GB2094638A - Elbow replacement prosthesis instrumentation - Google Patents

Abstract

Instrumentation for implantation of an elbow prosthesis comprises a humeral impactor 98 including an impactor head comprising a thin curved end member 102 of which a pushing surface 104 is formed complementarily to an articular surface of a numeral component, and a stem 100 extending from one end of the end member 102 in a direction perpendicularly away from the surface 104; an ulnar impactor 106 including an impactor head 110 of which a pushing surface 112 is formed complementarily to an articular surface of an ulnar component, the surface 112 being co-extensive with the latter articular surface; a chisel 114 including two parallel blades 122 bounding a channel open at both ends, the blades including respective parallel knife edges 124 extending along the channel; and a similar chisel 126, but with its knife edges 138 inset towards each other. <IMAGE>

Description

SPECIFICATION Elbow replacement prosthesis instrumentation This invention relates to instrumentation for implantation of a prosthesis for total or partial replacement of an elbow, especially arthritic or damaged elbow joints.

According to the present invention, there is provided instrumentation for implantation of an elbow prosthesis comprising a humeral component having an articular surface that is curved concave in a coronal plane and curved convex in a sagittal plane and an ulnar component having an articular surface that is curved convex in the coronal plane and curved concave in the sagittal plane and is complementary to said articular surface of said humeral component, said instrumentation comprising a humeral impactor including an impactor head comprised of a thin curved end member of which a pushing surface is formed complementarily to said articular surface of said humeral component, and a stem extending from one end of said end member in a direction substantially perpendicularly away from said pushing surface, whereby said end member extends unilaterally from said stem.

Preferably the instrumentation further comprises an ulnar impactor comprising a handle fixed to an end member having an external curved pushing surface whose curvature corresponds to the articular surface of the ulnar component. The instrumentation may include a pair of different bone chisels, each bone chisel having a head joined to a base member of inverted U-section by a stem, each limb of the U-section terminating in a chisel tip, and the blades of the U-section of each bone chisel lying in planes parallel to one another, and at least one of the bone chisels having its base member of inverted U-section inclined to its stem. The instrumentation may include a rasp orthe like to clear the surface of the olecranon during implantation of the prosthesis.

By way of example preferred embodiments of the present invention will be described with reference to the accompanying drawings, in which: Figure 1 is a fragmentary posterior elevation of one form of an elbow prosthesis illustrated as implanted in the humerus and ulna, Figure 2 is a fragmentary lateral elevation of the elbow prosthesis of Figure 1 with humerus and ulna in extension position (0 ), Figure 3 is a perspective view of one form of an ulnar component of the prosthesis, Figure 4 is a perspective view of one form of a humeral component of the prosthesis, Figure 5 is a perspective view of one form of a humeral impactor for implanting the prosthesis, Figure 6 is a perspective view of one form of an ulnar impactor for implanting the prosthesis, Figure 7A is a perspective view of one form of a bone chisel used to cut the humerus for implanting the humeral component, Figure 7B is a perspective view of the same bone chisel cutting the humerus for implantation of the humeral component, Figure 8 is a perspective view of one form of a trial humeral component used primarily for replacement of a totally destroyed elbow joint, Figure 9 is a perspective view of another form of a trial humeral component which is likely to be used more often in practice, Figure 10 is a perspective view of another form of chisel used in implanting the humeral component, Figure 11 is a perspective view of a rasp to clear the surface of the olecranon during implantation of the prosthesis, Figures 12A and 1 2B are side views of the pros- thesis to show range of pivotal movement, Figure 13 is a plan view of a more generally preferred form of humeral component of a prosthesis and similar to the humeral component of Figure 4, Figure 14 is a plan view of a special form of humeral component usable for replacement of a totally destroyed elbow joint, Figure 15 is a fragmentary perspective view of a form of chisel cutting the humerus for implantation of the humeral component, Figure 16 is a fragmentary perspective view of the humeral impactor pushing the humeral component onto the humeral bone during cementing, Figure 17 is a fragmentary perspective view of an ulnar impactor pushing the ulnar component onto the ulnar bone during cementing, Figure 18 is a perspective view of a radial head component that may be used on occasion in the elbow replacement prosthesis, Figure 19 is a posterior view of the prosthesis of Figures 12Aand 12B, Figure 20 is a diagrammatic view showing range of pivotal movement using a prosthesis such as that of Figure 19, Figure 21 is a diagrammatic view of an implanted prostehsis without any radial component, and Figure 22 is similar to that of Figure 21, but shows a radial component as part of the implanted prosthesis.

