Dr. Sandra Schultz (Kinesiology) received new funding from the North Carolina Biotechnology Center for the project “Optimization of a Precision Measurement Solution for a Tri-Axial Knee Arthrometer.” Dr. Randy Schmitz and Dr. Minjeong Kim are co-principal investigators on the project.
Knee laxity defines the looseness of the ligaments that stabilize the knee joint. There are natural variations in knee laxity among individuals, and individuals with greater laxity are more likely to suffer both acute and chronic knee injuries. Once injury occurs, the amount of knee joint laxity can determine if a ligament injury has occurred, [e.g. anterior cruciate (ACL) or medial collateral (MCL) ligament injury]. Thus, assessing knee joint laxity can help clinicians screen individuals who may be at greater risk for knee injury (allowing effective interventions to be delivered), diagnose ligament injuries, confirm ligament integrity post-surgery and during rehabilitation, and monitor joint health over time.
However, clinicians lack confidence in currently available tools to measure knee joint laxity (a.k.a. knee arthrometers), more often relying on their hands to make this assessment. While “manual stress tests” can effectively assess gross joint instability (when a ligament is fully ruptured), they are too subjective and imprecise for the purposes of injury risk screening, diagnosing partially torn ligaments, and serial assessments of joint health over time.
Criticisms of current devices are that they are too limited in scope (e.g. only measure knee laxity in one plane of motion), and lack accuracy and reproducibility because they are too difficult to use (require too much time and training), and do not adequately stabilize the limb within the device. Our overall objective is to develop a commercially viable instrumented knee arthrometer that accurately measures knee laxity in 3 planes of motion in 5 minutes or less with limited training. In prior funded work, we developed the mechanical aspects of the prototype to stabilize the thigh and mechanically manipulate the lower leg to load the knee in 3 planes of motion.
The researchers’ objective for this proposal is to develop and optimize the measurement system that will be integrated into the mechanical prototype to obtain accurate and repeatable measures of knee joint laxity that are reflective of true bone (joint) motion. Their approach will be to rigorously test our measurement system against the gold standard of true joint motion by: 1) identifying the candidate sensors that offer the greatest precision at the lowest cost to meet our measurement needs, 2) determining the sensor array on the device (and limb as needed) that best approximates true bony motion as compared to sensors embedded in the bones of cadaver limbs, and 3) confirming validity and reliability of the final measurement solution in 5 additional cadaver limbs and 10 human participants.
The researchers’ expectation upon completion of this work is that we will have successfully developed and optimized a measurement system that consistently meets our accuracy criteria (i.e. 95% Limits of Agreement) of 1±1mm for AP translations, 2±1o for VV laxity, and 2±2o for IER laxity, and our intra- and inter-tester reliability criteria of ICCs > .85 and SEMs < 0.5 mm for AP translations, and < 0.5o and 1.0o for frontal and transverse plane rotations. Successful completion of this work is a critical step in addressing the concerns of prior devices, thereby improving the clinical utility of knee arthrometers, strengthening consumer confidence; and attracting potential licensees, investors, and adopters. This will then pave the way for future feasibility testing with clinicians (putting the device in the hands of end users) to confirm clinical utility and obtain final feedback prior to moving toward commercialization.
