DE2139878B2 - Artificial hip joint assembly - has flay-topped head with suction passage between pump chamber and external surface - Google Patents

Abstract

The artificial hip joint comprises a socket section and a stem, the latter with a cylindrical boss acting as a plunger pump. A ball-shaped head with a recess for the boss slides on the latter, and has a lubricant passage leading into the recess, this connecting the pump chamber formed to the space between the socket and head. The head has a flat formed on the top, and whose surface area is greater than that of the end face of the boss. It also contains a suction passage connecting the pump chamber to the outside surface of the head not enclosed by the socket. A valve is mounted in the suction passage.

Description

The invention is based on a hip joint endoprosthesis, consisting of a joint socket and a Shaft that carries a cylindrical pin acting as a piston pump, on which a spherical pin Articulated head is slidably placed with a recess receiving the pin and in which the joint head has a lubrication channel leading into the recess for the pin, which through the the movement of the pin in the recess of the joint head with the space formed by the pump volume connects between the sliding surfaces of the joint socket and joint head.

Such a hip joint endoprosthesis is known from Swiss Patent 4 90 077, in which Attempts have been made to extend the service life of such a joint by "lubricating" the moving parts raise. However, this is not possible to the required extent with this construction of the prosthesis, because neither in the lubrication channel proposed for this nor in the one provided for the purpose of lubrication Adequate amounts of clearance between the head and the pan at any stage of the movement Synovial fluid can accumulate because the cylindrical pin, which is intended as a "piston pump", does not can take effect. In this way, the adhesive becomes approximately adhesive on the not yet articulating surfaces Liquid film at the beginning of the load phase when the surfaces are directed and / or rolled against each other displaced by these, so that there is no build-up of a load-bearing liquid layer

The reasons for the inadequate pumping effect are physically and anatomically conditioned as follows Circumstances to see:

On the one hand, the construction mentioned does not contain any element that would exert a restoring force on the piston could generate. Therefore, no axial movement of the pin is generated in the recess of the joint head

ίο and therefore no synovial fluid in any way conveyed preformed pump volume. So'.lte nevertheless in rare, anatomically peculiar cases, a slight shape in the relieving phase of the leg Axial displacement of the cylindrical pin in the distal direction

'S direction and thus through a lubrication channel If a minimal amount of liquid is sucked in, then the liquid is drawn in through this channel during the stress phase is fed back into the joint capsule, which at most closely adjoins parts

; » the surface of the pin can be wetted so that in this case the synovial fluid in constant alternation relief - load only in the lubrication channel and pump volume oscillates.

Under no circumstances can the liquid be pumped between the sliding surfaces of the joint socket and the joint head as this requires a valve action and also in accordance with the basic hydraulic law the area ratio of the end face of the journal or the pump volume to the free area of the joint head

JO fes at the outlet opening must be less than "one". With a sufficiently small clearance between the pin and the recess, the compression generated by the latter the liquid is an equal pressure in the pump volume and in that to the sliding surfaces

J5 leading lubrication channel caused. Since now at Beginning of the loading process due to the existing congruence of the sliding surfaces of the joint socket and joint head, these rest against one another in a form-fitting manner, the sliding surface of the joint socket closes the

Opening of the lubrication channel of the joint head. There is therefore no liquid from the pump volume between the sliding surfaces are promoted, as the result of the small opening cross-section of the lubrication channel force prevailing between the two sliding surfaces

• ' ^{5 is} less than the force acting on the end face of the pin with the same pressure. This means that the sliding surfaces cannot be separated.

This construction can also not exercise effective shock absorption, since the sliding surfaces also in the so-called »relief phase« cannot be separated from each other in order to re-establish themselves Load under elastic and / or hydraulic energy absorption to approach each other again.

The invention is therefore based on the object of improving shock absorption and lubrication the sliding surfaces between the joint socket and the joint head by injecting in the relief phase to achieve sucked synovial fluid at the beginning and during the exercise phase.

This object is achieved in that the joint head has a surface located at the zenith of its surface Has flattening, the area of which is larger than the end face of the pin, that the joint head one Has suction channel, which the pump volume with that of

⁽ ' ^{5 of} the joint socket does not connect the outer surface of the joint head, and that a valve is arranged in the suction channel.

This achieves the advantages of being sensible

a sufficient amount of synovial fluid in the Pump volume is available and that this in the further course of the movement of the Zapfeiu as a result of the Valve effect pressed into the lubrication channel and from there due to the flattening on the sliding surface of the Rod end is injected into the space between the sliding surfaces. During this process, the Sliding surfaces of the joint socket and joint head from one another, with the so between these The load-bearing liquid film created by the surfaces cancels the solid-state friction between the surfaces and so that an optimal diminishing effect is generated

In a further development of the invention, the joint head and the bearing pin have a play of at least 0.015 mm on. As a result, the back-up synovial fluid in the pressure phase causes the inner surface of the The recess and the running surface of the pin are lubricated at the same time, which does not significantly affect the injection efficiency impaired, and achieved a considerable ease of movement.

According to another development of the invention, between the joint head and the end face of the Pin arranged a spring element. This achieves a considerable elastic shock absorption, which likewise an increased service life of the hip joint endoprosthesis can be expected.

