THE EFFECT OF INTRAOPERATIVE HIP POSITION ON MAINTENANCE OF LUMBAR LORDOSIS - A RADIOGRAPHIC STUDY OF ANESTHETIZED PATIENTS AND UNANESTHETIZED VOLUNTEERS ON THE WILSON FRAME

Study Design. 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). Objectives. To evaluate the effect of hip position on total and segmental lumbar lordosis in patients and volunt eers in standardized positions: standing and with hips extended and fl exed on a Wilson frame. Summary of Background. Preservation of lordosi s during instrumented lumbar fusion is critical for maintenance of nor mal 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 affect s lumbar lordosis. Further, the question of how individuals are specif ically affected intraoperatively by differences of position on the sam e device remains unanswered. Methods. Preoperative standing and intrao perative lateral lumbar spine radiographs with patients' hips in stand ardized 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 mea sured. Data were analyzed for changes in total and segmental lordosis between standing and intraoperative positions for all subjects. Result s. In the patient group, 95% of preoperative standing lordosis was mai ntained with the patients' hips extended. With hips flexed from 19 deg rees 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 deg rees (mean, 28 degrees), 86% of lordosis was maintained. Conclusions. Hip flexion was associated with a significant decrease in lordosis in patients and volunteers. Positioning in maximal hip extension optimize s lordosis preservation. While other devices have been shown to have s pecific effects on lordosis, the Wilson frame can permit easy adjustme nt of the lumbar sagittal contour to facilitate either preservation or reduction in lordosis.