IN-VITRO VALIDATION OF A DEVICE MEASURING THE IBIO-FEMORACONTACT FORCES AND MOMENTS FOR ASSISTANCE DURING LIGAMENT BALANCING IN TOTAL KNEE ARTHROPLASTY

Abstract

Ligament balancing in total knee arthroplasty is believed to have an important influence on the joint stability and prosthesis lifetime. In order to provide quantitative information and assistance during the ligament balancing phase, a device that intra operatively measures knee joint forces and moments has been developed.

Thanks to its small thickness (6mm), the developed device fits after a tibial precut entirely in the tibio-femoral gap with thepatella in its anatomical place. The device measures the tibio-femoral contact force amplitude and location, thus allowing the computation of the net varus-valgus moment, which characterizes the ligamentous balance. Following an accuracy study, the device was validated with a plastic knee joint model equipped with spring-ligaments, which allowed the application of various degrees of ligamentous imbalance. Finally, the device was tested ina cadaver experiment by an experienced surgeon.

During the accuracy study, the absolute force amplitude and location error were respectively 1.4 N and 0.6 mm, which corresponds to a 3%relative error on the active measurement range. The expected linear relationship between the varus-valgus moments and the spring forces in the plastic bone experiment was experimentally verified and the slope corresponded effectively to the lever arm within 12%, which attests the device’s suitability for the purpose of ligament balancing. The cadaver experiment demonstrated the adequacy of the measurement scale (0–500N) as well as the consistency between the acquired data and the surgeon’s perception.

The design and first prototype of the proposed device has been experimentally validated. In a near future, the benefit of using such a device will be examined by a series of cadaver experiments.