DE2559402C3 - Ball socket for a hip joint prosthesis - Google Patents

Description

The invention is based on a ball socket for a ⁴ⁱ hip joint endoprosthesis, which can be anchored cement-free directly in a pelvic bone with profiled anchoring projections that are arranged at the corners of a triangle and extend outward from the convex side of the ball socket. ^M.

In a known ball socket of this type (US Pat. No. 10,978, FIGS. 7 and 8), each of the three anchoring projections is designed as a relatively long pointed mandrel running parallel to the longitudinal axis of the ball socket with several circumferential notches. The surgeon "drives the three spikes into the pelvic bone simultaneously with a striking tool without prefabricating receiving recesses for the spikes. This type of implantation of the ball socket is not positionally accurate, requires additional tools and exposes the patient to undesired impact stress. The spines penetrate relatively deeply into the pelvic bones. There is a risk of "sagging" and consequent uncontrolled bending stresses on the spines. The sharp-edged notches of the ^{h <} > spines create the risk of fractures, in particular stress corrosion fractures, of the spines, as the ball socket is exposed to loads that change in direction and size during operation (frictional moments from the movement of the joint) and both its shell and the mandrels are made of unprotected metal.

Since the mandrels are relatively thin, these loads also lead to relatively high Surface pressure on the bone bed with the risk of overload atrophy.

From DE-OS 20 39 73t is a ball socket known to be firmly anchored in a bed of bone cement with several outwardly protruding annular ribs and a button in the crown, all dovetail-shaped are backed up. The ribs and button penetrate the bone cement and kick with her Outer surface in each case with a hemispherical concave prepared bearing of the pelvic bone as a spacer between the pelvic bone and a shell of the ball socket in contact. To anchor the Bone cements are also three weakening deep holes in the ischium, the pubic bone and the Soft bone required. The outside of the button is only weakly complementary to the bearing in the pelvic bone rounded and therefore difficult or impossible to insert into a hole in the bone by hand press in.

The invention is based on the object of creating a ball socket for cement-free anchoring, which are extremely positionally accurate with only minimal impairment of the adjacent bone substance, can be implanted quickly and safely and prevents intraoperative falling out of its bone bed is prevented

This object is achieved according to the invention in that each anchoring projection as in a prefabricated Recess of the pelvic bone is formed by push-in, back-worked, button-like pegs This enables extremely precise positioning of the ball socket in the pelvic bone The three small mounting holes for the Cones can namely in the leg bone by means of A drilling template can be attached with high precision and also affect the pelvic bone only minimal. Furthermore, it is necessary to insert the ball socket into the pelvic bone The effort required is so low that the surgeon can remove the ball socket with the button-like socket without additional tools Can push the pin into the prepared holes in the pelvic bone by hand. This becomes the On the one hand, the operation time is shortened and, on the other hand, the patient is spared. Snap the button-like tenons each with its backwork in the area of the cortex of the pelvic bone. This becomes the They effectively secure the ball socket from falling out of its bone bed during the Operation and, on the other hand, excellent anchoring of the ball socket in the pelvic bone reached and the further ingrowth of the ball socket in the pelvic bone favors.

According to one embodiment of the invention, the pins are arranged such that the maximum resulting Force on the body joint runs at least approximately through the center of gravity of the triangle. This enables a particularly permanent and secure fit of the ball socket in the pelvic bone, whereby, because of the favorable introduction of force, microrelative movements between the ball socket and the Pelvic bones are largely avoided due to the constantly changing load conditions.

According to another embodiment of the invention one of the pegs is near the apex and the other two pegs are at least approximately halfway through Arranged at the height of the ball socket. This makes it easier for the surgeon to insert the ball socket into the -> Pelvic bones.

