Joint prosthesis with positionable head

A prosthesis assembly in one embodiment includes a stem configured to be implanted in a bone and including a first coupling portion, a head having a bearing surface configured to mate with at least one of a natural opposing joint component and a prosthetic opposing joint component, the head further having a second coupling portion, a coupler including a third coupling portion and a fourth coupling portion, the third coupling portion configured to couple with the second coupling portion, and an insert including (i) a fifth coupling portion configured to couple with the fourth coupling portion in any of a plurality of rotational orientations in combination with any of a plurality of roll angles and any of a plurality of pitch angles, and (ii) a sixth coupling portion configured to couple with the first coupling portion only when the insert assumes a predetermined rotational orientation with respect to the stem.

FIELD

The present disclosure relates to joint prostheses, and particularly to prostheses having articulating head components. More specifically, the disclosure relates to a system for achieving variable positions for the head component of a joint prosthesis relative to a bone-engaging portion of the prosthesis.

BACKGROUND

Repair and replacement of human joints, such as the knee, shoulder, elbow and hip, has become a more and more frequent medical treatment. Longer life spans mean that the joints are subjected to wear and tear over an extended period of time. Additionally, participation in sports activities results in a greater likelihood of serious joint injuries. Treatment of injuries, wear, and disease in human joints has progressed from the use of orthotics to mask the problem, to fusion of the joint, to the use of prostheses to replace the damaged joint component(s).

As the success rate for total or partial joint replacements has increased, so too has the need for modularity and universality in the joint prosthesis. Patient variety means that no single size or configuration of joint prosthesis provides optimum results for each patient. The physical dimensions of a patient's joint components vary, as do the bio-mechanic relationship between the components within a particular joint. By way of example, in a shoulder prosthesis, the relationship between the articulating humeral and glenoid components can be significantly different between patients. These relationships are especially important where only one component of the joint is being replaced and must integrate with the existing natural opposing joint component.

For instance, in many shoulder surgeries, only the humeral component is replaced, leaving the glenoid component intact. In this case, it is imperative that the articulating surface of the humeral component match the articulating surface of the glenoid component as perfectly as possible, both statically and dynamically. With a typical humeral prosthesis, version and inclination are adjusted by the geometry of the head of the prosthesis. In other words, certain pre-determined head geometries are available that can be selected for a mating glenoid component. Unless a virtually infinite variety of pre-determined head geometries are maintained in inventory, the resulting humeral prosthesis will rarely provide an optimum fit with the glenoid component of the shoulder joint.

In a typical surgical procedure, a trial component is used to determine the optimum component configuration for the permanent prosthetic device. In most cases, the surgeon is able to make a selection of components and configurations that fits the joint in an acceptable manner. In some cases, however, the functionality of the fit cannot be fully assessed until the surgery is completed and the patient has had an opportunity to utilize the repaired joint. In some cases, a revision surgery is necessary to replace a prosthetic device that is not optimally sized or configured for the particular patient. One type of revision surgery requires removal of the entire prosthesis from the bone and replacement with a different prosthesis.

There is a significant need for a joint prosthesis that is both modular and universal. A further need exists for a prosthesis that is easily manipulated during the surgery and capable being configured in a nearly infinite number of version and inclination angle combinations. Additionally, a need exists for a prosthetic device that is easily modified during a revision surgery. Yet a further need exists for a prosthetic device that is modifiable during a revision surgery without the need to completely remove the entire prosthetic assembly from the bone of the patient.

SUMMARY

A method and assembly for achieving variable positions of a head component of a joint prosthesis relative to a bone-engaging portion of the prosthesis is disclosed. In a one embodiment, a prosthesis assembly includes a stem configured to be implanted in a bone and including a first coupling portion, a head having a bearing surface configured to mate with at least one of a natural opposing joint component and a prosthetic opposing joint component, the head further having a second coupling portion, a coupler including a third coupling portion and a fourth coupling portion, the third coupling portion configured to couple with the second coupling portion, and an insert including (i) a fifth coupling portion configured to couple with the fourth coupling portion in any of a plurality of rotational orientations in combination with any of a plurality of roll angles and any of a plurality of pitch angles, and (ii) a sixth coupling portion configured to couple with the first coupling portion only when the insert assumes a predetermined rotational orientation with respect to the stem.

In a further embodiment, a prosthesis assembly kit includes at least one stem configured to be implanted in a bone, the at least one stem including a keyed stem coupling portion, a plurality of heads, each of the plurality of heads having a bearing surface configured to mate with at least one of a natural opposing joint component and a prosthetic opposing joint component, each of the plurality of heads further having a head coupling portion, at least one first coupler including an upper coupling portion and a lower coupling portion, the upper coupling portion configured to couple with the head coupling portion of each of the plurality of heads, and at least one insert including (i) a non-keyed insert coupling portion configured to couple with the lower coupling portion of each of the at least one first couplers in any of a plurality of rotational orientations in combination with any of a plurality of roll angles and any of a plurality of pitch angles, and (ii) a keyed insert coupling portion configured to couple with the keyed stem coupling portion of each of the at least one stems.

