DE4423020A1 - Joint prosthesis giving min. wear and resistance and abrasion - Google Patents

Abstract

The prosthesis has a fluid reservoir channel (10) in the joint socket (2) at the sliding surface (6) towards the ball (4) of the joint. When the prosthesis is assembled, a sliding gap (12) between the ball (4) and socket (2) gives a fluid connection to the reservoir, which is outside the main load-bearing zone (11). The materials for the sliding surfaces are paired with each other as metal alloy-metal alloy, metal alloy-polyethylene, ceramic-polyethylene or ceramic-ceramic. The anchoring shell (7) is of titanium with a polyethylene insert (8).

Description

The invention relates to a joint prosthesis that consists of a Articular head and an articular socket, the joint partially pan the joint head when assembled surrounds and is slidably supported on this.

Joint prostheses have been known for many years and are coming due to their relatively high level of technical maturity and the progress made in the operational area in have been achieved in recent years, more and more at Commitment.

An essential aspect of artificial joints is their friction behavior. Since the implanted prosthesis is under Movement is often exposed to relatively high loads is wear of the sliding surfaces in the prosthetic joint inevitable. To keep this wear as low as possible should occur between the sliding surfaces exercise to a minimum.

Hip prostheses in particular have been used in recent years increasingly important. Modern hip prostheses usually have an acetabular cup made of polyethylene len exists and use as joint head material either a metal alloy, mostly CoCrMo, or a ceramic mate rial, for example Al₂O₃. It has been shown that this Sliding partners work together to a high degree without friction and wear out slowly. However, there is no wear not attainable, and wear occurs with these mate rial pairings mainly on the somewhat softer polyethylene on the socket.

Investigations carried out in recent years further shown that the Po generated by wear  ethylene abrasion particles in the patient's body an un have the desired property. Store the abrasion particles into the tissue surrounding the prosthesis and form there foreign body granulomas develop over time, which lead to a Ga learning tissue and to dissolve neighboring bones can lead substance. This foreign body reaction leads to Over time to the so-called aseptic late loosening of the implant and the maximum dwell time of the Limit the implant in the patient's body.

Therefore, a reduction in polyethylene wear is both in With regard to wear reduction in the prosthesis joint as also with regard to the permanent anchoring strength the acetabulum in the hip bone is desirable.

An object of the invention is to provide a joint prosthesis special hip joint prosthesis with a further improved Friction behavior, d. H. with minimal wear and minimal to create abrasion. It also strives for that to ensure that what is inevitable in the prosthesis If possible, do not put abrasion material in the patient's body can reach.

To solve this problem it is provided that the joint pan in its sliding surface assigned to the joint head has as a joint fluid reservoir pit that in the assembled state of the prosthesis with the between the joint head and the joint socket existing sliding gap communicates and outside of between the condyle and joint socket occurring main load range is arranged.  

The invention takes advantage of the fact that the Rei Exercise and wear behavior of an artificial joint test besides the choice of suitable sliding partner materials influenced by the fluid dynamics within the sliding gap is. If, for example, a hip prosthesis is implanted is, it comes from the stress occurring when walking Changes in the artificial joint constantly to a compress sion or expansion of the sliding gap, which in terms of joint fluid present in the sliding gap to a suction or Pressure effect leads. Since the pit too - at least in part wise - filled with synovial fluid and with the glide gap is connected, it can expand the Sliding gap due to the suction effect supply it quickly with liquid and thus serves to ensure that the next loading process sufficient friction film to reduce friction between the sliding surfaces is built up. The pit is thus in Type of fluid reservoir synovial fluid available which is distributed in the sliding gap by pumping action and there reduces wear and abrasion. This will premature wear of the joint sliding surfaces counteracting increase in joint friction. Be if the socket is made of polyethylene, less is created Polyethylene abrasion, which eliminates the problem of the occurrence of Foreign body reactions mitigated or at least in time is pushed out. The result is with the invention Extended life and / or extended prosthesis maximum residence time created in the patient's body.

In addition, it is advantageous that from the pit outflowing and backflowing synovial fluid a ver better flushing effect between the sliding surfaces of the hip area steering prosthesis is created. Especially in the main area The area in which the most abrasion occurs is a ra Transport of the abrasion particles is desirable because this in turn when remaining between the sliding surfaces contribute to increased abrasion.  

It can also be assumed that at least the larger ones Collect abrasion particles (about 250 µm) in the pit and are therefore removed from the sliding surface area and also not can get into the surrounding tissue. This effect is desirable, since it is suspected that the larger ones in particular Abrasion particles cause the aseptic late loosening are.

