WO2008015284A1

WO2008015284A1 - Asymmetric formation of prosthetic components for the manipulation and suppression of natural frequencies

Info

Publication number: WO2008015284A1
Application number: PCT/EP2007/058122
Authority: WO
Inventors: Roman Preuss; Thomas Pandorf; Patricie Merkert; Heike Idink; Martin Dietrich
Original assignee: Ceramtec Ag
Priority date: 2006-08-04
Filing date: 2007-08-06
Publication date: 2008-02-07
Also published as: EP2049047A1; CN101522135A; JP2009545413A; KR20090038925A; CN101522135B; JP5388065B2; DE102007031663A1; KR101388594B1

Abstract

The invention relates to a shaft (1) of a hip joint prosthesis for implantation in the femur (5) of a patient, wherein the shaft (1) can be coupled with a ball head (2), which in turn can be inserted rotatably in the hemispherical recess of a socket insert (3). According to the invention, to avoid squeaking, it is proposed that the shaft (1) is formed asymmetrically in its outer and/or inner geometry and/or material composition.

Description

Asymmetric design of prosthetic components for manipulation and suppression of natural frequencies

The invention relates to a shaft of a hip joint prosthesis for implantation in the femur of a patient, wherein the shaft can be coupled with a ball head, which in turn is rotatably inserted in the calotte of a socket insert.

State of the art:

The market has a variety of prosthetic systems for the replacement of the natural hip joint. These usually consist of a shaft 1 coupled to a ball head 2 and a hip socket 4 coupled with a socket insert 3. Shank 1 and acetabulum 4 are connected to the body by ingrowth in the Oberschenkelbzw. The spherical head 2 is rotatably mounted in the calotte of the socket insert 3 - degree of freedom: 1 (see Figure 1).

During articulation of the ball head in the cup of the socket insert, undesirable solid friction between the sliding partners can occur for various reasons and particularly when using high durometer materials for ball and socket inserts (e.g., metal alloys, ceramics). In this case, different phenomena can occur, which can lead to a swing-up behavior of the components involved and thus to a development of noise, the so-called squeaking. Three phenomena are briefly described below.

1 . Depending on the material pairing, surface structure and relative speed of the two friction partners, it is possible during movement under the action of solid state friction a so-called stick-slip effect occur. That is, the quasi-continuous motion of the spherical head in the dome is composed of many very short motion cycles - one short motion followed by a sudden stop and then another sudden motion. This stick-slip effect is caused by a constant alternation of static and sliding friction.

The vibrations emitted as a result of the occurrence of the stick-slip effect act as excitation and lead to the oscillation of the individual components or component groups of the artificial joint. If one or more of the natural frequencies of the components or groups lie in the audible spectrum (approximately 16-20000 Hz), they may be used by the patient as the wearer of the artificial hip joint, e.g. in the form of the so-called squeaking, be perceived acoustically. This is undesirable to the patient, u. U. also perceived by its environment and possibly leads to a significant personal restriction.

2. Due to frequently repeated motion patterns and the occurrence of microseparation (the temporary separation of the tribological system ball-head insert during a cycle of motion), it can lead to the formation of stripe-wear on the ball head or the insert to form strip-like wear patterns, the have a certain regularity over the strip length. If, under certain individual conditions (body posture, movement sequence), the ball head moves relative to the insert in the area of the stripe-wear zone, this can lead to a self-excited vibration. If this excitement lies within the range of the natural frequencies of the components or component groups involved, this leads to the formation of eigenmodes and noise generation. If one or more of the natural frequencies of the components or groups lie in the audible spectrum (approximately 16-20000 Hz), they can be perceived acoustically by the patient as the wearer of the artificial hip joint, for example in the form of the so-called squeaking. 3. After the insertion of artificial hip joints, contact between the metal shaft and the metal socket or between the metal shaft and the ceramic insert may occur, in particular in the case of extreme socket positions. If this contact is not only pointwise, but by a corresponding leg movement over an angle, so that it comes to a "grinding" of the metal shank over Pfanne / Lnsert, this can lead to a self-excited oscillation, lies this excitement in the field of If one or more of the natural frequencies of the components or groups in the audible spectrum (about 16-20000 Hz) are present, they can be interpreted by the patient as "natural frequencies" of the components or component groups involved Carrier of the artificial hip joint, for example in the form of the so-called squeaking, be perceived acoustically.

The invention has the object of developing a shaft according to the preamble of claim 1 so that no squeaking occurs.

This object is achieved in that the shaft is formed asymmetrically in its outer and / or inner geometry and / or material composition.

