Endoprosthesis for part of the pelvis

The invention relates to an endoprosthesis for part of the pelvis having at least one base element which can be secured to a resected iliac bone and at least one hip shell attachable at a spacing thereto, with the base element having a first neck which in particular projects at an angle α from the orthogonal to a planar connection surface and the hip shell having a second neck which in particular projects at an angle β from its polar axis, with at least one separate intermediate element being provided which can be installed between the first neck and the second neck.

BACKGROUND OF THE INVENTION

The invention relates to an endoprosthesis for part of the pelvis having at least one base element which can be secured to a resected iliac bone and at least one hip shell attachable at a spacing thereto, with the base element having a first neck which in particular projects at an angle α from the orthogonal to a planar connection surface and the hip shell having a second neck which in particular projects at an angle β from its polar axis.

There are some tumor patients where the ilium, i.e. half the pelvic bone, has to be resected from below by one-third to two-thirds of its height. Without further aid measures, it was previously customary to amputate the associated leg in order to avoid complications due to a lack of attachment to the trunk. To avoid such amputations, endoprostheses for part of the pelvis have been developed which may not be put under excessive strain, but which exert at least a passive retainer function for the leg attached to it.

Such an endoprosthesis is shown in the patent application WO 88/01491 in which two necks are molded to a hip shell and each have a receiving bore for a spigot with a self-locking fixed fit. The spigots are each anchored at their other end to the resected ilium or pubic bone. The anchoring to the ilium in this process takes place via a plate-shaped base element.

A further endoprosthesis of this kind is known from the patent application EP 0 628 294 A1. Receiving bores for spigots having a self-locking fit are provided at a neck of a hip shell. The securing of a shaft part continuing the spigot takes place by intramedullary engagement into a groove milled into the stub of the ilium. A mechanical adjustment unit is additionally provided with the aid of which the shaft part can be adjusted in an elongate bore of a base element secured to the ilium.

It is, however, a disadvantage with the aforesaid endoprosthesis for part of the pelvis that the length of the spigot and the angular position of the spigot are fixedly predetermined relative to the base element and thus also the position and the alignment of the hip shell. The desired position of the hip bone must therefore already be taken into account on the resection of the iliac bone with respect to the height and direction of the resection incision.

SUMMARY OF THE INVENTION

It is therefore an underlying object of the present invention to provide an endoprosthesis for part of the pelvis of the initially named kind which is characterized by a design which is as simple as possible with simultaneously increased flexibility with respect to the positioning and/or alignment of the hip shell.

This object is satisfied in that at least one separate intermediate element is provided which can be installed between the first neck and the second neck.

Provision is made in the endoprosthesis for part of the pelvis in accordance with the invention for a further component to be installable between the neck of the base element and the neck of the hip shell. Increased flexibility of the endoprosthesis for part of the pelvis is ensured by the possibility of installing a separate intermediate element. This flexibility is in particular of advantage when the surgeon finds conditions during the surgical procedure which require a resection incision different from the original surgery plan.

Different relative positions between the base element and the hip shell can preferably be realized by means of the intermediate element. This in particular makes it possible for repositioning of the hip shell even after the anchoring of the base part to the iliac bone.

It is particularly advantageous for at least two intermediate elements to be provided which differ from one another and which can each be installed between the first neck and the second neck. The endoprosthesis for part of the pelvis in accordance with the invention hereby provides a kit of different intermediate elements which can be installed alternatively to one another between the first neck of the base element and the second neck of the hip shell. The surgeon inserting the endoprosthesis for part of the pelvis can choose that intermediate element from a set of intermediate elements differing from one another which permits the desired position for the hip shell most favorable for the respective patient.

Intermediate elements of different lengths are preferably provided so that the spacing between the base element and the hip shell, and thus the spacing between the resected stub of the ilium and the joint ball of the femur, can be varied.

Additionally or alternatively, at least one intermediate element can be cranked so that the center axes of the first neck and of the second neck can be tilted toward one another or can run in a parallel offset manner. Further relative positions are hereby made possible between the base element and the hip shell which cannot be realized by a mere extension by means of a straight intermediate element.

