Houston Methodist. Leading Medicine

General Spine News

FDA Keeps Tabs on Approved Devices for Spinal Fusion

Whatever happens to the patients in clinical studies testing a device or operation before it's approved? A special cage device for spinal fusion was approved in 1999 by the Food and Drug Administration (FDA). From 1991 to 1993 it was tried on a group of patients as part of a research study. The authors of this study report on the results of these patients 10-years after the cage was put in.

Cages are used to fuse two vertebral bones together in the spine. The disc material between the bones is taken out and the cage is put in its place. Bone chips fill the cage. Fusion occurs as the bone grows inside and around the cage.

The cage in this study was made of carbon-fiber that is somewhat elastic like bone. It's held in place with screws and plates. The design of the cage allows the screws to be put in different places at different angles. This is called the Variable Screw Placement (VSP) system.

Success was measured using pain, function, and medication usage. X-rays were also taken to show if there was a solid bridge of bone at the fusion site. X-rays also showed if there was any movement at the fusion site (a sign of failed fusion).

Thirty-three of the original groups were traced by telephone and by the internet. The authors report fusion success in all but one patient after 10 years. The X-rays did show degenerative changes at the next level in more than half of the patients. None of these patients were having any symptoms or problems from the degeneration.

The authors conclude that there is a high rate of long-term success with the VSP carbon-based cages used for lumbar fusion.


John W. Brantigan, MD, et al. The Lumbar I/F Cage for Posterior Lumbar Interbody Fusion with the Variable Screw Placement System: 10-Year Results of a Food and Drug Administration Clinical Trial. In The Spine Journal. November/December 2004. Vol. 4. No. 6. Pp. 681-688.

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