FR2666983A1 - Hip prosthesis - Google Patents

Abstract

The present invention relates to a new hip prosthesis device. The device comprises a metal cupola (1) which comprises tooth-shaped projections (21). The cupola (1) is anchored in the bone (25) by means of screws (10), which are equipped with a spherical surface on their head and matching the said tooth-shaped projections. Situated inside the cupola is a core (2) which is locked in rotation and translation by means of tongues (11) which project slightly inside the cupola. The said core comprises a protrusion (15) which prevents the spherical head (4) of the shaft (5), fixed to the femur of the patient, from escaping from the cavity (3) provided in the core. The technical field of the invention is that of prosthesis manufacture.

Description

 Hip prosthesis.

DESCRIPTION
The present invention relates to a new hip prosthesis device.

 Hip prosthesis methods and devices have been the subject of much research and are described in numerous documents.

 The FR patent. 2,406,433 describes a hip prosthesis device and its cementless implantation method, unlike the prostheses known before this document; according to this document, the prosthesis comprises an acetabular metal shell, intended to be sealed in a hip cavity, the shell comprising on its outer face, a porous and irregular surface for fixing the shell by intimate penetration of the bone into this surface, which prosthesis also comprises bolts making it possible to fix the shell during the period of penetration of the bone into the porous surface; The prosthesis also comprises a gasket, fixed on the shell, which receives the head of the femur and a femoral head a metal part provided with a cavity having also a porous or irregular surface, which metal femoral head can be fixed to the femur by a rod.

 This fixing process described in this patent is now well known under the term of hydroxylapatite.

 The FR patent. 2,578,162 describes a cup for hip prosthesis, which has radial lugs, which are detachably linked and adjustable in angular position at the peripheral edge of the cup; according to this document, the cup has a groove having a cross section undercut and the end of the legs linked to the cup have a profile section complementary to that of the groove.

 The FR patent. 2,626,168 describes a prosthesis which comprises a rod of suitable length, thanks to an interchangeable collar, which is inserted between the rod and the acetabulum, which can be cemented or anchored in the acetabulum.

 According to this document, the acetabulum comprises a part in the form of a half-sphere made of polyethylene, housed in a shell of identical shape in Titanium, which shell comprises lugs along planes parallel to the base of the shell.

 Patent application EP 353,171 describes a prosthesis which comprises a support cup, intended to be inserted into the bone of the joint, which comprises on its external face, an expandable peg and a plurality of expansion slots, one of which at least is extended to the pole of the cup, and which comprises at the base of its internal face, a thread which allows the fixing of the friction cup.

 Known hip prostheses still have many drawbacks.

 Indeed, the initial anchoring of the metal dome in the bone cavity is not easy to achieve by screws which press said shell into said cavity; moreover, the orientation of the screws which penetrate into the bone cannot be kept strictly coaxial and perpendicular with the range of screws provided in this dome; otherwise. these screws are not always sufficient to ensure good initial fixing, and the presence of pins along planes parallel to the base of the dome as described in FR. 2,626,168 does not facilitate this initial fixation.

 In addition, the problem posed to the surgeon during a hip prosthesis operation is the impossibility of being able to control the good contact of the external face of the shell with the bone cavity.

 Another important problem which is not resolved is the blocking of the plastic core inside the shell, in particular the blocking in rotation, as well as the blocking preventing the core from coming out of the shell after having been introduced into it.

 Finally, the major drawback of current hip prostheses is that of dislocations: indeed, the head (generally spherical) of the rod which is fixed on the femur, is simply engaged in the cavity formed in the plastic core; this means that in the event of poorly controlled movement of the patient, the head of the prosthesis can leave the cavity, which causes very great pain for the patient.

 The objective of the present invention is to remedy these drawbacks.

