Clinical evaluation and computed tomography scan analysis of screw tracts after percutaneous insertion of pedicle screws in the lumbar spine

Study Design. An examination of the accuracy of percutaneous pedicle screw placement in the lumbar spine. Using computed tomography scan analysis afte r implant removal, the screw tracts could be analyzed regarding the degree and direction of screw dislocation. Objectives. To investigate the misplacement rate and related clinical compl ications of percutaneous pedicle screw insertion in the lumbar spine. Summary of Background Data. The feasibility of the external fixation test h as been investigated in several studies. Although pedicle screw misplacemen t has been reported as one of the main complications, there are no reliable data on the misplacement rate for this difficult surgical procedure. Methods. In this study, 51 consecutive patients with suspected segmental in stability were investigated after external transpedicular screw insertion f or the external fixation test, Computed tomography scans of all instrumente d pedicles from L2 to S1 were performed after screw removal. The screw trac ts were analyzed, and the direction and deg ree of the pedicle violations w ere noted. In addition, the screw and pedicle angles were measured. Results. Of 408 percutaneously inserted pedicle screws, only 27 screws (6.6 %) were misplaced. There were 19 medial pedicle violations, 6 lateral corti cal defects, and only 1 cranial and 1 caudal displacement. With respect to the spinal level, S1 showed the highest misplacement rate, with 11 screw di slocations (12%). After surgery, found two nerve root injuries were found. Only one of the injuries (L4) was related to the malposition of a screw. Conclusions. This study has shown that percutaneous insertion of pedicle sc rews in the lumbar spine is a safe and reliable technique. Despite the low misplacement rate of only 6.6%, it should be kept in mind that the surgical procedure is technically demanding and should be performed only by experie nced spine surgeons.