MRI evaluation of dural sac enlargement by interspinous process spacers in patients with lumbar spinal stenosis: Does it play a role in the long term?

Abstract

To investigate dural sac enlargements and spinal alignments in patients who underwent indirect decompression with interspinous spacers. The subjects were 20 patients who underwent indirect decompression using an interspinous spacer (X-STOP) without laminectomy. Of these 20 patients, 1 patient underwent implant removal surgery 1 month after X-STOP surgery and two patients dropped out. Ultimately, 17 patients were included in this study. MRI and X-ray images were investigated before surgery, 1 week after surgery, 3 months after surgery, and 2 years after surgery. On MRI, the mean cross-sectional areas of the dural sac were 52.7 mm² before surgery, 73.2 mm² 1 week after surgery, 62.4 mm² 3 months after surgery, and 58.3 mm² 2 years after surgery. There was a significant 37% increase at 1 week postoperatively compared with that before surgery, but there were no significant differences between 3 months postoperatively and 2 years postoperatively. The disc angle in an extension posture was significantly decreased at 1 week after surgery compared with that before surgery, but there were no significant differences between before surgery, 3 months after surgery, and 2 years after surgery. The interspinous process spacer increased the dural sac area by 37% 1 week after surgery, but the enlargement was not maintained at 3 months or 2 years after surgery. The use of interspinous process spacers produced an enlargement of the dural sac by limiting extension of the stenotic level only. However, its effect diminished 2 years after surgery.