Computational study on the integration of a piezoelectric element into an uncemented revision hip stem for energy supply of smart implant functions

In the future, self-powered smart hip implants may enhance the longevity of total hip replacements. Uncemented hip stems aim to promote integration within the bone stock through electrical bone stimulation before loosening occurs, necessitating an internal energy source. Piezoelectric energy harvesting presents a viable solution. This study aimed to integrate a piezoelectric element into an uncemented revision hip stem in a manner that maximizes electrical output while preserving mechanical stability of the implant. Finite element (FE) analysis was used to evaluate cavities of varying sizes, based on the integrated piezoelectric element, and different positions in the medial neck area of the hip stem. An FE model with physiological boundary conditions during gait assessed the electrical power output, while a separate static FE model, based on ISO 7206-4, analyzed mechanical stress distribution and fatigue resistance of the implant. The most promising design was selected for endurance testing per ISO 7206-4. For the optimal design, the maximum stress was 315 MPa, with a fatigue life of >10⁹ cycles and a safety factor of 2.01 according to Soderberg criteria. The design successfully passed the ISO 7206-4 endurance test and achieved a calculated average electrical power output of 439 μW during gait. In conclusion, an uncemented revision hip stem can be modified to incorporate a piezoelectric element for energy conversion. Future work will focus on experimental evaluation of the electrical voltage and power generation during physiological activities.