Height of cervical foramina after anterior discectomy and implantation of a carbon fiber cage

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Object. The authors evaluate the effects of implantation of a carbon fiber cage after anterior cervical discectomy (ACD) on the height of the foramen and the angulation between endplates of the disc space.

Methods. Thirteen consecutive patients who were scheduled for standard microscopic ACD and interbody fusion underwent thin-slice (1.5 mm) spiral computerized tomography scanning 1 day preoperatively, 1 day postoperatively, and 1 year postoperatively. Oblique sagittal reconstructions were made through both foramina; the height of each foramen and the angle between the endplates were measured. Because 16 cages were implanted, 32 foramina were investigated. Preoperatively, the mean height of the foramina (± standard deviation) was 8.1 ± 1.5 mm (range 5.7–12 mm), and at 1 day postoperatively it was 9.7 ± 1.4 mm (range 7.5–12.8 mm). This difference reached statistical significance (p < 0.0005). The mean foraminal height after 1 year was 9.4 ± 1.4 mm (range 6.9–12.7 mm). In terms of the preoperative value, the 1-year measurement still reached statistical difference (p < 0.005) but not with the direct postoperative mean foraminal height. Preoperatively the mean value of the angle between the two adjacent endplates was 1.3 ± 2.4° (range 0–8°), and postoperatively it was 7.8 ± 2.9° (range 2–12°), which was statistically significant (p < 0.0005).

Conclusions. The cervical carbon fiber cage effectively increased the height of the foramen even after 1 year, which contributed to decompression of the nerve root. The wedge shape of the device may contribute to restoration of lordosis.

Article Information

Address reprint requests to: Ronald H. M. A. Bartels, M.D., Neurosurgical Center Nijmegen, University Medical Center Nijmegen St. Radboud, R. Postlaan 4, 6500 HB Nijmegen, The Netherlands. email: r.bartels@czzonch.azn.nl.

© AANS, except where prohibited by US copyright law.

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    Representative imaging studies obtained in a patient in whom an interbody cage was placed. Upper Left: Preoperative lateral radiograph of the cervical spine revealing slight kyphotic deformity, anterior osteophyte at C-5, and disc space narrowing at C5–6. Upper Right: Preoperative oblique sagittal CT reconstruction obtained through the left foramen. The height of the foramen is defined as the smallest distance between the pedicles (arrows). The angle between the endplates is also measured. Lower Left: Postoperative lateral radiograph clearly demonstrating the implanted cage (arrow), which is radiolucent except for the three markers. The height of the disc space is increased, as is the angle between the endplates. Center Right: Postoperative reconstructions of the CT scan confirming the radiographic findings. The height of the foramen is also increased. The impacted cancellous bone is clearly seen within the cage (arrow). Lower Right: Fifteen-month CT reconstruction revealing bone growth through and around the cage. Both VBs have fused; continuous cortical bone is seen at the anterior margin of the foramen and anteriorly at the VBs (arrows). The endplates are not visible.

References

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