 The objectives are achieved by providing a hip prosthesis of the type comprising a metal dome, which is capable of being fixed by screws in the pelvis of a patient, which dome receives a plastic core, at least part of which the external face marries at least part of the internal face of said dome, said core comprising a cavity, which can receive the head of a rod which can be fixed to the femur of said patient, and said dome comprises a part in the shape of a cap hemispherical limited by two parallel planes P2, P4, of internal radius R1 and center Cl, which is extended by a substantially tubular part, whose axis is perpendicular to said planes, and which is limited by one of said planes and by a Pl plane, parallel to said planes and which contains said center of said hemispherical cap and said outer face of said core comprises a substantially hemispherical part with center C2 and radius R 2, substantially equal to said radius R1, which hemispherical part of said core is limited by two parallel planes P6, P7, and is extended by a cylindrical part, the largest external diameter of which is substantially less than the internal diameter of said tubular part of said dome , which internal diameter has a value substantially less than twice said radius Ri and said dome comprises means for preventing relative movements of said core relative to said dome.

 Advantageously, said means for preventing relative movements of said core with respect to said dome comprise at least two tongues, which extend along a line substantially parallel to said planes P1, P2, which tongues are fixed by a first end to said tubular part of said dome, and the second end of which is free, said tabs being slightly prominent inside said tubular part of said dome, so that they allow the introduction of said core inside said dome, by means of a slight local deformation of said cylindrical part of said core opposite said free ends of said tongues, and so that said tongues then prevent the relative rotation of said core with respect to said dome; the thickness of said tubular part of said dome can advantageously be less than the thickness of said hemispherical part of said dome.

 Advantageously, said cylindrical part of said core comprises at least a first cylindrical part, which extends said hemispherical part, and whose external diameter is equal to said external diameter of said cylindrical part of said core, which first cylindrical part is extended by a second coaxial cylindrical part. with said first cylindrical part, which second cylindrical part has an outside diameter, substantially smaller than said outside diameter of said cylindrical part of said core, which second cylindrical part is extended by at least a third cylindrical part, coaxial with said second cylindrical part, and whose the outside diameter is substantially greater than the inside diameter of said tubular part of said dome, so that said second cylindrical part, which is located between said first and third cylindrical parts, constitutes a groove in the which said tabs are housed and thus prevent said core from coming out of said dome.

 In a preferred embodiment, each of said tongues is produced by machining an elongated light, which light is located in said tubular part of said dome, which light opens out at an end close to said end of said tongue , and at least two of said tongues are symmetrical with respect to a plane P8 perpendicular to said planes Pi, P2, which plane P8 passes through said center Cl of said part of said dome in the shape of a hemispherical cap, so that the rotation blocking of said core with respect to said dome, is perfectly realized.

Advantageously, said third cylindrical part is separated from said second cylindrical part by a plane P5 parallel to said planes P6, P7, which plane P5 contains said center.
C2 of said hemispherical part of said outer face of said core, and a part of said cavity of said core is bounded by said plane P5 and by said inner face of said core which is in the form of a hemisphere, of radius R3 less than said radius R2 and having for center said center C2, and said third cylindrical part is limited on a part of its rear face by a face which extends in a plane P9 parallel to said plane P5, at an angle A, which face is connected to said inner face by a chamfer, and said third cylindrical part is extended beyond said plane P9 by a promontory, which extends at an angle B, and said third cylindrical part and said promontory are limited by an internal surface which is located on said sphere having for radius said radius R3 and for center, said center C2.

 Said third cylindrical part and said promontory thus play the role of anti-luxation stop and said chamfer allows the introduction during operation of said head into said cavity of said core, which head is then retained by said anti-luxation stop.

 Advantageously, said chamfer makes an angle E with an axis perpendicular to said planes P5 and P9, the value of which is between 20 and 600 and, preferably, between 30 and 500. and said angle B has a value greater than 900, and preferably close to 1800.

 Advantageously, said promontory has a flat face, which makes an angle with said plane P9, the value of which is between 5 and 200. and preferably between 10 and 150.

 Advantageously, said hemispherical cap-shaped portion of said dome is pierced with at least two orifices which have a face located on a sphere of radius R4, which orifices are provided for receiving said screws, and the rear face of the head of said screw is of spherical shape with radius R5 substantially equal to said radius R4, so that the angle made by said screw with said dome can vary within a certain range, and so that the stresses due to this method of fixing are reduced.

 Advantageously, said dome comprises on its external face protuberances in the form of teeth, at least one face of which is substantially situated on a cylinder having for axis said axis, which protuberances improve the initial fixation of the dome on said pelvis of said patient, which protuberances are located in the vicinity of said orifices.

