Clinical and Radiographic Results After Posterior Wedge Osteotomy for Thoracolumbar Kyphosis Secondary to Ankylosing Spondylitis: Comparison of Long and Short Segment.

OBJECTIVE: To compare the efficacy of long and short segment instrumentation after pedicle subtraction osteotomy (PSO) for thoracolumbar kyphosis caused by ankylosing spondylitis (AS).

METHODS: Sixty-four consecutive AS patients were analyzed and divided into groups according to length of instrumentation. We defined short segment instrumentation (SSI) as construct length <7 levels (≤3 levels above and below the osteotomy) (n = 17). By contrast, long segment instrumentation (LSI) was defined as construct length ≥7 levels (≥4 levels above and ≥3 levels below the osteotomy) (n = 47). Both groups were matched cohorts. Radiographs were analyzed for correction, ossification, and complications.

RESULTS: Correction loss in global kyphosis (GK) and lumbar lordosis (LL) of the LSI group was slightly higher than that of SSI group. Notably, a significantly higher modified Stokes Ankylosing Spondylitis Spinal Score (mSASSS) was noted in the SSI group. Pearson correlation analysis demonstrated that thoracic and lumbar spine mSASSS were significantly associated with correction loss in GK and LL, respectively. Two cases of proximal junctional kyphosis and 1 case of rod fracture occurred in the LSI group.

CONCLUSIONS: Both approaches were able to maintain sustained surgical outcomes. Short segment instrumentation is recommended for AS patients with bridging syndesmophytes. Long constructs are better indicated for patients without fully ossified anterior longitudinal ligaments. Nevertheless, extension of the length of instrumentation might not prevent complications such as proximal junctional kyphosis or rod fracture in patients without fully ossified vertebrae.