Technical note: MRI device for active stress of the knee. The practical approach and preliminary data.

PURPOSE: The aim of this study was to test the potential application of a new nonmagnetic device capable of diagnostically evaluating stress of the knee joint during magnetic resonance imaging (MRI) investigation. MATERIALS AND METHODS: The Knee Loader prototype was applied to an MRI scanner with a 1.5-T superconducting magnet. Twenty healthy subjects were assessed in both baseline conditions and again after applying a known amount of force (in kg) to various joints. Standard MR techniques were employed. The degree of anterior and posterior tibial translation and variations in the width of the rim in varus and valgus were measured in millimetres. RESULTS: In 12 cases, the anterior drawer test demonstrated a rest-stress variation between 0 and 2 mm, and in two cases, the posterior drawer test was between 1 and 3 mm. In the four cases assessed at valgus angulations and the two cases assessed at varus angulations, the opening of medial and lateral compartment was between 1 and 2 mm. CONCLUSIONS: The preliminary data regarding this new MR method, performed using the Knee Loader prototype, demonstrate that it is possible to obtain functional images of the knee comparable with those obtained by traditional radiological techniques. Its potential advantage lies in the fact that, given the absence of ionising radiation, the investigation can be repeated as necessary, ensuring anatomical visualisation of all joint components under stress.