JPH11169352A - Bone strength measuring method and equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective means of measuring univasively the strength of the neck of the femur in particular. SOLUTION: The bone strength measuring method is designed to measure the strength of a bone from a resonance frequency obtained by applying impact to one end of the bone, detecting the waveform of vibration produced from the application of impact, and obtaining a resonance frequency of torsional vibration by the frequency analysis of the detected waveform of vibration. The bone strength measuring device is furnished with an impulse hammer 10 intended for applying impulsive impact to a bone, a bone vibration detector 11 incorporating a three-axis acceleration sensor, and an FFT analyzer 13 that analyzes acceleration detection signals outputted from the three-axis acceleration sensor in the bone vibration detector 11 and detects the resonance frequency of torsional vibration of the bone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the strength of a bone, such as a femur of a living body, which can be quantified and evaluated from the characteristics of torsional vibration generated when an impact is applied to the bone. And a measuring device.

[0002] Fractures of long limb bones are frequently caused by traffic accidents, occupational accidents, and sports injuries. On the other hand, the number of osteoporosis patients is increasing with the aging of the population, and it has been reported that the growth of bones in young people due to nutritional imbalance and decrease in the amount of exercise. These are easily broken by a slight external force. For this reason,
From the viewpoint of preventing fractures, it is desired to develop a measurement method that can easily determine the qualitative change in bone tissue. In the treatment of long limb long bone fractures, it is necessary to select an appropriate treatment method that ensures osteosynthesis, and to ensure early recovery of function. To this end, it is desirable that the degree of bone fusion be quantified and post-therapy corresponding to the degree of fusion be prescribed without excess or deficiency. The present invention provides an effective measuring means for that purpose.

[0003]

2. Description of the Related Art Conventionally, radiography has been the main means for diagnosing changes in the state of bone damage or osteoporosis of a living body. However, radiographic diagnosis is suitable for understanding the form of damage, but is not suitable for quantitative diagnosis of the degree of damage or the healing process.

[0004] Conventionally, there has also been a method of examining the characteristics of bone using sound or vibration. One of these methods is a diagnostic method that uses ultrasonic conduction.However, this method makes it difficult to distinguish between signals from a fracture site and signals from soft tissues such as muscles surrounding the bone, and makes it difficult to determine the state of a bone in a living body. It has been reported that it cannot be quantitatively evaluated.

As a method of diagnosing bone using vibration, studies have been made on a quantitative evaluation method based on bending vibration of bone. In this method, a forced vibration or impulse shock is applied at right angles to the longitudinal direction of the bone from the outside, and the natural condition of the bending vibration of the bone is changed to quantitatively evaluate the state of the bone, especially the recovery process of the fractured bone. It is aimed at doing. However, a major problem with this diagnostic method is that it is difficult to non-invasively detect the vibration of bone itself in a living body surrounded by soft tissue under the skin.

[0006]

In osteoporosis, the bones become thin and the bone cortex becomes thin, and the neck of the femur is easily broken by a slight load such as falling. In an aging society such as a femoral neck fracture, walking ability may be significantly reduced or bedridden compared to other fractures.
There are many points of concern. Since the neck of the femur is located in a deep part covered with thick muscles and joint capsules, no effective method for measuring its mechanical properties has been known.

An object of the present invention is to provide a means capable of noninvasively measuring the strength of the femoral neck.

[0008]

The present inventor has determined that when a vibration is applied to the femur, a specific torsional vibration is generated, and the resonance frequency of the torsional vibration correlates with the strength of the femoral neck. We also found that the resonance vibration of this torsion also appeared in the subtrochanteric soft trochanter and the lower end of the femur.
The present invention utilizes this to vibrate the lateral epicondyle distal to the femur, detects torsional resonance vibrations with a vibration sensor installed on the greater trochanter, and determines from the degree of frequency decrease the thighs. It measures the decrease in the strength of the bone at the bone neck.

FIG. 1 is a diagram illustrating the principle of the present invention. FIG.
, 1 is the femur to be measured, 2 is the head, 3 is the neck, 4 is the greater trochanter, 5 is the diaphysis, 6 is the medial condyle, 7 is the medial epicondyle,
8 is the epicondyle, 9 is the lateral epicondyle, 10 is an impulse hammer with a built-in acceleration sensor, 11 is a bone vibration detector with a built-in X, Y and Z-axis acceleration sensor, and 12 is a 4-channel high input impedance charge An amplifier, 13 is an FFT analyzer, and 14 is a processing device.