Basically, the pit with the exception of the main bela range anywhere in the sliding surface of the socket to be ordered, one in the implanted state relative to The main area of exposure lower lying is ahead moves. The pit can be in the form of an edge-free, flat Be formed trough and a lateral expansion in the loading ranging from about 0.5 to 1.5 cm and a depth in the range of have about 2 to 5 mm.

Preferably, the sliding surface of the socket is one or several channels open towards the sliding surface, that are in fluid communication with the pit. These channels and Support the described pumping and rinsing effect and wear thus essential to the solution of the invention task. Such channels can also be in relief be provided in the sliding surface of the joint head.

The channel distribution, channel width and channel depth can correspond depending on the load distribution to be expected in the joint be laid. The channels point in areas with higher loads preferably a smaller width than in the other areas chen on here to train a particularly viable To support liquid film. General is the channel structure on the sliding surfaces depending on the benet behavior of the sliding partners and the viscosity of the Ge to design steering fluid and can be done by laboratory experiments and / or determined by fluid mechanical calculations will.  

If the socket is provided with the sliding surface from one insert and an anchoring that receives the insert shell is built up; like this for example with the hip joint prosthesis is often the case, it may be preferable if the use of one or more substantially lower stitch running right to the sliding surface of the socket is penetrated, the one in the implanted state Sliding gap with a between insert and anchoring shell connect lying space. These branch channels serve in the same way as the Ka running in the sliding surface channels the liquid transport into predeterminable areas of the Sliding gap and also cause that in the area of sliding surface abrasion in the space between on set and anchoring shell can be stored.

In addition to the hip prostheses already mentioned, it can the u. a. also around a knee prosthesis, shoulder joint prosthesis, ankle pro act or finger joint prosthesis.

The invention will be based on the drawing wrote. In this shows:

Fig. 1 is a longitudinal sectional view of a hip joint prosthesis according to the invention,

Fig. 2 is a cut, perspective view of a joint socket according to the invention, and

Fig. 3 is a plan view of the sliding surface of the joint socket in FIG. 2.

According to Fig. 1, a Hüftgelenprothese of a shaft prosthesis 1 and a socket 2 is composed. The stem prosthesis 1 has a stem 3 with which the stem prosthesis 1 can be anchored, for example cemented, in the tubular bone of a thigh neck, not shown. At the upper end of the shaft 3 , a joint head 4 is provided, which has a substantially spherical shape. As shown in Fig. 1, the joint head 4 acts on its outer surface, hereinafter referred to as the sliding surface 5 , with a spherical half-shaped sliding surface 6 of the socket 2 .

The joint socket 2 has an outer titanium shell 7 which can be anchored in a hip bone, also not shown, via an external thread (not shown). The titanium shell 7 receives an insert 8 which is made of polyethylene. The polyethylene insert 8 is seen in the example shown in Fig. 1 ver on its inner surface with a metal insert 9 , on the inner surface of which the aforementioned sliding surface 6 is formed.

Exactly - and realized in practice in this form far more ger ger - it is possible that no metal insert 9 is present and the inner surface of the polyethylene insert 8 is formed directly as a sliding surface 6 .

The sliding surface 6 deviates from the spherical shape in that a depression in the form of a pit 10 or trough is formed in it. The transition between the spherical sliding surface 6 and the pit 10 is formed without edges and the pit 10 has a depth of about 3 mm and lateral dimensions on the order of 1 cm compared to the spherical sliding gap. The pit 10 can be of any shape, for example lenticular, cigar-shaped or circular disk-shaped.

Fig. 1 shows the hip joint prosthesis approximately in the position in which it is arranged in the implanted state. Accordingly, the arrow 11 in the direction of the maximum load forces that act in the joint and indicates the area in which the sliding surface 5 of the joint head 4 and the sliding surface 6 of the socket 2 are exposed to maximum wear during relative movements.

Furthermore, the Fig. 1 it can be seen that is present in a concentric arrangement of articulated head 5 and socket 2 between the two sliding surfaces 5, 6 is a slide slot 12 which communicates with the pit 10 in connection.

In the implanted state, a strictly concentric course of the sliding surfaces 5 and 6 is of course not guaranteed. Due to the slightly different diameter of the cooperating sliding surfaces 5 and 6, there is at least one crescent-shaped sliding gap between them. In the implanted state, the sliding gap 12 and the pit 10 are at least partially filled with joint fluid 13 , which is produced in the joint skin still partially present.

The operation of the invention is as follows.

When inserted, load changes or movements acting on the joint prosthesis lead to a change in the gap geometry and thus to a suction or pressure effect within the sliding gap 12 . Since the pit 10 is constantly in fluid communication with the sliding gap 12 , it acts as a liquid reservoir in such a way that when the gap volume is enlarged, liquid 13 from the pit 10 can quickly reach the sliding gap 12 by suction. In the event of a subsequent load, the liquid 13 present in the sliding gap 12 has a wear-reducing effect.

