WO2004105654A1

WO2004105654A1 - Femoral stem for hip prosthesis with macrostructures improvement

Info

Publication number: WO2004105654A1
Application number: PCT/IT2003/000332
Authority: WO
Inventors: Giorgio E. Curradini
Original assignee: Curradini Giorgio E
Priority date: 2003-05-29
Filing date: 2003-05-29
Publication date: 2004-12-09
Also published as: AU2003241164A1

Abstract

A femoral stem (1; 100) for hip (A) prosthesis (R) with improved macrostructures comprising a shaped body (2; 101) defined by a front surface (21) and a rear surface (22) comprises between a first side (23; 104) and a second side (24), in which there are: a main body (3) of a wedge shape with mainly longitudinal development inserted into the femoral canal (N) of the body (C) of the femur (F); a central body (4; 102) of a generally trapezoidal shape and integral with the main body (3), located at the proximal zone (T) of the femur (F); an appendix (5) projecting from the central body (4; 102) provided with a terminal pin (6) receiving spherical head (S) of joint into the cotyle (L) belonging to the prothesis (R) and inserted into the acetubular zone (B) of the pelvic bone (I). In the front surface (21; 103) and the rear surface (22) there are ribs (7, 8, 9, 10; 105) developed for a portion of the length (L1; L2) of the central body (4; 102) along corresponding directions incident to the first side (23; 104) of the shaped body (2; 101).

Description

FEMORAL STEM FOR HIP PROSTHESIS WITH MACROSTRUCTURES

IMPROVEMENT

The present invention relates to a femoral stem for hip prosthesis with improved macrostructures, particularly adapted to be used in the surgical technique of insertion of the femoral stem in the femur known by the practitioners as banana insertion.

It is well known that surgery of the hip joint are carried out generally on old people to treat pathologies such as arthrosis or dysplasia.

As a matter of fact this surgery consists in replacing the hip joint formed by the femur head engaged in the acetabular zone of the pelvic bone with a prosthesis comprising a femoral stem with a mainly longitudinal development, spherical head and a shell called cotyle of a generally hemispherical shape.

Surgery consists firstly in preparing in the acetabulum the seat where the prosthesis cotyle will be arranged, then cutting the femur neck, this operation being called osteotomy, and subsequently preparation of the femoral canal inside the femoral body, where the femoral stem of the prosthesis will be inserted.

The application of the prosthesis is done by inserting the femoral stem into the femoral canal, fixing to said stem the spherical head that is articulated in the cotyle previously inserted in the acetabular zone of the pelvic bone.

In this way the limb is restored in a configuration similar to the original one, restoring the joint function, so that the patient is able to have again a normal life for many years.

Different surgical techniques are nowadays existing to introduce the femoral stem inside the femoral canal.

The most used surgery provides for the introduction of the femoral stem along a generally vertical direction coincident with the femur axis.

In view of the particular shape of the femoral stems now available, having a rather considerable size in the proximal part, which is the part located at the trochanteric zone of the femur, this surgery has the drawback to be obliged to remove a considerable portion of the femoral bone in proximity of the greater trochanter, heavily compromising the original natural condition of the femur thus being very invasive.

This is worsened by the fact that above the trochanteric zone, there are many muscular insertions connected to the femur, that are seriously damaged by the bone removal, causing an extension of the patients recovery time. It was attempted to remove said inconvenience by making less invasive prostheses, comprising femoral stems with reduced section at the proximal part which is arranged in the trocanteric femoral zone. This constructional solution however must be handled with a different insertion method of the femoral stem.

