DE102010003279A1 - Device and method for the in situ measurement of the anchoring strength of endoprostheses - Google Patents

Abstract

The device and method are used for in-situ measurement of anchoring strength of endoprostheses. The object of the invention is to detect the state of the anchoring of endoprostheses with the aid of sensors in situ and to transmit the information ex-vivo. Furthermore, it is the object of the invention to develop a non-invasive measuring method with which the bony anchoring of endoprostheses can be determined reliably and without radiation. The device according to the invention is characterized in that a loosening sensor is arranged in-situ within the endoprosthesis and a membrane, which is arranged on the implant-bone boundary layer, stimulates oscillation. A measuring device ex-vivo the vibration behavior. For the method according to the invention, a loosening sensor within the endoprosthesis stimulates a membrane, which is arranged on the implant-bone boundary layer, to vibrate. A measuring device ex-vivo the vibration behavior, the measured vibration damping is the indicator of the anchoring strength of the endoprosthesis.

Description

The The device and the method are used for the in-situ measurement of the anchoring strength of endoprostheses.

State of the art

Of the Main reason for a hip prosthesis change is the aseptic implant loosening with a frequency of approx. 75%. The aseptic loosening of hip endoprostheses is predominantly based diagnosed clinical symptoms and X-rays, however, the sensitivities and specificities are suboptimal.

to Support of x-ray can be a contrast agent be injected into the joint capsule, so when loosening of the implant this contrast agent between bone and implant becomes visible.

EP 0579673 B1 discloses the measurement of the strength of a jaw implant in the jaw by a cantilever beam which is bolted to the implant when the measurement is to be made. A resonance frequency is measured whose changes in amplitude provide information about the quality of the implant / tissue connection. The device presented here is not suitable for making measurements on a hip endoprosthesis.

In WO 9006720 A1 a device is presented which is intended to determine the release of an implant in a bone. For this purpose, a vibrator is brought from the outside in the vicinity of the end of the bone opposite the implant and a scanning device at the level of the implant absorbs the vibrations transmitted through the bone implant composition. Detachment of the implant is detected when the recurrent pattern of the output signal transmitted through the bone implant composition shows overlays on the oscilloscope and / or significant secondary harmonic on the spectrum analyzer. This method can easily lead to inaccuracies, since the vibrations can rarely be measured directly on the bone.

A new form of loosening diagnostics is of high clinical relevance, on the one hand to avoid unnecessary operations and on the other hand the Emergence of large bone defects with belated ones Prevent revision.

Presentation of the invention

task The invention is the state of anchoring of endoprostheses with the help of sensors in-situ capture and information ex-vivo transferred to. Furthermore, it is the object of the invention to develop a non-invasive measurement method with which the Bony anchoring of endoprostheses reliable and radiation-free can be determined.

The Inventive device for in-situ measurement the anchoring strength of endoprostheses is characterized a loosening sensor is placed in-situ within the endoprosthesis is and a membrane attached to the implant-bone boundary layer is arranged to stimulate the swing. A measuring device intervenes ex-vivo the vibration behavior. The vibration damping serves as a measure of how firmly the implant anchors in the bone is. In one embodiment, the membrane is bone seen in the endoprosthesis arranged offset inwards.

Of the Loosening sensor consists of a spring and a ferromagnetic Mass oscillator, which is located near the membrane.

When Another version consists of the relaxation sensor from a Piezoelectric element for acoustic vibration excitation, which with a coil and a capacity is connected in series and on one Membrane is arranged. About a vertical or oblique Arrangement of the piezoelectric element on the membrane can be a vertical Sound (to use the Logitudinal- and transverse waves) or an oblique insonification (use of the transverse waves) will be realized.

Of the Loosening sensor and the membrane should, but need not, have the same natural frequencies. The membrane can also be approximately stiff be designed.

Become several loosening sensors at different locations within the Arranged endoprosthesis, can provide reliable information about the Anchoring strength can be recovered. The sensors can be individually controlling if their natural frequency is sufficient Dimensions differ from each other.

The method according to the invention for the in-situ measurement of the anchoring strength of endoprostheses is characterized in that a loosening sensor within the endoprosthesis excites a membrane, which is arranged on the implant-bone boundary layer, to vibrate. A measuring device ex vivo the vibration behavior of the membrane acoustically or magnetically inductive, the measured vibration damping is the indicator of the anchoring strength of the endoprosthesis. The measuring device attacks the vibration behavior of the membrane acoustically or magnetically inductive.

The Basis of the method according to the invention the impedance difference between the periprosthetic deposited biological Materials. Is soft on the outside of the membrane Tissue or fluid, results in a big one Difference in mechanical impedance. Consequently, the vibrations become largely reflected by the respective sensor and not forwarded, resulting in low attenuation entry. If the membrane is connected to solid bone tissue, this gives a small difference in mechanical impedance. The vibrations are mostly forwarded and sound fast. A strong damping signals hence solid bone contact. This effect is amplified when the excited oscillator and the adjacent membrane same natural frequencies exhibit. The measured damping of the vibration of the sensor is consequently, the anchor strength indicator Endoprosthesis.

