Spontaneous Remodeling of Spinal Canal After Sagittal Translation in Pedicle Subtraction Osteotomy for Correction of Thoracolumbar Kyphosis in Ankylosing Spondylitis

BACKGROUND: Sagittal translations (STs) secondary to osteotomy for the correction of ankylosing spondylitis (AS) kyphosis have drawn great attention, which is considered closely related to neurologic deficits and terrible fusion. Despite being discussed in several cases, there were no relevant reports about the transformation of ST and the spinal canal remodeling in AS patients. METHODS: Retrospective analysis was conducted on 16 patients with ST for the treatment of AS kyphosis through pedicle subtraction osteotomy during January 2011 to December 2014 in our hospital. Full-length free-standing spinal radiographs were available for all patients before and after surgery and also at the final follow-up. Radiologic parameters including global kyphosis (GK), thoracolumbar kyphosis (ILK), lumbar lordosis (LL), sagittal vertical axis (SVA), and ST were measured. Rates of ST transformation after the surgery and at 1-year follow-up were compared. RESULTS: The average follow-up was 22 months, ranging from 12-36 months. There was no internal fixation failure during this period. The preoperative GK was 59.9 +/- 21.0 degrees, TLK was 38.0 +/- 13.0 degrees, LL was 7.4 +/- 26.5 degrees, and SVA was 27.2 +/- 8.6 mm. The postoperative GK was 15.7 +/- 2.1 degrees, TLK was 5.6 +/- 2.6 degrees, LL was -36.1 +/- 2.9 degrees, and SVA was 6.1 +/- 4.3 mm. ST was 7.1 +/- 2.7 mm after surgery and 1.2 +/- 1.0 mm at 1-year follow-up. The difference was statistically significant (P < 0.05). The rate of ST transformation was 84.9% +/- 9.7%. According to Scoliosis Research Society surveys, the preoperative and the final follow-up satisfaction score was 1.6 +/- 0.3 and 4.7 +/- 0.4 respectively (P < 0.05). Remodeling of the spinal canal happened to all the patients with different degrees. CONCLUSIONS: All patients with ST after pedicle subtraction osteotomy for AS kyphosis occurred with spontaneous remodeling of the spinal canal at 1-year follow-up, by which ST can decrease in different degrees or even disappear, and favorable fusion can be achieved even without bone grafting into the osteotomy vertebra.