The effect of transpedicular screw misplacement on late spinal stability

Abstract

Background: In this article the authors investigated the consequences of misplaced thoracolumbar pedicle screws on late spinal stability.

Method: This study consisted of 16 patients with screws in the proper position (Group A) and a further 16 patients with screw misplacement (Group B) who had previously undergone transpedicular screw fixation following thoracolumbar injury. The authors retrospectively evaluated the bone fusion, anterior height of the fractured vertebrae and the kyphotic deformity on postoperative early neutral, and on postoperative long-term neutral and dynamic radiographs in both groups. The results and in addition a back pain questionnaire were compared within each group, and also between groups A and B.

Findings: The decreased anterior height of the fractured vertebrae and the increased degree of kyphosis on postoperative early radiographs in group B demonstrated that the correction of the deformity was inadequate in patients with screw misplacement. Furthermore, an additional increase in the degree of kyphosis on long-term neutral radiographs indicated a significant progression in late kyphotic deformity in group B, whereas it was not seen in group A. The evidence of significant motion on neutral-flexion and flexion-extension long-term radiographs demonstrated impaired stability in group B, whilst it was only evident in neutral-flexion radiographs in group A. Moreover, moderate to severe back pain was commonly reported by patients in group B and correlated with lack of bony fusion and significant motion.

Interpretation: The authors conclude that the screw misplacement decreased the original spinal stability provided by the instrumentation. Therefore, correct placement of pedicle screws is required to maintain long-term spinal stability.