WO2008152478A2

WO2008152478A2 - Femoral prosthesis construction with a partial resection of the femoral head

Info

Publication number: WO2008152478A2
Application number: PCT/IB2008/001501
Authority: WO
Inventors: Reinhold Ganz
Original assignee: Reinhold Ganz
Priority date: 2007-06-13
Filing date: 2008-06-09
Publication date: 2008-12-18
Also published as: WO2008152478A3; ITMI20071185A1

Abstract

A femoral prosthesis construction with a partial resection of the femoral head comprises a prosthesis stem and a substantially spherical prosthesis head which can be coupled to said prosthesis stem for example by a conical engagement, said prosthesis stem having a longitudinal axis and a transversal axis, said longitudinal axis having a length substantially larger than the length of said transversal axis, said prosthesis stem including a first proximal portion, a second middle portion and a third distal portion which are mutually integral to one another, characterized in that said first proximal portion of said stem has a substantially frustum-of-cone (100) shape and defines a minor base, an outer peripheral surface and a major base, said outer peripheral surface being adapted to be articulately engaged in a corresponding cavity of said spherical prosthesis head, said second middle portion also having a substantially frustum-of-cone shape and a major base meeting with said major base of said first proximal portion and a minor base, said third distal portion also having a substantially frustum-of-cone and/or tapering shape.

Description

FEMORAL PROSTHESIS CONSTRUCTION WITH A PARTIAL RESECTION OF THE FEMORAL HEAD

BACKGROUND OF THE INVENTION

The present ■ invention relates to a femoral prosthesis construction, with a resection of the femoral head thereof.

Femoral prostheses of a resurfacing prosthesis type, allowing to preserve the most part of the patient femoral head, are already known.

However, the above prior femoral prostheses are frequently affected by the problem that, during the surgical reconstructive operation, the medial femoral circumflex artery or MFCA, can be severely and definitely damaged, with a consequence that a femoral head necrosis can occur, which would lead to implant failure and re-operation. Thus, the above resurfacing prostheses are not suitable to be used in serious avascular conditions of the femoral head (AVN) , or in the presence of extended cysts. Moreover, a use of the above mentioned resurfacing prostheses would prevent a surgeon for properly and quickly adjusting muscular tension and the distance between the femoral bone and acetabulum.

For overcoming the above mentioned drawbacks of the disclosed resurfacing prostheses, further femoral prosthesis having a "standard" or a "femoral neck preserving" design have been provided: however, even if these latter femoral prostheses overcome some of the listed defects of the resurfacing prostheses, and even if they provide a possibility of anatomically reconstructing the femoral joint, they are still affected by drawbacks, such as the so-called "stress shielding". In fact, because of their design, the latter prostheses cause the joint loads to be transferred in a non physiologic manner, that is mainly near the tip of the prostheses. Thus, the proximal femoral bone cannot be properly stimulated and is reabsorbed, with a consequent failure of the prosthesis and a need of performing a revision surging thereof.

Moreover, the above "standard" or "femoral neck preserving" design prostheses need, to properly operate, a larger bone removal, in particular a larger removal of the proximal femoral portion, that is all the femoral head and a portion of or all the femoral neck, and, therefore, a lesser, and frequently insufficient, femoral bone stock would be available in a case a revision surgery should become necessary.

SUMMARY OF THE INVENTION

Accordingly, in view of the above mentioned drawbacks of prior femoral prosthesis constructions, in particular of their femoral stem, that is of that portion of the femoral prosthesis to be fixedly engaged in the femoral bone, the aim of the present invention is to provide such a femoral prosthesis including a femoral stem so designed as to provide an optimal transfer of the loads deriving from the femoral bone, while mostly preserving the femoral head, i.e. by osteotomizing only the actually diseased portion of said femoral head.

Within the scope of the above mentioned aim, a main object of the present invention is to provide such a femoral prosthesis construction designed for transferring the femoral joint loads to the proximal femoral bone, thereby preventing any stress shielding and bone resorption phenomena from occurring.

Another object of the present invention is to provide such a femoral prosthesis construction including a femoral prosthesis construction stem which can be easily and quickly applied, without using cement, for example by an impact method, to a femoral bone therefrom only the diseased head portion has been removed.

Yet another object of the present invention is to provide such a femoral prosthesis construction the stem of which can be optimally oriented with respect to the femoral bone trabecular path and which, moreover, is suitable to optimally fit the geometry of the femoral neck cross section, as well as the geometry of the medial curve of the proximal femur, thereby correspondingly optimally distributing the operating forces of the prosthesis. Yet another object of the present invention is to provide such a femoral prosthesis construction, which provides a very high stability of the femoral implant, in particular a very high rotational stability, and this without using, as aforesaid, cement materials.

