WO2009037284A2

WO2009037284A2 - Femoral stem of a non-cemented endoprosthesis of the mini-invasive type of a coxofemoral joint with high primary and secondary stability

Info

Publication number: WO2009037284A2
Application number: PCT/EP2008/062385
Authority: WO
Inventors: Carlo Fioruzzi; Umberto Fusco; Reinhold Ganz; Michael Leunig; Michele Lisanti; Mauro Oliveri
Original assignee: Plus Orthopedics Italy S.R.L.
Priority date: 2007-09-19
Filing date: 2008-09-17
Publication date: 2009-03-26
Also published as: WO2009037284A3; ITMI20071813A1

Abstract

A femoral stem (1) of an endoprosthesis of the mini-invasive type of a coxofemoral joint, comprising a distal portion (2), which is substantially longitudinally elongated and is suitable to be inserted in the bone cavity of a femur, the femoral stem comprising a proximal portion (13), which is suitable to be accommodated proximate to the trochanteric region of the femur and extends into a neck (4) provided with a shank (5) for coupling to a spherical head of the coxofemoral joint, the femoral stem, viewed on a frontal plane, having an inner side and an outer side, the outer side having a convex profile that comprises at least one first straight segment (20) that delimits the distal portion (2) and a second straight segment (30) that delimits the proximal portion (3), the second straight segment (30) being inclined with respect to the longitudinal axis of the distal portion (2) toward the coxofemoral joint at an acute trochanteric angle (β).

Description

FEMORAL STEM OF A NON-CEMENTED ENDOPROSTHESIS OF THE MINI-INVASIVE TYPE OF A COXOFEMORAL JOINT WITH HIGH PRIMARY AND SECONDARY STABILITY Technical Field The present invention relates to a femoral stem of a non-cemented endoprosthesis of the mini-invasive type of a coxofemoral articulation with high primary and secondary stability. Background Art

The expression "primary stability" is used to reference a condition of mechanical equilibrium of the endoprosthesis with respect to the bone that hinders relative macromovements between the endoprosthesis and the bone, preventing the two from separating, and which contains relative micromovements between the endoprosthesis and the bone within such threshold values as to ensure an osteointegration process. The expression "secondary stability" is used to reference a condition of equilibrium of the endoprosthesis with respect to the bone that is reached when the osteointegration process has occurred successfully, allowing the host bone to grow on the surface of, or within the surface pores, of the hosted endoprosthesis. Secondary stability can exist only if primary stability is ensured.

For the biomechanical reconstruction of the coxofemoral joint, it is known to use endoprostheses that comprise a femoral stem provided with a shank that mates with a spherical head that is engaged in an artificial cotyloid cavity that replaces the acetabular cavity. These endoprostheses can be of the cemented and non-cemented type.

Endoprostheses of the so-called "non-cemented" type are fixed to the bone tissues of the coxofemoral joint by mechanical and biological processes. Endoprostheses of the so-called "cemented" type are instead fixed by way of the adhesion of a layer of cement that surrounds the prostheses and bonds to the bone tissues of the joint. Regardless of the kind of the artificial cotyloid cavity, for the endoprostheses of the non-cemented type the shape of the femoral stem is fundamentally important.

In combination with so-called "banana insertion" in the bone cavity formed artificially in the femur that has a curvilinear path, said shape must in fact ensure a high level of primary stability and a high level of secondary stability.

It is known to use femoral stems having different shapes and geometries. Among these, curvilinear femoral stems are known which, in view of their curvilinear shape, facilitate "banana insertion".

As an alternative, substantially straight femoral stems are known which comprise a proximal portion provided with geometric tabs and suitable to be accommodated proximate to the trochanteric region of the femur.

Such geometric tabs, which comprise ribs with a sharp profile that are substantially parallel to the longitudinal axis of the femoral stem, are suitable to cut into the bone cortex during insertion so as to lock the femoral stem in the femur. Such known femoral stems, particularly of the straight type, are not devoid of drawbacks, which include the fact that the proximal portion has such a geometry as to force the surgeon to detach the muscles and some the soft parts, particularly proximate to the trochanteric region, to allow correct insertion of the prosthesis, and this entails long times for recovery of the functionality of the hip.