 Advantageously, said dome comprises in said hemispherical part, a bore having its axis as said axis, and said dome comprises at least one window, which opens into said bore, and the width of which is sufficient to allow visual control of the bone cavity of the pelvis during operation.

 In a preferred embodiment, said screws are provided with a thread for cancellous bone and the front end of said screw comprises a substantially cylindrical guide stud and two substantially radial slots so that said screw is self-tapping.

 The. numerous advantages provided by the invention will be better understood through the following description, which refers to the appended drawings, and describes without any limiting character particular embodiments of prosthesis according to the invention.

 Figure 1 is a cross-sectional view of a metal dome according to the invention.

 Figure 2 and a view along Il-Il of Figure 1.

 FIG. 3 is a view along III-III of FIG. 4.

 Figure 4 is a side view of a core according to the invention, which comprises a half view in side section.

 Figure 5 is a view of a screw according to the invention.

 Figure 6 is a side view of a complete prosthesis according to the invention.

 In Figure 1, on which is shown a metal dome according to the invention, which can be made of a titanium alloy for example, it can be seen that said dome comprises a part in the shape of a hemispherical cap 8, which is limited by two planes P2 and P4 substantially parallel.

 It can be seen that said hemispherical cap has an internal radius Ri and a center Cl. Said hemispherical cap is extended by a substantially tubular part 9, the axis ZZ1 of which is perpendicular to said planes P2, P4, and said substantially tubular part is limited by said plane P2 and by a plane Pi parallel to said plane P2, which plane Pi contains said center Ci of said hemispherical cap.

 Said metal dome comprises means for preventing the relative movements of said core with respect to said dome, which consist of four tongues 11, which extend along a line substantially parallel to said plane Pi and P2; said tongues 11 are fixed by a first end 11b to said tubular part 9 of said metal dome; the second end 11a of said tongues 11 is free; it can also be seen that the thickness of said tubular part of said cap is substantially less than the thickness of said hemispherical part of said cap.

Advantageously, the thickness of said tubular part is between 1 and 3 mm, and the thickness of said part in the form of a hemispherical cap is between 2 and 5 mm.

 Said tongues 11 are produced by machining an elongated lumen 12 in said tubular part 9 of said dome, which lumens 12 open out at one end 12a close to said end 11a of said tongue.

 Said portion 8 in the form of a hemispherical cap of said dome is traversed by at least one orifice 17, which has a face 17a situated on a sphere of radius R4; said orifices 17 are provided to receive the screws allowing the dome to be fixed in the bone cavity of the patient's pelvis.

 We see that on the outer face of the hemispherical part of said dome, protrusions 21 are provided, which have a tooth shape and one face 21a is substantially located on a cylinder having for axis said axis zzl; the protrusions 21 indeed significantly improve the initial fixing of the dome on the pelvis of said patient.

 Said dome also comprises in its hemispherical part, a bore 23 having for axis said axis zzl and said dome comprises a window 22, which opens into said bore 23 and which extends substantially along a radius of said hemispherical cap.

 Said bore 23 is mainly intended to allow the anchoring and the initial positioning of said metal dome in said bone cavity.

 Advantageously, the drilling axis of said orifices 17 makes an angle between 40 and 500 relative to the trace of said plane Pi in FIG. 1.

 In a preferred embodiment, the internal diameter D1 of said tubular part is very slightly less than twice the internal radius Ri of said part in the form of a hemispherical cap.

 In a preferred embodiment, the internal face 1b of said dome comprises a part in the shape of a hemispherical cap 6, which is limited by a plane P3 in which is located a surface 7, which comprises said bore 23.

 Said planes Pi, P2, P3, P4 which are orthogonal to the plane of the figure, are marked by their traces in the plane of the figure, which are respectively constituted by the axes xxl, xx2, xx3, xx4.

 In FIG. 2, which is a plan view of the metal dome, it can be seen that said metal dome comprises three orifices 17, and five tooth-shaped protuberances 21, which are located near said orifices 17.

 It can also be seen that said window 22 opens into said bore 23 and that said window 22 has a width L which allows visual control of the pelvic bone cavity during operation.

Advantageously, the width L of said window 22 is between 3 and 10 mm, and is preferably between 5 and 8 mm.

