WO2004058066A1

WO2004058066A1 - Device for measurement of tissue hardness

Info

Publication number: WO2004058066A1
Application number: PCT/IN2003/000047
Authority: WO
Inventors: Benjamin Joseph; Kishore Mulpuri; Sujesh Paravatty; Nagaraja; Sujatha U. Kamath; Renjit A. Varghese
Original assignee: Department Of Science And Technology
Priority date: 2002-12-27
Filing date: 2003-03-07
Publication date: 2004-07-15
Also published as: AU2003216706A1

Abstract

The application uses the simple principle of application a pre-determined linear force and the corresponding displacement of the underlying tissue to measure tissue hardness of an injured limb in an non-invasive manner. The device of the present application enables the diagnosis compartment syndrome non-invasively.

Description

DEVICE FOR MEASUREMENT OF TISSUE HARDNESS Field of the invention

The present invention relates to a device for measurement of tissue hardness. More particularly, the present invention relates to a device for the non-invasive measurement of tissue hardness. In particular, the present invention relates to a device for non-invasive measurement of tissue hardness of an injured limb of humans. The present invention also relates to a method for the non-invasive measurement of tissue hardness of an injured limb. Background of the invention

In the art, the diagnosis of compartment syndrome in clinical practice is confirmed by direct and invasive measurement of the intra-compartment tissue pressure. These techniques generally comprise passing or inserting a needle through the skin into the muscle of the compartment and measuring the pressure within the compartment with a transducer.

US Patent 5,564,435 discloses a device and a method to diagnose compartment syndrome by measurement of tissue hardness in limbs. The method of this patent comprises applying the apparatus to the limb with a known force, incrementally changing the pressure in the piston and measuring displacement of the piston plunger for each force applied. The relationship of the multiple data points of pressure applied to compression measured is then determined and a quantitative hardness curve formulated. A linear regression analysis of the multiple data points is then done. The device of this disclosure essentially comprises of a low friction piston probe mounted within a platform, attached to a holding brace and a pressure syringe. However, this device suffers from several disadvantages in that a cuff is required to be applied, multiple data points need to be recorded in order to generate the quantitative hardness curve and it needs to be linked to a computer for analysis of the data points.

US Patent 4,159,640 discloses a method and an apparatus for measuring hardness of a material. The device of this patent comprises a support that is applied against the material to be tested and a feeler carried by the support for displacement through a distance proportional to hardness of the material. A control circuit is provided for recording displacement of the feeler, which is then displayed on a digital voltmeter. The pressure sensor used in this device is a Wheatstone Bridge, which is energized by a low frequency alternating current. The pressure responsive elements are membranes carrying deposits of semi-conductor material. Although the device and method of this patent uses a single predetermined force and corresponding displacement, the device suffers from the disadvantages of requiring a current source, equipment to measure the force applied and a voltmeter to display the displacement of the feeler. Objects of the invention

The main object of the invention is to provide a device for non-invasive measurement of tissue hardness enabling easy diagnosis of compartment syndrome.

Another object of the invention is to provide a method, for determination of tissue hardness that is non-invasive, simple and accurate.

Another object of the invention is to provide a device for the non-invasive measurement of tissue hardness to enable easy diagnosis of compartment syndrome wherein the use of external power sources or display units are avoided.

A further object of the invention is to provide a device for non-invasive measurement of tissue hardness in an injured limb using a single pre-determined force and corresponding displacement.

Another object of the invention is to provide a method for determining tissue hardness in an injured limb using a single pre-determined force and corresponding displacement.

It is another object of the invention to provide a method for the measurement of tissue hardness to enable easy diagnosis of compartment syndrome wherein the use of external power sources or display units are avoided and which is economical.

It is another object of the invention to provide a pressure probe to measure tenseness of osteofascial compartments of limbs as a diagnostic tool for compartment syndrome. Summary of the invention The above and other objects of the invention are achieved by means of the device of the invention which uses the simple principle of application a pre-determined linear force and the corresponding displacement of the underlying tissue to measure tissue hardness of an injured limb in an non-invasive manner. The device of the present invention enables the diagnosis compartment syndrome non-invasively. Accordingly, the present invention provides a device for the non-invasive measurement of tissue hardness, the said device comprising a housing provided with a user control grip means on one end thereof, a tissue contact probe means protruding through a base piece means out of the said housing at the opposite end to the control grip, said tissue contact probe means being connected to a pressure application means provided inside said housing and movable thereby from a rest position to a measurement position inside said housing on the application of an externally applied predetermined pressure, a measurement means provided in the housing and connected to the tissue contact means to measure the displacement thereof on application of pressure. In one embodiment of the invention, the measurement means comprises a dial gauge.