Another drawback of known femoral stems, particularly of straight ones, consists in that during the insertion step the particular geometry of the proximal portion can damage or injure tendons, entailing long times to recover hip functionality. Still another drawback consists in that the geometry of the ribs of known femoral stems, particularly in the case of "banana insertion", creates grooves in the bone cortex which extend also transversely to the longitudinal direction of extension of the ribs, such grooves entailing a loss of primary and secondary stability. Another drawback of known femoral stems consists in that the ribs have a sharp profile along their entire extension; once such profile, during insertion of a femoral stem, has cut into the bone cortex the surgeon can no longer perform any adjustments to achieve correct positioning of the femoral stem. Another drawback of known femoral stems is the fact that they entail a removal of bone tissue whose extent does not allow a second operation, unless large bone resections are performed and therefore a considerable quantity of available bone is sacrificed.

Another drawback of known femoral stems consists in that they have an incorrect load distribution; this entails incorrect bone stresses that can lead to the onset of disorders affecting the bone and muscle system, such as for example born reabsorption. Disclosure of the Invention

The aim of the present invention is to eliminate the drawbacks cited above, by providing a femoral stem of a non-cemented endoprosthesis of the mini-invasive type of a coxofemoral joint that preserves as much as possible the organic tissues of the trochanteric region and simultaneously allows an implantation of the prosthesis with high primary and secondary stability.

Within this aim, an object of the present invention is to provide a femoral stem with such a geometry as to allow mini-invasive insertion without requiring the separation of muscles, tendons and soft parts.

Another object of the present invention is to provide a femoral stem that allows short recovery times for the muscles and for the functional mobility of the hip. Another object of the present invention is to provide a femoral stem whose geometry is such as to allow a correct distribution of the working loads between the prosthesis and the organic tissues of the trochanteric region so as to avoid causing the onset of disorders affecting the bone and muscle system. This aim, as well as other objects that will become better apparent hereinafter, are achieved by a femoral stem of an endoprosthesis of a coxofemoral joint comprising a distal portion, which is substantially longitudinally elongated and is suitable to be inserted in the bone cavity of a femur, and a proximal portion, which is suitable to be accommodated proximate to the trochanteric region of the femur and extends into a neck provided with a shank for coupling to a spherical head of the coxofemoral joint, characterized in that, viewed on a frontal plane, it has an inner side and an outer side, said outer side having a convex profile that comprises at least one first straight segment that delimits said distal portion and a second straight segment that delimits said proximal portion and is inclined with respect to the longitudinal axis of said distal portion toward the coxofemoral joint at an acute trochanteric angle (β). Brief description of the drawings

Further characteristics and advantages of the present invention will become better apparent from the description of a preferred but not exclusive embodiment of a femoral stem of a non-cemented endoprosthesis of the mini-invasive type of a coxofemoral joint with high primary and secondary stability according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein: Figure 1 is a front elevation frontal view of a femoral stem according to the invention;

Figure 2 is a side elevation view of a femoral stem according to the invention;

Figure 3 is a rear elevation frontal view of a femoral stem according to the invention; Figure 4 is a top view of a femoral stem according to the invention;

Figure 5 is a sectional view of the femoral stem according to the invention, taken along the line V-V in Figure 1 ;

Figure 6 is a sectional view of the femoral stem according to the invention, taken along the line VI-VI in Figure 1 ;

Figure 7 is a partial isometric view of a femoral stem according to the invention. Ways of carrying out the Invention

With reference to the figures, the femoral stem according to the invention, generally designated by the reference numeral I₅ comprises a distal portion 2, which is substantially longitudinally elongated and is suitable to be inserted in the bone cavity of a femur, and a proximal portion

3, which is suitable to be accommodated proximate to the trochanteric region of the femur and extends with a neck 4 that is provided with a shank 5 for mating with a spherical head of the coxo femoral joint, which is not shown.

Viewed on a frontal plane, the femoral stem 1 has an inner side and an outer side.

The inner side has a curvilinear profile with an average radius of curvature R and delimits the femoral stem 1 on the inside of the thigh.