Provision can furthermore be made in accordance with the invention for the intermediate element and the first and second necks each to be provided in contact areas with projections and recesses latchable at different angular positions. The projections and recesses in the contact areas can in particular correspond to a toothed Hirth coupling. It is hereby achieved, in particular when a cranked intermediate element and/or a hip shell not rotationally symmetrical with respect to its polar axis is used, that the latter, in particular its polar axis, can be oriented in different spatial directions so that further relative positions can in turn be realized between the base element and the hip shell. The projections and recesses additionally represent security against rotation.

Furthermore, contact planes of at least one intermediate element and defined by contact areas can stand at an angle ε to one another, in particular an acute angle, different from zero. In particular, contact planes standing at an angle ε to one another can be provided only with cranked intermediate elements. It is hereby made possible for cranked intermediate elements to be used alternatively to non-cranked intermediate elements whose contact planes extend parallel to one another.

In a particularly preferred embodiment, the intermediate element can be spanned between the first neck and the second neck via a draw rod. A particularly firm and secure connection can hereby be achieved between the intermediate element and the base element or the hip shell. The draw rod in this process can in particular be guided inside the respective intermediate element, made for example as a sleeve, and the two ends of the draw rod can be anchored in the base element and the hip shell.

Draw rods which match intermediate elements of different lengths are preferably provided.

It is furthermore proposed in accordance with the invention that a waisted bolt is provided as the draw rod.

The draw rod can engage into a head held in the first neck. The head can in particular be made as a ball joint. It can hereby be achieved that the head held in the first neck can cooperate both with non-cranked and cranked intermediate elements, in particular with differently cranked intermediate elements.

It is furthermore preferred for the head to be secured against rotation with respect to the intermediate element via a shape-matched plug-in connection. This is in particular of advantage when the head can be released from its holding in the first neck in a position achievable by rotation.

In a further preferred embodiment, the head has a spherical surface over an angular range γ of more than 180°, in particular of more than 200°, the spherical surface having a flattened section formed in the shape of a band extending beyond the pole, with the head being able to be inserted into a cavity formed in the first neck in an installation position rotated by 90° with respect to the functional position.

Differently sized anchoring spigots can be inserted into the base element to secure the base element to the iliac bone in order to anchor the endoprosthesis for part of the pelvis to the stub of the iliac bone so that a matching anchoring spigot can be selected in dependence on the respective anatomical demands.

An inner shell can furthermore be insertable into the hip shell with a snap connection. In particular a joint ball can be inserted into the hip shell together with an inner shell which surrounds the joint ball by more than 180° so that a femur can be secured to the endoprosthesis for part of the pelvis.

To achieve a particularly simple and effective holding of the joint ball, the inner shell can have a holding ring which can be secured to the hip shell after the insertion of a joint ball.

Base elements, hip shells and intermediate elements can be provided as parts of a trial kit which each consist of a plastic, which can be sterilized, and which serve for the location of a matching spatial position of the hip shell relative to the base element, with the trial hip shells each having a contact area matching to a joint ball so that an inner shell can be dispensed with.

The prosthesis parts for trial prostheses and for finally insertable prostheses can be characterized differently to prevent possible confusion. The engagement positions of intermediate elements and first and second noses can each be marked so that the matching spatial position of the hip shell determined by means of the components of the endoprosthesis for part of the pelvis consisting of plastic can easily be transferred to the finally insertable prostheses.

The invention will be further described in the following by way of example with reference to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1,2and3show different views of an endoprosthesis for part of the pelvis in accordance with the invention shown in the assembled state for the replacement of a part of the pelvis in the region of the hip joint having a base element1which can be secured to a resected iliac bone, a hip shell6for the receiving of a hip joint ball and an intermediate element which is designed as a sleeve8and is arranged between the base element1and the hip shell6.

A planar surface2of the base element1contacts the resection plane of the resected iliac bone (not shown). An anchoring spigot4, which engages into a bore provided in the stub of the iliac bone, is inserted into the base element1to secure the base element1to the iliac bone.

