Sagittal Translation in Opening Wedge Osteotomy for the Correction of Thoracolumbar Kyphotic Deformity in Ankylosing Spondylitis

Study Design. Retrospective. Objectives. To document sagittal translation (ST) of the vertebral column in opening wedge osteotomy (OWO) for ankylosing spondylitis (AS) kyphosis. Summary of Background Data. Surgeons recognize displacement at the hinge of correction in OWO as an accidental event between the vertebrae on the side of OWO rather than ST of the cranial or caudal vertebral column. No report documents ST in this context. Methods. We evaluated radiographic and clinical results in 127 patients (aged 17–49 years) for ST, or displacement of more than 2 mm between the cranial and caudal vertebral columns at the OWO level, over 5 years. Results. Thirty-four (27%) patients had ST. In 31 (94%), the kyphotic apex was at T11 to L4. ST was positively correlated with the correction of lumbar lordosis and preoperative lumbar kyphosis. Five (15%) of 34 patients with ST had neurologic complications compared with 2 (2%) of 93 who did not. Conclusions. ST is a basic mechanism for correcting sagittal imbalance and is likely to occur when the level of OWO is near the apex of deformity. Patients needing more correction of lumbar lordosis than others for best correction of sagittal imbalance need ST more to join the mechanism of correction.