Sacral tumor resection and the impact on pelvic incidence Clinical article

Object Pelvic incidence (PI) directly regulates lumbar lordosis and is a key determinant of sagittal spinal balance in normal and diseased states Pelvic incidence is defined as the angle between the line perpendicular to the S-1 endplate at its midpoint and the line connecting this point to a line bisecting the center of the femoral heads It reflects an anatomical value that increases with growth during childhood but remains constant in adulthood It is not altered by changes in patient position or after traditional lumbosacral spinal surgery There are only 2 reports of PI being altered in adults both in cases of sacral fractures resulting in lumbopelvic dissociation and sacroiliac (SI) Joint instability En bloc sacral amputation and sacrectomy are surgical techniques used for resection of certain bony malignancies of the sacrum High, mid, and low sacral amputations result in preservation of some or the entire SI Joint Total sacrectomy results in complete disruption of the SI Joint The purpose of this study was to determine if PI is altered as a result of total or subtotal sacral resection Methods The authors reviewed a series of 42 consecutive patients treated at The Johns Hopkins Hospital between 2004 and 2009 for sacral tumors with en bloc resection The authors evaluated immediate pre and postoperative images for modified pelvic incidence (mPI) using the L-5 inferior endplate, as the patients undergoing a total sacrectomy are missing the S 1 endplate postoperatively The authors compared the results of total versus subtotal sacrectomies Results Twenty two patients had appropriate images to measure pre- and postoperative mPI, 17 patients had high, mid, or low sacral amputations with sparing of some or the entire SI Joint, and 5 patients underwent a total sacrectomy, with complete SI disarticulation The mean change in mPI was statistically different (p < 0 001) for patients undergoing subtotal versus those undergoing total sacrectomy (1 6 degrees +/- 0 9 degrees vs 13 6 degrees +/- 4 9 degrees [+/- SD]) There was no difference between patients who underwent a high sacral amputation (partial SI resection, mean 1 6 degrees) and mid or low sacral amputation (SI completely intact mean 1 6 degrees) Conclusions The Pus altered during total sacrectomy due to complete disarticulation of the SI joint and discontinuity of the spine and pelvis, but it is not changed if any of the Joint is preserved Changes in PI influence spinopelvic balance and may have postoperative clinical importance Thus the authors encourage attention to spinopelvic alignment during lumbopelvic reconstruction and fixation after tumor resection Long-term studies are needed to evaluate the impact of the change in PI on sagittal balance pain, and ambulation after total sacrectomy (DOI 103171/2010 9 SPINE09728)