Knee spacer system with adjustable separator

Abstract

The invention relates to a knee spacer for temporary replacement of an artificial knee joint, whereby the knee spacer comprises a tibial component (11) and a separator (12), whereby the tibial component (11) comprises a running surface (14) by means of which the tibial component (11), in the patient-inserted state, can be placed against a femoral component (28) in mobile manner, and whereby the separator (12) comprises a contact surface (15) for placing on the tibia (22) and the contact surface (15) is adjustable at a variable distance from the running surface (14) of the tibial component (11). The invention also relates to a method for adapting a knee spacer to a treatment scenario, comprising a tibial component (11) and a separator (12), whereby the tibial component (11) comprises a running surface (14) for placing against a femoral component (28) in mobile manner, and the separator (12) comprises a contact surface (15) for placing on the tibia (22), whereby the method involves adjusting the distance between the contact surface (15) and the running surface (14). The invention also relates to the use of a knee spacer of this type as temporary place-holder in a knee of a patient.

Claims

1. A knee spacer for temporary replacement of an artificial knee joint, whereby the knee spacer comprises a femoral component comprising a sliding surface, a tibial component and a separator, whereby the tibial component comprises a sliding surface by means of which the tibial component, in a patient-inserted state, is adapted to be placed against the femoral component in mobile manner, and whereby the separator comprises a contact surface for placing on a tibia and the contact surface is adjustable at a variable distance from the sliding surface of the tibial component, wherein one or more opening(s) are situated in the contact surface of the separator through which a bone cement can extend by means of which the separator is affixed on the tibia, and a layer of bone cement is arranged between the contact surface and the tibia's tibial plateau.

2. The knee spacer according to claim 1, wherein a stem with an external thread is arranged on a side of the tibial component opposite from the sliding surface of the tibial component, whereby the separator comprising at least one feed-through is adapted to be screwed onto the stem by means of an internal thread that fits with the external thread of the stem such that the distance between the sliding surface of the tibial component and the contact surface is adjustable by screwing the separator onto the stem.

3. The knee spacer according to claim 1, wherein the femoral component and the tibial component are present as separate components, which are mobile with respect to each other in the patient-inserted state, whereby the tibial component and the femoral component are placed against each other in mobile manner in the patient-inserted state by means of their sliding surfaces.

4. The knee spacer according to claim 1, wherein the separator comprises a disc, preferably a plane-parallel disc, whereby one side of a disc forms the contact surface.

5. The knee spacer according to claim 1, wherein the knee spacer comprises a biocompatible material.

6. A method for adapting a knee spacer according to claim 1 to a treatment scenario, whereby the method comprises a step of adjusting a distance between the contact surface and the sliding surface of the tibial component.

7. The method according to claim 6, wherein the distance between the contact surface and the sliding surface of the tibial component is adjusted by rotating the separator on a stem having an external thread, whereby the stem is affixed on a side of the tibial component opposite from the sliding surface of the tibial component and the separator comprises at least one feed-through having an internal thread such that the separator is screwed up or down on the stem by rotating the separator.

8. The knee spacer according to claim 5 wherein the knee spacer comprises a cured polymethylmethacrylate bone cement containing at least one antibiotic, or at least one antiseptic, or both at least one antibiotic and at least one antiseptic.

9. A method for adapting a knee spacer to a treatment scenario, wherein the knee spacer comprises a femoral component comprising a sliding surface, a tibial component and a separator, whereby the tibial component comprises a sliding surface for placing against the femoral component in mobile manner in a patient-inserted state, and the separator comprises a contact surface for placing on a tibia and one or more openings which connect distal and proximal side of the separator, whereby the method comprises a step of adjusting a distance between the contact surface and the sliding surface of the tibial component, and a step of introducing bone cement through the one or more openings into a space between the separator and a distal side of the tibial component such that said space is filled completely and the tibial component is connected to the separator.

Description

(1) Exemplary embodiments of the invention shall be illustrated in the following on the basis of five schematic figures, though without limiting the scope of the invention. In the figures:

(2) FIG. 1: shows a schematic side view of a knee spacer according to the invention;

(3) FIG. 2: shows a schematic side view of a knee spacer according to the invention, in which the separator is screwed onto the tibial component;

(4) FIG. 3: shows a schematic top view onto the running surface of a tibial component for a knee spacer according to the invention;

(5) FIG. 4: shows a schematic top view onto a separator for a knee spacer according to the invention; and

(6) FIG. 5: shows a schematic partially cross-sectional view of a knee spacer according to the invention comprising a tibial component, a femoral component, and a separator.

(7) To some extent, identical or similar components are identified in the figures through the same reference numbers.

(8) FIG. 1 shows a schematic side view of a knee spacer according to the invention. The knee spacer comprises a tibial component 1 and a separator plate 2 that are fabricated from cured PMMA bone cement containing at least one antibiotic and/or at least one antiseptic. The tibial component 1 consists of an anatomically fitting plate and a cylindrical stem 3 that is arranged on the underside of the plate (on the bottom in FIG. 1). A running surface 4 is provided on the upper side of the plate of the tibial component 1 and is intended to serve as sliding surface for a running surface of a femoral component (not shown in FIG. 1).

