Joint socket for a joint prosthesis

Abstract

A joint socket (2) for a joint prosthesis (1) that can be fixed in a bone structure (6) and has a socket insert (3) for receiving at least a partially spherical joint body, wherein the joint socket (2) has at least one projection (7) facing the bone structure (6) and designed to engage in a groove-shaped recess (9) of the bone structure (6) that is radially spaced from a recess (8) for the socket insert (3) in the bone structure (6), which surrounds the socket insert (3) circumferentially, in particular concentrically, and wherein the projection (7) has at least a partially convex outer surface (10) and a concave inner surface (11) so that the projection (7) can be inserted into the groove-shaped recess (9) in a form-fitting manner with the outer surface (10) and the inner surface (11), characterized in thatthat the socket (2) has a retaining frame (14) with a passage width (D) that is variable, in particular against an elastic restoring force, and is less than the great circle diameter of the socket insert (3), and two projections (7) which are spaced apart from each other in the circumferential direction within an annular area limited by the outer contour and by the inner contour, and the retaining frame (14) in turn has two projections (7') which are connected flush with the two projections (7) of the socket (2).

Description

[0001] The invention relates to a joint socket for a joint prosthesis which can be fixed in a bone structure and has a socket insert for receiving a joint body which is at least partially spherical, wherein the joint socket has at least one projection facing the bone structure and intended to engage in a groove-shaped recess in the bone structure which is radially spaced from the depression for the socket insert in the bone structure, which projection encloses the socket insert circumferentially, in particular concentrically, at a small distance, and wherein the projection has at least partially a convex outer surface and a concave inner surface, so that the projection can be inserted into the groove-shaped recess with the outer surface and the inner surface in a form-fitting manner.

[0002] Joint prostheses with anchoring components that can be screwed into the bone are already known in various designs and applications, particularly in hip joint prostheses. In this case, the socket is inserted, tapered side first, into a surgically prepared recess in the bone.

[0003] In practice, conical or spherical acetabular cups are commonly used, each comprising a metallic outer shell and an insert or inlay arranged within the shell, usually made of ceramic, plastic or metal.

[0004] One advantage of using spherical cups is that less bone substance from the pelvic bone needs to be removed when pre-milling the spherical cavity than with a conical-shaped cup. The milling itself is also easier with spherical cups, as orientation has little influence.

[0005] In addition to the standard spherical cup design, which corresponds to a hemisphere, press-fit versions are also used. These press-fit cups are slightly flattened at the pole and slightly larger in diameter than the pre-milled hemispherical socket in the bone. This ensures a press fit of the cup in the pre-milled bone. A rough surface coating on the commonly used shells made of metals such as pure titanium facilitates the grafting of bone cells to the implant. This is intended to ensure optimal stabilization.

[0006] In contrast to the screwed cups, the spherical cups without thread and especially the press-fit cups are driven or pressed into the pre-milled bed in a linear movement.

[0007] A generic joint socket, in particular for a hip joint prosthesis, with a shell having a concave inner surface and with at least one anchoring part intended for anchoring in a bone is already known from WO 1985 / 02535 A1. A spherical cap-shaped recess in the bone serves to receive the shell, and an annular groove serves to receive the anchoring part. The anchoring part is preferably slightly pressed into the annular groove during insertion, so that the joint socket can be inserted into the bone as a whole without cement, and only a relatively small amount of bone material is removed for anchoring.

[0008] US 11 478 358 B2 discloses a humeral implant comprising a shell with a body defining a recess facing the bone. The recess has an annular surface and a convex surface, the annular surface having a profile that substantially corresponds to the profile of an outer bone ring. The annular surface or the convex surface can optionally comprise one or more retaining elements, for example, projections, ribs, or recesses, that engage the humerus.

[0009] EP 0 169 978 B1 discloses an endoprosthesis for an acetabular cup, consisting of an inner cup body and an outer shell, suitable for cementless anchoring. The cup body is provided with a conical shell and the outer shell with a cavity adapted to the shell. The outer shell and the cup body are held together by a locking structure. Several slots are evenly distributed around the circumference of the outer shell, and the surface of the outer shell is provided with a structure consisting of projections. The projections are pin-shaped and are placed on the surface of the expansion cup.

