Lumbar spinal osteotomy for kyphosis in ankylosing spondylitis: the significance of the whole body kyphosis angle.

Retrospective analysis of 11 consecutive patients with ankylosing spondylitis who underwent lumbar spinal osteotomy for severe kyphosis, with a mean follow up of 4 (2 to 8.5) years. The chin brow vertical angle, thigh flexion angle, and the whole body kyphosis angle (WBKA) were measured on the clinical photographs of the patient in standing. The lumbar lordosis, thoracic kyphosis, total kyphosis, sacral slope, and sagittal balance were measured on the standing radiographs. A closing wedge osteotomy at L3 was done in all patients. Intraoperative neuromonitor with sensory evoked potentials and motor evoked potentials was used routinely. Stable fixation of spine allowed early walking. There were no permanent neurologic complications. The average preoperative WBKA was 41 degrees (20 to 70 degrees). The average correction of lumbar lordosis was 40 degrees, from 21.4 degrees (-10 to 65 degrees) to 61.4 degrees (35 to 85 degrees). The thigh flexion angle improved from 9.7 degrees (4 to 20 degrees) to 0.4 degrees (-4 to 5 degrees), the sacral slope from 11.8 degrees (-5 to 35 degrees) to 31.8 degrees (20 to 45 degrees), and the chin brow vertical angle from 28.2 degrees (10 to 45 degrees) to 2.4 degrees (-5 to 18 degrees). Loss of correction of 5 and 10 degrees was seen in 2 patients. The ability to stand upright and look straight was restored in all patients. The WBKA correlated closely with the amount of lordosis correction in lumbar spine. The intraobserver and interobserver reproducibility of the WBKA was verified by statistical analysis. In our opinion the measurement of the WBKA on the preoperative photograph is helpful in planning the lumbar osteotomy.