Prognostic Analysis Of Patients With Sagittal Translation After Pedicle Subtraction Osteotomy For The Correction Of Thoracolumbar Kyphosis In Ankylosing Spondylitis

Objective: To analyze the prognosis in patients with sagittal translation (ST) after pedicle subtraction osteotomy in ankylosing spondylitis (AS) kyphosis. And to investigate the spontaneous remodeling of the spinal canal in patients with ST.Methods: Retrospective analysis was conducted on 149 patients with ST for the treatment of AS kyphosis through pedicle subtraction osteotomy during January 2010 to December 2015 in our hospital, containing 134 males and 15 females, aged 21～56(37.2±9.1). According to the existence and the degree of ST, patients were divided into three groups: Group N-ST, patients without ST (ST≤2mm); Group M-ST,patients with mild ST (2mm<ST ≤ 4mm); Group S-ST, patients with severe ST(ST>4mm). Full-length free-standing spinal radiographs and Computed Tomography of ST level were available for all patients before and after surgery and also at the final follow-up. Radiological parameters, including global kyphosis (GK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), sagittal vertical axis (SVA) and ST were measured. Preoperative and the final follow-up scores of SRS surveys as well as conditions about neurologic deficits were also collected. Change of ST and the transformation of the spinal canal on the after the surgery and at the final follow-up were compared.Results: The average follow up was 27.0 months, ranged from 12 to 48 months. There were no internal fixation failure during this period. 45 among 149 patients experienced ST, the incidence was 30.2%. 13 among 149 patients experienced neurologic deficits,the incidence was 8.7% (4.7% was transient while 4.0% was permanent). There was no difference among all groups in age and gender composition, pre- and postoperative radiographic parameters, preoperative and 1 year follow-up scores of SRS surveys(P>0.05). Incidence of permanent neurologic deficits was higher in Group S-ST compared with Group N-ST and Group M-ST (P<0.05) but no difference between the latter two groups (P>0.05). A decreased ST occurred in all cases. ST was (4.5 ±3.1) mm after surgery while (1.0 ± 1.4) mm at the final follow-up,the difference was statistically significant (P<0.05). Rate of ST transformation was (73.4±20.7) %. Remodeling of the spinal canal happened to all the patients with different degrees. Odds of spontaneous remodeling of the spinal canal was 100%.Conclusions: Patients with ST after pedicle subtraction osteotomy for AS kyphosis can obtain similar deformity correction, postoperative life quality and incidence of neurologic deficits when ST was less than 4mm compared with patients without ST.Whereas ST greater than 4mm can lead to high incidence of permanent neurologic deficits. Up to 1 year follow up all ST patients occurred with spontaneous remodeling of the spinal canal, by which ST will decrease or even disappear in different degrees.