Accuracy of Pedicle Screw Reinsertion in Revision Spine Surgery

Objective: The goal of this study was prospectively to evaluate the accuracy of placement of new Pedicle Screws (new-PSs) in revision surgery. Methods: A total of 181 new-PSs inserted in 31 consecutive patients undergoing posterior fixation in the thoracic or lumbar spine were evaluated. Placement of these screws was analyzed on postoperative Computed Tomography (CT) and compared with that of previously inserted Pedicle Screws (pre-PSs) on preoperative CT. Placement positions were classified as Grade 0: No perforation and screw completely contained in the pedicle, Grade 1: Perforations <2 mm, Grade 2: perforations ≥ 2 to <4 mm, and Grade 3: perforations ≥ 4 mm. Results: New-PSs were inserted with a free hand from Th6 to S1 for a broken rod, non-union, adjustment for segmental degeneration or proximal junctional kyphosis, and other conditions. There were 16 screws inserted into the thoracic spine and 165 into the lumbar spine. Three of the 10 new-PSs in the thoracic spine that had a larger diameter than the pre-PS resulted in a Grade 1 medial breach of the screw. In the lumbar spine, two new-PSs resulted in Grade 3 lateral breach, and 7 new-PSs resulted in breaches of Grade 2. The rate of Grades 2 and 3 new-PSs in the lower lumbar spine was significantly higher than that of pre-PSs in the upper lumbar spine. The mean depth from the skin to the position of screw insertion in MRI of the lower lumbar spine was significantly deeper than that of the upper lumbar spine. There was no neurovascular injury as a result of insertion of the new-PSs. Conclusion: New-PSs have a potential for malposition in revision surgery. In particular, reinsertion in the lumbar spine has a higher perforation rate and a tendency for an unintentional trajectory change, which might be due to limitations of the posterior and lateral back muscles during screw insertion. Therefore, new-PSs should be inserted carefully.