The targeted asymmetric design of the shank prevents the formation of intricate shapes of the shank and significantly attenuates the manifestation of vibrations in the component in the acoustically perceptible frequency range. The proposed asymmetry of the shank can be achieved by various measures that can be combined with one another: in the form of an asymmetric outer geometry in all three spatial directions (cross-sectional area and longitudinal axis), in the form of an asymmetric inner geometry in all three spatial directions (cross-sectional area and Longitudinal axis), as well as by asymmetric composition of the shank of materials with different stiffness and damping properties. - A -

In a preferred inventive embodiment, therefore, the outer and inner geometry is designed asymmetrically in all three spatial directions.

This can be done, for example, by the shaft having recesses on its surface.

Alternatively or in combination, the outer borders of the cross-sectional areas may be asymmetrically shaped and / or the shaft may be discontinuously shaped along the shaft axis.

In an inventive embodiment, the shaft has continuous transverse bores.

The asymmetric configuration of the inner geometry is achieved in one embodiment of the invention in that the shaft has inner cavities as different volume as possible.

In another embodiment, longitudinal bores are introduced in the shaft, which can adjoin one another discontinuously.

Another inventive embodiment is characterized in that holes of different diameters are introduced in the connecting web.

The asymmetrical configuration of the material composition can be achieved by the fact that the stiffnesses and / or damping properties and / or the material along the longitudinal axis of the shaft are different.

Hereinafter, the prior art and the invention will be explained in more detail with reference to figures.

FIG. 1 shows the state of the art. A hip prosthesis usually consists of a shaft 1 coupled to a ball head 2 and a hip socket 4 coupled 3. Shaft 1 and acetabulum 4 are connected to the body of the patient by ingrowth into the thigh or pelvic bone 15 and are carriers for the ball head 2 and cup insert 3, respectively. The ball head 2 is in the cup of the acetabular insert 3 rotatably mounted.

FIG. 2 shows a shaft 1 according to the invention, in which recesses are arranged on the surface for the asymmetrical design of the outer geometry.

FIG. 3 shows a cross section according to the invention through a shank (solid line), which is opposite to the cross section of a conventional shank (dashed line). The outer border 7 of the cross-sectional area of the shank is asymmetrically shaped to avoid squeaking. The shaft 1 is thereby formed discontinuously along the shaft axis 9.

For the asymmetrical design of the inner geometry of the shaft 1, Figure 4 shows continuous transverse bores 10. The diameter of these transverse bores 10 is chosen differently.

Figure 5 shows the asymmetrical design of the inner geometry of the shaft 1 inner cavities 1 1 in the cross-sectional area 8. The reference numeral 9, the shaft axis is marked. The volume of the inner cavities 1 1 is preferably different.

FIG. 6 shows a shaft according to the invention with longitudinal bores 12 which can adjoin one another discontinuously. A longitudinal bore 12 is also arranged in the connecting web 13.

FIG. 7a shows a shaft 1 with bores 14 in the connecting web 13. FIG. 7b shows a section along the line AA of FIG. 7a. Good to see that the diameter of the holes 14 is different. The asymmetrical configuration of the shank 1 can also be achieved in that the material or the material of the shank 1 changes along the shank axis 9. It is important here that the modulus of elasticity differs from the conventional shaft material. Thus, the recesses 6 in Figure 2 can also be filled by a second material deviating from the base material of the shaft 1 modulus of elasticity.

Claims

claims

1 . Shaft (1) of a hip joint prosthesis for implantation in the thighbone (5) of a patient, wherein the shaft (1) can be coupled to a ball head (2), which in turn is rotatably insertable in the calotte of a socket insert (3), characterized in that the shaft (1) is asymmetrical in its outer and / or inner geometry and / or material composition.

2. Shank according to claim 1, characterized in that the outer and inner geometry is designed asymmetrically in all three spatial directions.

3. shank according to claim 1 or 2, characterized in that the shank (1) on its surface recesses (6).

4. Shank according to one of claims 1 to 3, characterized in that the outer edges (7) of the cross-sectional surfaces (8) are asymmetrically shaped.

5. Shaft according to one of claims 1 to 4, characterized in that the shank (1) along the shaft axis (9) is discontinuous.

6. Shank according to one of claims 1 to 5, characterized in that the shank (1) has continuous transverse bores (10).

7. Shaft according to one of claims 1 to 6, characterized in that the shaft (1) has inner cavities (1 1) as different volume.

8. Shaft according to one of claims 1 to 7, characterized in that in the shank (1) longitudinal bores (12) are introduced, which can adjoin one another discontinuously.

9. shank according to one of claims 1 to 8 with a connecting web (13), characterized in that in the connecting web (13) bores (14) of different diameters are introduced.

10. Shaft according to one of claims 1 to 9, characterized in that the stiffness and / or damping properties and / or the material along the shaft axis (9) are different.