In yet another embodiment, a method of forming a prosthesis includes implanting a stem in a bone, the stem including a first coupling portion, determining a desired orientation of a head with respect to the stem, coupling the head with a first coupling portion of a coupler, coupling a second coupling portion of the coupler with an insert, aligning a key member of the coupled insert with the implanted stem, and coupling the aligned insert with the implanted stem.

The above-noted features and advantages, as well as additional features and advantages, will be readily apparent to those skilled in the art upon reference to the following detailed description and the accompanying drawings.

Corresponding reference characters indicate corresponding parts throughout the several views.

DETAILED DESCRIPTION

FIG. 1depicts a perspective view of a humeral prosthesis assembly100. The assembly100is the humeral component of a shoulder prosthesis that can be implanted in the humerus bone of a patient for articulating engagement with the natural glenoid or with a glenoid prosthesis. The assembly100includes a stem102configured to be implanted within the humerus bone in an acceptable manner. The assembly100further includes an insert104, a coupler106and an articulating head component108.

With further reference toFIGS. 2-4, the stem102includes a shaft110and a platform area112. The platform area112includes an upper surface114that faces toward the glenoid component of the joint when the stem102is implanted within a patient. The upper surface114defines a tapered bore116that includes a key member118.

The insert104, shown inFIGS. 1,5, and6, includes an outer wall120which generally tapers from an upper portion122to a lower portion124. A tapered bore126opens to the upper portion122and a threaded bore128opens at one end to the lower portion124and opens at the other end to the tapered bore126. A key member130is located near the lower portion124.

The coupler106includes an upper coupling portion132and a lower coupling portion134joined by a middle portion136as shown inFIGS. 7 and 8. The upper coupling portion132includes a bore138and a tapered outer wall140. The middle portion136includes a shoulder portion142which tapers inwardly from the tapered outer wall140to a neck portion144. The lower coupling portion134is bulbous shaped when viewed in profile (FIG. 7) and circular when viewed in plan (seeFIG. 8).

Referring toFIGS. 1 and 9, the articulating head component108includes an outer articulating surface148, which is shaped to articulate with a glenoid component, and a lower surface150. The lower surface150includes a protuberance152defining a tapered bore154. A recessed area156extends between the protuberance152and a lip158which circumscribes the lower surface150.

Assembly of the humeral prosthesis assembly100in one embodiment may be performed once the stem102has been implanted within the bone of a patient. A trial (not shown) is used to determine the head size and the version and inclination angle combination of the head that provides the desired joint configuration. The coupler106may then be joined with the articulating head component108of the desired size by aligning the tapered bore154with the upper coupling portion132as shown inFIG. 10.

The tapered bore154and the outer wall140of the upper coupling portion132in this embodiment have a five degree taper. The tapered bore154and the outer wall140thus provide for a Morse taper coupling. Accordingly, movement of the articulating head component108in the direction of the arrow160onto the upper coupling portion132provides the configuration ofFIG. 11. The articulating head component108and the coupler106are then firmly coupled by impacting the articulating head component108onto the coupler106.

With reference toFIG. 12, the lower coupling portion134of the coupler106is then aligned with the tapered bore126of the insert104and the articulating head component108and the coupler106are moved in the direction of the arrow162. Insertion and impacting of the lower coupling portion134within the tapered bore126results in the configuration ofFIG. 13. Specifically, the lower coupling portion134has a diameter that is larger than the diameter of the tapered bore126at a location spaced apart from the upper portion122of the insert104. Thus, while a Morse taper coupling is not formed, the lower coupling portion134may be firmly secured within the tapered bore126by application of sufficient force. Preferably, the force used to secure the lower coupling portion134within the tapered bore126is greater than the force used when forming a Morse taper coupling.

Once the head108, the coupler106and the insert104have been coupled, the lower portion124of the insert104is aligned with the tapered bore116as shown inFIG. 14. The key member130and the key member118are configured such that the lower portion124may be fully inserted into the tapered bore116in a single rotational configuration. Accordingly, the insert104must be rotated as necessary to align the key member130and the key member118. Consequently, the axis of the bore116is collocated with the axis of the insert104.

The tapered bore116and the outer wall120of the insert104in this embodiment have a ten degree taper. The tapered bore116and the outer wall120thus provide for a Morse taper coupling. Accordingly, movement of the insert104in the direction of the arrow164into the tapered bore116provides the configuration ofFIG. 15. The insert104and the stem102are then firmly coupled by impacting the articulating head component108to force the articulating head component108, the coupler106and the insert104toward the stem102.