The anchoring spigot4is inclined by an angle α with respect to an orthogonal19to the connection surface2. The anchoring spigot4tapers conically at its end projecting beyond the connection surface2in the direction of the iliac bone and has a surface with elongate ribs.

In addition to the anchoring spigot4, two bracket pieces3are provided for the securing of the base element1to the iliac bone and are connected to the base element1in a marginal region thereof, and each project from the connection surface2of the base element1at an angle of 90°. The bracket pieces3can each be secured to the iliac bone via a passage bore.

The base element1furthermore has a first neck5likewise projecting from the orthogonal19to the planar connection surface2at the angle α so that the inclinations of the first neck5and of the anchoring spigot4opposite the orthogonal19to the planar connection surface2correspond to one another.

The first neck5of the base element1is connected to a second neck7of the spherically shaped hip shell6via the cylindrically shaped sleeve8. The respective central axes of the anchoring spigot4, of the first neck5, of the sleeve8and of the second neck7form a common central axis9inFIGS. 1,2and3. The second neck7is inclined by an angle β with respect to the polar axis20of the hip shell6.

The sleeve8and the first and second necks5,7are each provided with projections and recesses12on their contact areas lying opposite one another, said projections and recesses being designed in the manner of a toothed Hirth coupling so that different angular positions of the sleeve8with respect to the central axis9are possible with respect to the first neck5and to the second neck7with respect to the sleeve8.

FIG. 4shows a cross-section of the endoprosthesis for part of the pelvis in accordance with the invention along the line IV-IV inFIG. 3. For reasons of simplicity, the representation of the projections and recesses12has been omitted inFIG. 4. It can be seen fromFIG. 4that the contact areas of the first neck5, of the sleeve8and of the second neck7are each made approximately planar. The contact planes10,11defined by the contact areas in the assembled state of the endoprosthesis for part of the pelvis are aligned parallel to one another.

It can furthermore be seen fromFIG. 4that the anchoring spigot4inserted into the base element1extends up to and into the first neck5of the base element1and is screwed into the base element1. In the first neck5of the base element1, a cavity is furthermore formed in which a spherical head14is held which will be explained in more detail in another passage and has a spherical surface over an angular region γ of 200° and which is secured against rotation with respect to the sleeve8via a shape-matched plug-in connection15.

An elongate waisted bolt26, which serves as a draw rod and clamps the sleeve8between the first neck5and the second neck7, engages into the spherical head14held in the first neck5. The part of the waisted bolt26not screwed into the spherical head14is arranged within the sleeve8or within a bore of the second neck7of the hip shell6. The sleeves8have a clearance25which is larger than the diameter of the waisted bolt26.

The head of the waisted bolt26is made as a hexagon24to permit the screwing of the waisted bolt26into the spherical head14held in the first neck5. The waisted bolt26furthermore includes a collar23which, in the assembled state of the endoprosthesis for part of the pelvis, is held in a cavity of the second neck7connected to the bore so that the sleeve8is clamped between the first neck5and the second neck7.

The spacing13between the base element1and the hip shell6can be varied in that sleeves8of different lengths and waisted bolts26of matching lengths thereto are provided which can each be installed or screwed between the first neck5and the second neck7.

FIGS. 5 and 6show an embodiment of an endoprosthesis for part of the pelvis in accordance with the invention with a cranked sleeve8, with respectively the same or corresponding parts being designated with the same reference numerals so that a repeat representation is dispensed with and only the differences of the embodiment shown in these Figures with respect to the first embodiment are explained.

In accordance withFIGS. 5 and 6, the sleeve8is cranked or bent like a hook. The crank22of the sleeve8has the consequence that the contact planes10,11defined by the contact areas stand at an acute angle ε to one another. A common central axis27of the anchoring spigot4and of the first neck5is inclined with respect to a common central axis28of the waisted bolt26, of the larger part of the sleeve8and of the second neck7. Due to the engagement of the waisted bolt26, the spherical head14shown inFIG. 6is tilted with respect to the spherical head shown inFIG. 4.

