Combined bipolar and unipolar trials

The present invention is directed to a set of trial prosthesis instrumentation for use in trial fitting of a medical implant such as a femoral hip prosthesis. The two piece set provides a combined bipolar and unipolar trial prosthesis instrumentation and comprises an outer component and a inner component. The outer component comprises an exterior surface characterized by a substantially hemispherical shape to correspondingly mate with a joint socket and an interior surface characterized by a substantially hemispherical shape, and an inner component that comprises an exterior surface that comprises a surface and that is shaped to correspondingly mate with the interior surface of the outer component and an interior surface characterized by a substantially columnar shape that correspondingly mates with a prosthetic stem. Methods of use are also contemplated.

TECHNICAL FIELD

The present invention is related to the field of medicine, particularly to the field of orthopedics. The invention provides a trial prosthesis comprising an outer component and an inner component compatible with the outer component, and may be utilized in either a bipolar or a unipolar hemiarthroplasty in which the proximal portion of the femur is replaced with a suitable prosthetic hip joint implant or implant assembly which articulates directly with the natural acetabulum.

BACKGROUND OF THE INVENTION

A successful hip replacement or arthroplasty procedure results, in part, from selection of prosthetic joint components that are dimensioned and positioned to closely approximate or replicate the geometry and functional characteristics of a natural, healthy hip joint. Typically, the component selection process includes a pre-operative analysis of joint images. The component selection process also includes temporary fixation of one or more provisional components to a bone or bones of interest prior to permanent fixation of the prosthetic joint. The provisional components are intended to mimic certain aspects of the permanent prosthetic joint in order for a surgeon to validate measurements and to test several different component sizes and configurations. Hence, provisional components are aptly known as “trials.”

Two different types of procedures are typically suitable for hemiarthroplasty procedures. Briefly, hemiarthroplasty is a surgical procedure in which a joint is partially replaced, i.e., the natural acetabulum is retained in the hip joint of the patient. One of these types is the use of a bipolar prosthesis member (for example, see U.S. Pat. No. 3,813,699 to Giliberty and U.S. Pat. No. 4,770,658 to Geremakis et al.). In general, a bipolar prosthesis has an external surface which articulates with the natural acetabulum and an internal surface which articulates with the spherical head member of a prosthetic femoral component. The other of these types is often referred to as a unipolar endoprosthesis in which the prosthetic femoral component includes a spherical head member which is large enough to articulate directly with the natural acetabulum. Both of the above hemiarthroplasty procedures enable articulation with the natural acetabulum.

These two procedures permit later conversion to a total hip replacement in which the acetabular portion is also replaced with a prosthetic acetabular component. With the bipolar procedure, the bipolar prosthesis is removed from the head of the hip stem, and an acetabular prosthesis is implanted which mates with the head of the remaining femoral component. With the unipolar endoprosthesis, the head is typically a separate component from the stem portion of the hip prosthesis. This permits the larger unipolar head to be removed and replaced with a smaller head without removing the femoral stem to enable the smaller head to mate with an acetabular prosthetic implant component

Determining the fit of a prosthesis or medical implant before implantation is generally accomplished using a trial prosthesis instrumentation. An example of a femoral prosthesis trial fitting device is described in U.S. Pat. No. 4,135,517 and corresponding application GB 2001247 to Reale, which disclose a trial head30and a bearing insert which removably fits within the trial head. The bearing insert may be removably mountable on either a femoral prosthesis stem or a trial handle.

U.S. Pat. No. 5,879,401 to Besemer et al. describes an acetabular trial system comprising an outer shell and an inner shell for placement within the outer shell that are rotatably fixed with a pin about a transverse axis that extends through the outer shell and that defines a range of anteversion angels, wherein the transverse axis is perpendicular to a sagittal plane of a patient's body. This trial system allows for the determination of an appropriate anteversion angle for the acetabular cup of the hip prosthesis. U.S. Pat. No. 4,528,980 and corresponding application EP 0140642 to Kenna describe an acetabulum sizer for properly sizing an acetabulum prior to receiving an acetabular cup prosthesis comprising a substantially hemispherical shell having an outside surface that generally conforms to the outside surface of the prosthesis, a circular peripheral rim, a handle means for manipulating the shell, wherein the shell is characterized by having viewing ports to enable visual inspection of the acetabulum during sizing.

