Does postoperative PI-LL mismatching affect surgical outcomes in thoracolumbar kyphosis associated with ankylosing...

To investigate if pelvic incidence (PI) and lumbar lordosis (LL) mismatching affects surgical outcomes for ankylosing spondylitis (AS) related kyphosis following 1-level lumbar pedicle subtraction osteotomy (PSO).

AS patients with thoracolumbar kyphosis, who underwent 1-level lumbar PSO from March 2006 and February 2014 in our institution, were retrospectively reviewed. The radiographic measurements and health-related quality of life (HRQoL) scores, including Oswestry Disability Index (ODI) and Visual Analogue Scale (VAS) for pain, were recorded at baseline and the last follow-up. Patients were divided into 2 groups according to PI-LL matching or not postoperatively (Match Group, Mismatch Group), and comparison of the aforementioned parameters between the two groups was performed.

Seventy patients were enrolled with a mean age of 34.60 ± 9.45 years (range, 17 yrs.-59 yrs.). Among them, 44 were included in the Match Group and 26 in the Mismatch Group. At baseline, patients in the Match Group had larger LL (p = 0.014) and smaller pelvic tilt (PT, p < 0.001) than patients in the Mismatch Group. At the last follow-up, along with larger LL (p = 0.004) and smaller PT (p = 0.001), Match Group patients also had significantly smaller sagittal vertical axis (SVA, 3.31 cm vs 6.27 cm, p = 0.001) than those in the Mismatch Group. Seventy-five percent (33/44) of the patients in the Match Group had a SVA < 5 cm at the last follow-up, while in the Mismatch Group, only 35% (9/26) of the patients did. However, no significant difference was found between the two groups regarding HRQoL scores.

Patients with postoperative PI-LL matching were more likely to have a better correction of SVA; they also tended to have a smaller preoperative PT. However, PI-LL mismatching didn't affect HRQoL scores at the last follow-up, which was different from the results of previous studies in the settings of ASD.