In a preferred embodiment, the radius of curvature R is approximately 100 mm.

The outer side has a convex profile that comprises a first straight segment 20, which delimits the distal portion 2, and a second straight segment 30, which delimits the proximal portion 3 and is inclined with respect to the longitudinal axis 6 of the distal portion 2 towards the coxofemoral joint at an acute trochanteric angle β.

The distal portion 2 is slender and has an optimized length so as to have a total length C of the femoral stem 1 , constituted by the sum of the lengths of the proximal portion and of the distal portion, that is reduced with respect to the length of known types of straight femoral stem by approximately 40%.

The total length C can assume different values ranging from 50 to 200 mm. More precisely, the total length C can have, for example, a value selected from the group that comprises: 75 mm, 77 mm, 79 mm, 81 mm, 83 mm, 85 mm, 87 mm, 89 mm, 91 mm and 93 mm.

The distal portion 2 is delimited by a front face 2a, by a rear face 2b, by an inner lateral portion 2c and by an outer lateral portion 2d, which are inclined so as to converge toward a rounded distal end 2e of the distal portion 2.

The outer lateral wall 2d forms the first rectilinear segment 20. The inner lateral wall 2c and the outer lateral wall 2d of the distal portion 2, viewed on a frontal plane (Figures 1 and 3), are mutually inclined in a substantially symmetrical manner with respect to the longitudinal axis 6 of the distal portion 2 by an angle η ranging from 1 ° to 20° and preferably equal to 6°.

The inner lateral wall 2c and the outer lateral wall 2d of the distal portion 2, viewed on a frontal plane (Figure 3), are blended at the distal end 2e with a straight bevel that is inclined with respect to the longitudinal axis

6 by a bevel angle θ whose breadth ranges from 5° to 45° and is preferably equal to 17°.

The front face 2a and the rear face 2b of the distal portion 2, viewed on a plane that passes through the longitudinal axis 6 of the distal portion 2 and at right angles to a centerline plane 7 that is parallel to the frontal plane, are mutually inclined symmetrically with respect to the centerline plane 7 by an angle λ whose breadth ranges from 1 ° to 10° and is preferably equal to 3°.

The front face 2a and the rear face 2b of the distal portion 2, viewed on a plane that lies transversely to the longitudinal axis 6, are mutually inclined symmetrically with respect to the central plane 7 by an angle μ whose breadth ranges from 1° to 15° and is preferably equal to 6°.

Thanks to the inclination of the front face 2a, of the rear face 2b, of the inner lateral wall 2c, of the outer lateral wall 2d, the bevel angles θ and the distal end 2e, the insertion of the femoral stem 1 in the bone cavity of the femur is facilitated; moreover, after insertion has occurred, they avoid the transfer of the load from the bone to the femoral stem 1 to the distal portion 2.

For better bonding between the femoral stem 1 and the bone cortex, it is known to use surface treatments performed on the front face 2a, on the rear face 2b, on the inner lateral wall 2c, on the outer lateral wall 2d, on the angle bevels θ and on the rounded end 2e, which can comprise for example a titanium plasma spray coating performed in vacuum or in air, deposition of HA and others. As already mentioned, the proximal portion 3 is delimited laterally and externally by the second straight segment 30.

The second straight segment 30 is inclined with respect to the longitudinal axis 6 of the distal portion 2 toward the coxofemoral joint at an acute trochanteric β angle. Such inclination facilitates the insertion of the femoral stem 1 in a femoral bone cavity according to a curvilinear path and allows to preserve the organic tissues that are present in the trochanteric region, thus allowing the mini-invasive procedure.

The trochanteric angle β has a breadth ranging from 2° to 30° and is preferably equal to 8°.

The proximal portion 3 comprises a blind hole 8, with an axis 8a that is parallel to the longitudinal axis 6, in order to accommodate the tools needed by the surgeon to position and possibly extract the femoral stem 1 in the bone cavity. The blind whole 8 is rounded proximally in order to be able to accommodate an appropriately provided impact tool and is threaded distally in order to be able to insert an instrument for extracting the femoral stem 1. The geometry described above allows to strike the femoral stem 1 without acting on the threads, which therefore are not damaged by the impacts experienced during insertion of the femoral stem 1.

