INTRODUCTION: In surgery for spinal metastasis, it is sometimes difficult to insert pedicle screw due to osteolytic or osteoblastic change of spinal vertebrae.
The aim of this study was to examine the accuracy of screw insertion for posterior fixation of spinal metastasis and to clarify the safety of screw insertion into metastatic vertebrae.
METHODS: We included 92 patients (mean age, 66.5± 12.5 years; 56 men, 36 women) who underwent posterior fixation with pedicle screws for metastatic spinal tumors excluding cervical spine between 2013 and 2022. The pedicle screws were inserted without the use of a navigation system. In open surgery, screws were inserted using a freehand technique, while in MISt surgery, percutaneous pedicle screws (PPS) were used under fluoroscopic guidance. The position of pedicle screw was evaluated using axial and sagittal images from postoperative CT and classified into four grades: Grade 0 (no deviation), Grade 1 (<2 mm), Grade 2 (2–4 mm), and Grade 3 (>4 mm). . The number of screws inserted into the pedicles with metastases was identified on preoperative CT images and MRI. We statistically analyzed whether metastases in the pedicles affected the deviation rate of pedicle screws.
RESULTS: Among the 92 patients, there were 62 cases who underwent in open surgery (Open group) and 30 cases in MISt surgery (PPS group). A total of 908 pedicle screws were inserted into 592 vertebrae and 1184 pedicles within the fixation range, with an overall screw density of 83.0%. Among 271 pedicles in metastatic spine (osteolytic change: 165 pedicles), 86 pedicle screws were inserted (osteolytic change: 23 pedicles). The overall screw perforation rates were10.8% (98 pedicles), and of each grade were 8.4% (76 screws) for Grade 1, 1.7% (15 screws) for Grade 2, and 0.8% (7 screws) for Grade 3. The perforation rate of screws inserted into the metastatic spine was limited to Grade 1: 8.6% (10 screws), which was not significantly different from the perforation rate of screws inserted into non-metastatic spine (p = 0.71). Comparing to open and PPS surgery, there was a significant difference in Grade 2 perforation between the Open group and the PPS group (13 screws vs. 2 screw, p = 0.04) and no significant difference in other grades. There were no case of postoperative neurological symptoms due to screw perforation. However, one case of Grade 3 perforation involving a screw inserted into the normal pedicle resulted in postoperative screw dislocation required screw removal, and one case of Grade 2 deviation were removed the screw at the time of reoperation for worsening neurological symptoms due to other causes.
DISCUSSION: Spine surgery for spinal metastasis is sometimes difficult to insert pedicle screw due to poor bone condition or massive bleeding, the results of this study showed that the rate of pedicle screw perforation was 10.8%. Fortunately, there was not significantly different between metastatic and normal spinal bodies. Whereas, the perforation rate of open surgery was higher than PPS surgery, MISt technique was should be used for surgery for spinal metastasis.