Design of a reverse shoulder implant to measure shoulder stiffness during implant component positioning

To avoid dislocation of the shoulder joint after reverse total shoulder arthroplasty, it is important to achieve sufficient shoulder stability when placing the implant components during surgery. One parameter for assessing shoulder stability can be shoulder stiffness. The aim of this research was to develop a temporary reverse shoulder implant prototype that would allow intraoperative measurement of shoulder stiffness while varying the position of the implant components. Joint angle and torque measurement techniques were developed to determine shoulder stiffness. Hall sensors were used to measure the joint angles by converting the magnetic flux densities into angles. The accuracy of the joint angle measurements was tested using a test bench. Torques were deter-mined by using thin-film pressure sensors. Various mechanical mechanisms for variable positioning of the implant components were integrated into the prototype. The results of the joint angle measurements showed measurement errors of less than 5 degrees in a deflection range of +/- 15 degrees adduction/abduction combined with +/- 45 degrees flexion/extension. The proposed design provides a first approach for intra-operative assessment of shoulder stiffness. The findings can be used as a technological basis for further developments.

Automated summary

This study developed a temporary reverse shoulder implant prototype that allows intraoperative measurement of shoulder stiffness. The stability of the shoulder can be assessed using joint angle and torque measurement techniques. The proposed design provides a method for intraoperative assessment of shoulder stiffness.