(9) The separator 2 is formed by a plane-parallel plate on the underside of which the contact surface 5 for placing on the tibial plateau is provided. The stem 3 comprises an external thread 6 that matches an internal thread 7 in a feed-through of the separator 2 (indicated by a dotted line in FIG. 1, since the internal thread 7 is actually not visible from the side). The separator 2 can be screwed onto the stem 3 by this means.

(10) FIG. 2 shows a schematic side view of the knee spacer according to FIG. 1, in which the separator 2 is screwed onto the tibial component 1 or the stem 3, as the case may be. The distance between the contact surface 5 of the separator 2 and the running surface 4 of the tibial component 1 can be adjusted by rotating the separator 2 about the axis of the stem 3. A rotation as indicated by the arrow in FIG. 2 displaces the separator 2 in the direction of the plate of the tibial component 1 and thus shortens the distance between the contact surface 5 and the running surface 4. Theoretically, a left-handed thread could just as well be arranged on the stem 3 and would invert the direction of rotation.

(11) FIG. 3 shows a schematic top view onto the running surface 4 of a tibial component 1 for a knee spacer according to the invention. For this purpose, the running surface 4 is designed to have a smooth surface such that a running surface of a femoral component can slide well over the running surface 4 of the tibial component 1.

(12) FIG. 4 shows a schematic top view onto a separator 2 for a knee spacer according to the invention. A central feed-through 8 is arranged in the separator 2 and has the internal thread 7 arranged in it. Designed as a plane-parallel plate, the separator 2 further comprises two more bore holes 9 that are arranged on both sides of the feed-through 8 having the internal thread 7 and extend fully through the separator 2. During insertion of the separator 2 into a knee of a patient, the separator 2 is affixed by bone cement on an artificially generated tibial plateau. In this context, the bone cement can flow through the bore holes 9 and anchors the separator 2 on the tibia once the bone cement is cured.

(13) FIG. 5 shows a schematic partially cross-sectional view of a knee spacer according to the invention or of a knee spacer system, as the case may be, comprising a tibial component 11, a femoral component 28, and a separator 12. The plate-shaped separator 12 screwed onto the tibial component 11 comprises, on its underside (on the bottom in FIG. 5), a contact surface 15 that is placed on a tibial plateau 24 of a tibia 22 (shin bone) and is affixed and/or embedded by means of bone cement 20.

(14) The whole part of the knee spacer relating to the tibia 22 and the tibia 22 itself are shown in a cross-sectional view, whereby the sectioned surfaces are indicated by hatching. The section is placed in a plane perpendicular to the sagittal plane and/or parallel to or in the frontal plane. The cross-sectional view enables depiction of the internal structure of the tibial component 11 and its anchoring. In contrast, the femoral component 28, which is affixed to a femur 26 of the patient by means of bone cement, is shown in a side view.

(15) The femoral component 28 comprises a rounded running surface 30 that can slide or roll off on the running surface 14 of the tibial component 11. As a result, an articulating two-part knee spacer is provided. A recess for accommodating the stem 13 is provided in the tibia 22. Depending on the amount of bone removed from the tibial plateau 24 of the tibia 22, the original position of the running surface 14 of the knee can be restored by screwing the separator 12 up to a certain height onto an external thread 16 of the stem 13. The separator 12 comprises a feed-through with a fitting internal thread for this purpose. By this means, it is feasible through little effort to adjust the distance between the running surface 14 of the tibial component 11 and the contact surface 15 of the separator 12 relatively accurately and thus to enable relatively accurate adjustment of the position of the artificial knee joint.

(16) The circular separator 12 has multiple bore holes 19 provided in it through which the bone cement 20 extends and thus stably connects and/or anchors the separator 12 and the tibial component 11 to the tibia 22.

(17) During a revision surgery of an artificial knee joint, the position of the joint of the articulating knee spacer can be adjusted by rotating the separator 12 on the stem 13 for the surgery following debridement of the tibial bone 22. Once the required distance between the contact surface 15 of the separator 12 and the running surface 14 of the tibial component 11 is adjusted, the tibial component 11 with the separator 12 is cemented onto the tibial plateau 24 using PMMA bone cement 20 and the intervening spaces between the tibial component 11 and the separator 12 as well as the bore holes 19 are filled up with the same PMMA bone cement 20. Likewise, the femoral component 28 is affixed on the femur 26 using the same PMMA bone cement.

(18) The knee spacer is thus inserted and functionally ready. If the parts 11, 12, 28 of the knee spacer and the bone cement 20 contain at least one antibiotic and/or antiseptic, the knee spacer can be used to control a site of infection in the knee.

(19) Knee spacers and/or the components 1, 2, 18 thereof preferably have rounded corners and edges rather than sharp edges and corners.

(20) The features of the invention disclosed in the preceding description and in the claims, figures, and exemplary embodiments, can be essential for the implementation of the various embodiments of the invention both alone and in any combination.

LIST OF REFERENCE NUMBERS

(21) 1 Tibial component 2 Separator plate 3 Stem 4 Running surface 5 Contact surface 6 External thread 7 Internal thread 8 Feed-through 9 Bore hole 11 Tibial component 12 Separator plate 13 Stem 14 Running surface 15 Contact surface 16 External thread 19 Bore hole 20 PMMA bone cement 22 Tibia 24 Tibial plateau 26 Femur 28 Femoral component 30 Running surface