Investigation into the Lubrication Regime for Lumbar Total Disc Replacement of the Spine

The lubrication regime of articulating surfaces plays an important role for the understanding of the tribological conditions and the resulting wear performance of total disc replacement (TDR) of the spine. In the present study the lubrication regime for lumbar TDRs with ball and socket design have been assessed by applying the Hamrock-Dawson elasto-hydrodynamic lubrication theory. The effect of varying articulation radii and different material combinations on the lubrication regime have been investigated considering load and motion cycles for a representative in vivo situation as well as for in vitro wear testing situations. Independent of geometry or bearing material combinations, the formation of a stable lubrication film is very unlikely for lumbar TDR. The study also reveals that in vitro testing conditions must be carefully selected in order to correlate with the lubrication regime for corresponding in vivo situations.