The bone vibration detector 11 is a trochanter 4 of the femur 1
Is pressed against the skin surface, and the torsional vibration and bending vibration of the bone generated by the impact when the impulse hammer 10 strikes the lateral epicondyle 9 are X,
It is detected as an acceleration waveform in three Y-axis directions.
The signals of the detected acceleration waveforms in the three axial directions are input to three channels of the four-channel charge amplifier 12, respectively. An acceleration waveform signal output from an acceleration sensor (not shown) built in the impulse hammer 10 at the time of impact is input to the remaining one channel of the charge amplifier 12.

Each acceleration waveform signal is amplified by a four-channel charge amplifier and input to the FFT analyzer 13. The FFT analyzer 13 detects the occurrence of an impact due to the operation of the impulse hammer 10 based on the acceleration waveform signal from the built-in acceleration sensor, and detects each impact from the bone vibration detector 11 installed on the greater trochanter 4 at the timing of the impact. Fast Fourier transform of the acceleration waveform signal to perform frequency analysis. The resonance frequency of the torsional vibration detected by the frequency analysis is input to the processing device 14 and the processing for obtaining the strength of the neck 3 of the femur is performed.

Next, the principle of the method for measuring the strength of the femoral neck using torsional vibration according to the present invention will be described in detail. Observation of Vibration Characteristics of Extirpated Human Wet Femur The present inventor performed a modal analysis of the extirpated human femur for the purpose of evaluating the mechanical characteristics of the femoral neck from the vibration characteristics.

FIG. 2 is a schematic diagram of the experimental system.
2, reference numeral 20 denotes a support, 21 denotes a femur to be measured suspended from the support 20, 20 denotes an impulse hammer with a built-in acceleration sensor, 23 denotes a three-axis acceleration sensor, 24 denotes a 4-channel charge amplifier, and 25 denotes a charge amplifier. Is a modal analyzer.

For the modal analysis, five human femurs extracted from a cadaver specimen for dissection training were used. The anterior, posterolateral, and posterior medial surfaces of the diaphyseal part of the femur were each divided into five equal parts to obtain 18 recording points, and 12 recording points were determined at the neck of the femur. Then, it was input to the modal analyzer 25 as a point on the three-dimensional coordinates with the origin of the outer condyle at the lower end of the femur. A three-axis acceleration sensor 23 was sequentially pasted on the 30 recording points, and the origin was vibrated by the impulse hammer 22 with a built-in acceleration sensor while moving each point, and responses were obtained for all 30 points. A signal from each acceleration sensor was sent to a modal analyzer 25 through a four-channel charge amplifier 24 to perform a waveform analysis. The vibration mode was subjected to moving image processing based on the obtained frequency response function, and observed on the display of the modal analyzer 25.

As a result of the modal analysis, it was confirmed that the femur has three vibration modes based on the shape of the amplitude and the vibration surface. Analyzing the animation of the vibration, the left-right vibration oscillating on the frontal plane (plane parallel to the body), the longitudinal vibration oscillating back and forth on the sagittal plane (plane perpendicular to the body), and the torsional vibration in order from the low frequency side It turned out to be.

FIG. 3 shows a vibration mode as a result of modal analysis on the extracted human femur. In the figure, (a) shows the positions of the recording points 1 to 30 arranged on the femur, and (b)
FIG. 4A shows a vibration mode of left-right vibration (270 Hz), FIG. 5C shows a vibration mode of front-back vibration (307.5 Hz), and FIG. 5D shows a vibration mode of torsional vibration (480 Hz). As shown in (b) and (c) of the drawing, the left-right vibration and the front-back vibration exhibit a first-order free primary bending vibration mode having two nodes in the diaphysis. The two vibration modes did not differ greatly in frequency, and both were lower than the torsional frequency in (d). In the torsional vibration, a belly of amplitude was found at the greater trochanter and the lower end of the femur. Also, the rotation directions of the greater trochanter and the lower end of the femur were opposite to each other and twisted.

Since almost no torsional vibration is observed in the modal analysis of the substantially cylindrical tibia, the torsional vibration in the femur is caused by the neck angle of the femoral neck (the diaphyseal axis in FIG. 1). Angle between the neck axis
A shape of the femoral neck having a anteversion angle (about 125 degrees) and a anteversion angle (when viewed from above, the femoral neck axis is twisted about 10 degrees forward with respect to the frontal plane) is conceivable.