Brief description of the illustrations

The The invention will be explained in more detail with reference to drawings. This shows:

1 the arrangement of the loosening sensor on the endoprosthesis in the bone camp in a partial sectional view;

2 the sectional view of an endoprosthesis in the surrounding bone stock with implant-bone boundary layer with looseness sensor consisting of a spring and a ferromagnetic mass oscillator

3 the sectional view of an endoprosthesis in the surrounding bone stock implant-bone boundary layer with looseness sensor consisting of a spring, a ferromagnetic mass oscillator and an inwardly offset membrane and

4 Sectional view of an endoprosthesis in the surrounding bone bed with implant-bone boundary layer with loosening sensor consisting of a piezoelement.

Embodiment of the invention

The Invention is based on two different types of sensors, which within the endoprosthesis are attached and described below become.

1 gives an overview of an endoprosthesis 1 in the bone camp 2 , In the partial sectional view is the loosening sensor 3 inside the endoprosthetic handle, pictured.

Of the acousto-mechanically oriented approach to in-situ loosening diagnostics based on mass oscillators, which are within the endoprosthesis are attached. The mass swingers are magnetic Ferrite body, which hung on a spring are. The magnetic north-south polarity of the ferrite bodies allows vibration excitation by means of external Alternating field impulse as well as a read out of the oscillation with help an extracorporeal coil. The advantage is used that the most common implant materials in endoprosthetics, Titanium and cobalt-chromium alloys, not ferromagnetic materials are.

2 shows a sectional view of an endoprosthesis 1 in the surrounding bone camp 2 with implant-bone interface 4 , The loosening sensor consists of a spring 5 and a ferromagnetic mass oscillator 6 which is attached to a membrane 7 borders.

Adjacent to the ferromagnetic mass oscillator 6 should the membrane 7 the vibrations on the neighboring bones 2 transfer. In the measurement of the anchoring strength, an alternating field pulse is initially applied by means of an extracorporeal coil, not further shown here, which alternates the mass oscillator 6 vibrated and on the membrane 7 to meet. Depending on the anchoring state of the membrane 7 In the bone, the vibration is more or less damped. This damping can also be done with the extracorporeal coil based on the resulting movement of the ferromagnetic mass oscillator 6 be registered. In order to prevent an unwanted oscillation of the ferrite body outside the measurements, should be with the spring 5 a certain mechanical bias can be applied, causing the ferrite body to the membrane 7 is pressed.

The membrane can be offset inwardly as seen from the bone, ie it does not terminate flush with the endoprosthesis surface ( 3 ). Thus, a distinction can be made in the measurements between a pressed-in and an ingrown implant. The ingrown bone will overcome the gap, but when the implant is pressed in there will be no bone contact with the membrane.

The piezo-acoustic based approach to in situ loosening diagnostics is based on piezoelectric elements 8th , which on a thin-walled membrane 7 located on the implant surface. 4 shows a sectional view of an endoprosthesis 1 in the surrounding bone camp 2 with implant-bone interface 4 , The loosening sensor consists of a piezo element 8th which is attached to a membrane 7 adjacent and connected in series with an inductance (Cl) and a coil (L1). By means of an external coil, not shown here, a voltage is induced in the implant and the piezoelectric element 8th excited to swing. Subsequently, the same circuit is used as a transmitter. The by swinging out of the piezoelectric element 8th generated voltages are converted by the internal coil into an electromagnetic field, which is registered externally.

There may be several loosening sensors 3 in different places within the endoprosthesis 1 to be placed. The various locations correspond to the characteristic locations at which the respective type of endoprosthesis shows the first loosening phenomena based on clinical experience. If the natural frequencies of the sensors deviate sufficiently from one another, they can be individually controlled and each emit their own measuring signals.

The Recording the vibrations of the mass oscillator with an extracorporeal Measuring device is either acoustically via a sound pickup or magnetic inductive z. B. realized with a coil.

The Recording of the vibrations of the piezoelectric element is about the internal coil and an extracorporeal measuring device with a realized another coil.

Around to distinguish whether the endoprosthesis is ingrown in the bone or is pressed in, the membrane can be offset inwards. Thereby finds a bone contact only through its active growth and not already by pressing the implant instead.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 0579673 B1 [0004]
• - WO 9006720 A1 [0005]

Claims (9)

Device for the in-situ measurement of the anchoring strength of endoprostheses, characterized in that a looseness sensor is arranged in-situ within the endoprosthesis and a diaphragm, which is arranged at the implant-bone boundary layer, to vibrate and a measuring device ex-vivo the vibration behavior taps. Device according to claim 1, characterized that the membrane seen from the bone in the endoprosthesis after inside is offset. Device according to claim 1 or 2, characterized that the looseness sensor of a spring and a ferromagnetic Mass oscillator, which is located near the membrane. Device according to claim 1 or 2, characterized that the looseness sensor consists of a piezoelectric element, which connected in series with a coil and a capacitor is and is arranged perpendicular to or at an angle to the membrane is. Device according to one of claims 1 to 4, characterized in that the loosening sensor and the membrane have the same natural frequencies. Device according to one of claims 1 to 5, characterized in that a plurality of loosening sensors at different Positions are arranged within the endoprosthesis. Device according to claim 6, characterized that the loosening sensors have different natural frequencies and individually controlled. Method for in situ measurement of anchoring strength of endoprostheses, characterized in that a loosening sensor within the endoprosthesis a membrane attached to the implant bone Boundary layer is arranged to stimulate oscillation and a measuring device ex vivo the vibration behavior picks up, whereby the measured vibration damping the indicator for the anchoring strength of the endoprosthesis is. Method according to claim 8, characterized that the measuring device acoustically the vibration behavior of the membrane or magnetically tapped.