A modal analysis study of interface failure of THA femoral component

This is a computer simulation investigation of the effects of failures at the bone-cement and cement-stem interfaces on a structural characteristic of the femoral component of total hip arthroplasty (THA). A computeraided design (CAD) construct comprising of bone, bone-cement interface, cement mantle, cement-stem interface, and implant stem is developed using Pro/Engineer [Parametric Technology Corp, Needham, MA]. Three types of failures are investigated - two single-interface failures (one for bone-cement and the other for cement-stem), and a dual-interface failure (bone-cement and cement-stem combined). Failure at the interface is defined as a void of various proportional lengths located proximally, centrally, or distally along the interface. Combinations of failure types, lengths, and locations resulted in a total of 54 imperfect constructs. A perfect construct was created for comparisons with the other constructs, and forms a basis for determining the significance of the rigidity of the imperfect constructs. Finite-element modal analyses of the CAD constructs are executed in a finite element analysis software called Algor [Algor, Inc, Pittsburgh, PA] to determine the natural frequencies and their corresponding mode shapes. From the natural frequency information, the results show that central failure has lesser effect on the structural characteristic of the construct whereas the failures at the proximal location have notable effect on the THA construct rigidity. As expected, the THA construct becomes less rigid as the lengths of the failure interface increases. In addition, it is noted that the THA construct rigidity is most sensitive to dualinterface failures than the single-interface failures. In the case of single-interface failures, the cases for bonecement failures tend to affect the rigidity slightly more than those of the cement-stem failures