The pit 10 thus allows that the sliding gap 12 FITS effectively with the lubricant acting joint fluid 13 is supplied, with the pump mechanism, the implanted joint replacement occurring naturally the stress and movement changes are exploited.

In Fig. 2, an alternative embodiment of a socket 2 'is shown, which differs from the socket 2 shown in Fig. 1 initially in that it does not have a metal insert 9 but the inner surface of the polyethylene insert 25 directly as a sliding surface 6 ' of this socket 2 'is formed.

In addition, the sliding surface 6 'of the socket 2 ' is provided with a channel system. With respect to the apex 20 of the sliding surface 6 ', as can be seen in Fig. 2, a with a pit 10 ' in connection ring channel 21 forms out, which is crossed by three radial channels 22 , 23 , 24 and is in fluid communication with them . The polyethylene insert 25 is like the insert 8 of FIG. 1 surrounded by a titanium shell 7 '.

Furthermore, it is possible that the sliding surface 6 'is not - as shown in Fig. 2, is formed on the inner surface of the polyethylene insert 25 , but that instead, as shown in Fig. 1, an inner metal insert or another surface, for example made of ceramic , Has, which is provided with the channel structure shown in Fig. 2 21 , 22 , 23 , 24 and the pit 10 '.

The width of the channels 21 , 22 , 23 , 24 is shown greatly enlarged in FIG. 2 and can be approximately 0.01 mm. The channel depth corresponds approximately to the channel width and can also be made deeper or shallower, as required. In particular, ring and radial channels 21 and 22 , 23 , 24 can be dimensioned differently.

Fig. 3 shows the sliding surface 6 shown in Fig. 2 'of the socket 2 ' in plan view from the direction of arrow 26 in Fig. 2. The dimensions of the annular channel 21 and the Radialka channels 22 , 23 and 24 are shown greatly enlarged.

In addition to the channel system 21 , 22 , 23 and 24 of the sliding surface 6 'of the joint socket 2 ' shown in FIGS. 2 and 3, a corresponding but not necessarily identical channel system can also be incorporated into the sliding surface 5 of the joint head 4 of the socket prosthesis 1 .

All surface channels in the sliding surfaces 5 and / or 6 or 6 'serve to support the inventive liquid transport between the pit 10 , 10 ' and the sliding gap area 12 . There are therefore a variety of un different structuring of the sliding surfaces 5 , 6 , 6 'conceivable and the structure shown in FIGS . 2 and 3 is only used to illustrate a special implementation option of such a channel structure according to the invention.

Optimized channel distributions and channel profiles can be determined using liquid mechanical calculations and laboratory measurements. Since the distribution pattern and the profile shape of the channels 21 , 22 , 23 and 24 is to be formed depending on the load distribution on the sliding surfaces 5 and 6 , 6 'and the main load area according to arrow 11 does not occur at the point 20 , it is to be expected that an optimized channel distribution is not necessarily symmetrical as shown in FIGS . 2 and 3 with respect to the vertex 20 .

If a channel structure 21 , 22 , 23 , and 24 both on the joint head 4 of the socket prosthesis 1 and on the joint socket 2 , 2 'is provided, the two structures can be designed so that they work together during the transport of joint fluid speed 13 .

Furthermore, the insert 8 , 25 and, if present, the metal insert 9 can be penetrated in a manner not shown by stitch channels, the sliding gap 12 with a gap between the poly ethylene insert, if not shown, in the schematic representations of FIGS. 1 and 2 8 , 25 and the titanium shell 7 , 7 'connects. These branch channels also allow the supply and removal of articulated fluid 13 located in the sliding gap 12 and can thus support a rinsing effect in the sliding gap area. In this case, abrasion products can be transported away from the sliding gap area 12 through the stitch channels and stored in the intermediate space. The arrangement and distribution of such branch channels on the sliding surface 6 , 6 'is relatively arbitrary and can be optimized according to experimental results.

Overall, the effect of the ring channel 21 , the Radialka channels 22 , 23 , 24 and any stitch channels present is comparable and always allows the targeted influencing of the liquid transport properties in the sliding gap 12 to reinforce the sliding and flushing effect achieved with the invention in the prosthetic joint.

