CT analysis of pedicles and screw tracts after implant removal in thoracolumbar fractures.

Twenty-one burst fractures of the thoracolumbar junction were stabilized with a transpedicular fixator by surgeons experienced in this technique. Screws 5 or 6 mm in diameter were used. After the removal of the device 1 year postsurgery, axial CT scans were obtained of the instrumented vertebrae. Eighty-two pedicles were examined. In 16 pedicles, medial or lateral cortical defects were found. Five screws had intruded into the spinal canal by a maximum of 3.5 mm. In 48 pedicles a correlative comparison with the preoperative examinations was possible. Compared with the dimensions of the pedicles on the preoperative CT scans, 31 had increased in width, and 14 showed deformation indicative of fractures of the lateral pedicle wall. When the screw diameter exceeded 65% of the pedicles' outer diameter, 85% of the pedicles expanded. One of four screws had penetrated the anterior wall of the vertebra. Pedicle screw penetration on the left side above L2 poses potential risk of erosion of the aorta. The use of pedicle screws at the thoracolumbar junction by experienced surgeons carries some risk for malplacement and neurological damage. Mismatch between pedicle dimension and screw size results in pedicle expansion and lateral wall fractures, probably during screw insertion. Preoperative CT examinations should be used to help in choosing appropriate screw diameter presurgery.