The effect of intraoperative hip position on maintenance of lumbar lordosis: a radiographic study of anesthetized patients and unanesthetized volunteers on the Wilson frame.

Abstract

The effect of intraoperative hip position on maintenance of lumbar lordosis was evaluated radiographically in 13 anesthetized patients and 14 unanesthetized volunteers positioned on a Wilson frame (MDT Corp., Torrance, CA). To evaluate the effect of hip position on total and segmental lumbar lordosis in patients and volunteers in standardized positions: standing and with hips extended and flexed on a Wilson frame. Preservation of lordosis during instrumented lumbar fusion is critical for maintenance of normal sagittal alignment. It is customary to extend the hips on certain positioning devices to maximize lordosis maintenance. However, little information exists concerning the degree to which this actually affects lumbar lordosis. Further, the question of how individuals are specifically affected intraoperatively by differences of position on the same device remains unanswered. Preoperative standing and intraoperative lateral lumbar spine radiographs with patients' hips in standardized flexed and extended positions were obtained (n = 13). Similar radiographs were obtained of asymptomatic volunteers (n = 14). Lumbar lordosis (L1-S1) and intervertebral body angles at each level were measured. Data were analyzed for changes in total and segmental lordosis between standing and intraoperative positions for all subjects. In the patient group, 95% of preoperative standing lordosis was maintained with the patients' hips extended. With hips flexed from 19 degrees to 48 degrees (mean, 33 degrees), 74% of lordosis was maintained. In the volunteer group, 98% of standing lordosis was maintained with volunteers' hips extended; with their hips flexed 20 degrees to 36 degrees (mean, 28 degrees), 86% of lordosis was maintained. Hip flexion was associated with a significant decrease in lordosis in patients and volunteers. Positioning in maximal hip extension optimizes lordosis preservation. While other devices have been shown to have specific effects on lordosis, the Wilson frame can permit easy adjustment of the lumbar sagittal contour to facilitate either preservation or reduction in lordosis.