Prosthetic knee implant with modular augment

A modular prosthetic knee implant system includes a femoral component, a femoral stem, a femoral stem collar, an augment and a bolt. The modular prosthetic knee system can be assembled in different ways. If assembled without the augment, the stem is at a valgus angle. If assembled with the augment, the stem is at a neutral angle. The stem collar has an inferior surface that is angled with respect to its superior surface, and the augment has a superior surface that is angled with respect to its inferior surface. The components also include mating anti-rotation members to fix the relative positions of the members.

BACKGROUND OF THE INVENTION

The present invention relates to modular components of a prosthetic joint, and more particularly to modular components of a prosthetic knee joint.

The knee joint basically consists of the bone interface of the distal end of the femur and the proximal end of the tibia. Appearing to cover or at least partially protect this interface is the patella, which is a sesamoid bone within the tendon of the long muscle (quadriceps) on the front of the thigh. This tendon inserts into the tibial tuberosity and the posterior surface of the patella is smooth and glides over the femur.

The femur is configured with two knob like processes (the medial condyle and the lateral condyle), which are substantially, smooth and articulate with the medial plateau and the lateral plateau of the tibia, respectively. The plateaus of the tibia are substantially smooth and slightly cupped thereby providing a slight receptacle for receipt of the femoral condyles.

When the knee joint is injured whether as a result of an accident or illness, a prosthetic replacement of the damaged joint may be necessary to relieve pain and to restore normal use to the joint. Typically the entire knee joint is replaced by means of a surgical procedure, which involves removal of the ends of the corresponding damaged bones and replacement of these ends with prosthetic implants. This replacement of a native joint with a prosthetic joint is referred to as a primary total-knee arthroplasty.

Prosthetic knee implants include femoral implants that are designed to be affixed to the distal end of the resected femur. A known modular femoral implant is illustrated inFIGS. 1-3. As there shown, the modular femoral implant10includes a femoral component12, an elongate stem member14, bolt16(shown in FIG.3), and a femoral stem collar18.

The modular femoral component12includes two spaced condylar portions20,22with articulating surfaces24,26to engage an articulating surface of a tibial implant (not shown). On the proximal side of the femoral component12, the two condylar portions20,22are connected by an intercondylar box or pad28. The intercondylar box or pad28has a pair of substantially vertical side walls30,32that are connected by a top or superior seating or mounting platform34. The pad mounting platform34is generally planar, and has an opening36(seeFIG. 3) that extends through the pad to define an open channel. The bolt16extends through the channel from the distal side of the femoral component and through the opening36to be connected to a female threaded opening in the femoral stem14.

The femoral stem collar18has a threaded male portion37(FIG. 3) for connection to a distal female threaded end of the stem member14. Thus, the stem member14, stem collar18and femoral component12can be assembled to secure the stem member14to the femoral component12. With this design, a variety of styles and sizes of stem members and femoral components can be assembled to best suit the patient's anatomy and joint conditions. For example, an implant kit could include a set of different sizes of stem members with outer surfaces adapted for cemented implantation as well as with fluted outer surfaces.

As shown inFIG. 2, when assembled, the stem member14is typically angled in a medial direction. The angle is labeled inFIG. 2as α. The angle α is between the axis40of the stem member14and a line41perpendicular to the plane42of the seating or mounting platform34of the intercondylar pad or box28. The angle α corresponds with the valgus angle when the implant assembly is implanted; the valgus angle is defined as the angle between the center line of the femur and the vertical axis connecting the distal femur and the center of the femoral head; the center line of the femur will correspond with the axis40of the stem member14, and the vertical axis connecting the distal femur and the center of the femoral head will correspond with the line41.

In the illustrated prior art modular assembly, the angle α is set by the structure of the femoral stem collar18. The femoral stem collar has a superior side or surface33lying in a plane and an inferior side or surface35lying in a plane that is not parallel to the plane of the superior side or surface33. The inferior surface of the collar is angled, defining an obtuse angle (90°+α) with the axis40of the stem. In typical implant sets, a plurality of femoral stem collars18are provided, shaped so that the angle α can be set to be any one of a number of angles. In one implant set available from DePuy Orthopaedics, Inc. of Warsaw, Ind., the femoral stem collars are shaped to define angles α of either 5° or 7°, but angles α may be in a typical range of 5-9°.

