Does postoperative PI-LL mismatching affect surgical outcomes in thoracolumbar kyphosis associated with ankylosing spondylitis patients?

Objective: 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).

Patients And Methods: 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.

Results: 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.

Conclusion: 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.