In an effort to simplify the trial process of a surgical procedure and expand the utility of conventional trial prosthesis instrumentation, combined bipolar and unipolar trial instrumentation were explored. For example, related U.S. Pat. No. 5,800,556 and U.S. Pat. No. 5,888,211 to Sanders et al. describe a bipolar to unipolar head trial adapter that may be inserted into or removed from a bipolar shell to convert the bipolar shell to a unipolar head. The adapter comprises a two piece system that provides an adjustable neck to eliminate the necessity for multiple unipolar head trials corresponding to different neck lengths for each of the different possible head sizes. U.S. Pat. No. 5,156,626 describes a multiple piece set of provisional instrumentation for a hemiarthroplasty that includes a common outer shell that releasably mates with two different types of inner components, wherein the combination of the shell and the first inner component is used for a bipolar procedure and the combination of the shell and the second inner component is used for a unipolar procedure.

The present invention further simplifies the trial instrumentation employed in trial fitting of a medical implant (i.e., joint prosthesis) by providing a two-piece trial prosthesis instrumentation for use in either a bipolar or a unipolar surgical procedure.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a system and method that describe and provide a trial prosthesis instrumentation for use in trial fitting of a medical implant. One embodiment of the present invention provides a combined bipolar and unipolar trial hip prosthesis instrument that includes an outer component as the bipolar trial and an inner component that is releasably inserted into the outer component to convert the bipolar trial to a unipolar trial.

Another embodiment of the invention is to provide a set of surgical hip instrumentation comprising a single style outer shell component for use as a bipolar prosthesis trial for hemiarthroplasty, and an inner (insert) component that removably fits into the outer component to provide an assembly for use as a unipolar endoprosthesis for hemiarthroplasty.

A further embodiment of the invention is to provide such an outer component that is also used as an acetabular sizing gauge.

A still further embodiment of the invention is to provide a set of trial hip prosthesis instrumentation comprising a common style outer component is used with an interchangeable style of an inner (insert) component, the set is useful for different types of surgical procedures and reduces inventory and manufacturing costs thereof.

Another embodiment of the invention is to provide a femoral trial system comprising a plurality of sizes of outer components and a plurality of sizes of mating inner components, each of which are used in a trial fitting of a medical implant.

LIST OF DESIGNATIONS FOR THE COMPONENTS IN DRAWINGS

5bipolar trial prosthesis7unipolar trial prosthesis10hip prosthesis12prosthesis stem14acetabulum socket16prosthesis head18prosthesis neck20outer component22exterior of outer component24interior of outer component25apical opening of outer component26shape of interior surface of outer component27split ring28annular groove in interior of outer component30inner component32exterior of inner component34interior of inner component35interior shape of inner component36annular groove in exterior of inner component38surface of inner component40space between surface of inner component and interior surface of outer component42annular groove in interior of inner component43spacing means44peripheral rim of inner component

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1–7illustrate a particularly advantageous embodiment of a set of trial instrumentation of the present invention. The invention is described with reference to preparing a hip prosthesis10using trial prosthesis instrumentation for a hip joint, such as illustrated inFIG. 1, and more particularly to the acetabulum14. However, it is understood that this description does not constitute a limitation upon the scope of the invention and that the principles of the invention may be suitable and applicable for other joints, such as the shoulder or the like and is equally applicable in veterinary uses.

The set of trial prosthesis instrumentation exemplified inFIG. 2is suitable for use in a trial fitting of a medical implant, such as is necessary with a hemiarthroplasty femoral hip replacement. The set comprises an outer component20and an inner component30. The outer component20includes an exterior surface22characterized by a substantially hemispherical shape to correspondingly mate with a joint socket, and an interior surface24. The inner component30includes an exterior surface32, which is shaped to correspondingly mate with the interior surface24of outer component20and has a surface38(FIG. 4), and an interior surface34characterized by a substantially columnar shape35therein. The inner component30is selectively inserted into the outer component20in mating contact with the interior surface24of outer component20.

