GB1597003A

GB1597003A - Hip joint prosthesis

Info

Publication number: GB1597003A
Application number: GB49177/77A
Authority: GB
Original assignee: Richards Manufacturing Co LP; Richards Manufacturing Co Inc
Current assignee: Richards Manufacturing Co LP; Richards Manufacturing Co Inc
Priority date: 1977-02-14
Filing date: 1977-11-25
Publication date: 1981-09-03
Also published as: SE7710780L; DE2805305A1; FR2380021A1; DE2805305C2

Description

(54) HIP JOINT PROSTHESIS (71) We, RICHARDS MANU FACTURING COMPANY, INC., a corporation organised and existing under the laws of the State of Delamare, United States of America, of 1450 East Brooks Road, Memphis, Tennessee 38116, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a prosthetic hip joint for use in the replacement of a defective hip joint.

In the use of prostheses for the replacement of hip joints there have been problems of failures in these total hip systems. There are tremendous forces exerted on the prostheses and the related bone structures during activity of the patient. Thus, in jumping from a 2-3 foot elevated surface to a lower surface the loads placed on the hip joint can for example, be many times the body weight, and for higher elevations the load factors will be greatly multiplied. The above-mentioned failures can occur in the breakdown of the bone, in the cement, and in the femoral prosthesis itself.

Before the introduction of the use of cement in the hip systems many different femoral component designs were utilized, and with the advent of the use of cement in such systems the femoral components, having sharp edges, would cut into the cement, causing cracking and other problems. Also, such prior devices had depressions or undercut portions, which when the cement hardened would lock the femoral prosthesis in place against removal so that if for some reason another operation were necessary to remove the prosthesis and replace it, then it would be difficult for the prosthesis to be removed.

According to the present invention there is provided a prosthetic hip joint for use in the replacement of a defective hip joint, said prosthetic joint comprising: (a) an acetabular component for implanting in the acetabulum, said acetabular component being formed of plastics material and being provided with a socket, the exterior surface of the acetabular component being provided with outwardly extending spaced apart rings defining cement receiving grooves therebetween; and (b) a metal femoral component including: (1) a head which can be movably received in said socket, (2) a stem for implanting in the femoral canal, said stem having proximal and distal ends, said stem being oval shaped in cross-section and having an uninterrupted outer surface and being continuously tapered from said proximal end to said distal end, and (3) a neck portion of oval cross-section rigidly joined at one end thereof to said stem at said proximal end of said stem and rigidly joined at the other end thereof to said head.

The stem of the femoral component has a smooth uninterrupted outer surface without any depressions and is continuously tapered from the proximal end to the distal end thereof in both the medial-lateral and anterior-posterior planes. This characteristic of the stem provides distribution of the load along the entire length of the stem, and provides wedging means for forcing the cement into the crevices of the bone when the prosthesis is put into place, and provides for easy removal of the stem in the event of a revision procedure. Thus, there is a firm support with the stem being locked tight against any undesired movement during use, yet is not locked into the cement against removal in the event of a revision procedure in which it is necessary to remove the stem.

The stem of the femoral component in cross-section is oval shaped with preferably the shorter axis of the oval being oriented in an anterior-posterior plane, and the longer axis of the oval being oriented in the lateralmedial plane so that an increased amount of material is provided in the lateral-medial plane where the stress during weight bearing movements of the leg is highest.

The outer surface of the stem is smooth and has rounded corners so that is no cracking or cutting into the cement.

The neck portion in cross-sectional dimensions is preferably narrower in its anterior-posterior dimension than in its lateral-medial dimension so that in the lateral-medial direction which takes the greatest load there is increased material, yet in the anterior-posterior dimension the material is decreased so that greater forward and rearward motion of the neck of the prosthesis is obtained and therefore of the leg of the patient in the forward and rearward direction.

The acetabular component preferably includes a substantially hemispherical body which has a constant thickness from the socket thereof outwardly to the exterior surface from which said rings project whereby there is longer wear life of the acetabular component as compared with previous devices in which grooves were cut into the body portion. Also, the acetabular component preferably does not overhang the head but is substantially flush therewith whereby there is greater movement of the femoral component relative to the acetabular component.

For the different sizes of femoral components a relationship has been established between the lengthened neck portion and the angle of the neck so that the leg or femur is kept in a straight position under the hip for better weight bearing. An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawings, in which Fig. 1 is a side elevational view of a femoral component of the hip joint prosthesis according to the present invention, Fig. 2 is a plan view thereof, Fig. 3 is a sectional view taken along the line 111-111 of Fig. 1, Fig. 4 is a sectional view taken along the line IV-IV of Fig. 1, Fig. 5 is a sectional view taken along the line V-V of Fig. 1, Fig. 6 is a sectional view taken along the line VI-VI of Fig. 1, Fig. 7 is a sectional view taken along the line VII--VII of Fig. 1, Fig. 8 is a partially sectionalized view showing a hip joint prosthesis according to the present invention implanted in the hip and femur, Fig. 9 is an elevational view of the acetubular component of the hip prosthesis of the present invention, Fig. 10 is a plan view of the acetabular component, Fig. 11 is a sectional view taken along the line XI-XI of Fig. 10, and Figs. 12, 13 and 14 are side elevational views showing the relationship of certain lengths, distances and angles of three sizes of the femoral components of the present invention.