Alternatively, the coupler106and the insert104may be positioned with the implanted stem102prior to coupling the head108with the coupler106. The head108is then positioned and coupled with the previously positioned coupler106and the insert104. This alternative may be used in rescission surgeries to allow for a smaller incision to be used to access the surgical site.

FIG. 15depicts a configuration wherein the axes of the tapered bore154of the articulating head component108, the coupler106, the insert104and the tapered bore116are substantially aligned. Because the articulating head component108and the coupler106form a Morse taper coupling as discussed above, the articulating head component108will assume a specific axial alignment with respect to the coupler106when the articulating head component108is coupled with the coupler106. Likewise, because the insert104and the stem102form a Morse taper coupling as discussed above, the insert104will assume a specific axial alignment with respect to the stem102when the insert104is coupled with the stem102.

Therefore, the axial alignment of the articulating head component108with respect to the stem102may be established by controlling the axial alignment of the coupler106with the insert104. Moreover, the key members118and130establish a specific rotational alignment of the insert104with respect to the stem102. Therefore, the rotational orientation of the articulating head component108with respect to the stem102may be established by controlling the rotational alignment of the coupler106with the insert104. Accordingly, the desired axial and rotational alignment of the articulating head component108with respect to the stem102may be established by controlling the rotational and axial alignment of the coupler106with the insert104.

Rotational and axial alignment of the coupler106with the insert104is discussed more fully with initial reference toFIG. 16.FIG. 16depicts the geometric center170of the lower coupling portion134. The lower coupling portion134is formed such that the diameter of the lower coupling portion134along a plane that includes the geometric center170and is located between the axes172and174is greater than a diameter of the tapered bore126at a location between the upper portion122of the insert104and the bottom of the tapered bore126.

Accordingly, the coupler106may be coupled with the insert104with any axial or rotational alignment so long as the lower coupling portion134is oriented within the tapered bore126such that a plane that includes the geometric center170, and is perpendicular to the axis176of the insert104, is located between the axes172and174.

By way of example, the axis180of the coupler106is aligned with the axis170(the axis180is depicted as offset from the axis170inFIG. 16for purpose of clarity). Additionally, the plane182, which includes the geometric center170, is perpendicular to the axis176of the insert104and is located between the axes172and174. Accordingly, the coupler106and the insert104may be coupled in the configuration shown inFIG. 16.

FIG. 17shows the coupler106pivoted in a direction away form the key member130, thereby generating an angle a between the axis180and the axis170. Nonetheless, the plane182, which includes the geometric center170and is perpendicular to the axis176of the insert104, is still located between the axes172and174. Accordingly, the coupler106and the insert104may be coupled in the configuration shown inFIG. 17. Similarly, the coupler106and the insert104may be coupled in the configuration shown inFIG. 18wherein the coupler106is pivoted in a direction toward the key member130, thereby generating an angle a between the axis180and the axis170.

Moreover, because the lower coupling portion134is circular when viewed from the bottom (seeFIG. 8), the coupler106may be pivoted from side to side with respect to the key member130. Thus, as shown inFIG. 19, the coupler106and the insert104may coupled in any desired combination of inclination and version angles that positions the axis180of the coupler106within a cone184originating from the axis170and having a cone angle of φ. In one embodiment, the coupler106may be positioned within about 15 degrees of the axis180in any direction, thereby providing a cone angle of about 30 degrees. The cone angle for a particular embodiment is typically limited by impingement of either the insert104on the shoulder142or impingement of the stem102on the lower surface150. Accordingly, the cone angle may be modified by selection of the shape and dimensions of, for example, the neck144and shoulder142of the coupler106, the protuberance152, the recessed area156and the platform112.

Disassembly of the assembly100is possible using the removal tool200ofFIG. 20. The removal tool200includes a base202and a shaft204. Two prongs206and208extend outwardly from the base202and an impact knob210is located on the shaft204. The prongs206and208are spaced apart by a distance corresponding to the diameter of the tapered bore116and are narrowed at the distal end portions212and214, respectively. The distal end portions212and214are thus proportioned to fit within a gap220(seeFIG. 21) between the protuberance152and the upper surface114of the shaft102. Even when the articulating head component108is angled with respect to the shaft102as shown inFIG. 22, the gap220is present.

Accordingly, disassembly of the assembly100is accomplished by maneuvering the prongs206and208between the articulating head component108and the upper surface114of the stem102as shown inFIG. 23. The recessed area156facilitates the positioning of the distal end portions212and214of the prongs206and208between the protuberance152and the upper surface114of the shaft102as shown inFIG. 24. Once positioned, the impact knob210is impacted. The force of the impact is transferred through the inclined surfaces of the tapered prongs206and208to the protuberance152forcing the articulating head component108away from the stem102. The impact will typically break the coupling between the outer wall140of the coupler106and the tapered bore154, allowing the articulating head108to be removed from the coupler106.