[0010] EP 0 242 633 B1 discloses an endoprosthesis for an acetabular cup, consisting of an inner cup body and an outer shell, suitable for cementless anchoring. The endoprosthesis has a structure consisting of several peripheral rows of projections in the equator-facing region of the outer shell surface. The projections are thorn-shaped and arranged on concentric circles on the surface of the expansion cup.

[0011] DE 35 18 246 A1 relates to an acetabular cup prosthesis with a conical outer shape for insertion into a correspondingly shaped hole in a bone, wherein the conicity of the conical shape is designed for permanent engagement with the surrounding bone.

[0012] In the joint prosthesis known from DE 29 25 089 A1, an inner cup and an outer ring are provided, wherein the cup is subjected to an annular bandaging load which is exerted on the cup by the outer ring either directly or by means of a possibly interposed intermediate ring piece which is arranged between the cup and the ring.

[0013] DE 33 47 983 C2 relates to a joint socket prosthesis, with a shell that can be fixed to a bone and with an insert that can be inserted into the shell and is composed of two bearing segments that enclose the joint ball without any division, wherein a slotted ring is elastically expandable so that it can be pushed over the joint ball.

[0014] DE 10 2006 019 620 B4 refers to an artificial joint socket with a number of radial through holes for the passage of a bone screw each for anchoring the socket in the adjacent bone area.

[0015] US 2006 / 0 167 556 A1 concerns a hip prosthesis in which a bipolar socket is provided between the head and the acetabulum, allowing the head to rotate within the bipolar socket and the bipolar socket within the acetabular cavity, thus preventing dislocation. A split ring with a reduced opening width serves to fix the head.

[0016] A disadvantage of the current state of the art is that bone implants weaken the bone substance due to the necessary indentations, resulting in an increased risk of possible fractures. This is especially true for revision surgeries, which are usually associated with further bone loss.

[0017] A particular disadvantage of expansion cups for hip joint prostheses is that the projections on the expansion cup are arranged in such a way that forces acting in the bone tissue opposite to the implantation direction of the expansion cup can cause the expansion cup to detach from the bone tissue.

[0018] A particularly disadvantageous factor is the direction of the fixation forces, which in most fixation options used in practice are essentially directed radially outward, creating spreading forces. These spreading forces can be a cause of a not uncommon reduction in the holding force of the acetabulum in the bone structure.

[0019] The invention is based on the object of creating a way to largely compensate for the inevitable weakening of the bone substance through the design of the acetabulum, so that the load-bearing capacity of the bone structure is not reduced but improved. In particular, the introduction of radial spreading forces into the bone structure surrounding the acetabulum is to be avoided.

[0020] This object is achieved according to the invention with a joint socket according to the features of claim 1. The further embodiment of the invention can be found in the subclaims.

[0021] According to the invention, a joint socket is provided in which the joint socket has a holding frame with a passage width smaller than the great circle diameter of the socket insert, wherein two projections are arranged spaced apart from one another in the circumferential direction within an annular region delimited by the outer contour and by the inner contour, and the holding frame in turn has two projections which are connected flush with the two projections of the joint socket.

[0022] As a result, a spherical joint body inserted into the socket insert is secured by the holding frame, thus preventing dislocation of the joint.

[0023] By arranging several projections within an annular area defined by the outer contour and the inner contour, spaced apart from one another in the circumferential direction, several, preferably geometrically matching, projections can be used for fixation, thus further increasing the fixation forces. For this purpose, the retaining frame itself has projections that are connected flush with the projections of the joint socket.

[0024] The passage width can be extended to the great circle diameter against an elastic restoring force of the holding frame, so that the joint body is secured in the socket insert according to the principle of a snap lock.

