Joint prosthesis with infinitely positionable head

IS 2 370 724 T3

DESCRIPTION

Joint prosthesis with head for infinite positions

The present invention relates to a joint prosthesis, and specifically to a prosthesis having a joint head component. More specifically, the invention relates to a system for achieving infinitely variable positions for the head component in relation to a bone-engaging portion of the prosthesis.

Repair and replacement of human joints, such as the knee, shoulder, elbow, and hip, has become an increasingly common medical treatment. The longer life expectancy means that the joints have to endure more wear and tear. More sports activities mean a greater chance of serious joint injuries. The treatment of injuries, wear and tear and disease in human joints has advanced from the use of orthopedics to hide the problem, to the fusion of the joint, to the use of prosthetics to replace damaged components of the joint.

As the success rate in total or partial joint replacements has increased, the need for modularity and universality in joint prostheses has also increased. The variety of patients means that a single size or configuration of joint prostheses is not enough. The physical dimensions of a patient's joint components vary, as does the biomechanical relationship between these components. For example, in a shoulder prosthesis, the relationship between the humeral and glenoidal components can be significantly different between patients. These relationships are especially important when only one joint component is being replaced and must be integrated with the existing, naturally opposite joint component.

In joint replacement procedures, the proximal end of a bone, such as the humerus, is resected to form a stable platform to receive the joint implant. In some cases, after the implant has been fixed in the bone, it is discovered that the resection was not appropriate for the patient's joint Correction of this problem requires, at a minimum, the removal of the implant and the implantation of a new implant to adjust the surface subjected to resection. The availability of an implant component of a different size or configuration is very beneficial and even more important if additional resection of the bone is necessary.

For example, in many shoulder surgeries, only the humeral component is replaced, leaving the glenoid component intact. In this case, it is essential that the articulation surface of the humeral component matches the articulation surface of the glenoid component as perfectly as possible, both statically and dynamically. With a typical humeral prosthesis, the version and inclination are adjusted according to the geometry of the prosthesis head. In other words, there are certain predetermined head geometries that can be selected for a fitting glenoid component. If there is not an infinite variety of predetermined head geometries, the resulting humeral prosthesis can only often obtain a best-fitting relationship to the glenoid component of the shoulder joint.

In a typical surgical procedure, a trial component will be used to determine the optimal final component to attach to the bone. In most cases, the surgeon can make a good selection that fits the joint very well. However, in some cases, the accuracy of the fit cannot be determined until the surgery is complete and the patient has had an opportunity to move the repaired joint. When significant problems arise, revision surgery may be necessary to replace an improperly sized or shaped joint component. A typical revision surgery requires the removal of the entire prosthesis from the bone and replacement with a different prosthesis.

US-6749637 discloses a shoulder joint prosthesis in which an angularly adjustable connector is held relative to a portion of the stem by a set screw. As long as the screw is loose, the rod head orientation can be adjusted. The orientation of the head is fixed by tightening the screw.

There is a significant need for a joint prosthesis to be both modular and universal. Such a prosthesis would be easily manipulated during surgery and could achieve practically infinite tilt angles and version. Furthermore, an optimal prosthesis would be readily available for modification in revision surgery without having to remove the entire prosthesis.

The present invention contemplates a joint prosthesis with an articulated component that must be positioned in a particular angular orientation to reproduce and adapt to the anatomical characteristics of the patient's joint.

IS 2 370 724 T3

Therefore, the present invention provides a joint prosthesis as defined in claim 1.

The prosthesis of the invention can be used in a procedure for preparing an articulated component of a joint prosthesis, the prosthesis having an implant attached to a bone of the joint, the method comprising the steps of:

determining an angular orientation of a trial joint component relative to the implant in the joint bone: positioning a final joint component on an insert component; reproducing the angular orientation of the trial link component in the final link component; Next, fix the final articulated component on the insert component and then mount the insert component on the implant attached to the joint bone.

