ANATOMIC CONSIDERATIONS FOR DORSAL SACRAL PLATE-SCREW FIXATION

Five cadaveric pelves and 40 dry bony specimens were used to assess th e feasibility of the lumbosacral plate fixation extending to beyond th e S1 region and quantitatively to evaluate the posterior sacroiliac re gion and the dimensions of S1 and S2 pedicle and lateral mass. Partial removal of the posterior ilium was undertaken to measure the surface area available for plate fixation on the dorsal aspect of the sacrum. The results showed that the average distances between the outer edges of S1 and S2 dorsal foramina and the medial edge of the posterior iliu m increased from 11.3 mm before removal of a portion of the medial pos terior ilium to 16.6 mm after removal at the S1 level, and from 8.4 mm before removal of partial medial posterior ilium to 13 mm after remov al at the S2 level, respectively. The average depths of the S1 and S2 pedicles were 37.1 and 32.2 mm in the direction anteromedial to the sa gittal Plane, respectively. The average depths of the S1 and S2 latera l mass were 37.3 and 33.9 mm in the direction anterolateral to the sag ittal plane, respectively In cases of vertebral metastases or osteopor osis, plating extending to S2 may be needed if good bony purchase cann ot be achieved by the S1 pedicle or lateral mass screw. This study sug gested also that partial removal of the posterior ilium enhances the s pace on the posterior aspect of the sacrum without severe compromise o f the sacroiliac joint.