LAUSR

Accurate and reliable information about 3D knee joint laxity can prevent misdiagnosis and avoid incorrect treatments. Nevertheless, knee laxity assessments presented in the literature suffer from significant drawbacks. In this study, we developed and demonstrated the applicability of a novel methodology for measuring 3D knee laxity in vivo, combining robotics- and image-based technology. To measure tibiofemoral movements, four healthy subjects were placed on a custom-built arthrometer located inside a low dose biplanar x-ray system with an approximately 60° knee flexion angle. Anteroposterior and mediolateral translation as well as internal and external rotation loads were subsequently applied to the unconstrained leg, which was placed inside a pneumatic cast boot. Bone contours were segmented in the obtained x-rays, to which subject-specific bone geometries from MRI scans were registered. Afterwards, tibiofemoral poses were computed. Measurements of primary and secondary laxity revealed considerable interpersonal differences. Regarding secondary laxity, a relationship was observed between AP translations and IE rotations. The method differs from those available by the ability to accurately track secondary laxity of the unrestricted knee and to apply coupled forces in multiple planes. Our methodology overcomes aforementioned complications and allows the acquisition of more accurate and reliable knee laxity information in three DOF.