The blind hole 8 is provided at the end of the proximal portion 3 and is adjacent to the neck 4.

The proximal portion 3 is delimited by a front surface 3a and by a rear surface 3b, which are substantially flat and symmetrical with respect to the centerline plane 7.

The front surface 3 a and the rear surface 3 b are respectively the extension of the front face 2a and of the rear face 2b and therefore have their same inclination. On the front surface 2a or on the rear surface 2b or on both one or more ribs 10 are provided, which engage the bone cortex. In the particular embodiment according to the invention the ribs 10 are six in number, of which three are on the front surface 2a and the other three are on the rear surface 2b, arranged symmetrically with respect to the centerline plane 7.

The ribs 10 comprise a proximal portion 1 Oa that has a sharp profile in order to cut into the bone cortex, facilitating bone integration and avoiding relative rotations between the femoral stem 1 and the bone.

The proximal portion 1 Oa with a sharp profile extends gradually and continuously with a flat distal portion 10b, which is inclined with respect to the front surface 3a and the rear of surface 3b. The proximal portion 10a with a sharp profile extends with a width that increases toward the distal portion 2 and a height that decreases toward the distal portion 2 substantially until it vanishes.

This extension facilitates the orientation of the femoral stem 1 during the first step for insertion in the spongy proximal region and facilitates good contact with the bone cortex. The ribs 10, viewed on a frontal plane, have an axis of symmetry 1 Oc that is inclined with respect to the longitudinal axis 6 of the distal portion 2 toward the coxofemoral joint by an acute angle of inclination p to prevent the sharp portions 10a from gouging into the bone cortex along a direction that is transverse to the insertion direction.

The inclination angle p has a breadth ranging from 1° to 30° and is preferably equal to 9°.

The ribs 10 are substantially parallel to each other.

The proximal portions 1 Oa having a sharp profile, viewed on a plane that passes through the longitudinal axis 6 of the distal portion 2 and is perpendicular to the centerline plane 7, are symmetrical with respect to the centerline plane 7 and are inclined so as to converge toward the distal portion 2 by an angle γ.

The angle γ has a breadth ranging from 2° to 10° and is preferably equal to 6°.

The flat distal portions 10b, viewed on a plane that passes through the longitudinal axis 6 of the distal portion 2 and is perpendicular to the centerline plane 7, are symmetrical with respect to the centerline plane 7 and are inclined so as to converge toward the distal portion 2 by an angle δ. The angle δ has a breadth ranging from 3° to 40° and is preferably equal to 13°.

The ribs 10, viewed in a cross-section taken transversely to the longitudinal axis 6 of the distal portion 2 along the plane V-V (Figure 5), have a height that decreases from the outer side toward the inner side in order to avoid causing the formation of cracks during insertion.

The crests of the proximal portions 1 Oa having a sharp profile of the ribs 10, viewed in the cross-section V-V (Figure 5), lie on two lines 1 1 that diverge toward the outer side and are mutually inclined symmetrically with respect to the centerline plane 7 with a transverse inclination ε whose breadth ranges from 0° to 45° and is preferably equal to 15°. The stem 5 is substantially frustum-shaped, with the larger end face blended with the neck 4 and with the central axis 12 that lies on the centerline plane 7.

The neck 4 is substantially frustum-shaped, with the smaller end face blended with the shank 5 and the larger end face blended with the proximal portion 3.

The central axis 12 of the stem 5 is inclined with respect to the longitudinal axis 6 of the distal portion 2 by a cervical-diaphyseal angle α, known as CCD angle, whose breadth ranges from 120° to 150° and is preferably equal to a value selected from the group that comprises: 128°,

135° and 140°.

Depending on the cervical-diaphyseal angle α, the femoral offset distance D, which is defined as the perpendicular distance between the longitudinal axis 6 of the distal portion 2 and the center of rotation of the spherical head associated with the shank 5 and not shown, has a variable value that ranges from 20.0 to 70.0 mm.

