Summary
No correlation was found between the 3 knee laxity tests during robotic testing; therefore, each test describes a unique measure of the joint and all 3 tests are needed for a complete knee exam.
Abstract
Historically, there has been debate on which type of laxity is of primary importance to knee stability. Patient satisfaction was correlated with the pivot shift test rather than with solely anterior translation in the early 2000’s suggesting that both components of knee stability, rotational and translational, are important in the integrity of the knee joint. The Varus/Valgus (VV) and the Dial Test describe knee rotation, and the Anterior/Posterior (AP) Test describes knee translation. The purpose of this study was to determine the correlation between these three tests during robotic knee testing.
Healthy subjects were placed within a robotic knee testing (RKT) device. The subject’s feet were attached to footplates and both thighs were clamped to limit femur motion. Clamps were placed over each patella with a downward force of 30 lbs. Three single-plane tests were run: AP translation, internal/external rotation, and VV rotation. Tibial motion relative to the femur was calculated during each test using an electromagnetic system. The coefficient of determination between each set of single plane tests was determined. This analysis was reported previously in an older version of the RKT. The same methods were used to test 12 patients with healthy knees on the latest version of the RKT which can provide a more precise measure of tibial motion.
In the earlier study, there was no correlation in knee laxity between the three tests. The R squared value for total AP translation versus total internal/external rotation was 0.001. The R squared values for total AP translation versus total VV rotation and total internal/external rotation versus total VV rotation were 0.017 and 0.059, respectively. Data analysis for the latest 12 patients is ongoing and will be completed prior to the meeting to see the level of correlation between the tests using the latest RKT.
These knee physical examination tests describe laxity independent from one another such that laxity in one test cannot be used to describe laxity found in the other two tests. Genetics determine rotational and translational ‘play’ or laxity in the knee. An injury can result in increased laxity by changing only the Dial Test or AP Test or VV Test. Since these tests are independent and each describes a unique feature of knee joint laxity, omitting one test may result in missing an injury specific to that test. Therefore, a complete knee examination requires an assessment of ALL three tests.