 It can be seen that said window 22, which extends along a radius of said hemispherical part of said dome has for its plane of symmetry a plane P8, which is radial with respect to said hemispherical cap, which passes through said center Ci and which contains said zzl axis.

 It can also be seen that said tongues 11 there are symmetrical with respect to said plane P8; said tongues 11 are fixed by one end 11b to said metal dome and have one free end 11a close to the through end 12a of said v lights.

 It can also be seen that said free ends of said tongues are slightly curved, so as to be slightly prominent inside said tubular part of diameter D1.

 In FIG. 3, where a plastic core according to the invention is shown, it can be seen that the rear face of said core 13 comprises a flat face 13a, a face 13b, a face 13c and a face 13d; said face 13a extends angularly in the plane of the figure at an angle A in the plane of Figure 3; said faces 13d and 13b delimiting a promontory 15 extend angularly at the angle B in the plane of Figure 3. We see that a chamfer 14 is provided to connect said surface 13a to the inner face 2b of said plastic core delimiting said cavity 3 intended to receive the head of the stem of the prosthesis.

 It can be seen that tapped holes 24 are provided in said part 13a of the rear face of said core; said tapped holes 24 are in fact useful for the surgeon to position said core angularly with precision in said metal dome, after said core has been introduced therein.

 We see in the embodiment presented in Figure 3, that said angles A and B have a value close to 1800.

 In Figure 4 is shown a plastic core of a prosthesis according to the invention. Said core 2 has an outer face 2a and an inner face 2b; the outer face 2a has a hemispherical part 10 with center C2 and radius R2, which radius R2 is substantially equal to said interior radius of said hemispherical cap of said dome.

 It can be seen that said hemispherical part 10 is limited by two parallel planes P6 and P7 and is extended by a cylindrical part 11, the largest external diameter D2 of which is substantially less than said internal diameter of said tubular part of said dome.

 It can be seen that said cylindrical part 11 of said core comprises a first cylindrical part 11a, which extends said hemispherical part 10 and whose outside diameter is equal to said outside diameter D2, which first cylindrical part 11a is extended by a second cylindrical part 11b coaxial with said first cylindrical part 11a, of axis zz2, whose outer diameter D3 is substantially smaller than said outer diameter D2, which second cylindrical part llb is extended by a third cylindrical part lic, coaxial with said second cylindrical part, whose outer diameter D4 is substantially greater than said inside diameter of said tubular part of said dome, so that said second cylindrical part 11b, which is located between said first and third cylindrical parts, constitutes a groove in which said tabs of said dome can come to lodge and thus prevent so that said core can come out of said dome.

It can be seen that, advantageously, said third cylindrical part lic is separated from said second cylindrical part lib by a plane
P5, parallel to planes P6 and P7, which plane P5 contains said center
C2 of said hemispherical part of said outer face 2A of said core and part of the cavity 3 of said core is bounded by said plane P5, by the inner face 2b in the form of a hemisphere of said core.

 It can be seen that the interior face 2b in the form of a half-sphere has a radius R3, which is less than the radius R2 of the outer surface 2a of said core, and having said center C2 at its center.

 Said third lic cylindrical part is limited on a part of its rear face 13 by a face 13a, which extends in a plane P9, parallel to said plane P5, which face 13a is connected to said inner face 2b of said core by a chamfer 14 .

 It can be seen that advantageously, said third lic portion is extended beyond said plane P9 by a promontory 15 and said third cylindrical portion lic and said promontory 15 are limited by an internal surface 16 which is located on the sphere having for radius said radius R3 and for center said center C2.

 It is seen that thus said cavity 3 of said core, bounded by said chamfer 14, said spherical surface 2b and said spherical surface 16 extending said surface 2b form a cavity, which can receive the generally spherical head of the stem of the prosthesis, such so that when the head of the stem of said prosthesis has been introduced into said cavity 3, a translational movement along arrow F slightly inclined relative to the axis zz2, of said spherical head, the diameter of which is substantially equal to twice of said radius R3, is made impossible by the presence of said surface 16, arranged in said third cylindrical part and said promontory 15, which thus form an anti-luxation stop.