For each value of the cervical-diaphyseal angle α, the femoral offset distance D assumes different values in order to obtain an optimum anatomical reconstruction. For example, the femoral offset distance D for a value of said cervical-diaphyseal angle (α) equal to 140° may have a value selected from the group that comprises: 36.0 mm, 38.0 mm and 40.0 mm; for a value of said cervical-diaphyseal angle (α) equal to 135°, it may have a value selected from the group that comprises 40.0 mm, 42.0 mm, 44.0 mm, 46.0 mm and 48.0 mm; and finally, for a value of said cervical-diaphyseal angle (α) equal to 128°, may have a value selected from the group that comprises: 48.0 mm, 50.0 mm and 52.0 mm.

In particular, the femoral stem is designed so that for a same stem size, upon variation of the CCD angle (α) and of the offset value D, the height of the center of rotation of the spherical head does not change; this allows greater intraoperative flexibility and allows to avoid dysmetrias of the limbs if the surgeon decides to pass from one offset value to a larger or smaller value in order to obtain a perfect balancing of the joint.

Operation of the femoral stem according to the present invention is as follows.

During so-called "banana insertion", the surgeon inserts the femoral stem 1 in the bone cavity, following a curvilinear path.

It is noted that the particular shape of the outer side of the femoral stem 1 and in particular of the second straight segment 30 allows insertion without requiring complete separation of the tendons, muscles and soft parts proximate to the trochanteric region of the femur.

Insertion consists of a number of steps. In a first step, the flat distal portions 1 Ob of the ribs 10 are designed to guide the surgeon so that he can orient the femoral stem 1 so as to obtain correct positioning of the femoral stem 1.

Then, as the femoral stem 1 is inserted, the proximal portions 10a having a sharp profile of the ribs 10 cut into the bone cortex, becoming wedged and thus blocking any rotations of the femoral stem 1 about the longitudinal axis 6 of the distal portion 2. Once inserted, the femoral stem 1 interacts with the remaining portion of the femur to bear the working loads of the leg of the patient, so as to not make them bear fully on the femoral stem 1 but also on the bone.

The load bears on the region of the proximal portion 3, preventing it from bearing on the region of the distal portion 2, which tapers appropriately, ensuring a correct application of forces to the bone and preventing the onset of disorders of the bone and muscle system, such as for example bone reabsorption.

In practice it has been found that the femoral stem according to the present invention fully achieves the intended aim, since it allows to preserve as much as possible the organic tissues of the trochanteric region, simultaneously ensuring high primary and secondary stability.

A further advantage achieved by the femoral stem according to the present invention consists in that the trochanteric angle β, in combination with the optimized longitudinal length of the distal portion of the femoral stem, allows mini-invasive insertion without requiring the separation of muscles, tendons and soft parts, preserving the bone as much as possible and ensuring maximum primary and secondary stability.

Another advantage achieved by the femoral stem according to the present invention consists in that the procedure, by being mini-invasive, allows short times for recovery of the muscles and of functional hip mobility.

A further advantage achieved by the femoral stem according to the present invention consists in that the preservation of the bone during the surgical procedure does not compromise the possibility to perform a second procedure if needed.

Another advantage achieved by the femoral stem according to the present invention consists in that the surface treatments on the front face, on the rear face, on the inner side wall, on the outer side wall, on the bevels with angles θ and on the rounded end of the distal portion, in combination with an adequate contact pressure with the bone, allow high primary and secondary stability of the implant, improving the osteointegration process.

Another advantage achieved by the femoral stem according to the present invention consists in that the proximal portions with a sharp profile of the ribs cut into the bone cortex, penetrating it without forming cracks, thus ensuring high primary and secondary stability and facilitating the osteointegration process.

Another advantage achieved by the femoral stem according to the present invention consists in that the inclination angle p of the ribs, viewed on a frontal plane, prevents the proximal portion with a sharp profile of the ribs from causing, during insertion along a curvilinear or so-called "banana" trajectory, grooves on the bone cortex along a direction that is transverse to the longitudinal direction of the ribs.

The femoral stem thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may further be replaced with other technically equivalent elements.