[0025] The load-bearing capacity of the bone structure, weakened by the loss of substance needed to accommodate the acetabulum, is restored by enclosing the acetabulum insert with one or more projections, similar to a ring clamp or a cuff. In particular, the introduction of radial spreading forces into the bone structure surrounding the acetabulum is avoided.

[0026] The load-bearing capacity of the bone that accommodates the acetabulum, for example the pelvic bone, is improved because the forces that act transversely to the axis - namely, on the one hand, the spreading forces due to the inserted acetabulum and, on the other hand, due to external forces, in particular those resulting from joint loading - can be reliably absorbed by the projection, thus avoiding additional forces acting on the bone structure. For example, bending forces of the bone are also absorbed because strains in the plane of the bone surface are absorbed by the at least one projection. The prosthesis can therefore also absorb tensile forces transversely to the axis of symmetry of the acetabulum. This creates a clamping effect in the surface, and the enclosed area supporting the shell insert remains free from unwanted forces.At the same time, the achievable fixation forces of the acetabulum are also increased, ensuring that it remains reliably fixed even under heavy loads and does not detach from the bone structure because the holding forces within the bone are significantly increased. It has been shown that the fixation can even prevent the progression of a fracture in the bone structure, and the acetabulum remains securely fixed even if such a fracture occurs. Due to the increased holding forces, the amount of bone structure that needs to be removed can be kept to a minimum.

[0027] It has already proven particularly advantageous if the projection is closed in a ring shape and encloses the cup insert on the periphery. This makes the effect of the circumferential clamping independent of direction, which also simplifies the fixation of the projection in the groove-shaped recess. In practice, the resulting clamping forces alone lead to sufficient fixation.

[0028] Furthermore, it is particularly promising if the projection has a circular cross-section with a constant wall thickness and concentrically encloses the acetabulum. Due to the rotationally symmetrical design of the circular or conical projection, the achievable holding forces are independent of the angular position, allowing the acetabulum to be inserted in any angular position, thus facilitating the operation. A core drill, preferably in conjunction with a depth stop, can be used particularly easily to create the groove-shaped recess, thus eliminating the effort associated with using milling tools.

[0029] The projections may have frontal angulations or bends that penetrate the bone structure when the acetabulum rotates.

[0030] Furthermore, the projections can transmit increased clamping forces if at least some of the projections are adjustable, for example, in order to clamp them within the recess against the limiting wall surfaces.

[0031] Particularly preferably, several projections spaced apart from one another are arranged evenly distributed around the circumference so that the holding forces are introduced into the bone structure evenly over the entire circumference.

[0032] The adjacent projections can have different geometries and also different lengths. However, it is particularly advantageous if the axial extension of the projection is constant in the circumferential direction and / or the axial extension of adjacent, in particular all, projections is identical, so that the socket reliably reaches a depth position within the bone structure specified by the groove-shaped recess and this position is permanently maintained.

[0033] Furthermore, according to a further useful modification of the invention, at least one projection can be fixed in different positions, particularly continuously, in the axial direction parallel to the axis of symmetry of the joint socket. This allows the depth position of the joint socket to be adjusted using the projection, thus achieving optimal positioning. By adjusting the axial depth position differently for several projections distributed around the circumference, a desired angle of inclination of the joint socket can also be set as needed.

[0034] In practical testing, it has already proven to be expedient if the radial distance of at least one projection from the socket insert is between 0.5 mm and 10 mm, the depth of the groove-shaped recess is between 5 mm and 35 mm and the distance between the convex outer surface and the concave inner surface is between 1 mm and 5 mm.

[0035] A further, particularly advantageous embodiment of the invention is achieved when at least one projection has ingrowth openings on its outer and / or inner surface. These ingrowth openings, also referred to as ingrowth indentations, promote the ingrowth of the surrounding bone substance and, after a short time, form undercuts with the acetabulum, which is thereby reliably fixed.

[0036] By having an underside of the socket facing the bone structure within the recess, which underside is inserted into the recess in the implanted position at a distance from the bone structure, a gap is created so that the fixation forces are introduced into the recess of the bone structure exclusively or at least largely by means of the projections.

