The efficacy and the selection of single-level and two-level pedicle subtraction osteotomy in the remodeling of lumbar lordosis curvature for patients with severe thoracolumbar kyphosis caused by ankylosing spondylitis

English Keywords:Ankylosing spondylitis  Severe thoracolumbar kyphosis  Pedicle subtraction osteotomy  Lumbar lordosis curvature

English Abstract:

  【Abstract】 Objectives: To analyze the remodeling of lumbar lordosis curvature between ankylosing spondylitis(AS) patients with severe thoracolumbar kyphosis(global kyphosis≥80°) who underwent single- or two-level pedicle subtraction osteotomy(PSO), and to determine the indications of single-level PSO and two-level PSO. Methods: 68 patients with AS-related severe thoracolumbar kyphosis were retrospectively studied, including 44 patients underwent single-level PSO and 24 patients two-level PSO. The average follow-up time was 36.50±15.07 months. All the patients filled out the Oswestry disability index(ODI) and the visual analogue scale(VAS) before PSO and at the final follow-up. Radiological parameters including global kyphosis(GK), sagittal vertical axis(SVA), thoracic kyphosis(TK), lumbar lordosis(LL), pelvic tilt(PT) and sacral slope(SS) were measured preoperatively, postoperatively and at the final follow-up. After comparison and analysis, the patients were divided into two groups based on the segment of postoperative apex of lumbar lordosis(LL apex): 30 cases in LL apex at L3 or L4 group and 38 cases in LL apex at L5 or other segments group. Satisfying remodeling of lumbar lordosis curvature was defined as the postoperative LL apex located at L3 or L4. 30 patients achieving satisfying remodeling of lumbar lordosis curvature were further screened out and then divided into single-level PSO group(20 cases) and two-level PSO group(10 cases). Receiver-operating characteristic(ROC) curve was used to find the cut-off value of preoperative parameters that were significantly different between the two groups. Results: In all 68 patients with severe thoracolumbar kyphosis, there was no significant difference in the relocation of LL apex between those underwent single or two-level PSO. However, longer operative time, more intraoperative blood loss and more levels of instruments were observed in those who underwent two-level PSO(P<0.05). After the patients were grouped based on the postoperative LL apex, the postoperative LL and SS in the L5 or other lumbar spine group were significantly smaller than those in the L3 or L4 group(P<0.001), while no significant difference in postoperative GK, SVA, TK and PT was observed between the two groups. The osteotomy methods and levels were not correlated with the relocation of LL apex. In 30 patients achieving satisfying remodeling of lumbar lordosis curvature, all the spinopelvic parameters except TK were significantly improved postoperatively in both single and two-level PSO groups, and ODI and VAS scores were also significantly improved(P<0.05). Besides, no significant loss of correction was observed during follow-up. In two-level PSO group, the preoperative GK, SVA and LL were significantly larger than those in single-level PSO(P<0.05), but other preoperative parameters were similar to those in single-level PSO. ROC curves showed that the cut-off values of GK, SVA and LL were 94.50°, 19.35cm and 12.00°, respectively. The complications in the single-level PSO group included 2 cases of vertebral subluxation, 1 case of postural brachial palsy, and 1 case of intraoperative dural tear, while those in two-level PSO group included 2 cases of postural brachial palsy, 1 case of vertebral subluxation and 1 case of rod breakage during follow-up. Conclusions: Both single-level and two-level PSO could achieve satisfying remodeling of lumbar lordosis curvature for AS patients with severe thoracolumbar kyphosis, and the surgical selection is depended on the severity of preoperative kyphotic deformity. For those with GK<94.50°, SVA<19.35cm, LL<12.00°, single-level PSO should be firstly considered to achieve satisfying remodeling of lumbar lordosis. Conversely, for AS patients with more severe spinopelvic sagittal malalignment(GK≥94.50°, SVA≥19.35cm, LL≥12.00°), two-level PSO should be more recommended.