Artificial Hip-joint With Detachable Insert

Abstract

An artificial hip-joint, wherein an endoprosthesis of the patient's acetabulum is hinged to an endoprosthesis of the proximal end of the patient's femur by way of an insertion piece. The height of the cavity defined by the interior spherical surface of the insertion piece is greater than the radius, but smaller than the diameter, of the head of the endoprosthesis of the proximal end of the femur. There are cut-outs in the distal portion of the insertion piece, with the blades between the cut-outs forming a collet enveloping the head. The insertion piece is fixed in the seat of the endoprosthesis of the acetabulum by a self-locking nut.

Description

BACKGROUND OF THE INVENTION

The present invention relates to artificial hip-joints employed in surgical intra-articular prosthetic replacement.

It is directed to assisting in regaining hip-joint mobility lost due to Bekhterev's disease, arthritis deformans, arthritis infectiosa, aceptic necrosis of the femoral head, as well as femoral neck fractures in the aged.

Those skilled in the art are aware of an artificial hip-joint, which incorporates an endoprosthesis of the patient's acetabulum and an endoprosthesis of the proximal end of the patient's femur comprising a head, a neck and a pin introduced into the femoral medullary canal.

The endoprosthesis of the acetabulum may be of different designs as regards both the exterior surface and the interior one contacting the head of the endoprosthesis of the proximal end of the femur.

According to one of the possible versions of the known aritificial hip-joint, the exterior surface of the endoprosthesis of the acetabulum is provided with a single long screw which is screwed through the acetabulum and into the wing of the patient's iliac bone, thereby immobilizing the acetabulum endoprosthesis in the pelvis.

The interior surface of this endoprosthesis is semi-spherical, and the head of the endoprosthesis of the proximal end of the femur is immersed into the semi-sphere of the acetabulum endoprosthesis to a depth equal to its diameter and left there without being fixed in any way.

Such an approach has a disadvantage which resides in the sophisticated technique required to introduce the long screw into the wing of the iliac bone; furthermore, the screw is liable to become loose and the endoprosthesis of the proximal end of the femur is likely to become dislocated from the endoprosthesis of the acetabulum.

There is another known artificial hip-joint whose endoprosthesis of the acetabulum is studded with spikes on its exterior surface. These spikes assist in cementing the acetabulum endoprosthesis.

The interior surface of this endoprosthesis is semi-spherical to accommodate the head of the endoprosthesis of the proximal end of the femur.

The disadvantage of this design lies in the need to use cement for immobilizing the endoprosthesis of the acetabulum. Another disadvantage is the likelihood of dislocation of the endoprosthesis of the proximal end of the femur.

The exterior surface of the endoprosthesis of the acetabulum may be provided with blades having apertures for the advancement of burgeoning bony tissue.

The interior surface of the endoprosthesis of the acetabulum has a seat which receives an insertion piece made up of two identical halves. The exterior surface of the insertion piece corresponds to the shape of the seat, whereas the interior surface of the insertion piece is spherical and envelops the spherical head of the endoprosthesis of the proximal end of the femur in such a way that the area of contact exceeds the semi-sphere of the head.

These insertion pieces are designed to couple the endoprosthesis of the acetabulum with the endoprosthesis of the proximal end of the femur. The coupling is achieved by riveting the ends of the insertion piece onto the exterior surface of the acetabulum endoprosthesis, thereby ensuring a non-detachable joint.

The disadvantages of such artificial hip-joints are the difficulties involved in their installation at surgery and also lack of interchangeability of their individual components. There is a further limitation which militates against their application: the endoprostheses can only be made of materials amenable to riveting.

Hence, some of the known artificial hip-joints are detachable but insecure against the dislocation of the endoprosthesis of the proximal end of the femur from the endoprosthesis of the acetabulum, whereas others are non-detachable and unwieldy both at surgery and when it is required to replace one of the component elements of the artificial hip-joint.

SUMMARY OF THE INVENTION

It is an object of the present invention, therefore, to provide a detachable artificial hip-joint, such as could be assembled during an operation.

It is another object of the present invention to provide an artificial hip-joint, which eliminates any possibility of dislocation of the endoprosthesis of the proximal end of the femur from the endoprosthesis of the acetabulum.

