Remodeling morphology of the subluxated osteotomy vertebra in closing–opening wedge osteotomy in ankylosing spondylitis: would the anterior bony beak blunt?

Introduction To investigate the remodeling morphology of subluxated osteotomy vertebra in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis after single-level closing–opening wedge osteotomy (COWO). Materials and methods Standing lateral radiographs were taken to evaluate sagittal parameters including lumbar lordosis (LL), C7 sagittal vertical axis (SVA), global kyphosis (GK), sacral slope (SS), and pelvic tilt (PT). Radiographic parameters of the osteotomy vertebra included osteotomized vertebra angle (OVA), sagittal translation (ST), anterior height (AH), posterior height (PH), and middle height (MH) of the osteotomy vertebrae. Furthermore, lateral projection area of the vertebral body was also measured to evaluate the remodeling of the osteotomy vertebrae. Results Sixty AS patients who underwent single-level lumbar COWO with a minimal 2-year follow-up were included. The cohort consisted of 54 males and 6 females with an average age of 36.6 years. All patients were divided into two groups according to the development of vertebral subluxation (VS): 15 in VS group (ST ≥ 5 mm), 45 in non-VS group (ST < 5 mm). There was significant difference in the correction of GK, SVA, and the loss of correction of SVA between AS patients with and without VS. Significant difference in vertebra-related parameters regarding AH and OVA was found between VS group and non-VS group ( P < 0.05). Conclusions After COWO, new bone formation narrowing the gap and adaptive resorption of the anterior bony beak at the osteotomy level during follow-up was surprisingly favorable. However, the ability of spinal canal remodeling is limited in patients complicated with VS.