The distance between the prongs206and208decreases from the distance at the distal end portions212and214and the distance at the base202. Specifically, the distance between the prongs206and208at a location between the distal end portions212and214and the base202corresponds to the diameter of the neck144. Accordingly, once the articulating head component108is removed, the prongs206and208are positioned adjacent to the neck144as shown inFIG. 25. The prongs206and208thus contact the shoulder portion142of the coupler106. If desired, the upper inner surface of the prongs206and208may be formed with an angle complimentary to the angle of the shoulder portion142as shown inFIG. 25. A subsequent impact on the impact knob210decouples the coupler106from the insert104.

Finally, the insert104is removed by insertion of a threaded decoupler220into the threaded bore128as shown inFIG. 26. As the threaded decoupler220is threaded into threaded bore128, the threaded decoupler220contacts the bottom of the tapered bore116. Additional rotation of the threaded decoupler220breaks the coupling between the insert104and the tapered bore116.

A new humeral prosthetic assembly may then be assembled using the stem102along with a new insert104, a new coupler106, and a new articulating head component108. The orientation of the new articulating head component108may be set in the manner described above. Instrumentation which may be used to couple the articulating head component108and the coupler106at the desired orientation with the insert104is described in U.S. Publication No. 2005/0288681, published on Dec. 29, 2005, which is herein incorporated by reference.

Subjecting a bone to high impact forces may cause further injury or fracturing of the bone. Additionally, applying high impact forces to an implanted stem could move the stem within the bone resulting in misalignment of the prosthesis. Coupling the insert104and the coupler106prior to implanting the insert104within the bone of a patient thus allows a much higher impact force to be used than would typically be used to form a couple while one of the components is implanted. The use of a higher force provides a stronger coupling which better resists further movement between the components.

Specifically, the impact force used to form the Morse taper coupling between the insert104and the stem102is passed through the coupler106. Because the axis of the coupler106may not be aligned with the axis176of the insert104, forming the Morse taper coupling applies a torque to the coupler106tending to change the alignment of the coupler106. Since the insert104and the coupler106may be coupled using a force higher than the force used to form a Morse taper coupling, however, passing the force necessary to couple the insert104to the stem102through the coupler106does not significantly change the alignment of the coupler106within the tapered bore126.

In the event the axis of the tapered bore154of the articulating head component108is desired to be parallel with the axis of the tapered bore116, the coupler106and insert104need not be used. Rather, the insert230shown inFIGS. 27 and 28may be used. The insert230includes an upper tapered wall portion232and a lower tapered wall portion234. A bore236extends from the upper surface238of the insert230to a threaded bore240.

The upper tapered wall portion232is configured with a taper that provides a Morse taper coupling with the tapered bore154while the lower tapered wall portion234is configured with a taper that provides a Morse taper coupling with the tapered bore116. The insert230may thus be used to couple the articulating head component108with the stem102as shown inFIG. 28wherein the insert230is coupled with the tapered bore116at a location above the key member128.

The humeral prosthesis assembly100is thus a modular system that can be used to provide a number of different orientations of an articulating head component with respect to a stem. Accordingly, a kit including stems102of different lengths, at least one insert104, at least one coupler106, at least one insert230, and a removal tool200provides a highly adaptable system that can accommodate a wide range of joint constructs.

Additional removal systems may be provided in a kit for use with the humeral prosthesis assembly100. By way of example, a removal tool250shown inFIG. 30may be used to decouple the insert104and the insert230from the stem102. The removal tool250includes a base252and a shaft254. Two prongs256and258extend outwardly from the base252and an impact knob260is located on the shaft254. The prongs256and258are similar to the prongs206and208. The prongs256and258, however, are much thicker than the prongs206and208.

The removal tool250is configured to work with a decoupler262shown inFIG. 31. The decoupler262includes a flange264and a stem266. The stem266includes a threaded portion268. Removal of the insert104is accomplished by insertion of the threaded portion268of the decoupler220into the threaded bore128as shown inFIG. 32. The prongs256and258are then positioned between the flange264and the upper surface114of the stem102. Once positioned, the impact knob260is impacted. The force of the impact is transferred through the inclined surfaces of the tapered prongs256and258to the flange264forcing the insert104away from the stem102.

Decoupling of the insert230is accomplished in a similar manner as the threaded portion268of the decoupler220is threaded into the threaded bore240as shown inFIG. 33. The prongs256and258are then positioned between the flange264and the upper surface114of the stem102. Once positioned, the impact knob260is impacted. The force of the impact is transferred through the inclined surfaces of the tapered prongs256and258to the flange264forcing the insert230away from the stem102.

If desired, a different removal tool may be provided for use with each of the inserts104and230. Moreover, other devices may be used to provide an impact to the flange264.

Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.