Possibilities for Shock Absorption in Disc Prostheses

By John Velasquez

Many in medicine believe the spine to be the center of bodily wellness, and health. Naturally, as the center of all mechanics of the body, it is subject to intense physical stress. Major improvements have been made in stabilizing the spine and resolving herniated or degenerative intervertebral disks. Before, such medical issues would require fusion, but would entail a total loss of function of the joint by essentially making one bone out of what used to be two (Spinehealth). Now, doctors can preserve the natural flexibility of the spine with new prostheses such as the prodisk variety. These designs make an excellent mimicry of the natural motion of vertebral joints, as do other prostheses (Synthes Inc.), however they fall short in replicating one crucial role that intervertebral disks play. In addition to acting as a ligament for a vertebral joint, discs act as necessary shock absorbers, protecting the network of bone and nerves from major traumas and force.

As of yet, no prosthesis or medical procedure can mimic the shock absorbing properties of natural disks. In fusions especially, this places the burden on other adjacent disks, and can result in a faster deterioration of the rest of the spine. (Goffin, et al) Naturally prosthesis without shock absorption is better than no prosthesis at all, but full mimicry, or at least majority replication of the natural shock control would be ideal and best for preventing further injury. Unfortunately it is also unknown how this could be achieved. So far, the only real progress in shock absorption is the shift from titanium to polyurethane or cobalt chrome alloy. This gives some extra shock protection, but nowhere near on the level of a real biological disk (Dahl, et al).

Many man made materials are capable of shock absorption, but they are not usually put to use inside a human body. Gel insoles, or rubber stoppers work well in a machine of steel that can be maintained by people in case of deterioration or replaced, but in a biological system they would be impossible to clean, and any erosion could interfere with other systems, or cause an inflammatory response. One can only imagine the problems that could arise from a chunk of prosthetic polymer broken off and lodged in the peripheral nervous system. Furthermore, such an invasive surgery could not be reasonably performed over and over again to constantly replace faulty prostheses. Consequently any viable option for shock absorbing disk prosthetics would have to be able to withstand the natural stresses of the body, and require no maintenance.

Perhaps the best way to fix this issue is not to try and copy nature or the miracle of the human body, but to use resources given by the body already. For this to happen, one option would be new treatment would be developed to repair discs, through rehydration and other methods. Another option would be transplant. This would require a readily available supply of discs, but because they aren’t renewable in the body, the supply that could be gathered from organ donors could not reasonably keep up with demand for new discs.

There are many obstacles to replacing intervertebral discs with shock absorption capabilities. However, if they could be overcome it would be a major improvement for spine medicine, as it would prevent exacerbation of deterioration. If the natural organs cannot be replaced with man-made substances, or transplants, there seems little hope of this happening. One can only hope that science can master the cultivation of organs in a lab in order to grow new intervertebral discs for use in transplants. Until then, prostheses with limited shock control will have to do.

References

1. Dahl, Michael C., PhD, Stephen Jacobsen, MD, Newton Metcalf, Jr., Rick Sasso, MD, and Randal P. Ching, PhD. "A Comparison of the Shock-absorbing Properties of Cervical Disc Prosthesis Bearing Materials." Www.sciencedirect.com. International Journal of Spine Surgery, 2011. Web. 7 June 2015.

2. Ullrich,, Peter F., Jr. "Lumbar Spinal Fusion Surgery." Spine-health. Spinehealth, 9 Aug. 1999. Web. 20 June 2015.

3. "ProDisc-C Total Disc Replacement." ProDisc-C Total Disc Replacement. Synthes, Inc., 3 May 2012. Web. 20 June 2015.

4. Goffin, J., F. Van Calenbergh, J. Van Loon, A. Casey, P. Kehr, K. Liebig, B. Lind, C. Logroscino, R. Sgrambiglia, and V. Pointilliard. "Result Filters." National Center for Biotechnology Information. U.S. National Library of Medicine, 15 Dec. 2003. Web. 20 June 2015.