Claims (21)

1. joint prosthesis from a joint head and a joint socket, wherein the joint socket partially surrounds the joint head in the assembled state and is supported on it in a slidable manner, characterized in that the joint socket ( 2 , 2 ') in its sliding surface associated with the joint head ( 4 ) ( 6 , 6 ') serving as a joint fluid reservoir ( 10 , 10 '), which in the assembled state of the prosthesis with the between the joint head ( 4 ) and the socket ( 2 , 2 ') consist of the sliding gap ( 12 ) in Liquid connection is and outside of the between the joint head ( 4 ) and joint socket ( 2 , 2 ') occurring main load area ( 11 ) is arranged. 2. Joint prosthesis according to claim 1, characterized in that the prosthesis is a hip joint prosthesis in which a shaft part ( 3 ) is attached to the joint head ( 4 ). 3. Joint prosthesis according to claim 1 or 2, characterized in that the pit ( 10 , 10 ') in the implanted state of the prosthesis with respect to the main loading area ( 11 ) is arranged low lying. 4. Joint prosthesis according to one of the preceding claims, characterized in that the pit ( 10 , 10 ') is designed in the form of an edge-free, fla chen trough. 5. Joint prosthesis according to one of the preceding claims, characterized in that the pit ( 10 , 10 ') has a lateral extent of about 0.5 to 1.5 cm and a depth of about 2 to 5 mm. 6. Joint prosthesis according to one of the preceding claims, characterized in that the sliding surface ( 6 , 6 ') of the socket ( 2 , 2 ') with one or more channels ( 21 , 22 , 23 ) towards the sliding surface ( 6 , 6 ') , 24 ) is provided, which are in fluid communication with the pit ( 10 , 10 '). 7. Joint prosthesis according to one of the preceding claims, characterized in that the sliding surface ( 5 ) of the joint head ( 4 ) is provided with one or more channels open towards the sliding surface ( 5 ). 8. Joint prosthesis according to claim 6 or 7, characterized in that the channels ( 21 , 22 , 23 , 24 ) of the socket ( 2 , 2 ') and / or the joint head ( 4 ) stungsbereich ( 11 ) extend into the Hauptbela . 9. Joint prosthesis according to one of claims 6 to 8, characterized in that the transition between the sliding surface ( 5 ; 6 , 6 ') and the channel ( 21 , 22 , 23 , 24 ) is edge-free. 10. A prosthetic joint according to one of claims 6 to 9, characterized in that the channels ( 21 , 22 , 23 , 24 ) have a cross-sectional profile which widens towards the sliding surface ( 5 ; 6 , 6 '). 11. A prosthetic joint according to one of claims 6 to 9, characterized in that the channels ( 21 , 22 , 23 , 24 ) have a cross-sectional profile tapering towards the sliding surface ( 5 ; 6 , 6 '). 12. Joint prosthesis according to one of claims 6 to 11, characterized in that the channel distribution and / or the channel width and / or the channel depth is designed locally according to the expected load distribution in the sliding gap ( 12 ). 13. A prosthetic joint according to claim 12, characterized in that the channels ( 21 , 22 , 23 , 24 ) in the main loading area ( 11 ) have a smaller width than in the other areas. 14. Joint prosthesis according to one of claims 6 to 12, characterized in that the sliding surface ( 6 , 6 ') of the socket ( 2 , 2 ') with respect to their apex ( 20 ) both of Radialkanä len ( 22 , 23 , 24 ) as well as ring channels ( 21 ) is set. 15. Joint prosthesis according to one of the preceding claims, characterized in that the joint socket ( 2 , 2 ') from a the sliding surface ( 6 , 6 ') with pit ( 10 , 10 ') having insert ( 8 , 25 ) and one the insert ( 8 , 25 ) receiving anchoring shell ( 7 , 7 ') is constructed. 16. Joint prosthesis according to claim 15, characterized in that the insert ( 8 , 25 ) of one or more substantially perpendicular to the sliding surface ( 6 , 6 ') of the Ge steering socket ( 2 , 2 ') extending embroidery channels is penetrated, which in Assembled state of the prosthesis, the sliding gap ( 12 ) with an intermediate space between the insert ( 8 , 25 ) and the anchoring shell ( 7 , 7 '). 17. Joint prosthesis according to one of the preceding claims, characterized, that the pair of sliding surfaces is a metal alloy-metal alloy pair, a metal alloy Po polyethylene pairing, a ceramic-polyethylene pairing or is a ceramic-ceramic pairing. 18. Joint prosthesis according to one of claims 15 to 17, characterized in that the anchoring shell ( 7 , 7 ') consists of titanium. 19. Joint prosthesis according to one of claims 15 to 18, characterized in that the insert ( 8 , 25 ) consists of polyethylene. 20. Joint prosthesis according to one of claims 15 to 19, characterized in that the insert ( 8 , 25 ) consists of polyethylene and has a metal alloy insert layer ( 9 ) as a sliding surface ( 6 , 6 '). 21. Joint prosthesis according to one of the preceding claims, characterized, that it is a prosthetic knee, shoulder joint pro thesis, ankle prosthesis or finger joint prosthesis acts.