[0037] The invention allows for various embodiments. To further clarify its basic principle, one of them is shown in the drawing and is described below. This shows in Fig. 1 a front perspective view of an acetabulum; Fig. 2 a posterior perspective view of a joint socket; Fig. 3 a front perspective view of a bone structure with a recess for a socket insert of the acetabulum and with a concentric groove-shaped recess; Fig. 4 a sectional view of the Fig. 3 shown bone structure with the recess for the cup insert of the lateral groove-shaped recess; Fig. 5 a front perspective view of the Fig. 3 shown bone structure with the acetabulum fixed in it; Fig. 6 a sectional view of the Fig. 5 shown bone structure with the joint socket fixed in it: Fig. 7 is a front perspective view of an acetabular cup according to the invention; Fig. 8 a rear perspective view of the Fig. 7 shown acetabulum; Fig. 9 is a front perspective view of another joint socket according to the invention; Fig. 10 a rear perspective view of the Fig. 9 shown acetabulum; Fig. 11 a perspective view of a holding frame; Fig. 12 which in Fig. 9 shows the acetabulum anchored in a bone structure; Fig. 13 a sectional view of the Fig. 12 shown bone structure with the acetabulum fixed in it; Fig. 14 a perspective view of another acetabulum with an eccentrically designed acetabular insert; Fig. 15 a sectional view of the Fig. 14 shown bone structure with the joint socket fixed in it.

[0038] A joint prosthesis 1 with a joint socket 2, which includes a socket insert 3 for receiving a joint body not shown, is described below with reference to the Fig. 1 to 15. The socket 2 has a cylindrical outer contour 4 in its basic form.

[0039] At a section facing away from an opening 5 of the joint socket 2, the outer contour 4 is designed as a circular tubular peripheral edge and thereby forms a projection 7 facing a bone structure 6 shown only as an example. The projection 7 is concentric to the socket insert 3, as can be seen in particular in the Fig. 4 and Fig. 5. The projection 7 serves to fix the joint socket 2 in a recess 8 intended for the socket insert 3 and, for this purpose, is inserted into a groove-shaped recess 9 in the bone structure 6 that radially encloses the recess 8, whereby the projection 7 concentrically encloses the socket insert 3 with a small radial distance. For this purpose, the projection 7 can be applied with its convex outer surface 10 and its concave inner surface 11 against a respective wall surface of the groove-shaped recess 9.As a result, the projection 7 forms a clamping sleeve around the socket insert 3, whereby the load-bearing capacity of the bone structure 6, which has been weakened due to the loss of substance caused by the depression 8 in the bone structure 6 for the joint socket 2, is restored by absorbing both radial spreading forces due to the fixation of the joint socket 2 and external forces, and the bone structure 6 is not subjected to any further stress. As can be seen particularly in the . Fig. 1, Fig. 2 and Fig. 5, the projection 7 has on its outer contour 4 several ingrowth openings 12 into which the surrounding bone substance 6 grows and thereby forms an undercut that fixes the joint socket 2.

[0040] As particularly in the Fig. 6 and Fig. 13, a bottom side 13 of the socket 2 is fixed in the bone structure 6 within the recess 8 in the implanted position at a distance A from the bone structure 6 in order to concentrate the force introduction on the projection 7.

[0041] In Fig. 11 shows a holding frame 14 which is inserted into the Fig. 9, Fig. 10, Fig. 12 and Fig. 13 can be seen in an assembled position. The holding frame 14 has a smaller opening width D than the great circle diameter of the socket insert. As a result, a spherical joint body inserted into the socket insert is secured by the holding frame, thus preventing dislocation of the joint. The holding frame 14, in turn, has two projections 7', which are connected flush with the projections 7 of the socket 2, as shown in the Fig. 9 and Fig. 10 recognizable.

