The present invention relates to a hip joint prosthesis, more specifically a talus component, for a multi-piece hip joint prosthesis.
In view of the many reasons for a mobile solution for a painfully destroyed upper hip joint, it was only logical to look for solutions for other joints after the initial successes of hip and knee joint prosthetics, especially since a promising alternative in the sense of resection arthroplasty was not available for the joints directly affected by the body weight.
The first hip replacements were cemented metal-polyethylene joints, and the most famous of this generation, the St. George endoprosthesis, had a sloth-like talus component articulating with a downward congruent, i.e. concave, tibial component.
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It was found that the mechanical requirements and thus the high long-term survival rate can only be met by a hip joint prosthesis with an anatomically and biomechanically compatible design, implanted with minimal bone resection and carried free of the remaining ligaments and tendons.
Endoprostheses are generally divided into single and multi-axial two-component endoprostheses and three-component endoprostheses, which generally consist of a tibial and a talus component and a slime between them.
For example, a three-component prosthesis (HINTEGRA®; Newdeal SA, Vienne, France) with an anatomical tibial and talus component and a free-moving polyethylene (PE) glide core of ultra-high density is known. The tibial component has a metal plate with tibial-like small anchor pyramids and a ventral shield, which allows a screw fixation through two oval holes and prevents the growth of scar tissue and thus restriction of movement. The talus component has a top shape similar to a cone with a narrower medial lateral glissus.
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The tibial component of another well-known prosthesis (LINK S.T.A.R.®; Waldemar Link GmbH & Co. KG) consists of a metal plate with a highly polished flat articulation surface, which has two cylindrical fixation steps arranged backwards to anchor it in the tibial bone.
A two-piece and a three-piece hip joint prosthesis are known from US 3,975,778 and WO 00/69373 A1 respectively.
The present invention is intended to provide a spring joint prosthesis that has an optimal fit of the tail prosthesis part with a simultaneous small bone resection, and to prevent lateral overlap of the glide core and thus the formation of an impingement.
This is achieved by the invention of a talus component for a multi-piece hip joint prosthesis, which has a bottom facing the bony talus after implantation, by having a concave spherical bottom facing the bony talus.
The concave design of the bottom of the talus component has been shown to allow for a particularly gentle preparation of the bone.
In a preferred embodiment, the concave spherical bottom has a means of anchoring to the bone.
Preferably, the product consists of a centrally placed tubular stem and a ventral pen.
The invention also relates to a three-piece hip joint prosthesis with a talus component, an inlay and a tibia component, which is characterised by the fact that it provides a talus component in accordance with the invention.
Another aspect of the invention concerns a tibial component-inlay combination for a multi-piece hip joint prosthesis, whereby the tibial component comprises a plate and a means of anchoring it in the bone and the inlay has a planar tibial surface.
This prevents the glide core from overhanging laterally and thus preventing the formation of an impingement.
The lift may be of a spherical shape and the expansion may be of a cylinder segment with spherical ends, the axis of the cylinder being in the A/P direction.
Preferably, the means of anchorage in the bone shall comprise a ventral arched wedge.
The following illustration illustrates the invention in more detail, with Figures 1 and 2 illustrating a cross-section or view of an embodiment of the talus component of the invention, Figures 3, 4 and 5 illustrating a cross-section or view of an embodiment of the tibia component of a tibia component-inlay combination, and Figures 6, 7 and 8 illustrating a cross-section or view of an embodiment of the inlay of a tibia component-inlay combination.Fig. 1 shows a cut through an embodiment of the talus component of the invention. This element is usually made of biocompatible metal, e.g. CoCrMo according to ISO 5832/4. Reference number 2 denotes the cylindrical convex surface facing the inlay. 3 denotes the concave spherical segment facing the talus, which is coated with, for example, tricalcium phosphate.Fig. 2 shows a view of the bottom 3 of the talus component.
The ventral part of the tubular stem 4 is a metal pen 5 which, for example, has a diameter of about 3 mm and is placed parallel to the direction of the central stem 4 in the figure.
Figure 3 shows a side view of an embodiment of the tibial component 6 of a tibial component-inlay combination. The tibial prosthesis element consists of a metal plate 7 e.g. 3 mm thick, which carries on the side of the inlay a spherical segmented elevation 8 which forms a part for the necessary forced conduction of the polyinlay. The elevation 8 is essentially centrally provided on the underside 9 of the metal plate 7 as shown in Figures 4 and 5.
To increase the osseous integration area and to ensure the rotation of the tibial component 6, this is provided with a wedge 10 cranially. This wedge 10 is significantly flattened at its lower boundary side 11 to facilitate the insertion of the tibial component 6.
Preferably, 9 wedges of different lengths can be individually mounted on the corresponding metal plate 7 as required. The longest revision wedge preferably has 2 holes for the reception of locking bolts. A mounting mechanism for the modular tibia wedges can be integrated into the spherical segmented mount 8 and the metal plate 7.
Fig. 6 shows a view of the tibial surface 13 of PE inlay 12, which may be made, for example, of ISO 5834 chirula.
The tibial surface 13 consists of a planar surface, in the centre of which, in a longitudinal direction, i.e. A/R direction, a groove-shaped incision 14 is provided, which is formed as a cylindrical segment with spherical segments at the ends. This incision 14 can be seen from the cross-sections along the lines B-B and A-A of Figure 6 shown in Figures 7 and 8.
The surface 15 of the inlay 12 facing the talus component 1 is, as shown in Figure 7, the corresponding concave cylinder surface.