BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a femoral head with a guide wire and a counterbore reamer for preparation of the femoral head in accordance with the present invention;
FIG. 2 is a side view of a femoral head with a guide wire and guide post-of the present invention;
FIG. 3 is a view as in FIG. 2 with an oversize cutter slidingly engaged on the guide post for preliminary preparation of the femoral head in accordance with the present invention;
FIG. 4 is a view as in FIG. 3 with the oversize cutter performing a preliminary preparation of a femoral head in accordance with the present invention;
FIG. 5 is a view as in FIG. 4 with the oversize cutter withdrawn after a preliminary preparation of a femoral head in accordance with the present invention;
FIG. 6 is perspective view of an offset guide post of the present invention;
FIG. 7 is plan view from 7-7 of FIG. 6 of an offset guide post of the present invention;
FIG. 8 is a view of a femoral head with an offset guide post installed in a counterbore preparatory to installing an offset guide wire according to the present invention;
FIG. 9 is a view of a femoral head as in FIG. 8 with an offset guide post being used to install an offset guide wire according to the present invention;
FIG. 10 is plan view of a femoral head from 10-10 of FIG. 9 with an offset guide post installed in a counterbore and an offset guide wire according to the present invention;
FIG. 11 is a view as in FIG. 9 with a final cutter slidingly engaged on an offset guide post for final preparation of the femoral head in accordance with the present invention:
FIG. 12 is a plan view from 12-12 in FIG. 11 with the final cutter performing a final preparation of a femoral head in accordance with the present invention; and
FIG. 13 is a view as in FIG. 12 showing the final preparation of a femoral head in accordance with the present invention after removing the tooling.
DETAILED DESCRIPTION
FIGS. 1-13 show an embodiment of the apparatus and method of the present invention to enable an accurately positioned preparation of a femoral head for installation of a hip surfacing implant.
FIG. 1 shows a femur 1 with an upper portion of the proximal femur 3, a femoral neck 5, and a femoral head 7. Based on pre-operative planning, imaging and measurements in situ, an initial guide wire 11, has been placed in the femoral neck 5. The guide wire 11 is impacted or inserted into the femoral head 7 toward the axis of the femoral shaft 3 creating a guide wire bore 9. The guide wire bore 9 and guide wire 11 have a central axis A-A. Coaxial with the axis A-A, the guide wire bore 9 and guide wire 11, is a guide post counterbore 15 located centrally on the femoral head 7. The guide post counterbore 15 is created by the guide post reamer 13. The guide post reamer 13 is cannulated to fit over the guide wire 11 and is capable of rotation about the guide wire. The guide post reamer 13 has cutting features at its distal end to create the guide post counterbore 15 when rotated by suitable tools engaged on a proximal shaft region of the reamer. The guide post reamer 13 is engaged on and guided by the guide wire 11 and brought into contact with the femoral head 7. The reamer 13 is rotated and the guide post counterbore 15 is cut to a predetermined depth. The creation of the counterbore 15 is a preferred embodiment of a step in the method of the invention to establish a datum and to establish axis A-A in subsequent operations as a datum axis for the location of tools to conduct subsequent operations of the invention. The depth of the counterbore serves as a datum to control the depth of the cutter, as will be explained later, should a cutter depth control be desired by the surgeon. While shown as a counterbore in the form of a right circular cylinder, the present invention includes other types of datum location features and corresponding tooling to determine the axis A-A and the distance along axis A-A from a known point in the femoral head as are known in the art. For example, the datum feature could be frustro-conical rather than cylindrical or could be formed by a broach so as to provide surfaces other than a surface of revolution to provide anti-rotation or indexing features.
Following creation of the counterbore 15, the reamer 13 is removed, a cannulated guide post 16 is then placed over the guide wire 11, and inserted, as necessary, to engage the guide post 16 with the femoral head 7 by fully seating the guide post 16 in the counterbore 15, as shown in FIG. 2. Guide post 16 has a guide post central bore 18 that closely engages the outer diameter of guide wire 11 and a datum locating cylinder 17 with a major outer diameter d1 that is a slip-fit or slight interference fit in counterbore 15 to insure that guide post 16 is coaxial with guide wire 11 and axis A-A to accurately establish the datum determined by counterbore 15. Also coaxial with axis A-A is a guide post minor diameter d2 extending along the shaft 20 of the guide post 16. The transition between the guide post major diameter d1 and minor diameter d2 is a radial step 19 which will function to limit the travel of a tool slidingly engaged on diameter d2. Of course, should the datum locating features be other than a cylindrical counterbore 15, the datum locating cylinder 17 is suitably reconfigured to locate the appropriate datum features. Optionally, the cutting features of the reamer 13, may be incorporated in the guide post 16. In that instance the reaming operation is performed by the guide post 16 which remains in place after reaming.
