KR101388594B1 - Asymmetric formation of prosthetic components for the manipulation and suppression of natural frequencies - Google Patents

Abstract

The present invention relates to a shaft (1) for hip prosthesis for implantation into a patient's femur (5), the shaft (1) being coupled to a ball head (2), the ball head being in turn a socket insert (3). Can be inserted in a rotatable manner within the semicircular recess. In order to prevent squeaking according to the invention, it is proposed that the shaft 1 be formed asymmetrically in the outer and / or inner shape and / or the material composition.

Description

Asymmetrical Formation of Prosthetic Components for Adjustment and Suppression of Characteristics Frequency {ASYMMETRIC FORMATION OF PROSTHETIC COMPONENTS FOR THE MANIPULATION AND SUPPRESSION OF NATURAL FREQUENCIES}

 The present invention relates to a hip prosthetic shaft for implantation into the patient's femur, where the shaft can be coupled with a ball head which can in turn be inserted in a rotatable manner into a semicircular recess of the socket insert.

A plurality of prosthetic systems are being marketed to replace the human hip joint. In general, they consist of a shaft 1 engaged with the ball head 2 and a bottom socket 4 engaged with the socket insert 3. The shaft 1 and the bottom socket 4 are connected to the body as a result of growth into the femur and pelvis bone and support the ball head 2 and the socket insert 3 respectively. The ball head 2 is rotatably mounted in the semicircular recess of the socket insert 3 with 1 degree of freedom (see FIG. 1).

For a variety of reasons and especially when materials with high levels of strength (eg metal alloys, ceramic materials) are used for the ball head and socket inserts, the slippage area during the joint movement of the ball head in the semicircular recess of the socket insert In between, undesirable friction between solid-body can occur. In this case, different phenomena are brought about as a result of the resonance behavior of the internal parts, whereby noise generation, so-called squeaking sounds can be produced. Hereinafter, three phenomena will be briefly described.

1. Depending on the material combination, the surface texture and the relative velocity of the two friction sites, the so-called stick-slip effect occurs during the motion under the friction effect between the object and the body. This means that in close engagement, the semi-continuous movement of the ball head in the semicircular recess forms a very temporary and very short movement cycle, in which case the short movement leads directly to a rapid stop and in turn leads to a sudden movement. This stick-slip effect is rooted in a constant shift of static sliding friction.

The vibration generated as a result of the occurrence of the stick-slip effect acts as excitation resulting in vibration of the individual parts or parts of the artificial joint. If one or more characteristic frequencies of the parts fall within the audible range (approximately 16 to 20000 Hz), they may be perceived as a sound, for example a squeak, to the patient as a carrier of the artificial hip joint. This is undesirable for the patient and also likely to be recognized by the person around the patient and, if applied, will result in significant personal limitations.

2. As a result of the frequently repeated movement pattern and micro-separation (slight breakup of the lubrication system ball-head / insert during the movement cycle), over the length of the strip and the formation of strip wear on each of the ball head or insert The development of strip wear patterns with a certain regularity can result. If the ball head is moved under special individual conditions (position, movement sequence) relative to the insert in the strip wear zone, this can lead to self excited vibration. If this self-oscillation falls within the characteristic frequency range of the component or internal components, this results in propagation and noise generation of the characteristic form. If one or more characteristic frequencies of the part or internal parts fall within the audible range (approximately 16 to 20000 Hz), it can be perceived as a sound, for example a squeak, to the patient as a carrier of the artificial hip joint.

3. After insertion of the artificial hip, contact may be brought about between the metal shaft and the metal socket or between the metal shaft and the ceramic insert, especially in extreme socket positions. If such a contact does not occur point to point, resulting in a corresponding drag motion over a certain angle resulting in a "descent" of the metal axis over the socket / insert, this will cause vibrations to self. If this self-oscillation falls within the characteristic frequency range of the component or internal components, this results in propagation of the characteristic form and generation of noise. If one or more characteristic frequencies of the part or internal parts fall within the audible range (approximately 16 to 20000 Hz), it can be perceived as a sound, for example a squeak, to the patient as a carrier of the artificial hip joint.

The primary object of the present invention is to further develop the shaft in accordance with the preamble of claim 1 so that no squeaking occurs.

This object is achieved by asymmetrically forming the inner and / or outer shape and / or material composition of the shaft.