Yet another object of the present invention is to provide such a femoral prosthesis construction suitable to minimize, in a definitely implanted and/or locked condition thereof, any risks of possible bony fractures.

Yet another object of the present invention is to provide such a femoral prosthesis construction the femoral stem of which can be easily fitted to a plurality of spherical heads, of a specifically dedicated type, and which spherical heads, in particular, are so designed as to easily adjust muscular tension and distance between femoral bone and acetabulum in order to obtain an optimal femoral joint reconstruction.

Yet another object of the present invention is to provide such a femoral prosthesis construction which can be easily applied to a femoral bone by a very simple and quick partial femoral osteotomy as well as by a correspondingly simple and quick press or impact fitting.

Yet another object of the present invention is to provide such a femoral prosthesis construction which, at a distal portion of the femoral stem thereof is so contoured as to easily control the related operations for fitting or engaging the femoral stem in a specifically formed seat in the femoral bone.

Yet another object of the present invention is to provide such a femoral prosthesis construction which can be easily made starting from conventional biocompatible materials, in particular, preferably, metal materials.

According to one aspect of the present invention, the above mentioned aim and objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by a femoral prosthesis construction with the partial resection of the femoral head having the features of the main claim. Further characteristics of the femoral prosthesis construction according to the invention are set out in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

Further details and features of the femoral prosthesis construction with a partial resection of the femoral head according to the present invention will become more apparent hereinafter from the following detailed disclosure of a preferred, though not limitative, embodiment thereof, with reference to the accompanying drawings, where: Figure 1 is a partial perspective view, on a real scale, of a presently preferred embodiment of the femoral prosthesis construction according to the present invention, in particular of the stem portion thereof, without the corresponding spherical head; Figure 2 is a further partial perspective view, also on a real scale, of the femoral prosthesis construction of the invention, in particular of the femoral stem thereof;

Figure 3 is yet another perspective view, as cross-sectioned, of the femoral stem of the preceding figures;

Figure 4 is yet another cross-sectional view specifically illustrating ribs integrally formed on a periphery of the femoral stem of the prosthesis construction according to the present invention; and

Figure 5 is a schematic view illustrating the subject femoral prosthesis construction, in particular the stem thereof, applied to a femur of a patient, the dashed lines in this figure showing the trabecular path of the femoral bone, and

Figures 6 and 7 respectively show the femoral ball head of the femoral prosthesis construction according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the above mentioned figures, the femoral prosthesis construction according to the invention comprises a femoral stem, generally indicated by the reference number 1, and a femoral ball head, to be connected to the femoral stem 1 and which has been generally indicated by 100 in figures 6 and 7. In this connection, it should be pointed out that such a femoral head will be a dedicated configuration ball head, designed, in particular, to be used for adjusting muscular tension and distance between the femoral bone and acetabulum to provide an optimal reconstruction of the femoral joint, as it will become more apparent hereinafter .

In actual practice, the core of the invention is the femoral prosthesis stem 1, which comprises a proximal portion 2, a middle or intermediate portion 3 and a distal portion 4, all the stem portions being integral with one another, and being made, for example, of a suitable biocompatible material, preferably a biocompatible metal material.

The femoral stem 1, in particular, has been specifically designed to be implanted without cement, for example by a press or impact implanting method, in the proximal femoral therefrom the femoral head has been partially resected away, as is specifically shown in figure 5. In particular, the prosthesis stem 1 defines a longitudinal axis and a transversal or cross axis, not specifically marked, the longitudinal axis having a length substantially larger than the length of the transversal axis.

The first proximal portion 2 of the femoral stem 1 has a substantially frustum-of-cone shape, and defines a peripheral surface, indicated by the reference number 5, a minor base 6 and a major base 7.

The peripheral surface 5 of said proximal portion 2, in particular, can be articulately engaged in a corresponding cavity of the spherical or ball prosthesis head, which, as stated, has not been herein shown.

The second middle or intermediate portion 3 of the femoral stem 1 also has, as is shown, a substantially frustum-of-cone shape, including a major base 8 and a minor base, not referenced, which integrally meets the major base 9 of the distal portion 4, or third portion of the prosthesis stem 1.

Said third distal portion 4 also has a frustum- of-cone or tapering shape, and comprises a minor base 10, or substantially rounded tip portion, to properly drive the stem for easily implanting it into its bone seat, as suitably prepared, and defining an outer surface 11, which advantageously has been suitably surface processed, for example by blasting, plasma spray, chemical processing and/or the like, to facilitate, according to an advantageous aspect of the present invention, an osteointegration and transfer of the stresses to the proximal femur.

