Using Stress Shielding in Hip Implants as a Case Study to Teach Loading of Composite Beams

A laboratory activity was developed in which the students modeled and analyzed the femoral portion of an artificial hip replacement as a composite beam. A historical challenge with artificial hip replacements has been that the stiffer artificial femoral component shields the surrounding bone from stresses during physiological activities. This phenomenon, known as “stress shielding,” results in bone resorption that can lead to implant failure. In this activity, the students investigated the extent of stress shielding for femoral implants of varying sizes and material properties for different loading conditions. The students discovered that making the femoral component smaller and of more compliant material minimizes the detrimental effects of stress shielding in hip replacements. The effectiveness of this hip implant activity was studied by comparing it with the traditional laboratory in which the students were tasked with designing a composite beam out of various materials to satisfy rigidity and cost constraints. Students from two laboratory sections completed the traditional composite beams exercise, and students from two laboratory sections completed the hip implant case study. The students from both groups were surveyed before and after the laboratory exercises to determine their confidence in the course material, their interest in the course, and their perception of the real-world relevance of the course. In the post-exercise survey, students were asked all of the questions from the pre-exercise survey as well as questions to determine the effectiveness of the exercise as a teaching tool and the adequacy of the instruction they received. Students consistently felt the hip implant activity was more effective as a teaching tool for the material and were more interested in biomedical engineering than those completing the traditional exercise. The students who completed the hip implant activity expressed greater confidence in their abilities to interpret the results for bending calculations and to design a machine using bending. Overall, the results of the student perception surveys indicate that the hip replacement activity was a better tool for teaching the composite beam theory and had the added benefit of introducing students to biomedical engineering applications of fundamental mechanics principles.