Although not shown inFIGS. 1-3, the illustrated prior art stem collar18has a central bore to receive part of the bolt16. The central bore has a central longitudinal axis defining an obtuse angle with at least one of the plane of the superior side33and inferior side35of the stem collar18.

To ensure that the angle α remains in the illustrated orientation, the intercondylar box or pad28typically has a pair of anti-rotation tabs46,48(seeFIGS. 1 and 3) that mate with opposing flats50,52on the femoral stem collars18.

As commercially supplied, the stem members14and stem collars18are supplied as a unit, connected together prior to being supplied to the surgeon.

Reference is made to the implant systems disclosed in U.S. Pat. Nos. 5,683,472 and 6,126,693, which are both incorporated by reference herein in their entireties.

Although the illustrated prior art system is versatile and economic, in some instances, it may be desirable to implant the femoral components with a neutral valgus angle.

SUMMARY OF THE INVENTION

The present invention provides an enhancement to prior art implant systems by allowing for setting the femoral stem member of a modular implant assembly at a neutral valgus angle.

In one aspect, the present invention serves this purpose by providing a modular prosthetic knee implant system comprising a femoral component, a stem member, a stem collar and an augment. The femoral component includes a pair of condylar portions and an intercondylar portion having a mounting platform. The stem collar has a superior side and an inferior side. In addition, the augment has a superior side and an inferior side. The femoral component, stem member and stem collar are capable of being assembled so that the stem member is in a first fixed angular relationship with the mounting platform. The femoral component, stem member, stem collar, and augment are also capable of being assembled so that the stem member is in a second fixed angular relationship with the mounting platform.

In another aspect, the present invention provides a modular prosthetic knee implant system comprising a femoral component, a stem member, a stem collar, and an augment. The femoral component has a pair of condylar portions and an intercondylar portion. The intercondylar portion has a mounting platform; at least part of the mounting platform lies in a plane. The stem collar has a superior side and an inferior side; at least part of the superior side and at least part of the inferior side lie in separate non-parallel planes. The stem collar also has a bore extending from the superior side to the inferior side; the bore has a central longitudinal axis that defines an obtuse angle with at least one of the plane of the superior side and the plane of the inferior side of the stem collar. The augment has a superior side and an inferior side; at least part the superior side and at least part of the inferior side of the augment lie in separate non-parallel planes. The augment also has a bore extending from the superior side to the inferior side; the bore has a central longitudinal axis that defines an obtuse angle with at least one of the plane of the superior side and the plane of the inferior side. The stem collar, augment and mounting platform of the femoral component further include mating anti-rotation members.

In another aspect, the present invention provides a modular augment for use with a prosthetic knee implant. The modular augment has a body with a superior side and an inferior side. At least a portion of the superior side of the augment lies in a superior plane. At least a portion of the inferior side of the augment lies in an inferior plane. A bore extends from the superior side to the inferior side of the augment. The bore has a central longitudinal axis that defines an obtuse angle with at least one of the superior plane and inferior plane.

In another aspect, the present invention provides a prosthetic knee implant comprising a femoral component, an augment, a stem collar, a stem and a bolt. The femoral component includes a pair of condylar portions and an intercondylar portion having a mounting platform with an opening. The augment has an inferior side on the mounting platform of the femoral component and a superior side; the augment also has a bore extending from the superior side to the inferior side. The stem collar has an inferior side on the superior side of the augment and a superior side; the stem collar also has a bore extending from the superior side to the inferior side and aligned with the bore of the augment. The stem member extends outward from the superior side of the stem collar. The bolt extends through the opening in the mounting platform of the intercondylar portion of the femoral component, through the bore of the augment and the bore of the stem collar to the stem member.