FIG. 3 shows an oversize cutter 21 engaged on the shaft 20 of the guide post 16 in preparation for the initial oversize preparation of the femoral head. In FIG. 3 and subsequent figures, the initial oversize cutter 21, along with a final cutter 41 to be introduced later, are depicted in a configuration for making a cylindrical cut of the femoral head 7. While not shown, other shapes of revolution about an axis, most preferably a cutter of conical shape for producing a frustro-conical cut of the femoral head 7, are also possible. For any shape of cutter, an important aspect of the present invention is that the initial cutter may be oversize to allow assessment of the correct final cutting axis position and provide sufficient excess bone stock to allow a final preparation by offsetting the final cutting axis from the initial axis.
The oversize cutter 21 has a central bore 22 with diameter d4. Diameter d4 is slightly larger than the diameter d2 of the guide post shaft 20 and the cutter 21 is journaled on the shaft 20 and can also translate on the shaft 20. Thus the shaft 20 serves a journal and axial bearing for the cutter 21. The distal or cutting portion of the cutter 21 has cutting features and, in the instance of a cylindrical cutter, an inner diameter d3 that will determine the diameter of the resulting cut of the femoral head 7. The cutter 21 also has a shoulder 23 that provides a planar surface that will engage the cutter stop 19 of the guide post 16 as the cutter translates distally while making the cut. Because the datum locating cylinder 17 is located in the counterbore 15, the guide wire 11, the guide post 16 and the oversize cutter 21 are all coaxial with the axis A-A so that the resulting prepared surface of the femoral head 7 will be a solid of revolution about axis A-A.
Optionally, the guide post 16 may be eliminated and the guide wire 11 is used directly to guide the cutter 21 to rotate and translate about axis A-A. The cutter 21 may be journaled directly on the guide wire 11 with the diameter d4 being reduced to slidingly engage the guide wire.
The use of the oversize cutter is depicted in FIG. 4. While rotating the cutter with a suitable driver, the surgeon directs the oversize cutter 21 toward the proximal femur 1 to engage the femoral head 7 and perform the preparation. If control of the depth of the cut is desired, the depth is controlled by the engagement of the cutter upper surface 23 with the cutter stop 19 at a pre-determined height. This height is determined by the depth of the guide post counterbore 15, the length of the guide post 16 from its distal surface to the cutter stop 19 and the length of the cutter 21 from the surface 23 to the distal cutting end. The axial lengths of these components can be available in various lengths to control the depth of cut. The depth of the cut has been previously determined to insure that the head 7 is completely prepared and yet the cutter blade does not contact any undesired portions of the femoral neck 5.
The purpose of the oversize cutter 21 is to create an oversize preparation of the femoral head 7 to allow visual confirmation and physical measurements to determine if the axis A-A is the proper axis for a final preparation or if adjustment of the cutting axis is necessary. An oversize cutter 21 with a sufficient inner diameter d3 is selected by the surgeon to ensure that sufficient bone stock is allowed to offset or reposition the final preparation cutting axis and final cut if necessary.
Turning to FIG. 5, the oversize cutter 21, guide post 16, and guide wire 11 have been removed from the now prepared femoral head. The femoral head 7 now has an oversize prepared surface 25. If visual inspection and measurements indicate that the oversize prepared surface 25 is properly positioned with respect to the femoral neck and anatomical considerations, the surgeon can proceed to reinstall the guide wire 11 along with the guide post 16. The surgeon can then use a final size cutter to complete the preparation of this portion of the femoral head.
However, as previously mentioned, it is often the case that the initial pin position and subsequent oversize prepared surface 25 is not in the optimum position. An example is seen in FIG. 5 where the prepared surface 25 is centered too low on the femoral head 7 with the result that the surface creates an overhang of the neck designated by a distance l1. Because the initial cutter 21 was oversize, it is possible to correct this problem by reducing the diameter of the cutter and offsetting a guide post to create a new axis of revolution of the cutter. While the actual selection of the final cutter diameter and the degree of offset is a matter of the surgeon's discretion, it will be seen that in this instance, a new cutter diameter that is nominally of a diameter equal to d3 minus l1, and a translation of the guide post axis upward and parallel to the original axis A-A by a distance of l1 divided by 2, will result in a prepared surface that will preserve a maximum of bone structure, yet eliminate the undesired overhang of the head designated by the dimension l1.
FIG. 6 shows a tool according to an embodiment of the present invention to allow the offset placement of a secondary guide wire and to function as an offset guide post for a final cutter to provide correction of an initial placement of a guide wire that is in a less than optimal position. This tool is an offset guide post 31. Similar to guide post 16, it has a datum locating cylinder 34 with a major diameter d1 sized to fit in the guide post counterbore 15 in the femoral head 7 to mount the guide post 31 on the head and re-establish the axis A-A based on the counterbore datum. When in place on the head, the cylinder 34 is coaxial with the original axis A-A. The offset guide post 31 has an offset bore 33 having an inner diameter of the bore that allows passage of a new guide wire 37. The center line of this bore is offset from the center line A-A by a distance l2 and designated by axis A′-A′. Coaxial with axis A′-A′, is an extended bearing or tool guiding surface 36 having diameter d2′ on the proximal tool guiding portion of the offset guide post 31. As shown, an offset guide cutter stop 35 is provided by the transition from diameter d1 to diameter d2′. FIG. 7 shows a plan view of the offset guide post shown in FIG. 6.