The prosthetic hip joint 11 of the present invention, as shown in Figure 8, includes a femoral component 13 for implanting in the medullary canal M of the femur F to which it is secured by cement C, and an acetabular component 15 for implanting in the acetabulum A to which it is secured by cement C.

The femoral component 13 is shown more clearly in Figures 1 to 7 and includes a head 17, a neck portion 19, a stem 21, and a shoulder 23 adjacent the juncture of the neck portion 19 and stem 21. Femoral component 13 is preferably integrally formed of a suitable rigid bio-compatible material, such as chrome-cobalt or stainless steel, with the head 17 being rigidly joined to one end of the neck portion 19 and the other end of neck portion 19 being rigidly joined to the proximal end 25 of stem 21.

Shoulder 23 is provided at the end of neck portion 19 adjacent its juncture with stem 21.

Head 17 has an outer surface with a major portion thereof as at 29 being part-spherical for fitting into a socket 31 of the acetabular component 15, as shown in Fig. 8. Head 17 is preferably flat along the bottom side 33 surrounding the juncture of head 17 with neck portion 19 and with a radius 33' being provided at the juncture.

Neck portion 19 in cross-section is elliptical with the narrower portion or shorter axis of the ellipse extending in an anterior-posterior direction (shown by the line A-P) and with the wider portion or longer axis of the ellipse extending in a laterial-medial direction (shown by the line L-M). It should be noted that the term "anterior-posterior and "lateral-medial" directions are determined by the orientation of the femoral component 13 relative to the body of the patient when implanted therein, that is, the anterior-posterior direction extends fore and aft relative to the body and lateral-medial extends sidewise relative to the body. From the foregoing, it will be seen that more metal in the stem 21 is provided in the lateral-medial direction or plane where the load forces are greatest and at the same time the neck portion 19 is thinner in the anterior-posterior direction or plane so that there is less interference with the acetabular component 15, thereby giving a greater range of fore and aft movement of the femoral component 13 and femur F. It will be noted that neck portion 19 is narrower in the area 37 just below the juncture with head 17 and flares outwardly to its termination where shoulder 23 is provided on the end of the neck portion 19 adjacent the juncture with stem 21. The shoulder 23 overhangs the proximal end 25 of stem 21 on the anterior, posterior and medial sides thereof, and the lateral edge of the neck portion 19 is substantially flush with the lateral portion of the proximal end 25 of stem 21.

Stem 21, when viewed from the side, as in Fig. 1, is curved and is thicker in the proximal portion 41 than in the straight distal portion 43. As viewed from the top, as in Fig. 2, the sides of the stem 21 are substantially straight.

One of the important features of the present invention is the configuration of the stem 21. It has a smooth uninterrupted outer surface 45 without any depressions and is continuously tapered from the proximal end 25 to the distal end 47 in both the anterior-posterior and lateral-medial dimensions or planes. Thus, the stem 21 in cross section is oval shaped with the oval becoming increasingly smaller from the proximal end 25 to the distal end 47, as is shown by the representative sections of the stem in Figs. 4, 5, 6 and 7. The longer dimensions or axes of the ovals are disposed along the lateral-medial direction or plane, as shown as at L-M, and the shorter dimensions or axes of the ovals are disposed along the anterior-posterior direction or plane. It will be noted that the edges are rounded and there are no sharp corners, which would otherwise cut into the cement and cause cracking of cutting of the cement.

Also, this particular configuration of stem 21 produces synergistic results which will be understood more fully in the description to follow of the use of the prosthetic hip joint 11.

There are preferably at least three sizes of femoral components 13, and they are so arranged that there is anatomical compatibility and yet there is a minimization of the concentration of stresses in the femoral components, with improved distribution of weight bearing and increased range of motion. Figs. 12, 13 and 14 show how the sizes are preferably related. Fig. 12 is the component with the smaller size neck portion, Fig. 13 with the medium size, and Fig. 14 the one with the longer neck portion. For clarity's sake, the component with the shorter length neck portion and its parts has been designated by the prime mark (e.g., 13'), the middle size by a double prime mark (e.g., 13") and the larger size by atriple prime mark (e.g., 13"').

It will be noted that the respective distances D', D", D"' between lines L', L". L"' through the centres of the heads 17', 17", and 17"' and parallel with lateral edges 44', 44" and 44"' of the straight portions 43', 43", and 43"' are the same on all of the sizes, and to provide for different neck dimensions the angles S', S" and S"' between the neck axes N', N" and N"' and the lateral edges 44', 44", and 44"' of straight portions 43', 43", and 43"' are different. The specific dimensions of the three sizes having the 25 mm. head are preferably as follows: Neck Neck length* angle Component 13 1.75" 135 Component 13, 2.00" 144" Component 13" 2.25" 149.70 *Neck length as measured from top of head to bottom of neck.