[0042] In the Fig. 14 and Fig. 15 shows yet another variant of a joint socket 2 with an eccentrically designed socket insert 3 in a perspective view and in a sectional side view. The joint socket 2 has a cylindrical outer contour 4 in its basic form with a circular ring-shaped edge as a projection 7, which is arranged concentrically to the outer contour 4 of the socket insert 3. A receptacle 16 for a joint ball (not shown) is not coaxial, but is arranged eccentrically with respect to the outer contour 4 with an offset V of a central axis 17 of the receptacle 16 relative to a central axis 15 of the joint socket 2, so that different edge distances R, r result in different circumferential sections. By changing the angular position of the projection 7 within the, for example, in the Fig.The groove-shaped recess 9 shown in Figure 13 allows the central axis 17 of the receptacle 16 to be easily aligned and positioned optimally relative to the bone structure 6. The recesses, designed as ingrowth openings, also serve as tool receptacles 18 for manually transmitting the rotational movement of the acetabulum 2. LIST OF REFERENCE SYMBOLS 1 joint prosthesis 2 acetabulum 3 pan inserts 4 Outer contour 5 Opening 6 Bone structure 7 lead 8 Deepening 9 Recess 10 Exterior area 11 Inner surface 12 Ingrowing opening 13 Subpage 14 holding frames 15 Central axis 16 recording 17 Central axis 18 Tool holder A distance D Passage width V Offset r, R edge distance

Claims

[1] A joint socket (2) for a joint prosthesis (1) which can be fixed in a bone structure (6) and has a socket insert (3) for receiving a joint body which is at least partially spherical, wherein the socket (2) has at least one projection (7) facing the bone structure (6) and intended for engagement in a groove-shaped recess (9) of the bone structure (6) which is radially spaced from a depression (8) for the socket insert (3) in the bone structure (6), which projection encloses the socket insert (3) in particular concentrically on its circumference, and wherein the projection (7) has at least partially a convex outer surface (10) and a concave inner surface (11), so that the projection (7) can be inserted into the groove-shaped recess (9) with the outer surface (10) and the inner surface (11) in a form-fitting manner, characterized bythat the joint socket (2) has a holding frame (14) with a passage width (D) which is smaller than the great circle diameter of the socket insert (3), in particular variable against an elastic restoring force, and two projections (7) which are arranged spaced apart from one another in the circumferential direction within an annular region delimited by the outer contour and by the inner contour, and the holding frame (14) in turn has two projections (7') which are connected to the two projections (7) of the joint socket (2) in a flush manner. [2] Joint socket (2) according to claim 1, characterized by that the two projections (7) spaced apart from one another are arranged evenly distributed around the circumference. [3] Joint socket (2) according to claim 1 or 2, characterized by that the axial extent of the projections (7) in the circumferential direction is constant and / or the axial extent of adjacent, in particular all, projections is the same. [4] Joint socket (2) according to at least one of the preceding claims, characterized by that at least one projection (7) can be fixed in different positions, in particular continuously, in the axial direction parallel to the axis of symmetry of the joint socket (2). [5] Joint socket (2) according to at least one of the preceding claims, characterized by that the radial distance of the projection (7) relative to the socket insert (3) is between 0.5 mm and 10 mm and / or the distance between the convex outer surface (10) and the concave inner surface (11) is between 1 mm and 5 mm. [6] Joint socket (2) according to at least one of the preceding claims, characterized by that the joint socket (2) and / or at least one projection (7) has ingrowth openings (12) on its outer surface (10) and / or its inner surface (11). [7] Joint socket (2) according to at least one of the preceding claims, characterized bythat the joint socket (2) has an underside (13) facing the bone structure (6) within the recess (8), which underside can be inserted at a distance from the bone structure (6) in the implanted position. [8] Joint socket (2) according to at least one of the preceding claims, characterized by that a receptacle (16) for a joint ball is arranged eccentrically relative to the outer contour (4) with an offset (V) of a central axis (17) of the receptacle (16) relative to a central axis (15) of the joint socket (2). [9] Joint socket (2) according to at least one of the preceding claims, characterized by that the pan insert (3) and the projections (7) are made in one piece and / or in one piece, in particular from a plastic.

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