In practice, the materials used, so long as they are compatible with the specific use, as well as the dimensions, may be any according to requirements and to the state of the art.

The disclosures in Italian Patent Application No. MI2007A001813 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A femoral stem of an endoprosthesis of a coxofemoral joint, comprising a distal portion, which is substantially longitudinally elongated and is suitable to be inserted in the bone cavity of a femur, and a proximal portion, which is suitable to be accommodated proximate to the trochanteric region of the femur and extends into a neck provided with a shank for coupling to a spherical head of the coxofemoral joint, characterized in that, viewed on a frontal plane, it has an inner side and an outer side, said outer side having a convex profile that comprises at least one first straight segment that delimits said distal portion and a second straight segment that delimits said proximal portion and is inclined with respect to the longitudinal axis of said distal portion toward the coxofemoral joint at an acute trochanteric angle (β).

2. The femoral stem according to claim 1 , characterized in that said distal portion has such a longitudinal length that when said length is added to the length of said proximal portion, it is equal to a total length ranging from 50 to 200 mm.

3. The femoral stem according to claim 2, characterized in that said total length has a value selected from the group that comprises: 75 mm, 77 mm, 79 mm, 81 mm, 83 mm, 85 mm, 87 mm, 89 mm, 91 mm and 93 mm.

4. The femoral stem according to one or more of the preceding claims, characterized in that said trochanteric angle (β) has a breadth ranging from 2° to 30°.

5. The femoral stem according to claim 4, characterized in that said breadth of said trochanteric angle (β) is equal to 8°.

6. The femoral stem according to one or more of the preceding claims, characterized in that said proximal portion is delimited by a front surface and by a rear surface, which are substantially flat and symmetrical with respect to a central plane that is parallel to said front plane.

7. The femoral stem according to claim 6, characterized in that at least one of said front and rear surfaces has at least one rib that engages the bone cortex of the femur.

8. The femoral stem according to claim 7, characterized in that each of said ribs comprises a proximal portion having a sharp profile.

9. The femoral stem according to claim 8, characterized in that said proximal portion having a sharp profile extends gradually and continuously into a flat distal portion that is inclined with respect to said front surface and rear surface with a width that increases toward said distal portion and a height that decreases towards said distal portion substantially until it vanishes.

10. The femoral stem according to one or more of claims 7 to 9, characterized in that each of said ribs, viewed on said frontal plane, has a longitudinal axis of symmetry that is inclined with respect to said longitudinal axis of said distal portion toward said coxofemoral joint by an acute angle of inclination (p).

1 1. The femoral stem according to claim 10, characterized in that said angle of inclination (p) has a breadth ranging from 1° to 30°.

12. The femoral stem according to claim 1 1 , characterized in that said angle of inclination (p) has a breadth of 9°.

13. The femoral stem according to claims 7 to 12, characterized in that it comprises a plurality of said ribs.

14. The femoral stem according to one or more of claims 7 to 13, characterized in that said ribs are substantially parallel to each other.

15. The femoral stem according to one or more of claims 7 to 14, characterized in that said plurality of said ribs comprises six of said ribs, three being formed on said front surface and three being formed on said rear surface.

16. The femoral stem according to one or more of claims 7 to 15, characterized in that said portions of said ribs having a sharp profile, viewed on a plane that passes through said longitudinal axis of said distal portion and perpendicular to said central plane, are symmetrical with respect to said centerline plane and are inclined so as to converge toward said distal portion, the angle (γ) having a breadth ranging from 2° to 10°.

17. The femoral stem according to claim 16, characterized in that said angle (γ) has a breadth equal to 6°.

18. The femoral stem according to claim 16 or 17, characterized in that said distal flat portions of said ribs, viewed on said plane that passes through said longitudinal axis of said distal portion and is perpendicular to said centerline plane, are symmetrical with respect to said centerline plane and are inclined so as to converge toward said distal portion, the angle (δ) formed between said flat distal portions having a breadth ranging from 3° to 40°.