The prosthesis of the invention can also be used in a procedure to reproduce an angular orientation of a trial articulated component in relation to an implant engaged in the bone of a joint, comprising the steps of:

removably mounting an insert component to the proximal portion of an implant engaged in the joint bone; positioning a trial hinge component on the insert component; determining an angular orientation of the trial articulated component relative to the implant; then fix the trial articulated component on the insert component; removing the insertion component of the implant with the articulated component intact; and using the insert component and trial link component to reproduce the angular orientation in a final link component.

The prosthesis of the invention can also be used in a procedure for performing a revision of a joint prosthesis having an implant engaged in the bone of the joint and an articulated component attached to an insert component removably mounted on the implant, comprising the Steps of:

removing the insertion component of the implant with the implant engaged in the bone with the articulated component attached thereto; preparing a new insert component with a new hinge component attached thereto; and mounting the new insert component to the attached implant in the bone.

The joint prosthesis may include a component configured for engagement in a patient's bone, such as in a prepared intramedullary canal. The component, or stem, can be configured as a trial stem or permanent implant. The proximal end of the stem includes a feature-defining platform surface for removably supporting a removable insert component. A fixation element is provided that is used to fix the insert component to the stem. In accordance with one embodiment of the invention, the fixation element is removable, although it is capable of achieving a rigid, substantially permanent fixation of the insert component on the stem.

The joint prosthesis includes an adaptive component having one part configured to fit the articulated component and another part configured to adjustably fit the insertion component. The adapter component is also provided with a hole to allow access to the fixation element when the adapter component is coupled to the insert component, to allow removal of the fixation element and thus, removal of the insert component from the stem with intact fitting component.

The insert component may include a plate portion and a base portion projecting from the plate portion. The insert component defines a sharp hole extending through it and a locking hole through the bottom wall of the base portion. The platform surface of the stem defines an insert cavity configured to receive the entire insert component therein. In particular, the insert cavity includes a base recess into which the insert base part fits snugly and a plate recess for receiving the plate part. Preferably, the recess of the plate is open at one edge of the platform surface to facilitate access to the insert part of the plate and ultimately to facilitate exit of the insert component from the insert cavity. .

The mating component includes a spherical portion that is configured to form a press fit into the tapered hole of the insert component. The matching component also includes a tapered cylinder configured to match a mating hole defined in the articulated component or head. Both ends of the matching component are therefore configured for a press fit engagement made using a typical compaction tool.

In accordance with a method of the present invention, a joint prosthesis is constructed by placing an insert component in a complementary shaped cavity defined in the proximal portion of a bone-engaging implant, such as a stem. A fastener, such as a screw, is used to secure the

ES 2 370 724 T3 insert into the stem. A mating component engages the insert component, such as a press fit coupling between a sharp hole in the insert and a compressible spherical portion in the mating component. An articulated component, such as a femoral head, then conforms to the adapter component, such as through a press-fit coupling.

In a further feature of the present invention, a screening procedure includes the step of accessing the fastener through openings defined in at least the matching component. The fastener is released from engagement with the stem so that the insert component is no longer attached to it. The insertion component is then removed, preferably with the fitting component and head components attached without alteration.

In yet another aspect, the removed insert component with the unaltered fitting component and the head component can be transported to a reproduction instrument. The angular position of at least the matching component can be determined relative to a fixed data using the instrument. This angular position can be transmitted to a new insert and fitting component, using the instrument. Once the three-dimensional angles have been adequately reproduced in the new prosthetic components, the fitting component can be attached to the insert component, preferably by compaction. The head component can also be coupled to the matching component, also preferably by compaction. The completed assembly is then driven to the stem that has not been removed from the patient's bone. The insertion component is placed in the insertion socket in the stem and the fixation element is used to rigidly connect the insertion component to the stem with the adapter component and the head component in their proper anatomical relationship to the bone. of the patient. These steps can be implemented in a true revision operation to replace an existing prosthesis or they can be carried out during an original joint replacement procedure.