DETAILED DESCRIPTION OF THE INVENTION

A femoral stem augment incorporating the principles of the present invention is illustrated inFIGS. 4-12at60. The femoral stem augment60of the present invention may be used with commercially available prosthetic knee components, as shown in FIGS.8-12, where the same reference numbers for prior art components and features of components are used as were used above in describing the prior art illustrated inFIGS. 1-3.

As shown inFIGS. 4-7, the femoral stem augment60comprises a body61having a superior side62and an inferior side64. As shown inFIGS. 6-7, the superior side62of the augment60lies in a superior plane and the inferior side64lies in a non-parallel inferior plane. The femoral stem augment has a central opening66in the superior side62, an enlarged-diameter opening67in the inferior side64, a pair of inferior anti-rotation flats68,69and a pair of superior anti-rotation tabs70,71.

As shown inFIGS. 4-5, the illustrated femoral stem augment60has an overall octagonal shape, in plan view, as illustrated inFIGS. 4-5. However, it should be understood that this shape is provided for purposes of illustration only. The present invention is not limited to any particular shape of femoral stem augment60unless expressly called for in the claims.

In elevation, the illustrated femoral stem augment60has a wedge shape, as shown inFIGS. 6-7. As there shown, the superior surface62of the augment60defines an angle θ with the inferior surface64. The angle θ corresponds with one of the valgus angles provided by the femoral stem collars18. For example, if an implant kit includes femoral stems and collars18defining angles of 5° and 7°, then the stem augment60should be provided to define a counter angle of either 5° and 7°. Although a kit could include stem augments60of both angles, only one set of augments with one angle should be necessary since the kit would generally include a complete set of stem members in both the 5° and 7° sizes.

In the illustrated embodiment, a bore or channel72extends between the apertures or openings66,67of the femoral stem augment. The bore or channel72has a superior cylindrical portion73and an inferior frusto-conical portion74. The illustrated frusto-conical portion74defines a countersink at the opening67in the inferior side64of the augment60. The illustrated channel72has smooth inner walls. A bolt75can extend through this channel72to connect to the prior art femoral stem collar18. The bolt75is similar to the bolt16of the prior art, but is slightly longer to accommodate the extra distance provided by the femoral stem augment60.

As shown inFIG. 7, the bore or channel72has a central longitudinal axis90that defines an obtuse angle with at least one of the superior plane92and inferior plane94of the augment. As shown inFIG. 14, when the augment60is assembled with the stem collar18, the bores of the two components share a single co-linear central longitudinal axis90that also defines an obtuse angle with respect to the plane of the inferior surface33of the stem collar18.

The anti-rotation tabs70,71of the illustrated femoral stem augment60define parallel flat surfaces76,78. These two parallel flat surfaces76,78are positioned opposite to one another in the illustrated embodiment, and are spaced by a distance slightly greater than the distance between the flats50,52of the femoral stem collars18, and substantially equal to the distance between facing opposing surfaces of the anti-rotation tabs46,48of the intercondylar pad or box28. Thus, when the components are assembled as shown inFIGS. 9-12, the flats50,52of the femoral stem collars18are received between the parallel flat surfaces76,78; these flats50,52,76,78prevent relative rotation between the femoral stem collar18and the femoral stem augment60.

The inferior anti-rotation flats68,69of the illustrated femoral stem augment60are defined by undercuts80,82in the femoral stem augment60beneath the tabs70,71. The inferior anti-rotation flats68,69are generally parallel to each other, and are positioned opposite to one another in the illustrated embodiment. The undercuts80,82are aligned with the tabs70,71, each undercut lying between one tab and the inferior plane94of the body61of the augment.

The distance between the inferior anti-rotation flats68,69is substantially equal to the distance between the flats50,52of the femoral stem collars and slightly smaller than the distance between facing opposing surfaces of the anti-rotation tabs46,48of the intercondylar pad or box28. Thus, when the components are assembled as shown inFIGS. 9-12, the anti-rotation flats68,69are received between the facing surfaces of the anti-rotation tabs46,48of the intercondylar box or pad28, and the tabs70,71of the femoral stem augment60overlie the tabs46,48of the intercondylar box or pad28.

