Evaluation of Pedicle Screw Placement in the Deformed Spine Using Intraoperative Plain Radiographs: A Comparison With CT Scans

Purpose: To develop the accurate way to detect malpositioned pedicle screws during thoracic and lumbar spinal deformity operations with intraoperative plain radiographs.

Methods: A total of 776 pedicle screws (618 thoracic and 158 lumbar screws) inserted from T1 to L4 in 49 patients with postoperative CT scan data were investigated. According to the diagnoses, the number of screws placed were: 692 for scoliosis (45 patients), and 84 for Scheuermann’s kyphosis (4 patients). The position of the pedicle screw inserted was graded as an accurate screw (n=711) with acceptable position vs inaccurate screw (n=65) with significant pedicle violation, defined as the central line of the inserted pedicle screw was out of the outer cortex of the pedicle wall with CT scans taken after operation. Comparative analysis of these sixty-five inaccurate screws (15 medial violations and 50 lateral violations) using postoperative CT scan and intraoperative plain radiographs was done. All CT scan evaluations were performed independently by three different spine surgeons who had not been part of the operation. 3 plain radiographic criteria were used to judge the accuracy of screw position: 1) Violation of the harmonious segmental change of the tips of the inserted screws (medial or lateral out), 2) no crossing of the medial pedicle wall by the pedicle screw inserted (lateral out), and 3) violation of the imaginary midline of the vertebral body using the posterior upper spinolaminar junction in the plain PA x-ray by the absolute position of the tip of the inserted pedicular screw after minor screw tip position adjustment according to the lateral x-ray (medial out).

Results: Among 15 inaccurate pedicle screws with medial wall violation, 13 screws demonstrated loss of harmonious segmental change in the screw tips and violation of the imaginary midline of the vertebral body (sensitivity 87%, specificity 97%). One case demonstrated only loss of harmonious change in the screw tip and the other one case did not demonstrate any significant plain x-ray findings. Among the 50 inaccurate pedicle screws with lateral wall violation, 47 cases demonstrated the loss of harmonious segmental change in the screw tips and no crossing of medial pedicle wall by the pedicle screw inserted (sensitivity 94%, specificity 88%). Two cases did not demonstrate any significant plain x-ray findings and the other one case demonstrated only violation of the harmonious segmental change in the screw tips. (See Attachment)

Conclusions: Intraoperative plain radiographs alone using 3 radiographic criteria was very sensitive to detect lateral wall pedicle screw violations, and specific for assessing for medial wall violations. This stresses the importance of careful intraoperative plain radiographic assessment after pedicle screw insertion to detect malpositioned screws to allow for possible revision during the index operation.