The joint prosthesis is modular and universal. These advantages are achieved by features that allow infinitely variable positioning of a mating joint component in a bone mating portion of the prosthesis.

The prosthesis of the invention can be easily modified, either during the initial implantation or during a subsequent revision procedure. A benefit of the invention is that this modification can be made without removing or altering the bone-matching component, or stem, of the implant.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a side view of a prior art humeral prosthesis.

Figure 2 is an enlarged cross-sectional view of a portion of a joint prosthesis with a mounting element configured to articulate engagement with the stem of the prosthesis to allow angular positioning of a head component in multiple degrees of freedom.

Figure 3 is a side exploded view of a modular prosthesis in accordance with an embodiment of the present invention that is adapted to facilitate modification or revision of the implant.

Figure 4 is a cross-sectional front view of the modular prosthesis shown in Figure 3 in an assembled configuration.

Figure 5 is a front perspective view of a stem component of the modular prosthesis shown in Figures 3-4.

Figure 6 is an enlarged cross-sectional view of a portion of the stem shown in Figure 5.

Figure 7 is a top perspective view of an insert component of the modular prosthesis illustrated in Figures 3-4.

Figure 8 is a side cross-sectional view of the insert component shown in Figure 7.

Figure 9 is a transverse side view of a fitting component of the modular prosthesis shown in Figures 3-4.

Figure 10 is a side view of a fixation component of the modular prosthesis shown in Figures 3-

4.

Figure 11 is a side view of a reproduction instrument for use in reproducing the orientation of the fitting component of the prosthesis shown in Figures 3-4.

Figure 12 is a perspective view of a dummy stem for use in the reproduction instrument shown in Figure 11.

In the following description, the prosthesis is identified as a humeral prosthesis for a shoulder implant. However, it is understood that the principles of this invention can be applied to other prostheses that include an adjustable component. The present invention is particularly suitable for prostheses that are amenable to replacement or adjustment in a revision operation.

IS 2 370 724 T3

Referring to the drawings, Figure 1 shows a typical joint prosthesis 10 of a type that is generally known, which is the humeral component of a shoulder prosthesis that can be implanted in the humerus bone for articular engagement with the natural or natural glenoid. with a glenoid prosthesis. The prosthesis 10 includes a stem 12 configured to be implanted in the humerus bone in a conventional manner. The stem 12 forms a platform surface 15 that is oriented to the glenoid component of the joint where the prosthesis is in its operative position. The surface of the platform 15 defines a sharp hole for use in mounting the articulated head component 14. The head component includes a sharp bracket 18 that can be snap or friction fit into the tapered hole 16 to securely mount the head component to stem 12.

The prosthesis 10 can be a modular prosthesis, which means that various stem and head geometries can be provided from which a selection can be made that most closely approximates the natural joint components of the patient. Thus, the angle of the platform surface 15 can be different between the rods 12. While all of the head components 14 include a generally spherical bearing surface 19, the orientation of this surface relative to the deck surface 15 may be changed. Specifically, the location of the bracket 18 relative to the bearing surface 19 may be changed. deviated from the center of the surface (that is, an eccentric head). In some cases, the angle of the bracket may be different between the head components 14.

An improved modular prosthesis features an articulating mounting element 30 between the stem 12 and a head component 20, as shown in Figure 2. An example of a suitable mounting element 30 is disclosed in US-A-2005 / 0143829.

This mounting element 30 disclosed in US-A-2005/0143829 includes a proximal part 33 that is coupled to the head component 20. In a specific embodiment, the proximal part 33 defines a sharp surface that is fitted by pressure or by friction to the complementary hole 21 defined in the head component.

The mounting element 30 further includes a hinge portion 34 which is preferably in the form of a ball hinge. The hinge portion is sized to achieve a press fit engagement in a sharp hole 16 of the stem 12 when the portion 34 is pushed sufficiently into the hole. The spherical shape of the hinge portion 34 allows the mounting element 30 to rotate about three dimensional axes x, y, z. In this way, the mounting element can rotate about its own axis (the x-axis), pivot about a version axis (the y-axis), or pivot about a tilt axis (the z-axis).