The other components of the femoral implant may be commercially available ones. The femoral stem members14, femoral collars18and femoral components12, as well as the tibial and patellar implants, can be those commercially available from DePuy Orthopaedics, Inc. of Warsaw, Ind., sold as the P.F.C.® SIGMA and P.F.C.® SIGMA RP Knee System. Typically, a modified system would include all of the standard elements of the currently available P.F.C.® SIGMA and P.F.C.® SIGMA RP Knee System, along with standard augments, and with standard variations in size and surface finishes. The modified system would also include one or more stem augments60defining an angle θ of corresponding with one of the angles α. However, it should be understood that the present invention is not limited to any particular knee system unless expressly limited by the claims.

In use, the surgeon can prepare the proximal end of the tibia and distal end of the femur in the standard manner, and resect these bones in the standard manner to receive the prosthetic components. As part of this process, the surgeon can ream the femoral intramedullary canal to receive the proximal end of the stem member. If the patient's anatomy is standard, the surgeon can assemble the prior art components as shown inFIGS. 1-3, with the femoral implant defining a valgus angle of 5°-9°. If the patient's anatomy makes such a standard implant undersirable, the system of the present invention has the versatility to allow the surgeon to intraoperatively assemble a femoral implant with a neutral axis, that is, one in which the central longitudinal axis40of the stem14is perpendicular to the plane of the superior seating or mounting platform34of the intercondylar box28.

The assembly of the femoral implant with a neutral axis is shown at100inFIGS. 9-14. The components12,14,18,60and75may be assembled as follows. First, the stem members14and stem collars18may be assembled in a standard manner prior to the kit being supplied to the surgeon, such as with a retaining ring. This same stem/collar sub-assembly can be used whether the implant system will be used to define a valgus angle or whether a neutral axis is desired.

If a neutral axis is desired and the stem augment60of the system has an angle θ of 5°, then a stem/collar sub-assembly with an angle α of 5° is selected. The length and other characteristics of the stem member, such as whether it is fluted or has a particular surface finish, are selected as well.

The stem augment60can then be positioned on top of the mounting or seating platform34of the intercondylar box28between the stem/collar sub-assembly and the femoral component12. The stem augment60is aligned so that the anti-rotation surfaces68,69of its undercuts80,82are received against the tabs46,48of the intercondylar box28to stabilize and prevent relative rotation between the stem augment60and the femoral component12. The inferior surface64of the augment rests against the superior surface of the mounting platform34. The stem/collar sub-assembly is placed with the inferior surface33of the stem collar18against the superior surface62of the augment. The elements14,18,60are assembled so that the flats76,78of the tabs70,71of the augment are juxtaposed with the flats50,52of the stem collar18to prevent relative rotation between the stem collar18and the augment60. To secure the components12,14,18,60together in the configuration shown, the bolt75is inserted from the inferior side of the intercondylar box28up through an opening in the mounting surface34, through the openings66,67and channel70of the augment, through the central bore88of the stem collar18and up into a threaded bore in the stem14.

Although in the illustrated embodiments relative rotation is prevented through the use of flats and tabs, it should be understood that the invention is not so limited. Any form of mating anti-rotation devices could be used, and the invention should not be construed as being limited to the use of flats and tabs unless expressly called for in the claims. For example, pegs and mating holes could be used.

It should be understood that the same system could be used for patient's requiring a standard valgus angle. The surgeon can decide intraoperatively to assemble the femoral component with a stem/collar sub-assembly without using the augment60. Thus, the system of the present invention provides versatility to the surgeon.

The augment60of the present invention can be made of any conventional material for orthopaedic implants, such as cobalt-chrome steel or titanium, or any other material that is in current orthopaedic use or becomes used in orthopaedic applications. The augment60can be made using standard manufacturing techniques, such as machining.

While only a specific embodiment of the invention has been described and shown, it is apparent that various alternatives and modifications can be made thereto. Moreover, those skilled in the art will also recognize that certain additions can be made to these embodiments. It is, therefore, the intention in the appended claims to cover all such alternatives, modifications and additions as may fall within the true scope of the invention.