In another embodiment of the invention, the predetermined weight of the housing and the measurement means together serve as a linear force.

In another embodiment, said housing is provided with at least one, preferably two, runner means and at least one, preferably two, corresponding runner guide bar means to limit the movement of the tissue contact probe means to a predetermined distance.

In another embodiment of the invention, the measurement means comprises of a light emitting diode connected to a light dependent resistor, the resistance of the light dependent resistor being inversely proportional to the intensity of light falling thereon, the movement of tissue contact means within the housing on the application of pressure affecting the resistance of the light dependent resistor and thereby its output.

In another embodiment of the invention, the tissue contact probe means comprises a needle with a rounded tip.

In another embodiment of the invention, the grip control means is a movable grip. In another embodiment of the invention, the measurement display means is provided with an external cover connected to the housing face to avoid damage during non-use.

In a further embodiment of the invention, the cover comprises of an opaque lid or a transparent material which enables unhindered view of the measurement display means. Brief description of the accompanying drawings Figure 1 depicts a device according to the invention where the measurement and display means is dial gauge and with a cover to protect the tissue contact point and the gauge.

Figure 2 depicts another embodiment of the device according to the invention wherein the measurement and display means is an LED and LDR assembly.

Figure 3 depicts a further embodiment of the invention of Figure 1 with the protective cover removed.

Figure 4 depicts a method of use of the device of the invention in order to measure tissue hardness of the flexor compartment of the forearm of a child.

Figure 5 is a graph of the tissue hardness plotted against intra-compartmental pressure measured in the anterior compartment of an amputated cadaveric lower limb. Figure 6 is a graph of measurements of intra-compartmental pressure and hardness of the compartment evaluated using the LED - LDR based device of the invention.

Figure 7 is a graph of measurements of intra-compartmental pressure and hardness of the compartment evaluated using the LED - LDR based device of the invention with two independent observers. Figure 8 shows the frequency distribution value curve of normal tissue hardness ot flexor compartment of a forearm measured using the dial gauge based device of the invention.

Figure 9 shows the correlation between the intra-compartmental pressure and tissue hardness measured of patients with closed fractures of the limbs.

Figure 10 shows the intra-compartmental pressure and tissue hardness values of patients with closed fractures.

Figure 11 is a graph of frequency distribution of tissue hardness ratios in one set of patients wherein the ratio of hardness of injured limb was measured with hardness of the normal limb.

Figure 12 of is a graph of frequency distribution of tissue hardness ratios in a second set of patients wherein the ratio of hardness of injured limb was measured with hardness of the normal limb.

Figure 13 is a graph of frequency distribution of tissue hardness ratios in a third set of patients where ratio of hardness of injured limb was measured with hardness of normal limb. Detailed description of the invention

The present invention essentially comprises a simple hand held device for measuring tissue hardness using a single pre-determined force applied to the tissue and the corresponding displacement. Indentation testing as a method for determination of hardness of materials is well known. Methods of indentation testing have also been used in the field of medical diagnosis, for example in ophthalmology to estimate intra-ocular pressure. The present invention resides in the use of indentation testing to determine the tissue hardness, which can then be used to confirm or disprove diagnosis of compartment syndrome. Prior art methods of diagnosis of compartment syndromes comprises invasive devices which suffered from several disadvantages - they were invasive and therefore carried the risk of transmittance of communicable diseases from one patient to the other, required external power sources and display mechanisms, relied on multiple forces being applied to confirm readings, required computing mechanisms to analyse the data obtained to arrive at a definitive conclusion. The device of the invention will now be explained with reference to the drawings accompanying this specification.