In addition to the press fit coupling, a second clamping capability is disclosed in USA-2005/0143829 which increases the coupling between the hinge portion 34 and the tapered hole 16. In particular, a machine screw 40 may be provided which includes a threaded portion 46 configured to engage a threaded hole 18 in stem 12. Hole 18 is concentrically disposed at the base of tapered hole 16. Screw 40 is inserted into threaded hole 18 through hinge mounting member 30.

As shown in FIG. 2, mounting member 30 defines a central passageway 36 that extends through the length of the member and is open at its proximal and distal ends. The passageway defines an internal bearing surface 38 at the distal end of the element or more specifically, at the base of the hinge portion 34. The screw includes a head 42 that includes a surface on the bottom 44 that complements the internal bearing surface. These two surfaces form a spherical bearing interface that allows mounting member 30 to experience its full range of angular motion without interference from screw 40, even when screw is loosely threaded into threaded hole 18. Articulation portion 34 defines a relief 39 at the distal end of passageway 36 to facilitate this full range of motion of the mounting element.

The passageway 36 in the mounting element allows the introduction of the screw 40 through the mounting element and into the threaded hole 18. The screw can be loosely threaded into the hole to allow movement of the mounting element. Once the proper position for the mounting element 30 has been reached, the screw can be adjusted using a tool engaged in the recess of the tool 43 in the head 42 of the screw. As the screw is tightened, it drives the hinge portion 34 deeper into the angled hole 16, thereby locking the mounting element against the hinge. The screw is thus combined with the property of friction or pressure fit to lock the model.

IS 2 370 724 T3

The mounting element 30 disclosed in US-A-2005/0143829 represents a significant improvement over the prior art prosthesis 10 in which the mounting element alignment process is greatly simplified, and ultimately, the head of the humerus at the proper anatomical angle for the patient's shoulder joint. In addition, the mounting element 30 allows for infinite positioning of the humerus head, rather than the limited selection of predefined angles available with the prior art prosthesis.

Although the mounting element 30 presents a significant advance over previous prostheses, problems still arise when performing revision surgery. During some primary procedures, the surgeon may discover that a different humerus head is necessary after the implant stem has been fixed in the humerus. In some cases, the precision of fit of the prosthesis components cannot be determined until after the surgery is complete and the patient has had an opportunity to move the repaired joint. When significant problems arise, revision surgery may be necessary long after the primary surgery to replace an improperly sized or shaped joint component. In most cases, the modular components of the prosthesis cannot be removed without also removing the component, or stem, attached to the bone. Removal or replacement of an implanted stem is often problematic and risks creating a low integrity revision cast.

The present invention addresses the problem of revision surgeries on prosthetic implants by providing an insert component that allows the component implanted in the bone to remain in the bone. In accordance with one embodiment of the invention, a prosthesis 50 is provided as illustrated in Figures 3-4 that includes a stem 52, an insert component 54, a fixation element 56, and an adapter component 58. Stem 52 is configured to be implanted in a patient's bone that may be mostly identical to anterior stems used in similar joint replacement procedures. More specifically, the portion of stem 52 that is implanted into the prepared intramedullary canal of the humerus may be identical to the prior art stem 12, shown in Figure 1. As with prior art stems, stem 52 includes a platform surface 60 that is aligned toward the mating aspect of the joint, or the glenoidal aspect in the case of a shoulder prosthesis.

However, the platform surface 60 of the stem 50 in the present invention exhibits different characteristics from the prior art. In particular, the platform surface is configured to receive an insert component 54 and a fastener 56 operable to rigidly secure the insert component to the stem. The insert component 54 is adapted to mate with the mating component 58 under conditions that allow adjustment of the angular orientation of said component. The adaptation component 58 is configured to receive an articulated component, such as the head of the humerus 20 shown in Figure 2.

