (postoperative visual analogue scale score < 3, Oswestry disability index < 20%, and Short-Form-12 Health survey score > 130 as standards). (4) Patients whose postoperative pelvic incidence-lumbar lordosis was in -10°-7° interval were as group A; those whose postoperative pelvic incidence-lumbar lordosis was not in -10°-7° interval were as group B. Independent sample t-test showed that there was no significant difference in the visual analogue scale score, Oswestry disability index, and Short-Form-12 Health survey score preoperatively in both groups A and B (all P > 0.05). Visual analogue scale score and Oswestry disability index were lower (P < 0.05, P < 0.01), but Short-Form-12 Health survey score was higher (P < 0.01) in group A postoperatively. (5) It is concluded that pelvic incidence-lumbar lordosis has a correlation with clinical outcomes. The patients whose pelvic incidence-lumbar lordosis was in the  -10°-7° interval can obtain better clinical outcome at the final follow-up.

Key words: degenerative scoliosis, pelvic incidence, lumbar lordosis, pelvic incidence-lumbar lordosis, imaging parameter