In this connection, it should be pointed out that also the remaining part of the femoral stem can be likewise processed.

Advantageously, as clearly shown in figures 3 and 4, the middle portion 3 of the femoral stem 1 comprises a substantially elliptical cross section 12, which can be fitted, according to a further aspect of the invention, to the geometrical configuration of the femoral neck portion.

Said middle portion 3 of the femoral stem 1 has a peripheral surface including two sides, that is an outer side 13 and an inner side 14 defining a contour which is so curved as to substantially fit or follow the trabecular path of the femoral neck portion and the medial curvature of the proximal femur. Advantageously, according to a further aspect of the present invention, the femoral stem 1 further comprises, on the peripheral surface of the second middle portion 3, a plurality of adjoining ribs 15, designed for increasing the rotational stability of the prosthesis stem in its as-implanted condition in the femoral channel, as is clearly shown, for example, in figure 5. Said adjoining ribs 15 have, according to a further advantageous aspect of the invention, a curvature corresponding to that of the two outer 13 and inner 14 sides of the middle portion 3 of the femoral stem 1.

Moreover, said adjoining ribs have, further advantageously, and as is clearly shown in figures 3 and 4, mutually different heights, for example from 0.5 mm to 4 mm, depending on the anatomic position occupied by said ribs in the femoral bone, for reducing to a minimum a risk of possible bony fractures, which could be caused by said ribs if the latter would be excessively invasive. According to yet another aspect of the invention, the major base of the middle portion 3 of the femoral stem defines a substantial flat proximal surface, which is inclined with respect to the cross axis of the stem, thereby providing said stem with a target orientation, with respect to the trabecular path of the femoral neck portion, to facilitate the transmission of the femoral joint forces to the proximal femur, while preventing said forces from being decomposed into undesired force components (such as shearing forces), thereby in turn preventing any stress shielding phenomenon from occurring. Said inclination angle is preferably from 40° to 70°. For affixing without cement the stem 1 in the femoral bone, said stem 1 is introduced into the femoral bone by any suitable pressure fitting or impact method, after having being surface treated, for example by a blasting, chemical attack, plasma spray process and/or the like, to provide an osteointegrating surface, as is known in the prior art.

Thus, according to a further important aspect of the present invention, and as disclosed, the cross section of the overall femoral stem 1 will decrease from the proximal end 2 to the distal end 4 thereof, with a substantially conical configuration.

In this connection, it should be further pointed out that the outer contour of the middle portion has been so curved as to follow the trabecular path in the femoral neck and the medial curvature of the proximal femur, to improve the distribution of the forces affecting the femoral joint.

In particular, the osteotomy operation should be so performed as to provide a proper orientation of the implant with respect to the trabecular path and medial curvature or bending of the proximal femur. Thus, and as stated, the proximal end of the prosthesis has a surface which is oriented with suitable angle with respect to the transversal of cross axis of the stem, to provide in turn a desired orientation of the femoral stem with respect to the trabecular path, as it is oriented parallel to the osteotomy. As stated, said plurality of ribs 15 are so designed as to improve the rotational stability of the implant, said ribs being also curved depending on the geometry of the femoral stem and having different heights to fit the anatomical position said ribs will occupy, so as to reduce to a minimum a risk of possible bony fractures which would be caused by excessively invasive ribs.

Moreover, all the implant is made starting from biocompatible materials, preferably biocompatible metal materials.

With respect to the spherical or ball head, it is so designed and used to properly adjust muscular tension and distance between the femoral bone and acetabulum (not shown) to provide an optimum reconstruction of the femoral joint.

With reference now to figures 6 and 7, said ball or spherical head, which has been generally indicated by the reference number 100, comprises a spherical head cavity 110 in a side thereof, to be coupled to the mentioned proximal portion 2 of said femoral stem construction 1. Said cavity 110 has a substantial frustum-of-cone shape, and may have different heights, to provide different positions of the center of the sphere with respect to the femoral prosthesis, to easily allow in turn a surgeon to properly adjust muscular tension and distance between the femur and pelvis .

According to the invention, said spherical head 100 is advantageously cut through according to a plane which is parallel to said flat surface of said major base of said middle portion 3 of the femoral stem 1.

More specifically, said ball head portion is cut by said cutting plane at such a height, as measured from the equatorial line thereof, that, as said ball portion is coupled to a femoral stem implanted in a femoral bone, it will allow to reconstruct a perfect ball. The remaining portion of said perfect ball or sphere, being provided by that part of the femoral head which has not been resected by the surgeon during the surgical operation.

