Indexed tri-planar osteotomy guide and method
Methods and devices for performing an osteotomy produce a bone cut producing a multi-planar change in the alignment of a bone portion by rotating it relative to another bone portion.
1. A method of performing an osteotomy on a metatarsal bone having a proximal portion and a distal portion, the proximal and distal portions defining a first relative position between them, the method comprising:
determining a desired positional change between the proximal portion of the metatarsal bone and the distal portion of the metatarsal bone in at least two anatomic reference planes;
mounting a guide on the metatarsal bone;
establishing an osteotomy plane or rotational axis with the guide;
guiding a cutter in the osteotomy plane or about the rotational axis to produce cut surfaces in the metatarsal bone such that the distal portion of the metatarsal bone and proximal portion of the metatarsal bone are relatively rotatable, the cut surfaces being oriented to incorporate the desired positional change in the at least two anatomic reference planes;
rotating the distal portion of the metatarsal bone relative to the proximal portion of the metatarsal bone to a second relative position different from the first relative position; and
fixing the distal portion of the metatarsal bone and the proximal portion of the metatarsal bone relative to one another in the second relative position with the cut surfaces of the proximal portion of the metatarsal bone and the distal portion of the metatarsal bone abutting one another.
2. The method of claim 1 wherein determining a desired positional change between the proximal portion of the metatarsal bone and distal portion of the metatarsal bone in at least two anatomic reference planes comprises determining a desired positional change between the proximal portion of the metatarsal bone and the distal portion of the metatarsal bone in three anatomic reference planes.
3. The method of claim 2 wherein establishing an osteotomy plane or rotational axis with the guide comprises placing a pin in the metatarsal bone, the pin having a longitudinal axis coincident with the rotational axis.
4. The method of claim 3 wherein the cutter is engaged with the pin for rotation about the pin.
5. The method of claim 3 wherein the cutter is a saw blade, the method further comprising engaging a saw guide with the pin, the saw guide defining a plane normal to the rotational axis, and guiding the saw blade in the plane defined by the saw guide.
6. The method of claim 5 wherein guiding a saw blade comprises:
guiding the saw blade to cut the metatarsal bone under the pin;
advancing the pin so that it engages the proximal portion of the metatarsal bone and the distal portion of the metatarsal bone on opposite sides of the plane defined by the saw guide; and
continuing the cut to complete mobilizing the distal portion of the metatarsal bone relative to the proximal portion of the metatarsal bone, wherein rotating the distal portion of the metatarsal bone relative to the proximal portion of the metatarsal bone comprises rotating the distal portion of the metatarsal bone about the pin.
7. The method of claim 1 wherein mounting a guide on the metatarsal bone comprises:
placing the guide on the metatarsal bone;
aligning the guide relative to a first anatomic plane to constrain two rotational degrees of freedom; and
aligning the guide relative to an anatomic landmark to constrain a third rotational degree of freedom.
8. The method of claim 7 comprising aligning a portion of the guide with a joint between the metatarsal bone and an adjacent bone.
9. The method of claim 7 wherein aligning the guide relative to a first anatomic plane comprises aligning the guide in the sagittal plane and wherein aligning the guide relative to an anatomic landmark comprises aligning the guide relative to a longitudinal anatomic axis of the metatarsus.
10. The method of claim 1 wherein determining a desired positional change between the proximal portion of the metatarsal bone and the distal portion of the metatarsal bone in at least two anatomic reference planes comprises determining a desired angular change in an intermetatarsal angle and a desired angular change in a pronation angle.
11. The method of claim 1 wherein the guide includes a plurality of saw guiding features, each saw guiding feature corresponding to an osteotomy plane incorporating a different positional change in at least two of intermetatarsal angle, pronation, and plantar flexion, the method further comprising selecting one of the plurality of saw guiding features, and guiding a saw blade in the corresponding osteotomy plane.
12. The method of claim 11 wherein the plurality of saw guiding features comprise a plurality of slots, each slot configured to produce a unique combination of change in intermetatarsal angle and pronation.
13. The method of claim 12 wherein the guide is provided as a plurality of guides, each guide having a plurality of slots in which each slot produces the same change in intermetatarsal angle but a different change in pronation, the change in intermetatarsal angle produced by each guide differing from the change in intermetatarsal angle produced by each other guide.
14. The method of claim 1 wherein fixing the distal portion of the metatarsal bone and the proximal portion of the metatarsal bone comprises installing one or more fixation elements selected from the group consisting of pins, screws, and plates.