It is also used for easy insertion and secure anchoring of the ball socket, if according to one embodiment of the invention, the axes of the three pins in at least approximately parallel and right-in are at an angle to a base of the ball socket extending planes, the axis of the apex Pin with a perpendicular on the base includes an angle which is smaller than that Angle that the axis of each of the two remaining pegs includes with a perpendicular on the base

According to a further embodiment of the invention, the peg close to the billet has a circumferential groove on its foot and the two remaining pegs each have a machining which is directed outward from the main axis of the ball socket. The special underworking guarantees a very firm fit of the ball socket in the pelvic bone and makes it easier to "button" the ball socket. - ³

The invention is explained in more detail below with reference to the exemplary embodiment shown in the drawings explained. It shows

F i g. 1 shows the partially sectioned view of a ball socket along line I-I in FIG. 2, jo

2 shows the top view of the ball socket according to F i g. I and

3 shows a longitudinal section through the ball socket according to FIG. I and 2 with associated ball and Pelvic bones. «

The F i g. I and 2 show a ball socket 50 for a total hip joint endoprosthesis. The outer surface of the Ball socket SO is with concentric grooves 52, S3 and 54 and with in planes through a main axis 65 of the Ball socket 50 provided running grooves 56 to 59, * < > the macroscopic ingrowth of new bone tissue into the surface of the spherical socket and thus facilitate and promote their secondary anchoring in a pelvic bone 48 (FIG. 3).

The anchoring of the ball socket 50 in the pelvic bone 48 is provided by three button-like pegs 61,

62 and 63, which are arranged at the corners of a triangle in such a way that the maximum resulting force Fk (FIG. 2) runs at least approximately through the centroid of this triangle parallel planes 80, 81 and 82, the axis of the pin oil with the main axis 65 of the ball socket 50 an angle 67 of 10 ° and the axes of the pin 62 and 63 each with a perpendicular on a base 69 of the ball socket 50 an angle 70 of Form 25 °. The pin 61 has a circumferential groove 72 at its foot, while the two remaining pins 62 and 63 are each provided with an undercut 74 directed outward from the main axis 65 of the ball socket 50.

3 shows the ball socket 50 in its in the Pelvic bones 48 inserted state. To prepare the pelvic jaw 48 for implantation, First of all, the physiological> Milled out with a spherical cutter in ufee spherical Milling out three holes for the pins 61, 62 and 63 are made using a drilling template The bores are moved closer to one another than a distance 78 in FIG. 1. Then the ball socket 50 is inserted in such a way that the undercuts 74 of the pins 62 and

63 over the edge of the cortex 79 of the pelvic bone 48. It becomes more contiguous cancellous bone is pressed on the side Milling inserted until pin 61 snaps into its bore. During this snapping into place the cortex 79 is elastically deformed between the pegs and locks after its spring back Ball socket 50 in the inserted position according to FIG. 3.

The special position of the pins 61, 62 and 63 with respect to the resulting force Fr means that additional shear stresses due to elastic deformation of the bone under the effect of the resulting force Fr do not occur when this force reaches its maximum value minimal.

The ball socket 50 can be metallic and coated with enamel on its entire surface.

1 sheet of drawings

Claims (5)

Patent claims: U spherical socket for a hip joint endoprosthesis, which is arranged with at the corners of a triangle, from the convex side of the ball socket to ϊ externally extending, profiled anchoring projections cement-free directly in a pelvic bone can be anchored, characterized in that that each anchoring projection as in a prefabricated receiving recess of the in Pelvic bone (79,48) is formed push-in, rear-worked, button-like peg (61,62,63). 2. Ball socket according to claim t. characterized in that the pins (61, 62, 63) are arranged in such a way that the maximum resulting force (Fg) on the body joint runs at least approximately through the center of the area of the triangle 3. Ball socket according to claim 2, characterized in that <k3 one (61) of the pins near the apex and the two remaining pins (62, 63) are each arranged at least approximately halfway up the ball socket (50). 4. Ball socket according to claim 3, characterized in that that the axes of the three pins (61,62,63) κ in at least approximately parallel and at right angles to a bottom fish (69) of the ball socket (50) extending planes (80,81,82) lie, and that the axis of the apex pin (61) with a vertical line on the base (69) «encloses an angle (67) which is smaller than that angle (70) which the axis of each of the other two pegs. (62,63) with a vertical includes on the base (59} 5. Kugetpfanne according to claims 3 or 4, thereby '* characterized in that the apex pin (61) has a circumferential groove (72) and the at its foot two remaining pins (62,63) each one of the Have the main axis (65) of the ball socket (50) outwardly directed underwork (74).