Development of a Force Amplitude- and Location-Sensing Device Designed to Improve the Ligament Balancing Procedure in TKA

Abstract

To improve the ligament balancing procedure during total knee arthroplasty a force-sensing device to intraoperatively measure knee joint forces and moments has been developed. It consists of two sensitive plates, one for each condyle, a tibial base plate and a set of spaces to adapt the device thickness to the patient-specific tibiofemoral gap. Each sensitive plate is equipped with three deformable bridges instrumented with thick-film piezoresistive sensors, which allow accurate measurements of the amplitude and location of the tibiofemoral contact forces. The net varus-valgus moment is then computed to characterize the ligamentous imbalance. The developed device has a measurement range of 0-500 N and anintrinsicaccuracyof0.5%fullscale.Experimentaltrialsonaplastic knee joint model and on a cadaver specimen demonstrated the proper function of the device in situ. The results obtained indicated that the novel force-sensing device has an appropriate range of measurement and a strong potential to offer useful quantitative information and effective assistance during the ligament balancing procedure in total knee arthroplasty.

A new approach to implant alignment and ligament balancing in total knee arthroplasty focussing on joint loads

“…By means of these measurement systems, loads transferred within the knee joint can be determined. Current systems for measuring forces or pressure distributions in the knee joint can be divided into three categories: pressure measuring foils [1,24,25,28,72] , instrumented tibial plateaus or inlays [13,14,33,46,47] and instrumented spreader devices [40 -42] . For detailed description and analysis, see Schmidt et al [63] .…”

“…Some of the instrumented tibial plateaus and inlays are designed for permanent implantation and cannot be used for " short time " ligament balancing. Other systems are less accurate [46,47] or result in changed load transfer due to geometrical changes of the prosthesis components [13,14] . Using instrumented spreader devices, the joint is loaded unphysiologically and the joint line is elevated during measurement as in the conventional procedure.…”

Low-firing thick-film piezoresistive sensors for medical instruments

“…The steel mechanical structure of the sensor and testing jig / procedure were the same as before [1], with the new low-firing thick-film materials system replacing the mainly commercial materials, and the conductor layout modified to reflect the abovementioned new layer sequence (see 2.3). A picture of the resulting sensor is given in Fig.…”

“…However, the high standard 850°C thick-film firing temperature is incompatible with high-strength metallic alloys, due to phase transitions, oxidation and annealing effects. This can be in part circumvented by the use of substrates such as solution-hardened high-nitrogen austenitic stainless steels [1], but these are very expensive to machine, and their high coefficient of thermal expansion (CTE) gives rise to problematic compressive stresses; in our first device intended to be fabricated with commercial thick-film materials only [1], a basic dielectric-conductor-resistor buildup (see Fig. 1a) was still possible, but the addition of crossovers (i.e.…”

“…Specific fillers for the dielectric layers increase adhesion on steel substrates and allow thermal matching to austenitic and ferritic / martensitic steels, as well as titanium alloys. The functionality of this materials system is successfully demonstrated here by implementing it into a previously developed ligament-balancing force sensor for total knee arthroplasty (TKA) [1]. …”