The interior surface24of the outer component20comprises a substantially hemispherical shape26therein (FIGS. 3A and 3B). This shape26of the interior surface24enables the outer component20to mate with a corresponding substantially hemispherical shaped provisional head16on stem12via neck18on stem12. It is noted that the trial outer component20may be utilized for trial fitting with the natural acetabulum during surgery in conjunction with such a trial provisional stem12and provisional head16combination. Alternatively, the outer component20may be used with the actual implant stem and head. Thus, the assembly5(shown inFIG. 6) is utilized as a trial in conjunction with a bipolar surgical procedure.

The shape26of the interior surface24also enables the outer component20to mate with inner component30. If inner component30is selectively inserted into the outer component20in mating contact with the interior surface24of outer component20, the assembly7(FIG. 7) provides a unipolar trial prosthesis. The configuration of the interior surface34of the inner component30comprises a substantially columnar shape as designated by35inFIGS. 5 and 7. This substantially columnar shape35of the interior surface34enables the inner component30to mate with a provisional stem12via a correspondingly shaped neck18on stem12, as shown inFIG. 7. The columnar shape35of the interior surface34need not be symmetric, provided the columnar shape35of the interior surface34is shaped to mate with the corresponding neck18. For example, the columnar shape35may be tapered so as to fit a conventional neck trial prosthesis, which may also be tapered. One of ordinary skill in the art is aware of common taper dimensions (i.e., diameter of the neck measured at two different points along its length) that are well-known in the art. It is noted that the trial inner component30in combination with a corresponding provisional or trial outer component20may be utilized for trial fitting with the natural acetabulum during surgery in conjunction with such a trial or provisional stem12, such as is illustrated inFIG. 7. Alternatively, the inner component30and outer component20assembly7may be used with the actual implant stem. Thus, the assembly5″ (shown inFIGS. 5 and 7) which includes outer component20and inner component30, is utilized as a unipolar trial prosthesis in conjunction with a unipolar surgical procedure. It is noted that the inner component30has a surface38, and, thus, when inner component30is correspondingly mated with the interior surface24of the outer component20, a space40is formed that may be accessed via apical opening25in outer component20. The apical opening25together with surface38allows access of a blunt instrument and a platform by which the inner component30is pushed out of outer component20. This disassembly is achieved by inserting the blunt instrument through apical opening25and applying a force to the surface38via the blunt instrument to disengage inner component30from outer component20.

The cross-sectional shape of the interior surface24of outer component20and the exterior surface32of inner component30may be substantially U-shaped, as shown inFIGS. 3Band5, although any suitable corresponding, mating interior surface24and exterior surface32may be utilized. The corresponding interior surface24and exterior surface32is sized to slide releasably in and out in frictional engagement with each other, with a slip-fit, friction fit, mechanical release, or other suitable equivalent known to those of skill in the art, between the outer component20and inner component30. Manual pressure may be all that is required to slide the inner component30into or out of outer component20. Finger pressure will connect the inner component30with the corresponding outer component20.

The outer component20further comprises an annular groove28about the interior surface24as shown inFIGS. 4 and 5. A resilient split ring27is retained in the annular groove28and maintained by a biased spring force. The inner surface of the split ring27has a dual chamfer, as shown inFIG. 4, to maintain the inner component30in outer component20. The split ring27is expandable and thus recedes further into the annular groove28upon insertion of the inner component30. The frictional pressure of split ring27against the exterior surface32of inner component30provides a positive lock that maintains the inner component30in outer component20until the user releases the inner component30back out to release it from the outer component20.

It is also noted that the inner component30may include an annular groove36on the exterior surface32that is located to correspond to split ring27on the interior surface24of outer component20(FIG. 4). The annular groove36of inner component30provides a recessed area in which the split ring27expands and recedes to further maintain the inner component30. The annular groove36also forms a peripheral rim44around the base of the exterior surface32of inner component30. The peripheral rim44does not protrude beyond the edge of exterior surface32.