FIG. 8 shows the offset guide post 31 mounted on a femoral head 7 by impacting the distal end defined by diameter d1 into the guide post counterbore 15. As previously noted, the datum locating cylinder 34 is now coaxial with the original axis A-A and the distal end of the offset guide post 31 engages the bottom of the counterbore 15 to establish a depth datum to allow control of the depth of the cut. During placement of the offset guide post 31, the surgeon rotationally orients the bearing or guide portion 36 about axis A-A to the desired angular orientation to achieve the proper direction of offset of the final preparation. In this instance, the guide 36 is positioned to offset the guiding section and consequently the cutter in the upward direction. Having achieved the proper angular orientation, a second guide wire 37 may be inserted through the offset bore 33 as shown in FIGS. 9 and 10 if desired. This guide wire 37 provides assurance that the offset guide post does not rotate and also provides a tool for defining the final preparation axis in additional surgical steps such as preparing the proximal portion of the femoral head and fitting the implant to the prepared femoral head. Optionally, the tool guiding surface 36 may be eliminated and the guide wire 37 may directly journal the final size cutter.
For a small offset, the location of the second guide wire 37 may overlap the existing guide wire bore 9, creating the possibility of play in the position of the guide wire when the offset guide post 31 is later removed. In this instance, the stability of the second guide wire 37 can be enhanced by making the diameter of the second guide wire 37 larger than the diameter of the guide wire bore 9 to create a suitable engagement with the bone and prevent movement of the pin.
Using the offset guide post 31 located on the datum established by the guide post counterbore 15, the surgeon may create a controlled offset of the tool guiding portion 36 provided by the minor diameter d2′ of the offset guide post 31 in a desired direction. While in the example depicted in FIGS. 1-13 only a single offset of a translation 12 is depicted to create the new axis A′-A′, it will be understood that the translation 12 may be any of a number of discrete offset distances. The tool guiding portion 36 may also incorporate an angle of rotation or angular offset such that axis A′-A′ may not be parallel to axis A-A and the axes either intersect or are skew. For convenience while performing surgeries, a kit of such tools 31 may be provided for the surgeon with different translational and angular offsets or combinations thereof to allow the surgeon flexibility in determining the translational and angular positioning of a final preparation cut.
FIGS. 11 and 12 show a final cutter 41 journaled on the guide 36 of the offset guide post 31 in preparation for making a final preparation cut on the femoral head 7. As previously discussed, the diameter of the final cutter d6 is smaller than the diameter d3 of the oversize cutter 21 as determined by the surgeon to remove desired areas of excess bone. In this example, the diameter d6 has been reduced by the distance l1 from the previous diameter d3. In conjunction with the offset of the offset guide post by distance l1 divided by 2 or l2, it can be seen that little or no material will be cut from the upper portion of the femoral head 7, while a relatively large amount of material designated in the prior figures by l1 will be removed from the cross-hatched area designated 43.
The operation of making a preparation with the final cutter 41 proceeds similarly to the operation described for the oversize cutter 21. The final cutter 41 has a central bore with diameter d5 journaled on the bearing or guide 36 and has an upper surface 42 that engages with the offset guide cutter stop 35 to determine the depth of cutting as the cutter 41 is rotated and translated distally along axis A′-A′ to make the final cut. Similar to the depth control features described for the initial preparation, guide post 16, the length from the distal end of the guide post 31 to the offset guide cutter stop 35 and the length from the cutter upper surface 42 to the distal end of the cutter can be varied to determine the depth of the cut to insure that a complete preparation is made and that the cutter does not travel too far in the distal direction and undercut the neck.
Following the completion of the final preparation cut, the final cutter 41, the offset guide post 31 and the guide wire 37 are removed from the proximal femur as shown in FIG. 13. The resulting final preparation of the femoral head is symmetrical about axis A′-A′. The prepared femoral head is now ready for additional steps required for installing a femoral head resurfacing implant. If desired, the guide wire 37 may be left in place or reinserted to serve as a tooling point for additional steps needing a guide wire. It will be understood that the various terms designated “final”, such as final preparation, are relative to the initial terms, such as initial preparation, and do not preclude subsequent preparations using the tools and methods of the invention or other types of preparations to further shape the femoral head.
Of course any combination of the above mentioned embodiments is contemplated by the present invention.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
Patent Application
20070299451