As a result of forming the shaft with a special asymmetry, the expansion of the shaft into a particular form can be prevented and the occurrence of vibration of the part within the audible frequency range can be significantly attenuated. In this case the asymmetry of the proposed axis is of the form

The shape of the asymmetric outer shape in all three directions (cross section direction and also the longitudinal direction) in the space, the shape of the asymmetric inner shape in all three directions (cross section direction and also the longitudinal direction) in space, as well as different strength and damping characteristics The asymmetric composite configuration of the axis by the material having it can be achieved by a number of methods which can preferably be combined with one another.

Thus, in the preferred embodiment, the outer and inner shapes are configured asymmetrically in three directions within the space.

This can be implemented, for example, with recesses on the surface of the shaft.

Alternatively or in combination, it is possible to mold the outer edge of the cross section asymmetrically and / or to discontinuously shape the axis along the axis of the axis.

In a preferred embodiment, the shaft has a through hole.

Asymmetrical expansion of the inner shape is achieved in accordance with an embodiment of the present invention in which the axis has as many internal volumes as possible.

In another embodiment, longitudinal bores are provided in the shaft that can be discontinuously adjacent to each other.

Another embodiment of the invention is distinguished in that bores of different diameters are provided in the connecting web.

Asymmetry of the material combination can be achieved by different combinations of material and / or damping properties and / or strength along the longitudinal axis of the axis.

The prior art and the present invention are explained in the following detailed description with reference to the drawings.

1 illustrates the prior art. The hip prosthesis generally consists of a shaft 1 which is engaged with the ball head 2 and a hip socket 4 which is engaged with the socket insert 3. The shaft 1 and the hip socket 4 are connected to the patient's body as a result of growth into the femur 5 and the pelvic bone 15 and respectively support the ball head 1 and the socket insert 3. The ball head 2 is rotatably mounted in the semicircular recess of the socket insert 3.

2 shows the axis 1 according to the invention in which the recesses are arranged on the surface for asymmetrical expansion of the outer shape.

3 shows a cross-sectional view (solid line) of an axis according to the invention as compared to a cross-sectional view (break line) of an axis according to the prior art. The outer edge 7 of the cross section of the shaft is formed asymmetrically to prevent squeaking. The axis 1 is consequently formed discontinuously along the axis 9 as a result.

4 shows a transverse hole 10 for asymmetrically forming the inner shape of the shaft 1. The selected diameters of these transverse holes 10 are different.

5 shows the inner cavity 11 in the cross section 8 for asymmetrically forming the inner shape of the shaft 1. The axis line of the axis is indicated as 9. Preferably the volume of the inner cavity 11 is different.

6 shows an axis according to the invention with longitudinal holes 12 which can be incombustibly adjacent to each other. The longitudinal holes 12 are also arranged in the connecting web 13.

7a shows an axis 1 with a hole 14 in the connecting web 13.

FIG. 7B shows a cross section along line A-A in FIG. 7A. It can be easily seen from this figure that the diameters of the holes 14 are different.

The asymmetrical configuration of the axis 1 can also be achieved by changing the material or material of the axis 1 along the axis 9. What is important in this configuration is that the modulus of elasticity is different from that of conventional shaft materials. 2 may therefore be filled by a second material which is different from the modulus of elasticity of the base material of the shaft 1.

Claims (10)

A shaft 1 can be coupled to the ball head 2, which allows the ball head to be implanted into the femur 5 of the patient, which can be inserted in a rotatable manner within the semicircular recess of the socket insert 3. As a shaft (1) for hip prosthesis for Characterized in that the shaft 1 is formed asymmetrically in at least one of an outer shape, an inner shape and a material composition, Hip prosthesis shaft for implantation into the patient's femur. The method of claim 1, The outer and inner shape is characterized in that it is configured asymmetrically in all three directions in the space, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, The shaft 1 is characterized in that it has a recess 6 on the surface, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, The outer edge 7 of the cross section 8 of the shaft 1 is characterized in that it is formed asymmetrically, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, The shaft 1 is characterized in that it is formed discontinuously along the axis 9, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, The shaft 1 is characterized in that it has a transverse through hole 10, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, The shaft 1 is provided with a plurality of inner cavities 11, characterized in that two or more of the plurality of inner cavities 11 have different volumes, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, Characterized in that the longitudinal holes 12 are provided in the shaft 1 which can be discontinuously adjacent to each other, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, The hip joint prosthesis has a connecting web 13, Characterized in that holes 14 of different diameter are provided in the connecting web 13, Hip prosthesis shaft for implantation into the patient's femur. 3. The method according to claim 1 or 2, Characterized in that at least one of the material, the damping properties and the strength is different along the axis 9 of the axis, Hip prosthesis shaft for implantation into the patient's femur.

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