In patients with ankylosing spondylitis (AS) with thoracolumbar kyphosis, functional pelvic orientation was adjusted by global spinal alignment, according to data published in Archives of Orthopaedic and Trauma Surgery.

Investigators in this single-center prospective study sought to examine the arc of pelvic motion from standing to sitting in patients with AS with thoracolumbar kyphosis and the effect of spinal osteotomy on the arc of pelvic motion. A total of 36 patients with AS who underwent pedicle subtraction osteotomy from January 2016 to July 2018 were enrolled in the study.

The researchers obtained pre- and post-operative EOS 2D standing and sitting images. Radiographic parameters measured on the sagittal radiographs included lumbar lordosis, thoracic kyphosis, pelvic incidence, pelvic tilt, sacral slope, sagittal vertical axis, spinosacral angle, anterior pelvic plane angle, and knee flexion angle.

The study results showed that the anterior pelvic plane angle increased from sitting to standing by a mean of 14.7° (P <.001) and 3.0° (P <.083) before and after surgery, respectively. The increase in anterior pelvic plane angle from standing to sitting was correlated with the pre-operative standing sagittal vertical axis (P <.001).

After pedicle subtraction osteotomy, the change in anterior pelvic plane angle was associated with the change in spinosacral angle in the sitting and standing positions (P =.022 and P <.001, respectively). Investigators also found that the anterior pelvic plane angle from standing to sitting was reduced post-operatively in 11 patients with standing C7 plumb line posterior to the femoral head.

“When making the [total hip arthroplasty] strategies for [patients with AS], the spinal sagittal alignment should be considered to provide better joint motion and stability,” the investigators concluded.

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Reference

Zhao SZ, Qian BP, Qiu Y, Qiao M, Liu ZJ, Huang JC. The relationship between global spinal alignment and pelvic orientation from standing to sitting following pedicle subtraction osteotomy in ankylosing spondylitis patients with thoracolumbar kyphosis [published online January 9, 2019].  Arch Orthop Trauma Surg. doi:10.1007/s00402-018-03107-1