Referring in detail to the drawings, an elbow replacement prosthesis 2 basically comprises a humeral component 4 that is implanted in the humerus 6 and an ulnar component 8 implanted in the ulna 10. Optionally, it may comprise a radial component 12 (Figure 18) that is implanted in the radius 14.

The humeral component 4 has a concave surface 16 in the coronal plane that is joined laterally to a convex boundary surface 18' limiting the partcylindrical surface 18, the latter partially replacing the capitulum bone of the humerus upon implantation. In the saggital plane, the surface 16 becomes convex at 20 at the level of the concave surface in the coronal plane for articulation with the ulnar component 8. The surfaces 16, 18, 18' and 20 form articular surfaces of the humeral component 4.

A slightly different form of humeral component 4A is employable in the prosthesis for replacement of a totally destroyed elbow joint (see Figs. 8 and 14). The component 4A is the same in all particulars to component 4 except that a concave articular surface 1 6A in the coronal plane extends right across the whole length of the component 4A and although there is a convex boundary surface 18' there is no convex sur face extending in the coronal plane corresponding to convex surface 18 in component 4 (Fig. 4) or to convex surface 36 in component 70 (Fig.9).

The surface for attaching the humeral component 4 to the humerus comprises a superior U-slot 22 with an anterior wall 24, posterior wall 26 and flat floor 28.

The walls 24 and 26 may be anterior or posterior depending on whether it is the right of left elbow in which the prosthesis is to be inserted-the same prosthesis can be used for right and left. Longitudinal grooves 30 are formed in the walls 24 and 26 for keying of cement for implantation of the component 4. The lateral wall 32 has a peripheral groove 34 and the medial wall 36 a similar groove 38 for keying of cement. Annular wire markers 40 are embedded in the walls 32 and 36 and a longitudinal wire marker 42 is embedded in the floor 28 so that position of the prosthesis can be determined by X-ray inspection, after implantation, of both the coronal and sagittal planes by means of the three markers.

The main articulating surface of component 4 describes a gentle concave curve in the coronal plane which allows for simple and effective engagement with a convex surface 44 in the coronal plane of the ulnar component 8. Thus, a limited amount of sideways rotation motion is allowed which may at times become necessary in order to avoid undue strain on the bony attachments to the prosthetic components.

In the saggital plane of the component 4, the concave articulating surface 16 increases in radius from its centre in both the medial and lateral directions until it meets the boundary convex surfaces 181 and convex surface 20.

The articular surface of ulnar component 8 comprises the convex surface 44 in the coronal plane and a concave surface 46 in the sagittal plane. These surfaces allow for accurate and easy articulation with surface 16 of the humeral component 4.

The bone-attaching portion of the ulnar component 8 comprises a longitudinal dove-tailed keel 48 with grooves 50 running longitudinally along beside the keel 48 for keying of cement in implantation. A stem 52 depends from the keel 48 and under-surface 54 of the articulating area for insertion into the ulna.

The stem 52 has nipples 56 on both the medial (or lateral) surface 58 and surface 60 for keying into cement for implantation. Surface 60 is lateral if surface 58 is medial or surface 60 is medial if surface 58 is laterla. The length of stem 52 may be increased for special circumstances or other reasons.

The ulnar component 8 is adapted to fit onto and into a surgically prepared ulna. The angle which the stem 52 describes with the articulating area is selected to control anteversion seating of the component 8 in the ulnarbone 10. This is important for antero-posterior stability of the reconstructed elbow joint.

A reconstructed elbow joint employing a prosthesis embodying the invention may also include a radial component 12(Fig. 18). In actual fact, although the head of the radius 14 is always removed for insertion of the prosthesis (Fig. 21), it is not always necessary to replace this removed bone. However, in necessary cases, the bone may be replaced with a radial component 12 (Figs. 18 and 22) which comprises a distal key portion 62 having cement keying grooves 64 and an integral proximal bearing button 66 with dished surface 68. If the radial component 12 is used, it will in practice be implanted into the surgically prepared radius 14 and fixed in place with cement in a manner similar to implant of the ulnar component 8.

