Three-dimensional knee analyzer validation by simple fluoroscopic study

Introduction: The complexity of the knee articulation makes its clinical evaluation extremely difficult. Insufficiency of existing instruments for knee evaluation prevents physicians from providing a diagnosis of injury and/or an evaluation of different treatments. To this end, our research group has developed a functional knee analyzer, which allows a three-dimensional evaluation of the knee in motion. The goal of this study is to scientifically validate the functional knee analyzer before using it in clinical setting. Materials and methods: The three-dimensional knee analyzer includes an orthoplastic exoskeleton attachment system, a kinematic tracking device, a screen for graphical display and a C⁺⁺ program with a user interface for calculating kinematic indices. A fluoroscopic study was performed on five healthy subjects with a mean age of 28. The experiment was set-up to determine the reduction of skin movement with respect to the underlying bone by using a knee exoskeleton attachment system. The root mean square (RMS) errors of markers movement about the abduction-X (RMSRx) and tibial rotation-Z (RMSRz) axes and displacement in the XZ plane (RMSpxpz) were calculated, once by placing markers directly on the skin and once on the exoskeleton attachment system. Results: Our results demonstrated that RMSpxpz, RMSRx and RMSRz were reduced by a factor of 6 (min 1.8, max 26), 4.3 (min 0.75, max 21) and 6.2 (min 2, max 26.4) on average, respectively, for four subjects out of five when the exoskeleton attachment was used.