[The best preferable sagittal vertical axis for the ankylosis spondylitis with thoracolumbar kyphosis following one-level pedicle subtraction osteotomy under different cervical range of motion]

Objective: To analyze the influence of cervical range of motion on the preferable sagittal vertical axis in ankylosis spondylitis (AS)-related thoracolumbar kyphosis following single-level pedicle subtraction osteotomy (PSO). Methods: The clinical data of sixty-five AS patients who underwent single-level PSO from February 2012 to November 2018 in the Drum Tower Hospital of Nanjing University Medical School were retrospectively reviewed. Of the patients, 59 were males and 6 were females with a mean age of (34.2±9.2) years. Radiographic parameters including cervical range of motion (CROM), global kyphosis (GK), C₇ sagittal vertical axis (C₇SVA), thoracic kyphosis (TK), lumbar lordosis (LL), spinosacral angle (SSA), pelvic tilt (PT), pelvic incidence (PI), sacral slope (SS) and chin-brow vertical angle (CBVA) were measured preoperatively, 10 days after surgery and at the last follow-up. Oswestry disability index (ODI) and visual analogue scale (VAS) of pain were recorded for all patients preoperatively and at the final follow-up. Based on preoperative CROM, patients were divided into cervical flexible group (CROM>20°, group Ⅰ) and cervical ankylosis group (CROM≤20°, group Ⅱ). The patients were further divided into four groups according to the C₇SVA at the last follow-up: group ⅠA, CROM>20°, C₇SVA<50 mm; group ⅠB, CROM>20°, C₇SVA≥50 mm; group ⅡA, CROM≤20°, C₇SVA<50 mm; and group ⅡB, CROM≤20°, C₇SVA≥50 mm. Differences among baseline data, clinical efficacy and radiographic parameters between different groups were compared, and the optimal sagittal alignment balance after PSO in AS patients with thoracolumbar kyphosis under different CROM was explored. Results: All patients were followed-up for (31.0±10.2) months. A total of 65 patients were included, with 31 cases in group Ⅰ, comprising 16 cases in group ⅠA and 15 cases in group ⅠB, and 34 cases in group Ⅱ, with 18 cases in group ⅡA and 16 cases in group ⅡB. There was no significant difference in the age, gender and level of osteotomy between groups ⅠA and ⅠB and groups ⅡA and ⅡB (all P>0.05). Comparing between ⅠA and ⅠB groups, no significant difference was observed in radiographic parameters(all P>0.05), excepted for C₇SVA [(14.3±27.6) mm vs (80.3±24.1) mm, P<0.001]. At the last follow-up, ODI and VAS scores were significantly lower in group ⅠA than in group ⅠB [(7.1±6.2) points vs (13.3±7.0) points and (0.9±0.9) points vs (1.9±1.3) points] (both P<0.05). Compared with group ⅡA, PT was significantly greater in group ⅡB before the operation, 10 days after surgery and at the final follow-up (all P<0.05); the SSA and CBVA were also significantly greater in group ⅡB at the last follow-up (both P<0.05). At the last follow-up, the quality-of-life scores were better in group ⅡB than those in group ⅡA [ODI: (12.6±10.7) points vs (22.9±12.5) points; VAS: (1.2±1.6) points vs (2.8±2.0) points] (both P<0.05). The complications in group ⅠA included 1 case of rod fracture, while 2 cases of osteotomized vertebral subluxation and 2 cases of intraoperative dural tear occurred in group ⅠB. The complications in group ⅡA included 1 case of rod fracture and 1 case of screw malposition, and 2 cases of postoperative postural brachial palsy and 2 cases of osteotomized vertebral subluxation occurred in group ⅡB. Conclusions: The impact of CROM should be fully evaluated when developing a sagittal vertical axis reconstruction protocol for patients with AS thoracolumbar kyphosis. C₇SVA<50 mm is crucial to acquire ideal clinical outcome in AS with flexible cervical spine. However, in AS with cervical ankylosis, C₇SVA≥50 mm is a preferable choice.