In order to assess the depth of humeral bone to be removed and also for sizing of a component to fit a particular patient, trial humeral components may be used, e.g. humeral component 70 (Fig. 8) or the more usual humeral component 72 (Fig. 9). The component 70 corresponds to the component 4A (Fig. 14) and component 72 to the component 4 (Figs. 2, 4 and 13).

The component 70 (Fig. 8) comprises a concave surface 74 in the coronal plane, lateral wall 76 and medial wall 78. component 70 has U-shaped slot defined by the posterior wall 80, anterior wall 801 and floor 82.

The component 72 (Fig. 9) comprises a concave surface 84 in the coronal plane, convex boundary surface 861 and convex surfaces 86 and 88, medial wall 90, lateral wall 92 and a U-shaped slot defined by posterior wall 94, anterior wall 941 and floor 96.

The components 70 and 72 unlike their counterparts 4 and 4A do not include wire markers or keying grooves, but, aside from this, components 70 and 72 are similar to 4A and 4.

In reconstruction of an elbow joint, only one style of components 4, 4A, 70 or 72 need be used.

A variety of materials is available from which to construct components 4, 8 and 12. Advantageously, the humeral component is formed of inert plastics material, e.g. high density polyethylene, and the ulnar component 8 and radial component 12 are advantageously made of corrosion-resistant metal, e.g. the chromium-containing alloy "Alivium". The impactors and chisels employable for implanting the prosthesis are advantageously formed of stainless steel or equivalent metal or alloy except for the end of the ulnar impactor adapted to make contact with the ulnar preferably metallic prosthesis.

The design of the components 4 and 8 as described enables them to be made and used in an average size adaptable to a large number of patients.

However, it should be recognized that different sizes may be necessary and this can be determined by use of differently dimensioned trial components 70 or 72.

Instrumentation for reconstruction of an elbow joint is described with reference to Figs. 5 to 7B, 10 and 11.

As seen in Fig. 5 humeral impactor 98 (sometimes referred to as a pusher) comprises a T-shaped handle 100 adapted to be fixed in the coronal plane to an integral distal end member 102 having its internal curved pushing surface 104 formed complementarily to the concave-convex surface 16 of component 4. This enables impactor 98 to be put in position upon the humeral component easily and be held there accurately while cement hardens during implantation.

An ulnar impactor 106 (Fig. 6) also has a T-shaped handle 108, but this is adapted to be fixed in the saggital plane to an integral dismal end member 110.

The external curved pushing surface 112 is formed complementarily to the articulating surface 44 of component 8 to again provide easy placement and accurate holding during cementing.

Bone chisel 114 (Fig. 7A) comprises a mallet head 116, stem 118, base member 120 and two wings 122, each with chisel tips 124. The stem 118 is fixed to the base member 120, but offset from the centre thereof for ease of access to the elbow joint. Chisel 114 is used to mark out the antero-posterior breadth of the humeral bone to be removed in order to fit into the slot 22 of component 4 (Fig. 4). It also marks the depth equivalent to that of the depth of the slot 22 in component 4.

Bone chisel 126 (Fig. 10) comprises a mallet head 128, stem 130, base member 132, wings 134 with inset ends 136 and chisel tips 138. The wings 134 are in a different plane (relative to stem 130) from the wings 122 of chisel 114 (Fig. 7A).

Chisel 126 (Fig. 10) is used for accurately marking out the length of humeral bone to be removed and also to mark the depth since the inset ends 136 of the chisel are sized in length (i.e. reduced or increased in length) to correspond with the length of the body of component 4. Use of chisel 126 to mark out and cut away humeral bone from the humerus 6 is shown in Fig. 15. Chisel 114 (Fig. 7A) is then used in the opposite plane to mark out the antero-posterior breadth of bone removal. Upon completion of humeral bone removal in such manner, the humeral component 4, with cement applied to the surfaces of slot 22 is applied to the humerus 6 and held in place with inpactor 98 as shown in Fig. 16 until the cement has set.The keel of the prepared humeral bone sits in the U-slot of component 4 and its medial and lateral ends sit against the medial and lateral walls of the prepared lower humerus.