To disassemble the inner component30from the outer component20, outer component20is held while the interior surface34of inner component30is gripped with finger pressure and pulled out. Depending on the size of the interior surface34of the inner component30, it may be difficult to grip in this manner, thus it is contemplated that a blunt instrument may be used, as described above, to disassemble the inner component30from the outer component20.

The set of combined bipolar and unipolar trial prosthesis instrumentation as described herein may include a plurality of outer components20of varying sizes and/or a plurality of inner components30of varying sizes. The varying sizes are not shown in the accompanying figures, but it is understood that sizing may vary and that mating components have corresponding/mating sizing features as desired.

The use of the trial assembly5for a bipolar trial fitting with the acetabulum requires that the correct size of outer component20must be selected. The exterior surface22of outer component20includes a hemispherical portion of a sphere, although more than half of a sphere may be provided, as shown in the Figures. It is important to match the exterior shape of outer component20as accurately as possible with the shape of the natural acetabulum.

Further, the interior surface34of inner component30may have an annular groove or recessed area42proximal to the opening of the interior (FIG. 7). The groove42may be fitted with suitable spacing means43to maintain snug fit in th prosthesis stem12. Non-limiting examples of such spacing means may be annular rings, multiple mating tapers, o-rings, gaskets, ball detents, etc. One of ordinary skill in the art recognizes that any of these examples or other equivalent components may be used for this purpose The spacing means43expands and thus recedes into the recessed area42upon insertion of the neck18of provisional stem member12. The spacing means43facilitates a snug contact and mate between the provisional prosthesis stem12with the neck18of stem12even where dimensions of the neck18vary from a trial to a permanent prosthesis or among different manufacturers who may have different standards for measuring or sizing the neck18. The interior surface34having the annular groove42fitted with means43of inner component30is dimensioned to releasably fit over correspondingly shaped neck18.

In use, the surgeon determines whether a bipolar hemiarthroplasty procedure (in which case outer components20are used) or a unipolar hemiarthroplasty procedure (in which case the combination of outer components20and inner components30are used) is to be performed. Again, the present invention enables the user to use a common style outer trial component20with an inner trial component30to adapt the trial system for a different type of surgical procedure. Alternatively, the outer component20, which is used in the trial assembly of5and/or7, may be used without an inner component as an acetabular gauge to size the natural acetabulum for trial fitting a medical implant thereto. Specifically in use in a hemiarthroplasty, the outer component20is positioned against the acetabulum to observe the fit therebetween. Thus, the exterior surface22of outer component20is bone-contacting. If there is not good mating contact with the outer component20and acetabulum, another outer component20with a different size exterior surface22is selected. This process is continued until an outer component20with the desired fit between the exterior surface22and the acetabulum is determined. After the correct outer component20is chosen, a provisional substantially spherical head member16(or the like spherical implant head member) is inserted into the interior surface24of outer component20. Upon insertion, the split ring27expands and thus recedes into recessed area28. Once the head passes split ring27, the ring contracts to its rest position capturing the head16in the interior24of outer component20.

Alternatively, if the surgeon desires to perform a unipolar trial fitting, the appropriate outer component20is selectively chosen as described above and then the desired mating size of the inner component30is selected. The selected inner component30is then inserted into the selected outer component to form a unipolar trial prosthesis for use in a unipolar trial fitting.

If outer component20is selected for a bipolar trial fitting, this trial assembly5provides trial dual joint articulation, with articulation about exterior surface22of outer component20against the natural acetabulum, and with articulation about interior surface24of outer component20about head16. Alternatively, if inner component30is selected for use with outer component20for a unipolar trial fitting, this trial prosthesis instrument also provides dual articulation, with articulation about exterior surface22of outer component20against the natural acetabulum, and with restricted articulation about interior surface24of outer component20about exterior surface32. The restricted articulation about interior surface24of outer component20about exterior surface32results from a free rotation about a vertical center axis3, i.e., spinning, of inner component30(FIGS. 4 and 5) while in mating contact with the interior surface24of outer component20.