Referring to Figures 5-6, details of the surface of the platform 60 of the stem 50 are illustrated. The surface of the platform defines an insert cavity 62 with a base recess 64 embedded in the stem and a plate recess. 66 that opens on the platform surface. As shown in Figure 5, the base recess 64 is preferably cylindrical, for ease of manufacture and to facilitate placement of insert component 54 in insert cavity 62. However, other transverse configurations may be acceptable. for the base entree.

The plate recess 66 is generally rectangular with an edge 67 that opens at the upper end 61 of the surface of the platform 60. The plate recess preferably includes a round inner end to facilitate fabrication of the recess 66. For example, The base recess 64 can be formed by drilling a specified depth into the platform surface 60 of the stem 52. The plate recess 66 is thus initially formed by the perforation concentric with the recess in the base, but with a larger diameter and a greater depth. The deck surface can be sawed to create the open edge 67 of the plate recess.

Insert component 54 is configured to fit snugly into insert cavity 62, as can be seen in Figures 7-8. In particular, the insert component includes a base portion 70 that is configured to be comfortably received in the base recess 64. Thus, the cross section of the base portion preferably simulates the cross section of the base recess, this that is, the base portion 70 is cylindrical in the illustrated embodiment. The insert component further includes a plate portion 72 that is also configured to be comfortably received in plate recess 66. As with the base portion, plate portion 72 follows the configuration of plate recess 66 so that the base part is generally rectangular with a round inner edge. In the preferred embodiment, plate portion 54 includes tab 80

ES 2 370 724 T3 extending from a cylindrical base portion 70 so that the free end 81 of the tab is accessible at the open edge 67 of the plate recess. Preferably, the free end 81 substantially coincides with the open edge.

The plate portion 72 defines a bottom surface 78 that rests on the plate recess 66. The insert component is preferably sized so that the base portion 70 is slightly offset from the bottom wall 77 of the base recess 64 when the surface Bottom 78 of plate portion 72 is located in the plate recess. The free end 81 of the plate portion 72 includes a lower round edge 79 to provide a small access for a removal tool between the insert component and the insert cavity, as discussed in more detail herein.

In one feature of the invention, insert component 54 defines a tapered hole 74. The tapered hole engages by press fit with mating surface 85 of a spherical portion 84 of matching component 58 (FIG. 9). This press-fit engagement performs a final attachment of the mating component 58 to the stem 52. This interface may be similar to the push-fit coupling used in the components disclosed in US-A-2005 / 0143829. The mating component preferably includes a tapered barrel 82 that is configured to snap-fit ​​into the complementary hole 21 of the head of humerus 20 (figure 2). The mating component includes a central hole 87 that may be configured for a press fit engagement with a male property on the head of the humerus, in place of or in addition to press fit against the outer surface of the tapered cylinder 82.

In order to fix the mating component to the stem 52, a fixation element 56 is provided which secures the insert component 54 to the stem. In the preferred embodiment, the stem insertion cavity 62 defines a threaded hole 68 in the base recess 64. The fastener 56 constitutes a screw, as shown in Figure 10, with a threaded stem 92 adapted to engage the tapped hole 68. Screw head 94 preferably includes a hexagonal recess 96 for receiving a hexagonal driving tool of known design. The insert component 54 includes a fixator hole 76 through the bottom wall 77 of the component to receive the fixator therethrough. In this way, the insert component is secured to the stem 52 using the fastener or screw 56, as shown in FIG. 4. The spherical portion 84 of the matching component 58 preferably defines a flared opening 89 to prevent contact between the matching component and the screw head when the matching component 58 impacts the sharp hole 74.

