Acoustic analysis of prosthesis seating behaviour and risk of periprosthetic fracture

J. Bätz, G. Campbell, M.M. Morlock

Uncemented hip prostheses ensure high long term stability by bone ingrowth. Good secondary anchorage requires high primary stability, which is achieved during implantation. The primary stability is based on a press-fit connection between bone and prosthesis, which determines the position of the implant by friction and allows for bone ingrowth.  The press-fit is created by multiple hammer blows on the prosthesis. A common reason for revision of hip implants is loosening, which is indicative of an insufficient initial press-fit.

The initial press-fit is depending on the created bone cavity as well as on the size and final position of the implant. If the ideal final position is not yet reached or an inappropriate implant size is used, loosening of the prosthesis could occur. If the prosthesis is impacted further than to the ideal final seating position, risk of periprosthetic femur fracture will increase. 

To obtain ideal size and position, surgeons are guided by tactile, visual and especially auditory feedback during the cavity preparation and implantation process. The decision is based on the subjective experience of each surgeon.

This project examines the accessibility of an objective guidance by intraoperative frequency analysis during broaching and implantation. Impaction sounds of the different implantation steps in artificial, animal and human bone are recorded with high-precision microphones and spectral analyses are performed.  Numeric modelling helps to understand the vibrations of the system.

Results may help to minimize loosening and intraoperative periprosthetic fracture risks.