It is yet another object of the present invention to provide an artificial hip-joint which allows a wide choice of construction materials irrespective of their amenability to riveting.

Accordingly, there is provided an artificial hipjoint, comprising an endoprosthesis of the patient's acetabulum, whereof the exterior surface is adapted to be impacted in the bony tissue of the patient's pelvis, and which has a seat, and an endoprosthesis of the proximal end of the patient's femur incorporating a head with a spherical surface rigidly connected by way of a neck to a pin introduced into the femoral medullary canal, and intermediate the surface of the seat and the exterior spherical surface of the head there is provided an insertion piece ensuring a hinged connection of the two surfaces, which insertion piece has a spherical interior surface interacting with the spherical surface of the head, wherein, in accordance with the invention, the height of the cavity of the insertion piece defined by the interior spherical surface thereof is more than the radius, but less than the diameter, of the head, with cut-outs provided in the distal portion of the insertion piece, the blades between these cut-outs forming a collet enveloping the head of the endoprosthesis of the proximal end of the femur, whereas the insertion piece is fixed in the seat of the acetabulum endoprosthesis by a self-locking nut.

The aritificial hip-joint of this invention offers a number of advantages.

For example the instant artificial hip-joint enables the endoprosthesis of the acetabulum and the proximal end of the femur to be put in place independently of each other in the process of an operation. This feature, in turn, ensures high precision of installation and firm impaction of the endoprosthesis in the bone. Only one of the endoprosthesis may be replaced, if desired.

Since the two endoprostheses are reliably interconnected, all possibility of dislocation of the endoprosthesis of the proximal end of the femur out of the endoprosthesis of the acetabulum is altogether eliminated.

The design of the insertion piece having cut-outs in its distal portion, with the blades between the cut-outs forming a collet, affords a wider choice of materials from which the endoprostheses may be constructed and ensures higher anti-friction properties of the joint surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 is a general view, partly in section, of an artificial hip-joint in accordance with the present invention;

FIG. 2 is a general view, partly in section, of the artificial hip-joint of this invention, shown dismantled;

FIG. 3 is a general view of the artificial hip-joint of this invention taken along the arrow A in FIG. 2;

FIG. 4 is a general view of the artificial hip-joint of this invention taken along the arrow B in FIG. 2;

FIG. 5 is a general view of the artificial hip-joint of this invention taken along the arrow C in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The artificial hip-joint of the invention comprises an endoprosthesis 1 (FIGS. 1 and 2) of the patient's acetabulum, whereof the exterior surface is adapted to be impacted in the bony tissue of the patient's pelvis, hinged to an endoprosthesis 2 of the proximal end of the patient's femur.

The endoprosthesis 1 of the acetabulum is provided on the exterior surface thereof with a plurality of blades 3 with tapered edges, which blades are arranged in tiers one above another and have apertures 4, wherethrough the burgeoning bony tissue of the patient's pelvis may advance. There is a seat 5 formed on the other side of the surface of the endoprosthesis 1 of the acetabulum (FIG. 2), which seat has an intricate shape comprised of a cylindrical and a conical surface. The seat may be of a through type, as illustrated in the drawing, or of a non-through type. The distal part of the seat is provided with a thread 6.

The endoprosthesis 2 of the proximal end of the patient's femur comprises a head 7 (FIGS. 1 and 2) with a spherical surface, which head 7 is rigidly connected by way of a neck 8 with a tapered pin 9 introduced into the femoral medullary canal. For burgeoning bony tissue to advance into the pin 9, apertures 10 are provided in the latter. In its proximal portion the pin 9 extends into a bearing pad 11 provided with a pin 12 serving to immobilize the trochanter major.

An insertion piece 13 is installed intermediate the exterior spherical surface of the head 7 and the surface of the seat 5 to provide for a hinged connection of the endoprosthesis 1 of the acetabulum and the endoprosthesis 2 of the proximal end of the femur. The exterior surface of the insertion piece 13 by its shape conforms to the shape of the interior surface of the seat 5 with a chamfer in the distal section, while the interior surface of the insertion piece 13 is spherical and interacts with the spherical surface of the head 7.

The height of the cavity of the insertion piece 13 (FIG. 2) defined by the latter's interior spherical surface is more than the radius, but less than the diameter, of the head 7. In the distal portion of the insertion piece 13 (FIGS. 2 and 3) there are cut-outs 14 extending to the diameter of the spherical surface of the insertion piece 13, with the blades 15 between the cut-outs 14 forming a collet enveloping the head 7.

