Cement debonding process of total hip arthroplasty stems.

Retrieval studies have indicated that debonding of the stem cement interface in total hip arthroplasty precedes clinical failure of femoral components. This study addressed the mechanisms that play a role in the debonding process by analyzing how debonding is likely to proceed in the course of time. It was investigated whether debonding is an immediate process or if it is likely to develop slowly with time, which interface stress components contribute particularly to its progression, and whether the mechanical integrity of the cement mantle is likely to be compromised by the debonding process. To answer these questions, a 3-dimensional finite element model of a femoral total hip arthroplasty reconstruction was developed and used to simulate the debonding process. The results showed that debonding was governed by the shear stress component at the interface. Debonding started in the tip region and the proximal, medial anterior region. These debonded regions expanded until the whole interface was de bonded. Cement stresses slowly increased at the end of the debonding process to a level twice as high as the initial one. The probability of debonding, as measured by an interface failure index, remained constant as debonding progressed. This indicates that, for this particular design, much less surface area is required for load transfer than is provided by the stem, and the debonding process does not necessarily accelerate quickly once debonding is initiated.