Hip involvement negatively impact the postoperative radiographic outcomes after lumbar pedicle subtraction osteotomy in ankylosing spondylitis patients with thoracolumbar kyphosis-a retrospective study

Abstract

Background: Lumbar pedicle subtraction osteotomy (PSO) can significantly correct thoracic kyphosis and relieve the compensatory pelvic backward tilt. However, hip involvement occurred in some advanced AS patients could restrict the rotation of the pelvis around the femoral heads, which may affect the postoperative radiographic outcomes after lumbar PSO. The aim of the study is to identify whether hip involvement will negatively impact the postoperative radiographic outcomes after lumbar PSO in AS patients with thoracolumbar kyphosis.

Methods: From March 2009 to June 2013, a total of 44 consecutive AS patients with thoracolumbar kyphosis undergoing one-level lumbar PSO were retrospectively reviewed. All the patients had more than 2-year follow-up. Hip involvement was evaluated based on the Bath ankylosing spondylitis radiology index-hip (BASRI-hip) and defined by a score of at least 2. All patients were divided into group A (patients without hip involvement) and group B (patients with hip involvement). Radiographical measurements included sagittal vertical axis (SVA), global kyphosis (GK), thoracic kyphosis (TK), local kyphosis (LK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS).

Results: The preoperative SVA and PT was not significantly different between group A and group B (SVA: 14.0 ± 6.3cm vs. 14.7 ± 6.0cm, P > 0.05; PT: 36.8° ± 7.1° vs. 37.3° ± 7.7°, P > 0.05), and both groups had similar magnitudes of kyphosis corrections (LK correction: 44.9° ± 4.9° vs. 44.2° ± 8.3°, P > 0.05). However, group B had significantly larger SVA and PT than group A (SVA: 7.6 ± 4.5cm vs 3.5 ± 3.4cm, P < 0.05; PT: 28.1° ± 8.6° vs. 19.0° ± 8.0°, P < 0.05) at the last follow-up.

Conclusion: In AS patients with thoracolumbar kyphosis, hip involvement lead to insufficient correction of SVA and PT after lumbar PSO, which negatively impact postoperative radiographic outcomes. For these patients, additional osteotomies may be recommended for satisfactory correction outcomes.

Key words: ankylosing spondylitis, thoracolumbar kyphosis, pedicle subtraction osteotomy, hip involvement