The insertion piece 13 (FIG. 2) is fixed in the seat 5 by a self-locking nut 16, whereof the exterior surface is provided with a thread 17 corresponding to the thread 6 of the seat 5 of the acetabulum endoprosthesis 1. The interior surface of the nut 16 is chamfered to conform to the chamfer of the distal section of the exterior surface of the insertion piece 13. The nut 16 is provided with a locking device consisting of a longitudinal slot 18 and a screw 19.

The longitudinal dimension of the nut 16 exceeds the diameter of the head 7 of the endoprosthesis 2 of the proximal end of the femur.

If the nut 16 is longitudinally less than the diameter of the head 7 of the endoprosthesis 2 of the proximal end of the femur (for example, if it is required to make the insertion piece of a material susceptible to yield under pressure), then the nut 16 must be fitted in advance over the neck 8 when assembling the endoprosthesis 2 of the proximal end of the femur or at the side of the distal end of the pin 9, in which case the dimensions of the bearing pad 11 are accordingly reduced.

The nut 16 (FIGS. 2 and 4) has four lugs 20 facilitating the operations of screwing and unscrewing.

FIG. 3 shows the insertion piece 13 viewed from the distal end with cut-outs 14 arranged circumferentially such that the working zone bearing the most load in walking has no cut-out 14.

The insertion piece 13 (FIGS. 1, 2 and 5) is provided at the proximal end thereof with a tetrahedral protrusion 21 to fit into a corresponding aperture 22 (FIG. 2) of the acetabulum endoprosthesis 1. The shape of the protrusion 21 and the aperture 22 prevents the insertion piece 13 from turning in the endoprosthesis 1 of the acetabulum. However, when the insertion piece is made of materials susceptible to yield, the design should be free from the aperture and the protrusion.

The artificial hip-joint, in accordance with the invention, is installed in the patient's body in the following manner.

Prior to the operation, the artificial hip-joint is in a dismantled form, which is achieved by unscrewing the self-locking nut 16, thereby separating the endoprosthesis 1 (FIG. 2) of the acetabulum from the endoprosthesis 2 of the proximal end of the femur and from the insertion piece 13. In the course of operation, the acetabulum endoprosthesis 1 is impacted in a depression preformed in the bony tissue of the patient's pelvis. Then the endoprosthesis 2 of the proximal end of the femur, with the insertion piece 13 and the nut 16 prefitted over the head 7 and the neck 8 respectively, is impacted into the appropriately prepared medullary canal of the patient's femur. Finally, the insertion piece 13 with the head 7 is fitted into the acetabulum endoprosthesis 1 and fixed by the self-locking nut 16.

The artificial hip-joint of this invention simplifies the surgical procedures involved, provides for the interchangeability of the individual parts of the prosthesis, permits a wider choice of materials for constructing the endoprostheses with a view to minimizing the intra-articular friction and rules out any possibility of dislocation of the endoprosthesis of the proximal end of the femur out of the endoprosthesis of the acetabulum.

Claims

What is claimed is:

1. An artificial hip-joint for use in a patient's body, comprising: a first endoprosthesis means of the patient's acetabulum, having an exterior surface for impacting in the bony tissue of the patient's pelvis, and a seat portion; a second endoprosthesis means of the proximal end of the patient's femur hinged to said first endoprosthesis means; a head member of said second endoprosthesis means having a spherical outer surface; a neck portion of said second endoprosthesis means rigidly connected with said head member; a pin of said second endoprosthesis means rigidly connected with said neck portion for introducing into the medullary canal of the patient's femur; an insert member installed intermediate the surface of said seat portion and the exterior spherical surface of said head member, which insert member provides for a hinged connection of said first and second endoprosthesis means and has an interior spherical surface interacting with the spherical surface of said head member, whereof the cavity defined by said interior spherical surface is greater than the radius, but smaller than the diameter, of said head member, said insert member having cut-outs in the distal portion thereof to form a plurality of blades disposed between said cut-outs comprising a collet enveloping said head member; a self-locking nut operatively associated with said insert member for screwably fixing said insert member in said seat portion.