Intervertebral Disk Replacement - Keivan Anbarani's Electronic ...

apparent translation. Titanium screws located anteriorly in the vertebral body are screwed
to the bone for affixation. Additional stability is achieved through compression of lower
and upper vertebral bodies against ridges in the metal prosthesis.
The second generation of all metal prosthesis was the Bristol Disc-­‐ a modification of the
Cummins design, through a ball-­‐and-­‐trough articulation to allow for more physiologic
translation at the level of replacement. The Prestige Disc also using stainless steel, has a
similar design but with a lower profile and improved instrumentation for easier
implantation (Figure 12a). Metal implants may also reduce osteolysis, however, not yet
observed in TDR. Other metals such as titanium-­‐on-­‐titanium have historically been a poor
bearing surface. However, promising metal designs have looked, these devices are also
usually very large and bulky; the majority not getting much further than the patent
application approval (G.M. McCullen et al., 2003) Other metal-­‐on-­‐metal discs include the
Kineflex|C Disc, and the Cervicore Disc, both of which currently have unavailable clinical
experience at the present time (Figure 12b).
Metal-on-Polymer
Figure 12. a) Cervicore and b) Prestige Disc
Source: Spine-Health, 2010
The combination of metals and polymer are the most commonly used materials for
artificial disc design. Polymers have a higher wear rate but lower stiffness and may offer
some degree of shock absorption. In addition, materials such as elastomers (silicone,
polyurethane, polyethylene) possess similar mechanical qualities than that of metals. With
a lower modulus of elasticity, it is easier to replicate disc dynamics. Although this type of
design may lessen the degree of heavy wear debris, metal-­‐on-­‐polymer designs also show a
higher inflammatory response as well as a wear rate twice as high than that of an all metal
design (A.T. Villavicencio, MD, et al, 2007).
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