More particularly the stem is inserted in the femoral canal prepared starting from the zone in which osteotomy was carried out, thus following a curved path. This surgical technique known as banana insertion, allows to obtain savings in removing the femoral bone in proximity of the greater trochanter, better reserving the natural condition of the femur, thus accelerating and facilitating the functional recovery. It is however clear that this surgical technique is particularly efficient if it is matched with a geometry of the femoral stem that is the least cumbersome possible in the proximal part because in the contrary case, the benefits of saving the bone obtained by the banana insertion of the stem would be lost. At the same time geometry of the stem should in any case be such to keep the greater trochanter stimulated and reactive. Just to facilitate the bone integration, the femoral stems of the prior art are provided with one or more ribs of different shape, protruding along the entire or partial length of the front and rear surfaces defining the shaped body. A limitation of this kind of stems consists in that the ribs are developed along a generally vertical direction which is well matched with the insertion along the femur access as above mention, whose inconvenience was already pointed out, while it hardly matches the stem banana insertion technique. Indeed in the later case during insertion the ribs rub and remove the spongy bone which is the innermost and brittle, thus creating in the bone longitudinal hollow zones that the body hardly succeeds to fill with time and preventing a correct and complete integration of the femoral stem within the femur.

A second limitation of this femoral stems of the prior art consists in that the hollow zones are a seat in which chips are nested, for instance produced by contact between spherical head and cotyle, that are clearly dangerous for the prosthesis efficiency. Moreover another limitation comes from the fact that the removal of the spongy bone reach of many blood vessels, causes a considerable loss of blood which is always to be avoided.

The removal of the spongy bone is very harmful considering the predominant role due to its structure in obtaining a quick integration of the femoral stem in the bone.

A last but not least limitation particularly to be found in smaller femurs, consists in that sometimes during the banana insertion of the stem, the ribs remove totally the spongy bone until they contact the harder and more compact cortical bone. In this case the ribs stick against the bone, thus hindering the correct and complete stem insertion inside the femur, with the inevitable disadvantages in terms of prosthesis efficiency and patient's pain.

It is therefore correct to state that the ribs of the femoral stems made according to the prior art have drawbacks in the surgical techniques using the bananas insertion, because they make the bone integration and the postoperative course more complicate.

The present invention aims at removing the above mentioned limitations. More particularly the main object of the present invention is to provide a femoral stem with reduced invasive structure in the insertion phase relative to equivalent stems of the prior art when used in surgical operations of banana insertion of the stem in the femur.

A second object is to improve the ability of integration in the femoral bone in comparison to similar stems of the prior art introduced into the femur by the surgical method of banana insertion. A further object is to limit the possibility that chips of different nature are nested between the bone and the femoral stem.

The foregoing objects are attained by femoral stem for hip prosthesis with improved macrostructures that according to the main claim comprises a shaped body defined by a front surface and a rear surface comprised between a first and a second side, wherein there are:

- a main wedge shaped body with mainly longitudinal development, adapted to be inserted into the femoral canal of the femur body;

- a central body of a generally trapezoidal shape integral with said main body, adapted to be arranged in the proximal zone of said femur; - an appendix projecting from said central body, provided with a terminal pin adapted to receive a spherical joint head in the cotyle belonging to said prosthesis and inserted in the acetabular zone of the pelvic bone, and it is characterized in that one or more ribs are made in said front surface and said rear surface, said ribs being developed for at least a portion of the length of said central body along corresponding directions incident with said first side of said shaped body.

Advantageously, the femoral stem of the invention allows to fully exploit the advantages offered by the surgical method of banana insertion of the femoral stem into the femur, matching said method with a limited removal of spongy bone.

This leads to a better and more efficient ability of integration of the femur with the stem in comparison with the prior art.

Also advantageously this allows to limit the blood loss generally associated with the surgery, thus increasing further the ability of bone integration with the femoral stem.

Still advantageously the banana insertion of the stem of the invention into the femur involves the creation of hollow zones between stem and femoral bone of reduced size in comparison with the prior art, that the body succeeds to fill more easily with time, thus improving the ability of bone integration of the femur.

