Development of a capacitive force sensor for artificial joint

Abstract

Soft tissue tension is thought to have a great effect on the clinical performance of total joint replacement; such as shoulder, hip, knee, or ankle. However, there have been no reports quantifying these soft tissue tensions intraoperatively. For the shoulder, reverse total shoulder arthroplasty has been used in Japan since 2014. So the purpose of this study is to develop an instrument which tells us soft tissue tension intraoperatively. Surgeons would be able to utilize the measured values when assessing stability of the joint intraoperatively. We are developing the instrument using capacitive one-dimensional force sensors to measure the soft tissue tension for reverse shoulder arthroplasty. A capacitive one-dimensional force sensor can be made less than 1mm in thickness. And an electric circuit which measures its amount of capacitances also could be made pretty small. That's because we use capacitive force sensors for measuring the soft tissue tension. The whole instruments have to be sufficiently small enough such that its outer geometry could be same to an existing prosthesis. While a capacitive force sensor is good in its dimensions, however, it is very sensitive to noise. We try to improve signal noise ratio having whole dimensions small enough. Now, we have designed a 5mm diameter capacitive one-dimensional force sensor to operate in the 0–150N force range. This direction hopefully would be one of the promising ways for good clinical outcomes of joint replacement.