G: transverse elastic modulus, L: length, ρ: density,
n: In the mode, the torsional frequency f ₀ is

[0019]

(Equation 1)

## EQU1 ## Therefore, it can be seen that the torsional frequency decreases as the transverse elastic coefficient decreases. Analysis of the relationship between torsional vibration of the femur and the strength (torsion stiffness) of the femoral neck Torsional vibration is based on the characteristic shape of the femoral neck with cervical angle and anteversion angle and the mass of both ends of the femur. It was presumed that it was caused by a big thing. Therefore, an experiment was conducted on how torsional vibration changes when the strength (torsion stiffness) of the femoral neck is reduced. Using a total of eight human femurs extracted from a cadaver specimen for dissection training, a femoral neck was gradually divided (four femoral necks and four were intertrochanteric), The relationship between the depth of the torsion and the resonance frequency of the torsion was investigated. FIG. 4 is a schematic diagram of the experimental system.

In FIG. 4, 26 is a sponge sheet for absorbing vibration, 27 is a femur placed on the sponge sheet 26, 28 is a femoral neck, 29 is a trochanter, 30 is an impulse with a built-in acceleration sensor. Hammer, 31 is a uniaxial acceleration sensor, 32 is a 2-channel charge amplifier, 33 is FF
T analyzer.

As a result of the experiment, as shown in the graph of FIG.
When the femoral neck 28 was split, the resonance frequency of both the left-right and torsional vibrations of the diaphysis decreased as the split depth increased. However, the resonance frequency of the torsional vibration showed a sharp decrease from a point in time when the depth was smaller than that of the left-right vibration. In other words, the left-right vibration does not change until the depth of the split placed in the neck is about 60%, and when it exceeds that, it starts to decrease greatly, whereas the frequency of torsion is at the time when the split depth is about 20%. From the point where the depth exceeded 50%. The frequency of the left-right vibration after the neck was completely cut off was larger than the value before cutting.
This tendency was observed in all four femurs subjected to cervical amputation experiments. On the other hand, the case where the intertrochanter 29 is broken is shown in the graph of FIG.
The pattern of reduction of both vibrations was similar to the neck fracture experiment, and the four femurs in the experiment had the same results.

As described above, the following conclusions are derived from the results of the observation of the vibration characteristics of the isolated human wet femur and the analysis of the relationship between the torsional vibration of the femur and the strength of the femoral neck. That is,
(A) In the isolated human femur, three vibration modes are excited by vibration. (B) Among them, the torsional vibration is on the higher frequency side than the other two bending vibration modes, and varies most sharply in the mechanical strength of the femoral neck. (C) The resonance frequency of the torsional vibration decreases sharply and sharply in the narrow part of the femoral neck and between the trochanter and the mechanical strength at those parts.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The results of the above-mentioned modal analysis of the extracted femur indicate that the antinodes of the amplitude of the torsional vibration are at the greater trochanter and the lower end of the femur, where the maximum amplitude is obtained. In these sites, the subcutaneous tissue is thin in the living body,
It is suitable for excitation and signal detection in vibration measurement. In addition, the torsional frequency is always on the higher frequency side than the bending frequencies of the two diaphysis, and both can be separated even in a living body.

An embodiment in which the torsional vibration of the femur in a living body is measured will be described below. The target is Shinshu University Hospital,
We receive each orthopedic surgery of Koseiren Shinmachi Hospital, Kamijo Memorial Hospital,
Healthy subjects and patients with femoral neck fractures who received informed consent for this test were used. The measurement position is
The subject was placed in a supine position on the bed, and the upper body and soles were placed on the bed or sponge, and the hip joint was bent at about 70 degrees and the knee joint at about 120 degrees. The lower extremity condyle of the femur is vibrated by an impulse hammer with a built-in acceleration sensor, and the response waveform is detected by an acceleration sensor manually installed with a preload of about 1.5 kgf applied to the greater trochanter or the lower extremity condyle of the femur. did.
These signals were sent to a two-channel FFT analyzer, and the resonance frequency was determined from the frequency response function. As a result, in a healthy person, the signal detection unit may be the greater trochanter or the lower end condyle,
The torsional vibration was detected at any part.

FIG. 7 shows the resonance vibration measurement data of a healthy femur of a 70-year-old woman. The lower condyle of the lower femur was vibrated and detected at the lower condyle. The knee and hip flexion positions were taken in the supine position, and the sole was measured with the limb placed on the bed. 21
The large peak at 0 Hz represents the resonance frequency of the torsional vibration of the femur, and the small peak at 100 Hz represents the resonance frequency of the femoral shaft.

