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Stand-Alone Cages for Lumbar Fusion Don't Stand Up Under Low Loads

Aging isn't always kind to us. Degeneration of the discs and vertebrae in the spine is all too common. Pain and loss of motion can limit function. Spinal fusion may be needed.

Spinal fusion at one or more levels restores alignment and stops motion at those levels. One new way to fuse the spine is with interbody fusion cages. These cages are often made of titanium, graphite, or bone and look like spiral-shaped barrels. They fit between the vertebrae where the disc used to be.

The surgeon can go in from the front of the body, remove the disc, and insert the cage. In this study a special "stand-alone" interbody cage was tested. These cages don't need extra screws or metal plates to hold them in place.

The purpose of the study was to see what happens when the cages were subjected to an outside load. This kind of load or force occurs with muscle contraction. Increased force is also caused by the lifted position of the spine when the cages are in place. With greater distraction, the spinal joints are more open, allowing motion to take place when it shouldn't. This puts more load on the fusion, too.

The results show that the stand-alone interbody fusion cages don't limit spinal extension under low loads. This means the spine is not stable right away after surgery. The stability increases with increasing loads.

Lying down on the back is one example of a low load. Larger loads occur with standing and walking. The authors suggest anterior stand-alone cages may not be stable enough. Bone graft, metal plating, or extra screws may be needed to get a good enough fusion in the beginning. The authors predict greater stability will occur as the cages settle into the vertebrae.

References: Avinash G. Patwardhan, PhD, et al. Compressive Preload Improves the Stability of Anterior Lumbar Interbody Fusion Cage Constructs. In The Journal of Bone and Joint Surgery. September 2003. Vol. 85-A. No. 9. Pp. 1753-1756.

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