Sparse contact femoral jig mechanism
A femur cutting jig mechanism (FCJM) is provided having a number N1 of spaced apart FCJM contact points that correspond to a number N1 of spaced apart femur contact points on at least one of a medial condyle, a lateral condyle, and a trochlear groove on the patient's knee. The FCJM contact points are positioned in contact with the knee contact points, and a cut bar mechanism is positioned in contact with the FCJM to provide a location and an angular orientation of a cut bar plane that is to be used to resection and remove a selected portion of the patient's, knee. The FCJM is removed from the patient's knee, and a selected portion of the patent's knee is resectioned and removed. The number N1 is at most 12 in some embodiments.
1. A cutting jig for positioning a femur cutting tool on a femur including a first condyle and a second condyle with a trochlear groove defined therebetween, the femur further including an intercondylar fossa, the cutting jig comprising:
a substrate including:
a first jig contact point oriented to contact the first condyle proximate the trochlear groove when the jig is positioned on the femur for a procedure;
a second jig contact point oriented to contact the second condyle proximate the trochlear groove when the jig is positioned on the femur for a procedure, the second jig contact point coronally spaced apart from the first jig contact point;
a third jig contact point proximate the first jig contact point, the third jig contact point oriented to contact the first condyle when the jig is positioned on the femur for a procedure;
a fourth jig contact point proximate the second jig contact point when the jig is positioned on the femur for a procedure, the fourth jig contact point oriented to contact the second condyle;
a fifth jig contact point oriented to contact the first condyle when the jig is positioned on the femur for a procedure, the fifth jig contact point posteriorly positioned relative to the first jig contact point;
a sixth jig contact point oriented to contact the second condyle when the jig is positioned on the femur for a procedure, the fifth jig contact point posteriorly positioned relative to the second jig contact point; and
a cut guide,
wherein the first, second, third, fourth, fifth, and sixth jig contact points and their placements on the femur are chosen to allow the cutting jig to be positioned on the femur in a stable location and orientation such that the trochlear groove's shape and the first and second condyles where the first, second, third, fourth, fifth, and sixth jig contact points contact the femur cooperatively constrain the cutting jig from posterior movement, and
wherein the first, second, third, fourth, fifth, and sixth jig contact points are determined using a plurality of two-dimensional MRI images or slices of an anatomical surface of the femur, with each MRI image or slice containing one or more spaced apart contact points between the anatomical surface of the femur and the cutting jig.
2. The cutting jig of claim 1 wherein at the least the first jig contact point is defined on a first curvilinear projection from the substrate.
3. The cutting jig of claim 2 wherein the first jig contact point and the second jig contact point are defined along the first curvilinear projection and wherein the first curvilinear projection defines a first semi-circle with a first radius.
4. The cutting jig of claim 3 wherein the third jig contact point and the fourth jig contact point are positioned along a first linear surface aligned with the first curvilinear projection.
5. The cutting jig of claim 3 wherein the fifth and sixth jig contact points are defined along a second curvilinear projection extending from the substrate, the second projection defining a second semi-circle with a second radius larger than the first radius.
6. The cutting jig of claim 5 wherein the first radius is about 15 millimeters and the second radius is about 18 millimeters.
7. The cutting jig of claim 1 further comprising a cutting guide support extending from the substrate, the cutting guide support positioned to retain the cutting guide.
8. The cutting jig of claim 7 wherein the cut guide is a slot configured to receive a saw to perform a resection of the femur, the slot positioned to orient the saw to cut transverse a femoral axis.
9. The cutting jig of claim 1 further comprising a first substrate portion and a second substrate portion, the first substrate portion substantially perpendicular the second substrate portion.
10. The cutting jig of claim 1 further comprising a plurality of apertures, wherein in each aperture is configured to receive a respective anchor to secure the jig to the femur.