INTRODUCTION
In recent years, the use of long instrumented fusion with pedicle screws has increased in patients with trauma, degenerative diseases, and deformity. However, early pull-out of pedicle screws sometimes occurs after posterior instrumentation surgery, and is one of the major indications of revision surgery. The reduced bone mineral density of osteoporosis bears upon the anchorage of pedicle screws, but there are few reports on surgical procedure and pedicle screw pull-out. The purpose of this study is to verify the factors involved in early pedicle screw pull-out after posterior instrumentation surgery.
METHODS
Seventy consecutive patients underwent pedicle screw fixation of three or more vertebrae between July 2014 and December 2022. Except 11 patients who underwent revision surgery for adjacent segmental disease, 59 patients (male, 37; female, 22; mean age, 69) were retrospectively reviewed. The pathologies included degenerative diseases in four, spine trauma in 20, osteoporotic vertebral fracture in 23, metastatic spinal tumor in seven, spinal infection in five. Pedicle screw insertion was the open method in 30 and the percutaneous pedicle screw (PPS) method in 29. Cases with pedicle screw pull-out within 3 months after surgery were defined as early pull-out cases. We compared age, gender, number of fused segments, with anterior column reconstruction, with decompression, with vertebral osteotomy, presence of diffuse idiopathic skeletal hyperostosis (DISH), and the method of pedicle screw insertion between the groups with and without early pedicle screw pull-out. Multiple logistic regression analysis was applied for statistical comparison, and P<0.05 indicated statistical significance.
RESULTS
Six patients (10.2%) developed early pedicle screw pull-out, and three of the six patients required additional surgery. The pathologies were osteoporotic vertebral fracture in four, spine trauma in one, and spinal infection in one. No significant differences between groups were found for the age, gender, number of fused segments, with anterior column reconstruction, with decompression, with vertebral osteotomy, and presence of DISH. A significant difference was found only for the PPS method (P=0.008).
DISCUSSION
Generally, screw pull-out can occur if there is a gap between the shape of the rod and actual spinal alignment. In the PPS system, early pull-out may easily occur at the time of inserting the set screws because the gap between the rod and screw head is not visible. The most important aspect of the PPS method is to ensure appropriate rod bending and gently connect the rod to each screw head. The current study showed that the prevalence of early pedicle screw pull-out was significantly higher with the PPS method than with the open method. PPS is a risk factor for early pedicle screw pullout after posterior instrumentation surgery.