The foregoing objects and advantages, and others that will be pointed out in the following description, will be better understood by the description of preferred embodiments of the invention given as a non limiting illustrative example with reference to the accompanying sheets of drawings in which: - Fig. 1 is a front view of the femoral stem of the invention inserted in the partially sectioned femur;

- Fig. 2 is a front view of the femoral stem of fig. 1 ;

- Fig. 3 is a side view of the femoral stem of fig. 1 ;

- Fig. 4 is an enlarged detail of fig. 2; - Fig. 5 is a front view of an executive variation of the femoral stem of fig. 2;

- Fig. 6 is a front view of the femoral stem of fig. 2 during insertion into the partially sectioned femur;

- Fig. 7 is a longitudinal section of a simplified illustration of the femoral spongy bone at the proximal zone as it results from the banana insertion of a non femoral stem; and - Fig. 8 is a longitudinal section of a simplified illustration of the femoral spongy bone in the proximal zone as it results from the banana insertion of the femoral stem according to the invention. In fig. 1 the femoral stem of the present invention, generally indicated with numeral 1 and belonging to the prosthesis generally indicated with R, having the function of restoring the hip joint, generally indicated with A, is shown in the applicative configuration, that is inserted into the femoral canal N prepared in the body C of the femur F. One can see that the femoral stem 1 , preferably but not necessarily made of titanium alloy such as vanadium, comprises a shaped body generally indicated with 2, defined by a front surface 21 and a back surface 22, both shown in fig. 3, of which in fig. 1 only the front surface 21 can be seen, comprised between a first side 23 and a second side 24. As it is well shown in fig. 3, in this case the front surface 21 and rear surface 22 are preferably identical and symmetrical arranged relative to a longitudinal symmetry plane 11 of the femoral stem 1.

According to another embodiment of the invention not shown in the sheets of drawings, peculiar for the so called anatomic femoral stems, the front surface may have a different longitudinal section from the rear surface. In fig. 1 one can also see that in the shaped body 2 there are a main body 3 of wedge shape with a mainly longitudinal development, to be inserted in the femoral canal N of the body C of the femur F, and a central body 4 of a generally trapezoidal shape and integral with the main body 3, that is arranged at the proximal zone T of the femur F. In the shaped body 2 there is also an appendix 5 projecting from the center body 4 and provided with a terminal pin 6 that can be seen only starting from fig. 2, receiving a spherical head S of joint in the cotyle L belonging to the prosthesis R, and inserted into the acetabular zone B of the pelvic bone I and internally coated with a material P for instance made of plastics like polyethylene, metal or ceramics.

According to the invention, in each front surface 21 and rear surface 22 there are two ribs indicated with numerals 7, 8 for the former surface and 9, 10 for the later surface, developed for at least a portion of the length Li of the central body 4 along corresponding directions incident to the first side 23 of the shaped body 2. More particularly as better seen in fig. 2, the rib 7 is developed for almost the entire length l_ι of the central body 4, while the rib 8 is shorter. Clearly also the ribs 9, 10 of the rear surface 22 have the same development of the corresponding ribs 7, 8 along the central body 4. According to other embodiments of the invention not shown in the appended drawings, some or all the ribs may extend in the same amount and develop for a portion or the entire length of the central body.

In further embodiments also not shown in the drawings, at least one of the ribs may be partially provided also on the main body of the femoral stem. With reference to fig. 2, according to the preferred embodiment now described, each of the directions defined by the ribs 7, 8, 9, 10 consists of straight line defining a longitudinal symmetry access Y for the corresponding rib 7, 8, 9, 10. Preferably but not necessarily the directions defined by the ribs 7, 8, 9, 10 are generally parallel to each other. Obviously in a further embodiment of the invention not shown in the accompanying sheets of drawings, each of the directions of development of the ribs may consist of a curved line instead of a straight line. Still in fig. 2 one can see that the second side 24 of the shaped body 2 consists of a concave convex surface, while the first side 23 consists of a generally plane first surface 23a belonging to the central body 4 and a second generally plane surface 23b belonging to the main body 3, connected to the first surface 23a by a generally convex radiused zone 23c. Therefore the first surface 23a defines with the extension of the second surface 23b an acute angle α. This particular constructional measure allows to obtain a femoral stem 1 of a sufficiently widened geometry at the proximal zone T to give a good torsional stability through the implant and at the same time a not very invasive structure to obtain a saving in bone removal at the zone adjacent to the greater trochanter G, an indispensable condition to maximize the advantages given by the banana insertion of the femoral stem 1 into the femur F.

