DE2139878C3 - Hip joint prosthesis for implantation in the human body - Google Patents

Description

The invention is based on a hip joint prosthesis, consisting of a joint socket and a shaft, which has a cylindrical piston pump Pin carries, on which a spherical joint head with a pin receiving Recess is slidably placed and in which the joint head is inserted into the recess for the Has pin leading lubrication channel, the through the movement of the pin in the recess of the Joint head formed pump volume with the space between the sliding surfaces of the joint socket and swivel head connects.

Such a hip joint endoprosthesis is from Swiss patent 4 90 077 known in which an attempt was made to extend the service life of such a joint by »lubrication« of the moving parts /> i raise. However, this is the case with this construction Prosthesis not possible to the required extent because neither in the Schmicrkanal proposed for this However, in any clearance between the head and the pan provided for the purpose of lubrication Phase of the movement sequence, sufficient amounts of synovial fluid can be accumulated since the Cylindrical journals imagined as "piston pumps" cannot be effective. Thus, the one is not yet articulating surfaces have an adhesive film of liquid at the beginning of the exposure phase Sliding and / or rolling of the surfaces gegencinan the displaced by these, so that it does not build up a load-bearing liquid layer comes.

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 preformed pump volume should be promoted in rare, anatomically peculiar cases In the relief phase of the leg, a slight axial displacement of the cylindrical pin in the distal direction Direction take place and thus a minimal amount of liquid is sucked in through a lubrication channel, so The fluid is returned to the joint capsule through this channel during the stress phase returned, whereby at most closely adjacent parts of the surface of the pin can be wetted, so that in this case the articular fluids drop Alternating unloading - loading only oscillates in the lubrication channel and pump volume.

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

X) fes at the outlet opening must be less than "one". If the clearance between the pin and the recess is sufficiently small, the compression of the liquid produced by the latter results in an equally high pressure in the pump volume and in that of the sliding surface

} 5 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 swivel head, these lie against each other in a form-fitting manner, closes the sliding surface of the joint socket

■ Ό Opening of the lubrication channel of the joint head. It can therefore no liquid is conveyed from the pump volume between the sliding surfaces, as the result The force prevailing between the two sliding surfaces of the small opening cross-section of the Schm, erkanal is less. than ne with the same pressure on the Front surface of the pin acting force. This means that the sliding surfaces cannot be separated.

This construction cannot be effective either Exercise shock absorption as the sliding surfaces are also in the so-called »F.ntlasuingsphase« cannot be separated from each other in order to re-establish themselves To approach each other again with elastic and / or hydraulic energy absorption.

The invention therefore has the object of providing a Improvement of the shock absorption and the lubrication of the sliding surfaces between the joint socket and the joint head by injecting synovial fluid sucked in during the relaxation phase at the beginning and in each case to be achieved during the exertion phase.

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

^{h5 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 that at the beginning

a sufficient amount of synovial fluid in the Pump volume is available and that this in the further course of the movement of the pin 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 from the joint socket and joint head from one another from, the supporting liquid film thus created between these ι ο surfaces the Removes solid friction between the surfaces and thus creates an optimal lubricating effect.

In a further development of the invention, the joint head and the bearing pin has a play of at least 0.015 mm ι ■> 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 a considerable ease of movement achieved.

According to another development of the E: 'indung a spring element is arranged between the joint head and the end face of the pin. This becomes a considerable elastic shock absorption is achieved, which also increases the 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 is achieved that in the event of a temporary possibly Occurring partial accumulation of the secondary joint capsule from a free sector of the same Liquid finds access to the suction channel. J5

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

F 1 jt. 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 (F I).

1 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 joint / fluid, the spring element (8). the groove (15) and the cut (10) of the penetration of the spherical head (4) and the cylindrical neck part (11).

The with reinforcement ut.d fastening ribs as well Bolt-like projections, which also serve for anchoring in the pelvic bone, provided joint socket (5) has a sliding surface (7) on the inside. which is used to move the ball head (4).

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 ') schematically represent 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 from the floor via the thigh bone (19') into the joint is initiated. The pin (1) or the shaft (2) is shown in its upper end position (B) or (B ') , ie 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, the valve (17), designed as a ball valve in the example, is closed and the spring element (8) is pretensioned by the load (G) or by the reaction force (G '). The pump volume of the recess (3) has decreased by the piston stroke AB and the incompressible synovial fluid is through the lubrication channel

(6) flowed into the volume (V) formed by the flattening F2 of the head sliding surface (14) and the sliding surface (7) of the joint socket (5). Here, the pressurized fluid exerts on the flattening (F 2) of the joint head (4) on the hydraulic principle, a force K 2 o ^f this, which is greater than that of the pin end face (Ft) generated in ^r; Pla on. the force acting on the socket K 1.

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

(7) of the 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 sliding surface of the joint head into the outer space, ie π down 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. Consequently, cn negative pressure 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) as 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), a relative ease of movement is achieved during the function explained and at the same time the sliding surfaces of the pin (I) and pump volume (3) through the backed up liquid in the pressure phase and through the liquid sucked in self-lubricated during the unloading phase without significantly affecting the injection process explained

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 as a 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 area of which is larger is as the end face (F 1) 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 a valve (17) is arranged in the suction channel (9). 2. Hip joint endoprosthesis according to claim 1, characterized in that the joint head (4) and the pin (1) has 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 \) of the pin (1). 4. Hip joint endoprosthesis according to one of the preceding claims, characterized in that that the joint head (4; on the outer surface not surrounded by the joint socket (5) with a groove (15) is provided, of which the Suction channel (9) leads to the pump volume (3).