STABLE PARTIAL DEBONDING OF THE CEMENT INTERFACES INDICATED BY A FINITE-ELEMENT MODEL OF A TOTAL HIP-PROSTHESIS

A simplified three-dimensional finite element model of the femoral com ponent of a cemented total hip prosthesis was used to investigate whet her partial debonding at the stem-cement or bane-cement interfaces pro pagates in a stable or unstable manner, and to assess the resultant va riation of the stresses within the cement layer. The likelihood of uns table debonding under tensile failure mode was assessed both by a conv entional monotonic strength criterion and by a fracture mechanics appr oach that took into account debonding due to fatigue loading. The mode l predicted that partial debonding at the cement interlaces would be s table and would not precipitate complete debonding. Among the various bonding conditions that were investigated, the maximum tensile stress within the cement layer was least with a small amount of debonding rat her than with complete bonding. These results were consistent with cli nical observations of nonprogressive or slowly progressive separation at cement interfaces in cemented femoral components that were otherwis e well functioning and asymptomatic.