From the above disclosure it should be apparent that the invention fully achieves the intended aim and objects.

While the femoral prosthesis construction according to the invention has been hereinabove disclosed with reference to a presently preferred embodiment thereof, it should be apparent that the disclosed embodiment is susceptible to several modifications and variations, all of which will come within the scope of the invention, as defined by the following claims.

Claims

1. A femoral prosthesis construction with a partial resection of the femoral head comprising a prosthesis stem and a substantially spherical prosthesis head which can be coupled to said prosthesis stem for example by a conical engagement, said prosthesis stem having a longitudinal axis and a transversal axis, said longitudinal axis having a length substantially larger than a length of said transversal axis, said prosthesis stem including a first proximal portion, a second middle portion and a third distal portion which are mutually integral to one another characterized in that said first proximal portion of said stem has a substantially frustum-of- cone shape and defines a minor base, an outer peripheral surface and a major base, said outer peripheral surface being adapted to be articulately engaged in a corresponding cavity of said spherical prosthesis head, said second middle portion also having a substantially frustum-of-cone shape and a major base meeting with said major base of said first proximal portion and a minor base, said third distal portion also having a substantially frustum-of-cone and/or tapering shape, with a major base meeting said minor base of said second middle portion and a minor base defining a distal tip portion.

2. A femoral prosthesis construction according to claim 1, characterized in that said second middle portion of said femoral stem has a substantially elliptical cross section, to be fitted to the geometric configuration of a femoral neck portion and head.

3. A femoral prosthesis construction according to claims 1 and 2, characterized in that said second middle portion of said femoral stem has a peripheral surface defined by an outer side and an inner side defining a contour having such a curvature as to substantially follow a trabecular path and medial curvature of said femoral neck portion.

4. A femoral prosthesis construction according to one or more of the preceding claims, characterized in that said peripheral surface of said second middle portion comprises a plurality of adjoining ribs designed for improving a rotational stability of said prosthesis stem.

5. A femoral prosthesis construction according to claims 3 and 4, characterized in that said adjoining ribs have a rib curvature substantially corresponding to a curvature of said outer and inner sides of said middle stem portion.

6. A femoral prosthesis construction according to claims 4 and 5, characterized in that said adjoining ribs have mutually different rib heights, preferably from 0.5 mm to 4 mm.

7. A femoral prosthesis construction according to claim 1, characterized in that the third distal portion of said femoral stem defines a peripheral surface which is surface treated by a blasting, spray plasma, chemical attack method, to facilitate an osteointegrating process and a transmission of stresses of a femoral joint, and that said third distal portion has a substantially frustum-of-cone and/or tapering shape to facilitate an engagement of said prosthesis stem in a femoral bone cavity and that said distal tip portion of said third distal portion of said femoral stem has a substantially rounded contour.

8. A femoral prosthesis construction according to one or more of the preceding claims, characterized in that said major base of said second middle portion of said femoral stem defines a substantially flat stem proximal surface, said proximal surface being inclined with respect to a transversal axis of said stem at an angle from substantially 40° to 70°, to provide a desired orientation of said stem with respect to a trabecular path of said femoral neck portion, to facilitate a transmission of femoral joint forces to the proximal femur, while preventing said forces from being decomposed into undesired force components, thereby preventing any stress shielding phenomenon from occurring .

9. A femoral prosthesis construction according to one or more of the preceding claims, characterized in that said femoral stem is designed to be fixedly engaged in said femoral bone by a press fitting mechanism, said stem being surface processed, for example, by a blasting, acid attack, plasma spray processing method, to facilitate an osteointegrating process thereof in said femoral bone.

10. A femoral prosthesis construction according to claim 1, characterized in that said prosthesis head comprises, in a side thereof, a cavity having a substantially frustum-of-cone shape designed to be coupled to said proximal portion of said femoral stem, said cavity having different cavity heights to provide different positions of a center of said prosthesis head with respect to said femoral stem, to allow a surgeon to properly adjust a muscular tension and a distance between a patient femur and pelvis.

11. A femoral prosthesis construction according to one or more of the preceding claims, characterized in that said prosthesis head is cut through by a cutting plane substantially parallel to said flat surface of said major base of said middle portion of said femoral stem, at such a height, as measured from an equatorial plane of said head, to define, with said femoral stem implanted in said femoral bone, a perfectly spherical contour.

12. A femoral prosthesis construction, with a resection of the femoral head, characterized in that said femoral stem and said spherical head portion are made of biocompatible materials, preferably biocompatible metal materials, and substantially as disclosed and illustrated for the intended aim and objects.