Factors affecting the static shear strength of the prosthetic stem-bone cement interface.

Debonding of the stem-cement interface has been implicated in the initiation of failure of cemented femoral stems. The objective of this work was to examine some of the parameters which influence the interface static shear strength, including surface finish, cement type, pre-treatments and porosity. Surface finish was found to have the greatest effect on the interface strength. Increasing the surface roughness by a factor of 100 increases the interface shear strength by a factor of 20. However, increasing the surface roughness above a certain value was found to have no additional affect. This was due to failure in the cement itself rather than at the cement-stem interface. There were significant differences between some of the different cement types regarding the interface strength. Pre-heating the stem produced a six fold reduction in cement porosity at the stem-cement interface, however, resulting in only a minor influence on the static interface strength. Generally, no significant correlation was found between the cement porosity and the static interfacial shear strength.