 It can be seen that said chamfer 14 makes an angle E with said axis zz2 perpendicular to said plane PS, the value of which is between 20 and 600. and preferably between 30 and 500.

 It can be seen that the face 13b of said promontory forms an angle F with said plane P9, the value of which is between 5 and 200 and, preferably, between 10 and 150.

 In Figure 5. we see that according to the invention, a screw for fixing said dome in the pelvis of a patient has a countersunk head, the front face 18b is substantially planar, said head 18 advantageously comprising a recess 20 allowing said screw to be screwed, said head 18 comprising a milled rear face 18a according to a radius R5 substantially equal to said radius of the range of said orifices provided in said metal dome.

 Advantageously, the head diameter of said thread 19 of said screw 10 is substantially greater than the passage diameter of said orifice arranged in said metal dome and the foot diameter of said thread 19 is substantially less than the drilling diameter of said orifice.

 It can be seen in FIG. 5 that the front end of said screw comprises a substantially cylindrical guide pin 26 and two substantially radial slots 27 so that said screw is self-tapping.

 In Figure 6 is shown a complete prosthesis according to the invention. During the implantation of said prosthesis in the bone 25 of the patient's pelvis, one begins by impaction implanting said metal dome 1 in said bone 25, the anchoring of which is facilitated by said tooth-shaped protuberances 21; said anchoring can be achieved by means of a threaded rod passing through said bore 23.

 Said screws 10 can then be screwed into said bone 25 of said pelvis and. thanks to the spherical face of their heads, orient themselves in said spherical bearing surface of said orifices 17 of said metal dome, so as to induce the minimum of mechanical stress and therefore so as to limit the pains resulting from the operation.

 Thanks to the invention, and to said large width of said window 22, the surgeon will be able to verify that said metal dome perfectly matches the cavity produced in the bone of the pelvis 25; advantageously, the external surface of said metal dome is coated with a calcium hydroxylapatic and has undergone a sandblasting treatment, so as to facilitate intimate connection with said bone cavity.

 We can then introduce said core 2 into said metal dome, which will be locked in rotation and cannot then escape thanks to said tongues il, which are slightly prominent inside said tubular part of said dome, so that they allow the introduction of the core inside said dome, with a slight local deformation of said cylindrical part of said core opposite said free ends of said tongues.

 It is also seen, after introduction of the spherical head 4 of the rod 5 fixed to the patient's femur, that said head 4 cannot come out of the cavity 3 provided in said core according to arrow F, thanks to the presence according to the invention of the surface 16 provided inside said core, in particular at the level of said promontory 15, playing the role of anti-dislocation stop.

Claims (11)