FIG. 8 shows resonance vibration measurement data of a healthy thigh bone of a 28-year-old man. The lower condyle of the lower femur was vibrated and detected at the greater trochanter. The knee and hip flexion positions were taken in the supine position, and the sole was lifted from the bed and placed on a sponge for measurement. The peak at 380 Hz represents the resonance frequency of the torsional vibration of the femur, the peak at 180 Hz represents the resonance frequency of the femoral shaft, and the peak at 480 Hz represents its secondary mode.

FIG. 9 shows resonance vibration measurement data of a femoral neck fracture in a 67-year-old woman. The case was fixed internally with cannulated hip screws 20 days after the injury. Two months after the operation, the torsional vibration of the normal (upper) and fracture side (lower) femurs was measured. For the measurement, the lower extremity of the femur was vibrated, and a signal was detected at the lower end condyle.

From the measurement results of the torsional vibration of the femur in the living body described above, 1) the torsional vibration of the femur can be measured by reducing the restraining conditions at both ends of the femur as much as possible in the living body and taking a free limb position. It is possible. 2) When the excitation is performed at the lower end of the femur, signals can be detected at the lower condyles of the lower end of the femur and the greater trochanter at the torsional vibration detection site. This was consistent with the results of the modal analysis of the extracted femur. 3) The torsional frequency should be considered to reflect the strength of the femoral neck in the living body. This suggests that the torsional frequency increases with the progress of bone fusion in the case of neck fracture, and that the frequency of elderly women is clearly lower than that of men in their 20s. However, since the torsional frequency is affected by the shape and mass of the femur as shown in the equation (1), the torsional frequency has a high correlation with the strength of the femoral neck by adding these parameters to the torsional frequency. It is necessary to find new indicators.

Currently, the most frequently used index for predicting the risk of femoral neck fracture in clinical practice is Dual X-ray Absorpt.
femoral neck bone mineral density (bone m) by iometry (DXA) method
ineral density, BMD). Previous reports by researchers have suggested that the contribution of bone density to bone strength is about 80%. Bone strength involves, in addition to bone density, the shape of the femur, especially the thickness of the bone cortex, and the nature of the matrix that binds bone mineral

[0031]

The radiographic method conventionally regarded as the most reliable in the diagnosis of bone strength has limitations in estimating the mechanical failure of fracture, is an invasive test, and is expensive. There is a drawback that requires a special device. On the other hand, the present invention is a nondestructive mechanical test, and has an advantage that it can be measured with an inexpensive device.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of an apparatus according to the present invention.

FIG. 2 is a schematic diagram of an extracted femoral modal analysis system.

FIG. 3 is an explanatory diagram showing an analysis example of a vibration mode of an extracted femur.

FIG. 4 is a schematic diagram of a femoral malleolar cutting execution system;

FIG. 5 is a graph showing changes in torsional frequency and left / right frequency due to the splitting of the femoral malleolus.

FIG. 6 is a graph showing changes in the torsional frequency and the left-right frequency due to cutting of the intertrochanteric region of the femur.

FIG. 7 is a graph showing an example of measuring resonance vibration of a healthy femur of a 70-year-old woman.

FIG. 8 is a graph showing an example of measuring resonance vibration of a healthy femur of a 28-year-old man.

FIG. 9 is a graph showing an example of resonance vibration measurement of a 67-year-old woman who has had a femoral neck fracture.

[Explanation of symbols]

 1: femur 2: bone condyle 3: neck 4: major trochanter 5: diaphysis 6: medial condyle 7: medial epicondyle 8: lateral condyle 9: lateral epicondyle 10: impulse hammer 11: bone vibration detector 12: Charge amplifier 13: FFT analyzer 14: Processor

Claims (3)

[Claims] An impact is applied to one end of a bone, a waveform of a vibration generated as a result is detected, and a frequency of the detected vibration waveform is analyzed to determine a resonance frequency of the torsional vibration. And measuring the bone strength. 2. A shock is applied to a lower extremity condyle of a femur, and a vibration waveform generated in the femur as a result is detected by a greater trochanter or lower end condyle, and the detected vibration waveform is subjected to frequency analysis to torsional vibration. Measuring the strength of the neck of the femur from the height of the resonance frequency. 3. A bone impulse hammer for applying a bone impulse shock, a bone vibration detector incorporating a three-axis acceleration sensor, and an acceleration detection signal output from each of the three-axis acceleration sensors in the bone vibration detector are analyzed. And a FFT analyzer for detecting a resonance frequency of torsional vibration of the bone.