A New Handheld Tool to Select the Correct Tibial Insert Thickness by Measuring the Force to Push a Trial Insert Into Position During Total Knee Arthroplasty Surgery

Abstract

During total knee arthroplasty (TKA) surgery, an important step is determining the correct insert thickness for each patient. If the insert is too thick, then stiffness results. Or conversely, if the insert is too thin, then instability results. One common method used to determine the insert thickness is by manually assessing the joint laxity; this is a qualitative method that depends on the surgeon's experience and “feel” and is unreliable. The lack of objective methods to reliably determine the correct insert thickness creates a need to develop such a method. One possible method is to measure the force required to push a trial insert into position, requiring a specialized tool to measure the push force. Hence, a new measuring tool was designed to measure the push force intra-operatively, accurately, and safely. To demonstrate functionality, the tool was tested on three patients. During the tests, the surgeon determined the appropriate thicknesses of the insert to trial and proceeded to position three different insert thicknesses ranging from 10 mm to 12 mm, and example push forces were recorded. The new tool met all the design criteria, and the example results from the patient testing show potential in using the peak push force to identify the insert with the correct thickness.