Does relocation of the apex after osteotomy affect surgical and clinical outcomes in patients with ankylosing spondylitis and thoracolumbar kyphosis?

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Relocation of the apex is often found in patients with ankylosing spondylitis (AS)–associated thoracolumbar/lumbar kyphosis after corrective surgery. This study evaluates the influence of different postoperative apex locations on surgical and clinical outcomes of osteotomy for patients with AS and thoracolumbar kyphosis.


Sixty-two patients with a mean age of 34.6 ± 9.7 years (range 17–59 years) and a minimum of 2 years of follow-up, who underwent 1-level lumbar pedicle subtraction osteotomy for AS-related thoracolumbar kyphosis, were enrolled in the study, as well as 62 age-matched healthy individuals. Patients were divided into 2 groups according to the postoperative location of the apex (group 1, T8 or above; group 2, T9 or below). Demographic data, radiographic measurements (including 3 postoperative apex-related parameters), and clinical outcomes were compared between the 2 groups preoperatively, postoperatively, and at the last follow-up. Furthermore, a subgroup analysis was performed among patients with a postoperative apex located at T6–11 and postoperatively the entire AS cohort was compared with normal controls regarding the apex location of the thoracic spine.


In the majority of the enrolled patients, the apex location changed from T12–L2 preoperatively to T6–9 postoperatively. The sagittal vertical axis (SVA) differed significantly both postoperatively (25.7 vs 59.0 mm, p = 0.001) and at the last follow-up (34.6 vs 59.9 mm, p = 0.003) between the 2 groups, and the patients in group 1 had significantly smaller horizontal distance between the C7-vertical line and the apex (DCA) than the patients in group 2 (67.5 vs 103.7 mm, p = 0.001). Subgroup analysis demonstrated similar results, showing that the patients with a postoperative apex located at T8 or above had an average SVA < 47 mm. Notably, a significant correlation was found between postoperative SVA and DCA (r = 0.642, p = 0.001). Patients who underwent an osteotomy at L3 had limited apex relocation but larger SVA correction than those at L1 or L2. However, no significant difference was found in health-related quality of life between the 2 groups.


AS patients with an apex located at T8 or above after surgery tended to have better SVA correction (within 47 mm) than those who had a more caudally located apical vertebra. For ideal postoperative apex relocation, a higher (closer to or at the preoperative apex) level of osteotomy is more likely to obtain the surgical goal.

ABBREVIATIONS AS = ankylosing spondylitis; BASFI = Bath Ankylosing Spondylitis Functional Index; DCA = distance between C7 and apex; DOA = distance between osteotomized vertebra and apex; DSA = distance from sacrum to apex; GK = global kyphosis; HRQOL = health-related quality of life; LL = lumbar lordosis; MEP = motor evoked potential; ODI = Oswestry Disability Index; PI = pelvic incidence; PSO = pedicle subtraction osteotomy; PT = pelvic tilt; SS = sacral slope; SSEP = somatosensory evoked potential; SVA = sagittal vertical axis; TK = thoracic kyphosis; VAS = visual analog scale.

Article Information

Correspondence Bang-ping Qian: Drum Tower Hospital, Medical School of Nanjing University, Nanjing, China.

INCLUDE WHEN CITING Published online March 15, 2019; DOI: 10.3171/2018.12.SPINE18752.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.



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    Schematic illustration of the spinopelvic parameter measurements and the three apex-related parameters on standing lateral radiographs. A: Regular spinopelvic parameters including GK, TK, LL, SVA, SS, PT, and PI. B: DCA is the distance measured horizontally from a C7 plumb line to the posterior margin of the apical vertebra. C: DSA represents the horizontal distance between the posterosuperior corner of the sacrum and the posterior margin of the apex. D: DOA refers to the distance between the posterior margin of the osteotomized vertebra and the posterior margin of the apex horizontally.

  • View in gallery

    Distribution of the apex location of AS patients preoperatively and postoperatively, and normal controls. Pts = patients.

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    Lateral radiographs of a 33-year-old male patient with AS whose apex translated from L1 to T8 after 1-level PSO at L2, with an SVA value of 117 mm preoperatively (A), 43 mm postoperatively (B), and 27 mm at 2 years’ follow-up (C).

  • View in gallery

    Lateral radiographs of a postoperative AS patient (left) and a normal control (right) who presented with the same apex location (T8). The SVA and DCA measurements were 32 versus −18 mm, and 100 versus 66 mm, respectively.



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