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.
ABBREVIATIONSAS = 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.
HuaWBZhangYKGaoYLiuXZYangSHWuXH: Analysis of sagittal parameters in patients undergoing one- or two-level closing wedge osteotomy for correcting thoracolumbar kyphosis secondary to ankylosing spondylitis. Spine (Phila Pa 1976)42:E848–E8542017
JohariJSharifudinMAAb RahmanAOmarASAbdullahATNorS: Relationship between pulmonary function and degree of spinal deformity, location of apical vertebrae and age among adolescent idiopathic scoliosis patients. Singapore Med J57:33–382016
LonnerBSParentSShahSASponsellerPYaszayBSamdaniAF: Reciprocal changes in sagittal alignment with operative treatment of adolescent Scheuermann kyphosis—prospective evaluation of 96 patients. Spine Deform6:177–1842018
QianBPJiangJQiuYWangBYuYZhuZZ: Radiographical predictors for postoperative sagittal imbalance in patients with thoracolumbar kyphosis secondary to ankylosing spondylitis after lumbar pedicle subtraction osteotomy. Spine (Phila Pa 1976)38:E1669–E16752013
QianBPWangXHQiuYWangBZhuZZJiangJ: The influence of closing-opening wedge osteotomy on sagittal balance in thoracolumbar kyphosis secondary to ankylosing spondylitis: a comparison with closing wedge osteotomy. Spine (Phila Pa 1976)37:1415–14232012
SchwabFJBlondelBBessSHostinRShaffreyCISmithJS: Radiographical spinopelvic parameters and disability in the setting of adult spinal deformity: a prospective multicenter analysis. Spine (Phila Pa 1976)38:E803–E8122013
XuHZhangYZhaoYZhangXXiaoSWangY: Radiologic and clinical outcomes comparison between single- and two-level pedicle subtraction osteotomies in correcting ankylosing spondylitis kyphosis. Spine J15:290–2972015