Critical Examination of Stress Shielding Evaluation of Hip Prostheses.

In vitro evaluation of the load transfer of hip prostheses has been performed in recent years for the purpose of understanding the stress shielding phenomena. Over 200 papers were reviewed to determine if a standard exists to evaluate and compare the performance of hip stems. Surprisingly, it was found that little agreement exists in the testing protocol. This makes it very difficult to compare the results reported in different investigations. In several cases very incomplete data are reported about the testing conditions, thus making it impossible to compare the results. This article focuses on: (1) how the loading conditions should be chosen based on physiological loading in a way to give a reproducible setup; (2) how the femur should be constrained; (3) how to generate the same system of loads in the intact and the implanted femur; (4) how to define a reference system; (5) how the specimen type and sample size are chosen; (6) the advantages and limitations of the different strain measurement techniques; (7) how the testing parameters have been chosen in the literature; and (8) how the accuracy of the results has been reported in the literature.