Fixation element 56 represents a beneficial feature of prosthesis 50 of the present invention. Specifically, the fixation element allows removal of the insert component 54 from the stem of the prosthesis 52 at any time, even when the adapter component 56 is solidly attached to the insert component. This feature facilitates the revision of the articulated component or head of the humerus, at any time, simply by unscrewing the fixation element 56 from the threaded hole 68 in the stem. When the fastener 56 is removed, the insert component 54 can be immediately removed from the insert cavity 62 in the stem. Preferably, it may be pressed with a tool between the rounded edge 79 of the tongue portion 80 of the insert component and the surface of the stem platform 60 to help remove the insert without touching the adapter component 58. Once removed, the insertion component and the fitting component can serve as a trial component that is reproduced in a final prosthesis.

Whether it is a final implant or a trial implant, when fitting portion 58 is installed in tapered hole 74, spherical portion 84 may initially be loosely positioned in hole 74 so that orientation can be adjusted. Angle of the matching component 58. This adjustment may occur with the articulated head component 20 mounted on the matching component. Once the proper angles have been determined, the matching component can be attached to the sharpened hole by compaction in a known manner, and the head of the humerus can be similarly added. It may be noted that since the adapter component is engaging a removable insert component 54, the compaction steps may occur outside of the implant stem 52. Thus, compaction of the matching component in the insert component, and compaction of the link head in the matching component can occur in one device. Rigid fixation of the final implant can be done by means other than compaction, but this fixation can also take place outside of the implanted stem in the patient's bone.

Preferably, the adjustment of the angular position of the fitting component for use in a final prosthesis can occur using a reproduction instrument, such as the instrument disclosed in US-A2005 / 0288681.

IS 2 370 724 T3

The instrument 100 depicted in FIG. 11 includes a base assembly 102 carrying a stationary fixture 104 and a movable fixture 106. An adjustment mechanism 108 can be manually operated to move the movable fixture toward the fixture. stationary 104. The neck of the prosthesis stem 52 is provided with positioning grooves 53a and 53b. The upper slot 53a accepts the fixed fastener 104, while a pair of inner grooves 53b is configured to engage the movable fastener 106. When the neck of the stem is engaged by the fasteners 104, 106, a fixed data D that is perpendicular to the platform surface 60. The spatial angular orientation of the matching component 58 is calculated relative to this data. The base assembly 102 thus establishes a fixed spatial position for this data that can be used to reproduce the angles of the matching component.

To accomplish this reproduction, the instrument 100 further includes a reproduction device 110 that is mounted on the base mount 102. The device includes a platform 112 with legs 114 that abut the base mount. Platform 110 includes an annular dome 116 that supports a spherical washer 118 on one surface and a cannulated guide member 120 on the opposite surface. The guide member includes a hollow stem portion 121 that passes through the dome 116 and washer 118. The stem portion 121 is threaded to receive a lock nut 122 to fix the angular orientation of the guide member 120 relative to the data D.

The cannula of the guide member 120 allows the passage of an alignment tool 125 and more specifically, the guide shaft 127 of the tool. The distal end of the guide shaft is sized to fit snugly into the bore 87 of the tapered barrel 58. When the guide shaft 127 is located in the barrel of the adapter component used as part of the trial assembly, the guide member 120 and washer spherical 118 assume a corresponding spatial angle relative to dome 116. At this point in the procedure, the locking nut is tightened, thereby fixing, the three-dimensional angular position of guide member 120. Reproduction device 110 is then removed and stem 52 is released from the base mount. A definitive humerus prosthesis configured as the prosthesis 50 shown in Figures 3-4 can then be secured in the base assembly with a final fitting 58 loosely coupled to the tapered hole 74 of a final insert component 54. The alignment tool is reinserted into the guide member and the guide shaft engages the matching component to reproduce the angular orientation of the trial component. The alignment tool 125 is configured with a compaction end 129 that can be struck with a mallet to impact the adapter element on the insert component to form the final reproduced model. Once the head of the humerus impacts the adaptation component, the insertion component can be positioned in the insertion socket 62 of a stem 52 implanted in the prepared intramedullary canal of the patient's bone. The insert component is then secured in place using a fastener 56.