As it is well shown in the detail of fig. 4, according to the present embodiment, the longitudinal symmetry axis Y of each rib 7, 8 is generally parallel to the direction defined by the first surface 23a belonging to the central body 4 of the first side 23. Each rib 7, 8 has a cross sectional conical profile 7', 8' and is arranged in proximity of the first surface 23a of the first side 23.

One can see that in the illustrated example the length of ribs 7, 8 is decreasing from the first surface 23a to the appendix 5 projecting from the shaped body 2, confirming that it is not necessary that all the ribs made on the front surface of the shaped body have the same length. Clearly what has been stated for the ribs 7, 8 of the front surface 21 with reference to fig. 4, is applicable also for the corresponding ribs 9, 10 of the rear surface 22.

Fig. 5 is an example of a constructional variation of the femoral stem of the invention now generally indicated with 100, which is different from the embodiments previously described and cited because each of the front and rear surfaces, of which one can see only one indicated with 103 of the shaped body generally indicated with 101 , has a single rib 105 developed for the entire length L₂ of the central body 102 according to straight line defining a longitudinal symmetry axis Y' and incident to the first side 104 of the shaped body 101.

During the surgical operation, the surgeon introduces the femoral stem 1 into the canal N prepared inside the body C of the femur F starting from the zone in which osteotomy M was carried out. In this way one obtains bone saving in the zone close to the greater trochanter G, leaving the natural condition of the bone unaltered and warranting a better ability of the functional recovery.

As shown in fig. 6, the femoral stem 1 is inserted into the femoral canal N along a curved path, different from the femoral axis C, to define the so called banana insertion. The advantage given by the present invention is to obtain just in the phase of insertion of the femoral stem 1 into the canal N and is given by the particular inclination of ribs 7, 8, 9, 10 projecting from the front surface 21 and rear surface 22 of the shaped body 2. Such an inclination has preferably a value between 6 degrees and 9 degrees relative to a vertical reference direction and depends upon the medial femur curve, the amount of trochanter cut and the length of the femoral stem. In the insertion phase, the ribs 7, 8, 9, 10 remain always tangent to the path traveled by the femoral stem 1 , these preventing their rubbing in a considerable and dangerous way against the spongy bone J, digging hollow zones in the femur F of limited size that the body succeeds to fill more easily with time in comparison with those caused by the stems of the prior art.

The comparison between fig. 7 and fig. 8 helps to understand better the advantage given by the femoral stem 1 of the invention.

More particularly in fig. 7 the result produced by the banana insertion of femoral stems of the prior art provided with ribs developed along a generally vertical direction is shown, thus not being incident to the side of the shaped body of the femoral stem.

The hollow zones \ digged by the ribs, have a depth and above all a width that are greater than those shown in fig. 8 and indicated with V₂ produced by the banana insertion into the femur of the femoral stem of the invention.

The ribs of the stem of the invention are almost totally integrated with the tracks V₂ made during insertion, while the ribs of the stems of the prior art are matching only a portion of the hollow zones \ leaving open other portions that can be hardly filled by the body and finally complicating the process of bone integration of the femur.

Therefore the advantages obtained by the femoral stem of the invention are clear, because the lower amount of removal of spongy bone allows to improve the ability of integration of the femoral bone with the stem implanted in it, because the spongy bone better grips the stem and smaller hollow cavities are formed in the femur.

A not negligible importance consists also in obtaining the advantage to leave as much as possible intact the spongy bone inside the femur, thus reducing the blood loss during the surgery. It is also clear that the femoral stem of the invention reduces the ability of chips produced by the mutual rubbing of the prosthesis parts subject to wear to penetrate inside the hollow space generated during the stem insertion phase. The particular inclination of the ribs, together with their conical profile, allows to obtain the most possible benefits from the banana introduction of the femoral stem into the femur. It is also prevented the danger very frequent in some femoral stems of the prior art that the ribs during the insertion remove completely the spongy bone even reaching the cortical bone where they are stopped causing the incorrect insertion into the femur. On the basis of the foregoing one can understand that the femoral stem of the invention attains all the previously mention objects and advantages. In the executive phase modifications to the femoral stem of the invention may be made for instance consisting in a different number of ribs on the front and rear surfaces of the shaped body, according to the configuration of the patient's femur into which the stem should be implanted. Moreover even the configuration of the shaped body may be different from the shape illustrated in these description without impairing the advantage given by the present invention.

