A PROBE

Abstract

A method of assessing the stiffness of bone comprising the steps of: placing an elongate probe into a predrilled aperture in the bone to be assessed; exciting the elongate probe to physically oscillate; and monitoring the resonance frequency of the probe. The resonance frequency is analysed to determine the quality, density and/or stiffness of the bone.

Claims

1. A method of assessing the quality, density and/or stiffness of bone comprising the steps of: placing an elongate probe into a predrilled aperture in the bone to be assessed; exciting the elongate probe to physically oscillate; and monitoring the resonance frequency of the probe; wherein the resonance frequency is analysed to determine the quality, density and/or stiffness of the bone.

2. A method according to claim 1, wherein the method comprises the further step of removing the probe from the bone once the analysis has been undertaken.

3. A method according to claim 1, wherein the resultant output resonance frequency is amplified and/or filtered before being analysed.

4. A method according to claim 1, wherein the analysis is undertaken by a central processing unit and wherein the central processing unit further comprises non-volatile memory.

5. A method according to claim 4, wherein a look-up table and/or calibration data is provided on the non-volatile memory and the information thereupon is accessed by the central processing unit during analysis of the resonance frequency.

6. A method according to claim 1, wherein a graphical display of the calculated quality, density and/or stiffness is produced.

7. A method according to claim 1, wherein the probe is provided with markings along its length to indicate the depth to which it is inserted into the aperture.

8. A method according to claim 1, wherein the probe is provided with a threaded or spiral external profile.

9. A method according to claim 1, wherein the size and profile of the probe is matched to that of a drill bit used to create the aperture.

10. A method according to claim 1, wherein the excitation means for exciting the elongate probe are bonded to the probe.

11. A method according to claim 1, wherein the excitation means comprises a coil acting directly upon the probe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0025] FIG. 2 shows probes for use in the method of the present invention;

[0026] FIG. 3 is a diagram showing a schematic of an arrangement for use in the present invention; and

[0027] FIG. 4 chart showing the relationship between resonance frequency and bone quality.

DESCRIPTION OF EXEMPLARY EMBODIMENT

[0028] FIG. 2 shows probes 10 comprising an elongate section 12 and a top section 14. The top section is provided with activation means for exciting the probe 10, which include: [0029] a) a direct electromagnetic connection comprising coils 16 wrapped around or bonded to the top section 16, in which the coils cause excitation and also measure the response of the probe. [0030] b) a direct piezoelectric connection 18 comprising piezoelectric crystals that are attached to, and may be bonded to, the probe 10 to act as transmitters and receivers. [0031] c) an indirect electromagnetic connection 20 comprising a magnet or ferrous material 22 at the top section 14c , thereby allowing part or all of the probe to be excited and measured by remote coils 24 in close proximity of the probe 10 to create an inductive effect.

[0032] The probe 10 has two ends: a first, passive end with no attachments; and a second end 14 that is provided with connection means 16, 18 and 20 to electromechanically excite the probe 10 and to measure the resulting resonance frequencies.

[0033] The apparatus comprises the probe 10 and excitation means connected directly or indirectly thereto. A central processing unit 30 is provided that sends an alternating current signal to the excitation means. The amplitude, waveform and character of this signal will match the appropriate requirements of the specific transducer used in the excitation means. This signal is synthesized digitally by the central processing unit 30 and passed through a digital to analogue converter 32.

[0034] The resultant output signal from the probe 10 is be amplified, filtered and conditioned by a filter-amplified 34 and then analysed by the central processing unit 30. The central processing unit 30 obtains information from a look-up table to compare measured and calibration data 36 to generate a quantitative value or graphical display, which is provided by an output 38 for interpretation by the operator.

[0035] During implant site preparation a number of drill bits of increasing diameter and/or length are typically used. This serves a number of purposes, including changing the potential alignment during preparation, reducing heat generation by cutting in small stages and shaping the drill hole for the implant size and shape. As such, it is very common to use a small, typically a 2 mm diameter drill, to prepare a pilot hole in the bone, however, the drill could range from 1 mm to 10 mm depending upon the requirements. Once the hole has been created, a probe can be inserted at least partially into the hole.

[0036] The characteristics of the probe, for example its shape and length, will depend upon the requirements. Therefore, whilst the cross section of the probe is, preferentially, circular, it may be oval, square or irregular, and it may have geometrical features. The diameter of the probe may vary in the range of 1 mm to 10 mm, although around 2 mm is the preferred diameter.

[0037] It is important that the probe is designed to have a constant stiffness between it and the bone it is measuring in order to achieve a reliable measurement. This is addressed by matching the diameter and profile of the pilot drill with that of the probe in order to enables the interfacial stiffness to be eliminated in any measurement of bone quality.

[0038] The probe can be readily calibrated by test holes in samples of homogeneous, isotropic materials that simulate bones' mechanical properties. This data enables the probe to be calibrated to give a value of bone quality and quantity as a function of resonance frequency. This technique can also be applied to damping measurements from the probe.

[0039] The probe may comprise metal, typically aluminium or titanium, and/or other materials. Ideally, the probe comprises material(s) that are intended to resist corrosion in the surgical environment and during sterilization.

[0040] A wide range of alignments and orientations exist for the transducers attached to the probe and these may be used to gather further data related to orientation.

[0041] It will be appreciated that an excited cantilever beam may exhibit a number of resonance frequencies related to its modes of vibration. The probe may measure any or all of these modes if present.

[0042] The present invention may be employed to measure bone quality in diseases where bone density or quality may be reduced, for example in osteoporosis, osteomalacia or vitamin deficiencies. Additionally, it may be employed not just in dental situations but also in respect of orthopaedic matters where it is advantageous to know the bone quality and stiffness.