As shown in FIG. 11, the reproduction instrument 100 is attached to a prosthesis 50 that can be configured as a final or trial prosthesis. However, for the purpose of providing a reference for reproducing the angular orientation of the articulating components of the joint, a bone implant is not necessary. Thus, in an alternative procedure to reproduce the necessary angles, a dummy prosthesis 150 is provided as shown in Figure 12. The dummy prosthesis 150 meticulously simulates the proximal portion of the trial or final prosthesis 50 to provide proper alignment. of the data line D (figure 11). Thus, the dummy prosthesis includes a truncated stem 152 that includes positioning grooves 153a, 153b that are identical to grooves 53a, 53b described above. These dummy grooves are engaged by fixing elements 104, 106 in the manner described above. The proximal end of the sham prosthesis 150 defines an insert cavity 162 with a base recess 164 and a plate recess 166, all configured to receive insert component 54.

The dummy prosthesis 150 functions the same as a final or trial prosthesis when mounted on the reproduction instrument 100. However, the dummy stem 152 does not require the features found in an implantable stem, since the dummy prosthesis 150 is not configured to its implantation in the patient's bone. Preferably, the stem 152 is approximately 1/3 the length of the stem of the final prosthesis so that it is easy to manipulate and fix the dummy prosthesis in the reproduction instrument.

As explained above, the illustrated embodiment provides a prosthesis for the humeral aspect of the shoulder joint. In this way, the prosthesis 50 and its components have the appropriate dimensions for implantation in the bone of the humerus of the patient. In a specific embodiment, the base portion 70 of the insert component 54 has a diameter of 1.27 cm and a height of 4.62 mm to fit into a base recess of comparable dimensions. Plate portion 72 is 13mm wide, 2.5mm thick, and 19.1mm overall length to fit into a plate recess 66 of the same dimensions. The threaded shank 92 of the set screw 56 has a length of 5.0 mm to pass through the bottom wall 77 of the

ES 2 370 724 T3 insert part and into a hole 76 threaded to a depth of 4.45 mm. Preferably, the plate portion 72 of the insert is sized to seat substantially flush with the platform surface 60 of the prosthesis 50.

Also, the components of the prosthesis are formed of medically acceptable materials appropriate for the particular function served by the components. For example, the stem is formed of a material suitable for implantation in a prepared intramedullary canal. The insert component and the adaptation component are formed of biocompatible material, suitable for the adaptive coupling between these components.

The matching interference between the insertion component and the matching component can be reversed. Specifically, the tapered hole can be incorporated into the matching component, while the spherical portion projects from the insert component. The same modification can be made to the fitting interface between the head of the humerus and the fitting part.

In the preferred embodiment, the fastening element is a machine screw; however, other forms of attachment or fastening are contemplated. For example, instead of a screw that requires multiple turns to complete fixation, the element may incorporate a rotary locking cam or bayonet support arrangement. As a further alternative, the fastener may incorporate a snap feature where the element is pressed into the hole and locked in place, as in a spring clamp construction. The fastener must be able to obtain a rigid connection of the insert component to the stem. Furthermore, it is preferred that the fixation element can be removed without disturbing or damaging the implanted stem.

In accordance with the preferred embodiment of the invention, the insert component can be removed to facilitate revision or replacement of the angularly adjustable components. In a specific application, the insertion component is implemented solely as a trial implant in which the insertion component is removably attached to the stem to allow positioning of the adapter component and the femoral head in a suitable anatomical orientation. With the fitting component locked in its acceptable position, the inserting component can be removed and placed in the reproducing instrument. The orientation of the fitting component can then be reproduced in a definitive prosthesis that does not include the insertion component.

The present invention provides advantages even if the insert component is permanently attached to the stem. When the definitive implant includes the insert component, the insert component may be permanently attached to the implanted stem with an appropriate fixation element. This variation still benefits from the ability to establish a definite angular orientation of the fitting component outside of the surgical site.