 1. Hip prosthesis of the type comprising a metal dome (1), which can be fixed by screws (10) in the pelvis of a patient, which dome receives a plastic core (2), one of which at least part of the external face (2a) matches at least part of the internal face (lb) of said dome, said core comprising a cavity (3), which can receive the head (4) of a rod (5) which can be fixed to the femur of said patient, characterized in that said dome comprises a part in the shape of a hemispherical cap (8), limited by two parallel planes (P2, P4), of internal radius Ri and of center Ci, which is extended by a substantially tubular part (9), the axis (zzl) of which is perpendicular to said planes (P2. P7), and is extended by a cylindrical part (it). whose largest outside diameter (D2) is substantially less than the inside diameter (D1) of said tubular part (9) of said dome, which inside diameter (D1) has a value substantially less than twice said radius (Ri), and that said dome includes means for preventing relative movements of said core with respect to said dome. P4), and which is bounded by said plane (P2) and by a plane (Pi), parallel to said plane (P2) and which contains said center (C1) of said hemispherical cap, and in that said outer face (2a) of said core comprises a substantially hemispherical part (10) with center C2 and radius R2 substantially equal to said radius R1, which hemispherical part of said core is limited by two parallel planes (P6,  2. Prosthesis according to claim 1, characterized in that said means for preventing relative movements of said core relative to said dome comprise at least two tongues (11), which extend along a line substantially parallel to said planes (P1, P2), which tongues are fixed by a first end (lob) to said tubular part (9) of said dome, and the second end (lia) of which is free, said tongues being slightly prominent inside said tubular part of said dome, so that they allow the introduction of said core inside said dome, by means of a slight local deformation of said cylindrical part (11) of said core opposite said free ends of said tabs, and so that said tabs then prevent the relative rotation of said core relative to said dome.  3. Prosthesis according to claim 2, characterized in that said cylindrical part of said core comprises at least a first cylindrical part (lia), which extends said part (10) hemispherical, and whose outside diameter is equal to said outside diameter (D2) , which first cylindrical part (11a) is extended by a second cylindrical part (nib), coaxial with said first cylindrical part, which second cylindrical part has an outside diameter (D3), substantially smaller than said outside diameter (D2), which second part cylindrical is extended by at least a third cylindrical part (lac), coaxial with said second cylindrical part, and whose external diameter (D4) is substantially greater than said internal diameter (Dl), so that said second cylindrical part (nib), which is located between said first and third cylindrical parts, constitutes a groove in which said lan lookouts are housed and thus prevent said core from coming out of said dome.  4. Prosthesis according to any one of claims 2 to 3, characterized in that each of said tabs is produced by machining an elongated lumen (12), which lumen is located in said tubular part (9) of said dome, which light emerges at one end (12a) close to said end (11a) of said tongue, and in that at least two of said tongues are symmetrical with respect to a plane (P8), perpendicular to said planes (P1 , P2), which plane (P8) passes through said center (Ci), so that the blocking in rotation of said core relative to said dome, is perfectly achieved.  5. Prosthesis according to any one of claims 3 to 4, characterized in that said third cylindrical part (lac) is separated from said second cylindrical part (nib) by a plane P5, parallel to said planes P6 and P7, which plane P5 contains said center C2 of said hemispherical part of said outer face (2a), and in that a part of said cavity (3) of said core which is bounded by said plane P5 and by said inner face (2b) which is in the form of a half sphere of radius R3 smaller than said radius R2 and having for center said center C2, and in that said third cylindrical part (lac) is limited on a part of its rear face (13) by a face (13a), which extends in a plane P9 parallel to said plane PS, at an angle (A), which face (13a) is connected to said inner face (2b) by a chamfer (14), and in that said third cylindrical part (lake) is extended beyond said plane P9 by a promontory (15), which extends at an angle B, and said third cylindrical part and said promontory (15) are limited by an internal surface (16), which is located on said sphere having for radius said radius R3 and for center said center C2.  6. Prosthesis according to claim 5, characterized in that said chamfer makes an angle (E) with an axis (zz2) perpendicular to said planes P5 and P9, whose value is between 20 and 600 and, preferably, between 30 and 500, and in that said angle (B) has a value greater than 900. and preferably close to 1800.  7. Prosthesis according to any one of claims 5 to 6, characterized in that said promontory comprises a planar face (13b), which makes an angle (F) with said plane (P9), the value of which is between 5 and 200, and preferably between 10 and 150.  8. Prosthesis according to any one of claims 1 to 7, characterized in that said part (8) in the form of a hemispherical cap of said dome, is pierced with at least two orifices (17) which have a face (17a) , located on a sphere of radius (R4), which orifices are provided for receiving said screws (10), and in that the rear face (18a) of the head (18) of said screws, is of spherical shape with radius (R5 ) substantially equal to said radius (R4), so that the angle made by said screw with said dome can vary within a certain range, and so that the stresses due to this method of attachment are reduced.  9. Prosthesis according to any one of claims 1 to 8, characterized in that said dome comprises on its outer face (la) protuberances (21) in the form of teeth, at least one face (21a) of which is substantially situated on a cylinder having for axis said axis (zzl), which protrusions improve the initial fixation of the dome on said pelvis of said patient, which protuberances are located in the vicinity of said orifices (17).  10. Prosthesis according to any one of claims 1 to 9, characterized in that said dome comprises in its hemispherical part, a bore (23) having for axis said axis (zzl), and said dome comprises at least one window (22 ), which opens into said bore (23), and whose width (L) is sufficient to allow visual control of the pelvic bone cavity during operation.  11. Prosthesis according to any one of claims 1 to 10, characterized in that said screws are provided with a thread for cancellous bone and in that the front end of said screw comprises a substantially cylindrical guide pin (26) and two substantially radial slots (27) so that said screw is self-tapping.