Fig. 11 shows a rasp with a mallet head 140, stem 141 and base member 142 having a roughened surface and is employable to clear the surface of the olecranon during implantation of the prosthesis.

The ulna is prepared to receive the stem 52 of ulnar component 8 (Fig. 3). Cement is then applied to the stem 52 and under-surface 54 and the component 8 is inserted into and onto the upper end of the ulna 10. The component8 is held in position as shown in Fig.17, with impactor 108 until the cement is fully set. In the reconstructed joint, the ulnar component sits on the olecranon process of the ulnar bone and the stem 52 seats within that bone to give good stability to the component 8.

A preferred cement for use in the new joint reconstructions is self-hardening methyl methacrylate cement, but other body-compatible cements may be used.

A spreviously indicated, trial humeral components may be used in order to assess the depth of humeral bone to be removed and also forsizing of a component to fit a particular patient.

It is the be understood that Figs. 15 to 17 are illustrative only and do not attempt to depict the actual appearance of the operations. Obviously, the actual surgical procedures would be conducted under sterile conditions with the surgeon's hands gloved and there would be flesh around the humerus and ulna.

In an elbow joint reconstructed by use of a prosthesis embodying a preferred form of the invention, the articulating surfaces, e.g. 16 and 44, fit easily together and generally give a range of flexible movement between full extension (0 ) to flexion position (approximately 140 ). Stability is provided, in particular, by the intact medial ligament of the eblow and also by the lateral ligament, the anterior and posterior joint capsule and the adjacent musculature. Hence, any tendency for dislocation of the prosthesis is resisted by the natural anatomy and any lateral shift of the ulna is discouraged by the lateral convex boundary surface 18' of the humeral component 4. This is useful if trauma or undue strain is delivered to the elbow joint.Further, the prosthetic articulating arrangement allows for rotation of the ulna at the elbow, thus avoiding or minimising strain on the seating of the two components in strain situations.

Minimal bone is removed in the operative procedure which is a distinct advantage if there should be failure of the prosthesis for any reason, in which event, other surgical procedures can be easily accomplished.

The three humeral wire markers allow for accurate visualisation of the prosthesis by X-ray which is important in assessing wear andidisplacement after accidental trauma or loosening of the humeral component for any reason.

Figs. 1 2A and 1 2B show the range of pivotal movement of a prosthesis embodying the invention, Fig. 1 2A showing one extreme position and Fig. 126 showing the other extreme position of possible pivotal movement. Figs. 19 and 20 also illustrate the pivotal movement (Fig. 20) providing an angular range of 140" or more and Fig. 19 shows with the twe curved arrows pointing in opposite directions the possibility of medio-lateral gliding and limited rotation.

Figs. 21 and 22 are concerned with implanted prosthesis employing prosthesis embodying the invention wherein in Fig. 21 a radial component 12 is used fitted to the radius 14 and in Fig. 22 this is omitted, part of the radius bone having been removed by surgery as shown.

This Specification has been divided out of the specification of my co-pending Patent Application 7918348.

Claims (5)

1. Instrumentation for implantation of an elbow prosthesis comprising a humeral component having an articular surface that is curved concave in a coronal plane and curved convex in a saggital plane and an ulnar component having an articular surface that is curved convex in the coronal plane and curved concave in the saggital plane and is complementary to said articular surface of said humeral component, said instrumentation comprising a humeral impactor including an impactor head comprised of a thin curved end member of which a pushing surface is formed complementany to said articular surface of said humeral component, and a stem extending from one end of said end member in a direction substantilly perpendicularby away from said pushing surface, whereby said end member extends unilaterally from said stem.

2. Instrumentation as claimed in claim 1, and further comprising an ulnar impactor including an impactor head of which a pushing surface is formed complementarily to the said articular surface being arranged to be substantially coextensive with said articular surface of said ulnar component.

3. Instrumentation as claimed in claim 1 or 2, and further comprising a chisel including two substantially parallel blades bounding therebetween a channel open at both ends thereof, the blades including respective substantially parallel knife edges extending along the channel.

4. Instrumentation as claimed in claim 3, wherein said knife edges are inset towards each other.

5. Instrumentation for implantation of an elbow prosthesis, substantially as hereinbefore described with reference to the accompanying drawings.