A METHOD FOR RADIOGRAPHIC EVALUATION OF PEDICLE SCREW VIOLATION OF THE VERTEBRAL END-PLATE - TECHNIQUE

Study Design. This study evaluated the utility of intraoperative radio graphs for minimizing the risk of pedicle screw tip violation of the s uperior vertebral endplate. Objectives. An intraoperative radiographic technique is demonstrated that ensures that a screw has not penetrate d the intervertebral disk. Summary of Background Data. Although method s to avoid penetration of the medial pedicle cortex and the anterior b ody cortex have been described, no study has discussed screw penetrati on of the superior endplate and disc. Methods. Pedicle screws were ins erted into 11 cadaveric lumbar spines, randomly, with the tip inferior to the endplate, at the endplate, and through the endplate. Radiograp hs were evaluated to measure the penetration, if any, of the screws. S pine segments were dissected and evaluated anatomically. The anatomic and radiographic results were then compared. Results. The overall erro r rate for radiographs was 22/312 (7%). Oblique radiographs gave a muc h higher error rate. Conclusions. A true lateral or anteroposterior ra diographic view of the vertebra provides a high degree of certainty th at the screw has not crossed the endplate when a ''safe zone'' of 3 mm remains superior to the screw tip. Intraoperative radiography can red uce concern about violation of the superior vertebral endplate.