Also, other size heads are preferably provided, for example, 32 mm., which would have different neck lengths.

The acetabular or cup component 15 is preferably integrally formed from a suitable plastics material, such an ultra-high molecular weight polyethylene. Acetabular component 15 includes a substantially hemispherical body 55 with the inner surface thereof being defined by socket 31 and having an exterior surface 57 spaced outwardly from socket 31. One of the important features of the acetabular component 15 is that body 55 is of a constant thickness from socket 31 to exterior surface 57 on which the rings 59 are provided so that there is a uniform wear thickness or portion which is not thin in areas such as with some of the previous acetabular cups in which cement grooves were formed in the exterior surface extending towards the socket to reduce the thickness of the body in these areas, and with rings being provided between these grooves. In contrast, with acetabular component 15 there are no depressed grooves into the body 55 but rather there are a plurality of rings 59 integrally attached to and proJecting outwardly from the exterior surface 57 of body 55 and spaced apart to define cement receiving grooves 61 therebetween.

Acetabular component 15 includes an entrance opening 63 which opens into socket 31. An annular base portion 65 of acetabular component 15 surrounds entrance opening 63 and is integrally joined with body 55 and terminates in an annular surface 67. Notches 69 are provided in rings 59 and annular base portion 65, and are spaced around the rings 59 and the base portion 65.

In implanting the prosthetic hip joint 11, surgical procedures well known to those skilled in the art are utilized to implant the acetabular component 15 in the acetabulum A and the femoral component 13 in the femur F utilizing cement C. There are several synergistic results which are provided by the present invention, particularly in connection with the structure and configuration of the components of the present invention. These results include among others, the wedging or forcing outwardly of the cement into the cavities of the bone when the stem 21 is inserted into the medullary canal M of the femur F due to the stem being continuously tapered from the proximal end to the distal end. Also, due to this wedging action when the cement is hardened, the stem 21 is held firmly against wobbling, there is an even distribution of the load along the entire length of the stem rather than concentrating in one area that would place stress upon the area and cause possible fracture of the stem, and yet the continuous taper permits easy removal of the stem later on if necessary as for example in a revision procedure. In addition, due to the angular relationship heretofore mentioned with the increased length of the neck portion, anatomical compatibility is provided at an improved level of femoral support. Also, other advantages which have heretofore been pointed out are provided.

Although the invention has been described and illustrated with respect to a preferred embodiment thereof, it is to be understood it is not to be so limited since changes and modifications may be made therein which are within the scope of the

Claims

appended claims. WHAT WE CLAIM IS:

1. A prosthetic hip joint for use in the replacement of a defective hip joint, said prosthetic joint comprising: (a) an acetabular component for implanting in the acetabulum, said acetabular component being formed of plastics material and being provided with a socket, the exterior surface of the acetabular component being provided with outwardly extending spaced apart rings defining cement receiving grooves therebetween; and (b) a metal femoral component including: (1) a head which can be movably received in said socket, (2) a stem for implanting in the femoral canal, said stem having proximal and distal ends, said stem being oval shaped in cross-section and having an uninterripted outer surface and being continuously tapered from said proximal end to said distal end, and (3) a neck portion of oval cross-section rigidly joined at one end thereof to said stem at said proximal end of said stem and rigidly joined at the other end thereof to said head.

2. A prosthetic hip joint as claimed in claim 1, in which the longer axis of the oval cross-section of the stem when the stem is implanted in a femoral canal is oriented in a lateral-medial plane and the shorter axis in an anterior-posterior plane, said stem being tapered as considered relative to both the lateral-medial direction and the anteriorposterior direction.

3. A prosthetic hip joint as claimed in claim 1 or claim 2, in which said neck portion in cross-sectional dimensions is narrow in its anterior-posterior dimension than in its lateral-medial dimension; wherein said neck portion is elliptical in cross-section.

4. A prosthetic hip joint as claimed in any of claims 1 to 3, in which the outer surfaces of said neck portion are smooth.

5. A prosthetic hip joint as claimed in any of claims 1 to 4, in which the neck portion is jointed at said proximal end to form a shoulder juncture.

6. A prosthetic hip joint as claimed in any of claims 1 to 5, in which said acetabular component includes a substantially hemispherical body with the inner surface thereof being defined by said socket and having an exterior surface spaced outwardly from said socket and from which said rings project, said body having a constant thickness from said socket outwardly to said exterior surface.

7. A prosthetic hip joint as claimed in any preceding claim, in which said head is substantially flat on the end thereof that is joined to said neck portion, and said acetabular component includes an entrance opening to said socket and an annular base portion surrounding said entrance opening, integrally joined with said body, and terminating in an annular surface; said flat side of said head being movable to a position substantially flush with said annular surface.

8. A plurality of the prosthetic hip joints claimed in any preceding claim, in which the neck portions of each of the plurality of femoral components are of a different length and the distance between a first line aligned with one lateral edge of said stem and a second line through the centre of said head and parallel to said first line are the same for each of said plurality of femoral components.

9. A prosthetic hip joint substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.