An inner shell16likewise made in spherical shape is inserted into the hip shell6, with the two shells6,16each having a shoulder33being connected to one another by means of a snap connection29. The inner shell16surrounds a joint ball18, in particular an artificial joint ball, by more than 180° in this process. The inner shell16includes for this purpose a holding ring17which, after the insertion of the joint ball18into the inner shell16, is connected to the latter.

To ensure a correct relative positioning of the inner shell16with respect to the hip shell6, the inner shell16has a nose34in its polar region which projects in the direction of the hip shell6and engages, in the assembled state of the endoprosthesis for part of the pelvis, into a cut-out of the hip shell6continuing the cavity of the second neck7.

FIGS. 7 and 8show a further embodiment of an endoprosthesis for part of the pelvis in accordance with the invention which differs from the two aforesaid embodiments in particular by the design of the base element1. To permit application directly at the sacrum, the endoprosthesis for part of the pelvis in accordance withFIGS. 7 and 8has a bracket-shaped connection surface2.

FIGS. 9,10,11and12show different views of the spherical head14already mentioned above. The spherical head14has a spherical base shape with a spherical surface extending over an angular range γ of 200°. The spherical head furthermore has a continuous threaded bore31which is formed along the polar axis30of the spherical head14and into which the waisted bolt26engages in the assembled state of the endoprosthesis for part of the pelvis.

A plug projection32through which the bore31passes is formed at the side of the spherical head14remote from the pole. The plug projection32is made substantially square in planes extending to the polar axis30, with the plug projection32, in the assembled state of the endoprosthesis for part of the pelvis, projecting into the correspondingly shaped passage of the sleeve8so that the spherical head14is secured against rotation.

The spherical surface of the spherical head14has a flattened section made in the shape of a band21extending beyond the pole. The spherical head14thus has a circular shape—interrupted by two oppositely disposed flattened sides—in planes extending perpendicular to the polar axis30. The inlet opening of the cavity of the first neck5has a corresponding shape so that the spherical head14inserted into the cavity can be held in the first neck5in a functional position rotated through 90° with respect to the installation position.

The assembly of an endoprosthesis for part of the pelvis in accordance with the invention will be described in the following with reference to the Figures.

The base element1is first secured to the resected iliac bone by means of the anchoring spigot4and of the two bracket pieces3so that the connection area2of the base element1contacts the stub of the ilium. The spherical head14has already been inserted into the cavity of the first neck5before the attachment of the base element1to the stub of the ilium, but can alternatively also only be inserted after the attachment of the base element1.

The surgeon then selects that sleeve8from a set of sleeves8, which differ from one another and which permit different relative positions between the base element1and the hip shell6, which permits the most expedient relative position under anatomical aspects. The sleeves8can have different lengths and/or be cranked.

Subsequently, a waisted bolt26matching the length of the selected sleeve8is selected from a set of waisted bolts of different lengths. The waisted bolt26is then led through the bore formed in the second neck7of the hip shell6and through the sleeve8and is screwed into the bore31of the spherical head14held in the first neck5.

The waisted bolt26is tightened while taking into account the orientation of the hip shell6, and optionally the crank22of the sleeve8, so that the projections and recesses12of the contact areas of the first neck5, of the sleeve8and of the second neck7engage into one another. The plug projection32of the spherical head14engages into the interior of the sleeve8so that a shape-matched plug-in connection15secured against rotation is formed with respect to the sleeve. When a cranked sleeve8is used, the spherical head14is tilted accordingly due to the engagement of the waisted bolt26(FIG. 6).

The inner shell16is finally inserted into the hip shell6and is secured thereto by means of the snap connection29(FIG. 6). The joint ball18held in the inner shell16by the holding ring17was previously inserted into the inner shell16, with the inner shell16including the holding ring17surrounding the joint ball18by more than 180°.

An endoprosthesis for part of the pelvis in accordance with the invention thus has increased flexibility with respect to the positioning and alignment of the hip shell6due to the available intermediate elements8, which are in particular of different lengths and/or cranked, so that the relative position between the base element1and the hip shell6can be achieved during a surgical treatment which is respectively most expedient for anatomical reasons. In particular greater degrees of freedom are made possible for the surgeon on the setting of the resection incision at the iliac bone.