The components of the present invention are made in accordance with any suitable manufacturing practices. Additionally, any suitable material useful for temporary surgical use may be utilized. Examples of such suitable materials include, but are not limited to a variety of copolymers and plastics, such as polyoxymethylene which is generally known as Celcon®, polyetherimide, polyethylene, polypropylene, polyphenyl sulfone, which is commercially known as Radel®, nylon and mixtures thereof, a metal, such as aluminum and stainless steel or other suitable materials that are well-known in the art. It is further understood that any suitable material may be utilized for any of the components. For those components the are resilient, any material that possess shape memory may be used including, for example, polymeric and/or metallic materials such as acetal copolymer, polyethylene, polypropylene and nylon.

The various sizes of outer components20and inner components30may vary in accordance with the surgical needs. For example, the outer components20may be provided with various external diameters. External diameters typically may run incrementally from 30 mm to 72 mm, although the sizes are not limited thereto. The external diameter of the various sizes of outer components20correspond to the various sizes of the outer diameters of the bipolar implant components or to the various sizes of the outer diameter of the unipolar endoprosthesis heads, which are to be selected for implantation. In general, the sizing of trial prostheses is designed to correlate with the corresponding prosthetic components to be implanted. The inner hemispherical surface26of outer component20and/or the exterior surface32of inner component30may vary in accordance with the corresponding sizes of spherical head members with which it will mate. Examples of typical size ranges for the diameter for the inner hemispherical surface26are 22 mm, 28 mm and 32 mm, although the sizing is not limited thereto. The inner surface34of inner component30is basically sized to releasably slide on and off a corresponding neck member of a stem such as12via the neck18. The interior of the various outer components20are sized and shaped to correspond with the exteriors of any mating size of inner components30. The size of the substantially columnar inner region34of inner component30may vary in accordance with the corresponding sizes of columnar neck members such as18with which it will mate. Alternatively, a sleeve may be inserted into the substantially columnar shape35of interior surface34of inner component30to vary accordingly the size of the interior surface34as desired. Sleeves suitable for the purpose of varying and/or adjusting the size of an acetabular trial include, for example, neck taper sleeves. Other suitable equivalents, known to those of ordinary skill in the art, may also be used.

A set of trial instrumentation in accordance with the embodiments described and illustrated herein may be provided as specific to size. For example, the inner component30is provided with the respective outer component20to which it correspondingly mates. For example, an outer component20with an interior surface24having an inner size A corresponds and mates with inner component30having an exterior surface32having an outer size A. The dimensions of inner size A and outer size A are suitably designed to releasably mate together, as previously described. Accordingly, inner size B mates with outer size B, inner size C with outer size C, and inner size D with outer size D. Thus, in certain embodiments, the present invention provides a femoral trial system comprising a plurality of outer components, each characterized by a specific size of the interior surface24or of the exterior surface22. In further embodiments, the femoral trial system further comprises a plurality of inner components, each characterized by a specific size of the interior surface34or of the exterior surface32.

For the convenience of the user, each of the plurality of outer components and/or each of the plurality of inner components may be color-coded, such as according to the specific size. For example, the inner size A and outer size A components are all red, so that any red inner component30will mate correctly with any red outer component20. Accordingly, all size B's are black, all size C's are white, and all size D's are blue. It is understood that the color-coding may be varied as desired. Further, it is recognized that certain variations in the mating scheme may be suitable in systems and methods of the present invention. For example, an inner component30having an outer size D may be indicated to mate with a 60 and a 63 mm outer components20comprising inner size D. However, any outer size D component could mate with any inner size D component. Therefore, it is understood that the outer size D inner component30could actually mate with the other inner size D outer components too.

The present invention enables selective attachment of inner trial components with outer trial components to provide a set of trial prosthesis. The trial components are adapted and styled for two different types of surgical procedures. While this invention has been described and exemplified, in terms of a particularly advantageous embodiment, those skilled in the art can appreciate that modification can be made without departing from the spirit and scope of this invention

REFERENCES