Another embodiment of the invention is the formation of a groove on that of the joint socket not included outer surface of the joint head, from which the suction channel leads to the pump volume. Herewith it is achieved that in the event of a temporary accumulation of the secondary Joint capsule finds access to the suction channel from a free sector of the same fluid.

The invention is explained in detail with reference to the drawings. It shows

F i g. 1 the main parts of the hip joint endoprosthesis according to the invention: the stem-shaped shaft (2), which is fastened in the thigh bone with its piston-like pin (1), and the pin face (Fi).

Fig. 1 also shows the joint head (4) with its cylindrical neck part (11), the lubrication channel (6) which connects the recess (3) of the joint head with the flattening (F2) of the sliding surface (14) of the head (4), the suction opening (9 ') for the synovial fluid, the spring element (8), the groove (15) and the intersection line (10) of the penetration of the spherical head (4) and the cylindrical neck part (11).

The ones with reinforcement and fastening ribs as well as bolt-like projections, also those of the anchoring serve in the pelvic bone, provided joint socket (5) has on the inside a sliding surface (/), which the movable mounting of the ball head (4) is used.

F i g. 2 shows the hip joint endoprosthesis composed of its individual elements (2), (4) and (5), for example anchoring in the pelvic bone (19) and in the thigh bone (19 ') on an enlarged scale. (18) and (18 ') show schematically the zones filled with bone cement. (G) is the load given by the body weight and the respective movement phase, (C) is the reaction force that moves from the floor via the thigh bone (19') into the Joint is initiated The pin (1) or the shaft (2) is in its upper end position (B) or. fß'J shown, d. H. at the end of a stroke from (A) to (B) or /. from (A ') to (B'), i.e. at the end of a load phase of the movement sequence. In this state, in the example designed as Kugelventiil valve is closed (17) and the spring element (8) through the load (G) and by the reaction force (C) The pumping volume biased the recess (3) has at the piston stroke A - B decreases and the incompressible synovial fluid is through the lubrication channel

(6) in the result of the flattening F2 of Kopfgleitfläche (14) and the sliding surface (7) of the joint socket (5) volume formed (V) flowed Here exerts the pressurized liquid to the flattening (F 2) of the joint head (4) according to the hydraulic principle, a force K 2 is exerted on the latter, which is greater than the force K 1 generated by the journal face (Fi) in the direction of the socket.

As a result, the joint head (4) is against the tension of the spring element !; (8) from the sliding surface

(7) lifted off the joint socket and the liquid flows under high pressure on all sides into the space (16) thus formed between the sliding surface (7) of the socket (5) and the sliding surface (14) of the joint head (4) and flows from here along the The sliding surface of the joint head into the outer space, ie into the joint capsule. In the subsequent relief process, the pin (1) moves by the stroke from (B) to (A) and with it the shaft (2) anchored in the thigh bone from (B ') to (A') under the elastic force of the spring element (8 ) away from the socket in the axial direction. A negative pressure consequently arises in the pump volume (3). Since the space (16) between the joint surfaces is now closed, the valve (17) opens. The negative pressure now occurring at the suction opening (9 ') sucks the synovial fluid located in the joint capsule at (C) into the suction channel (9). If the liquid present at (C) is insufficient, the groove (15) at the neck end of the joint head (4) ensures an inflow from areas of the capsule that are further away from (C). As a result of the negative pressure, the liquid flows through the suction channel (9) into the pump volume (3), where it is available for the next injection process, which is caused by the upward movement of the pin (1) from (A) to (B) in the manner shown is initiated. The stroke of the pin (1) depends within limits on the nature of the entire joint area and is approximately 4 mm. As a result of the clearance of 0.015 mm between the pin (1) and the joint head (4), relative ease of movement is achieved during the function explained and at the same time the sliding surfaces of the pin (1) and pump volume (3) through the backed up liquid in the pressure phase and through the liquid sucked in self-lubricated during the relief phase, but without significantly impairing the injection process.

For this purpose 2 sheets of drawings

Claims (4)

Patent claims: 1. Hip joint endoprosthesis, consisting of a joint socket and a shaft which carries a cylindrical pin acting sis piston pump, on which a spherical joint head with a recess receiving the pin is slidably placed and that the joint head has a lubrication channel leading into the recess for the pin, which connects the pump volume formed by the movement of the pin in the recess of the joint head with the space between the sliding surfaces of the joint socket and joint head, characterized in that the joint head (4) has a flattening (F2) at the zenith of its surface, the surface of which is larger is as the end face (FX) of the pin (1) that the joint head has a suction channel (9) which connects the pump volume (3) with the outer surface of the joint head (4) not encompassed by the joint socket (5), and that in Suction channel (9) a valve (17) is arranged. 2. Hip joint endoprosthesis according to claim 1, characterized in that the joint head (4) and the pin (1) have a radial play of at least 0.015 mm. 3. Hip joint endoprosthesis according to claim 1 or 2, characterized in that a spring element (8) is arranged between the joint head (4) and the end face (F 1) of the pin (l). - 4. Hip joint endoprosthesis according to one of the preceding claims, characterized in that that the joint head (4) on the outer surface not encompassed by the joint socket (5) with a groove (15) is provided, from which the suction channel (9) leads to the pump volume (3).