Method and system for measuring the laxity of a joint of a human or an animal

#This is the § 371 U.S. National Stage of International Application No. PCT/DK2018/050003, filed Jan. 8, 2018, which was published in English under PCT Article 21(2), which in turn claims the benefit of DK Application No. PA 2017 70017, filed Jan. 11, 2017, which is incorporated herein in its entirety.

#The present invention relates to the determination of the laxity of a joint of a human or an animal, and in particular to such determination which can be performed in a well-defined and reproducible way.

#The ligaments of a joint play a critical role in stabilizing the joint. The stability of the joint, also referred to as the joint laxity, is therefore an indicator of the functioning of the ligaments. In order to assess the ligaments for injury, plan treatment or follow up after intervention, information about the laxity of the joint is therefore important. Such an evaluation of the laxity of a joint is also relevant e.g. during the process of the implementation of a knee prosthesis or the replacement of ligaments. In practise, this evaluation is often done by a doctor manually applying a force to a part of the body connected to the joint and manually sensing the resulting movement of the joint. However, such a determination is highly dependent on the experience of the person making the assessments.

#The method and system for determining the laxity of a joint of a human or an animal according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

#FIG. 1 is a flow-chart of a method according to the invention.

#FIG. 2 shows an example of a constructed 3D model of a bone based on a MRI image.

#FIG. 1 schematically shows a flow-chart of the method of determining the laxity of a joint of a human or an animal according to the present invention; more details of the method steps will be given in the following figures. The method comprises the following steps which will be described in details below: (A) providing at least one patient-specific geometrical model of at least one bone and/or at least one prosthesis comprised by the joint, (B) providing a series of actual images of the joint obtained while known loads were applied to the joint or to a part of the body connected to the joint, (C) registering the at least one patient-specific geometrical model onto the actual images, (D) based thereon calculate relative displacement and/or rotation of the at least one bone and/or at least one prosthesis as a function of the applied loads, and (E) based on the calculated relative displacement and/or rotation determine a measure of the laxity of the joint.

#The steps shown in FIG. 1 will each correspond to a part of a system according to an aspect of the invention.

#The at least one patient-specific geometrical model may e.g. be obtained from at least one medical image and/or at least one CAD model. FIG. 2 shows an example of how a 3D-model 1 can be constructed from digital images 2 (only one shown in the figure) obtained by a MRI scanner. The arrows in the figure schematically show which part of the contours in the digital image that matches the resulting bone contour in the model. FIG. 3 shows an example of a 3D model 3 of a prosthesis. FIG. 3.a shows the model as solid, and FIG. 3.b shows the same model as line drawing. The two different representations are given to show the features of the model as comprehensively as possible.