All the described and cited variations not shown in the accompanying sheets of drawings, when falling within the scope of the appended claims, should be considered protected by the present patent.

Claims

1) A femoral stem (1 ;100) for hip (A) prosthesis (R) with improved macrostructures comprising a shaped body (2; 101) defined by a front surface (21 ) and a rear surface (22) comprised between a first side (23; 104) and a second side (24) where the following elements are defined:

- a main body (3) with a wedge shape with mainly longitudinal development, adapted to be inserted into the femoral canal (N) of the body (C) of the femur (F);

- a central body (4; 102) of a generally trapezoidal shape integral with said main body (3), adapted to be located at the proximal zone (T) of said femur

(F);

- an appendix (5) projecting from said central body (4; 102), provided with a terminal pin (6) adapted to receive a spherical head (S) of joint in the cotyle (L) belonging to said prosthesis (R) and inserted into the acetabular zone (B) of the pelvic bone (I), and it is characterized in that in said front surface (21 ; 103) and said rear surface (22) one or more ribs (7, 8, 9, 10; 105) are made, developed for at least a portion of the length (L-i; L₂) of said central body (4; 102) according to corresponding directions incident to said first side (23; 104) of said shaped body (2; 101 ).

2) The femoral stem (1 ; 100) according to claim 1 ) characterized in that each of said directions consist of a straight line defining a longitudinal symmetry axis (Y; Y') for the corresponding ribs (7, 8, 9, 10; 105). 3) The femoral stem (1 ) according to claim 2) characterized in that said directions are generally parallel to each other.

4) The femoral stem according to claim 1 ) characterized in that each of said directions consist of a curved line.

5) The femoral stem (1 ; 100) according to claim 1 ) characterized in that at least one of said ribs (7, 8, 9, 10; 105) is developed for the entire length (Li; L₂) of said central body (4; 102).

6) The femoral stem according to claim 1 ) characterized in that at least one of said ribs is developed for the entire length of said central body and is extended at least partially on said main body. 7) The femoral stem (1 ; 100) according to claim 1 ) or 2) characterized in that said first side (23; 104) consist of a generally plane first surface (23a) belonging to said central body (4; 102) and a second generally plane surface (23b) belonging to said main body (3) connected to said first surface (23a) through a generally convex radiused zone (23c). 8) The femoral stem (1 ; 100) according to claim 1 ) characterized in that said second side (24) consists of a concave-convex surface.

9) The femoral stem (1 ; 100) according to claim 7) characterized in that said first surface (23a) defines together with the extension of the direction defined by said second surface (23b) an acute angle (α).

10) The femoral stem (1 ; 100) according to claim 7) characterized in that said longitudinal symmetry axis (Y; Y') of each of said ribs (7, 8, 9, 10; 105) is generally parallel to the direction defined by said first sur ace (23a) of said first side (23; 104)

11) The femoral stem (1 ; 100) according to claim 7) characterized in that each of said ribs (7, 8, 9, 10; 105) is arranged in proximity of said first surface (23a) of said first side (23; 104).

12) The femoral stem (1 ; 100) according to claim 7) characterized in that the length (L-i; L₂) of said ribs (7, 8, 9, 10; 105) is decreasing from said first surface (23a) to said appendix (5) projecting from said shaped body (2; 101 ).

13) The femoral stem (1 ; 100) according to claim 1 ) characterized in that each of said ribs (7, 8, 9, 10; 105) has a cross sectional conical profile (7', 8'; 105').

14) The femoral stem (1 ; 100) according to claim 1 ) characterized in that said front surface (21 ) and said rear surface (22) are identical and symmetrical arranged relative to a longitudinal symmetry plane