19. The femoral stem according to claim 20, characterized in that said angle (δ) has a breadth of 13°.

20. The femoral stem according to one or more of claims 7 to 19, characterized in that said ribs, viewed in a cross-section taken transversely to said longitudinal axis of said distal portion, have a height that decreases from said outer side toward said inner side.

21. The femoral stem according to one or more of claims 7 to 20, characterized in that the crests of said proximal portions of said ribs having a sharp profile, viewed in a cross-section taken transversely to said longitudinal axis of said distal portion, lie on two lines that diverge toward said outer side and are mutually inclined symmetrically with respect to said centerline plane with a transverse inclination (ε) whose breadth ranges from 0° to 45°.

22. The femoral stem according to claim 21, characterized in that said transverse inclination (ε) has a breadth equal to 15°.

23. The femoral stem according to one or more of the preceding claims, characterized in that said shank is substantially frustum-shaped, with a larger end face that is blended with said neck and a central axis that lies on said centerline plane.

24. The femoral stem according to claim 23, characterized in that said central axis of said shank is inclined with respect to said longitudinal axis of said distal portion with a cervical-diaphyseal angle (α) whose breadth ranges from 120° to 150°.

25. The femoral stem according to claim 24, characterized in that said cervical-diaphyseal angle (α) has a value selected from the group that comprises: 128°, 135° and 140°.

26. The femoral stem according to one or more of the preceding claims, characterized in that the femoral offset distance, defined as the perpendicular distance between said longitudinal axis of said distal portion and the center of said spherical head, ranges from 20.0 mm to 70.0 mm, depending on the value of said cervical-diaphyseal angle (α).

27. The femoral stem according to claim 26, characterized in that said femoral offset distance, for a value of said cervical-diaphyseal angle (α) equal to 140°, has a value selected from the group that comprises: 36.0 mm, 38.0 mm and 40.0 mm.

28. The femoral stem according to claim 26, characterized in that said femoral offset distance, for a value of said cervical-diaphyseal angle (α) equal to 135°, has a value selected from the group that comprises: 40.0 mm, 42.0 mm, 44.0 mm, 46.0 mm and 48.0 mm.

29. The femoral stem according to claim 26, characterized in that said femoral offset distance, for a value of said cervical-diaphyseal angle (α) equal to 128°, has a value selected from the group that comprises: 48.0 mm, 50.0 mm and 52.0 mm.

30. The femoral stem according to one or more of the preceding claims, characterized in that said distal portion is delimited by a front face, by a rear face, by an inner lateral wall and by an outer lateral wall, which are inclined so as to converge toward a rounded distal end of said distal portion.

31. The femoral stem according to claim 30, characterized in that said outer side wall and said inner side wall of said distal portion, viewed on said frontal plane, are mutually inclined in a substantially symmetrical manner with respect to said longitudinal axis of said distal portion by an angle (η) whose breadth ranges from 1° to 20°.

32. The femoral stem according to claim 31, characterized in that said angle (η) has a breadth equal to 6°.

33. The femoral stem according to one or more of claims 30 to 32, characterized in that each one of said outer lateral wall and said inner lateral wall of said distal portion, viewed on said frontal plane, is blended with said rounded distal end with a straight bevel that is inclined with respect to said longitudinal axis by a bevel angle (θ) whose breadth ranges from 5° to 45°.

34. The femoral stem according to claim 33, characterized in that said bevel angle (θ) has a breadth equal to 17°.

35. The femoral stem according to one or more of claims 30 to 34, characterized in that said front face and said rear face of said distal portion, viewed on said plane that passes through said longitudinal axis of said distal portion and is perpendicular to said centerline plane, are mutually inclined symmetrically with respect to said centerline plane by an angle (λ) whose breadth ranges from 1° to 10°.

36. The femoral stem according to claim 35, characterized in that said angle (λ) has a breadth equal to 3°.

37. The femoral stem according to one or more of claims 30 to 34, characterized in that said front face and said rear face of said distal portion, viewed on a plane that lies transversely to said longitudinal axis, are mutually inclined symmetrically with respect to said centerline plane by an angle (μ) whose breadth ranges from 1° to 15°.

38. The femoral stem according to claim 37, characterized in that said angle (μ) has a breadth equal to 6°.