It must be understood that the figures accompanying this specification are illustrative and should not be construed as limiting the scope of the invention in any manner. Referring now to both Figures 1 and 3, line drawing of the device of the invention is given. The device (1) comprises of a housing (2) and is provided with a control grip (3) on one end. A tissue contact means (4) is provided within the housing (2) and protrudes through a base piece (5) out of the housing (2) at the end thereof which is opposite to the control grip (3). The movement of the tissue contact means (4) is obtained by the application of a pressure through the control grip (3) due to the weight of the device (1) alone. As a result of the application of such external pressure which is applied due to the weight of the housing (2) and the measurement and display means (6), which is a dial gauge in the shown embodiment, the tissue contact means (4) moves from a rest position where it protrudes out of the housing (2) to a final stop position inside the housing (2) which is dependant on the reverse pressure applied on the tissue contact means (4) as a response to the applied pressure by the contact position on the tissue being tested.

The housing (2) is provided with at least one, preferably two runner(s) (7) and at least one, preferably two corresponding runner guide bar(s) (8) which enables the limiting of the movement of the tissue contact means (4) to a predetermined distance range. The displacement of the tissue contact means (4) is measured using a measuring mechanism (6) provided on the face of the device (1). In the embodiment of Figure 1, the measurement mechanism is a highly sensitive and calibrated dial gauge.

Figure 2 shows an alternate embodiment of the device of the invention wherein the measurement means comprises a light emitting diode (LED) (26) connected to a light dependent resistor (LDR) (27). The resistance of the light dependent resistor (27) is inversely proportional to the intensity of light falling thereon. As a result, the movement of the tissue contact means (24) within the housing (22) on the application of pressure (due to the presence of the predetermined weight) affects the resistance of the light dependent resistor (27) and thereby its output. This enables the device (21) of the invention to function as an optical probe. The LED (26) is placed in a casing (25) with an aperture (28) in the front to ensure that the light is produced in only one direction and along a plane perpendicular to the axis of the plunger (29). The device (21) can be covered with any opaque means to ensure that the response of the LDR (27) is not influenced with any external light sources. The tissue contact means in both the above embodiments preferably comprises of a pointed needle. The user grip control means comprises of a movable grip. The base plate provided at the bottom end of the housing serves the purpose of preventing any further retraction of the tissue contact means beyond that which can be measured by the device. This occurs because at the maximum pressure that can be applied, the base plate comes to rest on the tissue contact site and the tissue contact means is fully retracted into the housing. Additionally, the presence of the runner bars and runner guide ensure that the movement of the device is limited to a pre-determined range of displacement. The combination of the runner guide bar and runners ensure that the user is also alerted as to whether or not a pressure external to the pressure applied due to the weight is being imposed on the device.

It is quite possible that the measurement display means may suffer damage during transit or use or storage. In order to prevent or minimize the potential for damage, the measurement display mechanism can be covered wither by a opaque cover which ensures that the display mechanism is closed from view during non-use periods or a transparent cover made of a rigid material which is impermeable to normal shocks. Of the two embodiments, the latter is preferable since it also provides unhindered viewing of the device even during use. One such embodiment is shown in Figure 4. Figure 4 depicts a method of use of the device of the invention in order to measure tissue hardness of the flexor compartment of the forearm of a child. The user holds the device vertically by the sliding grip cover. The device is then placed on the limb at the site where the measurement of tissue hardness is to be obtained. The tip of the probe must be positioned such that it is at the spot where the measurement is to be taken. The weight of the device then exerts a downward pressure through the sharp tissue contact means (tip of the probe) on the limb. This base plate through which the tip protrudes in the rest position then rests on the limb surface. The user is made aware if any pressure other than the weight of the device by observing the movement of the runners provided on the housing. If the upper end of the runner guide grooves are in contact with the runner guide bars, excessive force is being applied. If on the other hand, the lower ends of the runner guide grooves are in contact with the runner guide bars, the entire weight of the probe may not be resting on the limb and the pressure being applied may be inadequate. The reading on the dial gauge is noted once the device is placed correctly in position. As can be seen, the advantage of the device of the invention is in that the readings can be read of immediately without requiring expensive and complicated computing means to analyze the data.

The dial gauge is preferably a plunger type dial gauge of 5 mm range with 0.001 LC and a sharp contact point which functions as the tissue contact point. The housing is preferably made of acrylic or other light and sturdy material such that is easy to hold while ensuring that the predominant pressure being applied is due to the weight provided on the upper end thereof. The invention will now be further described with reference to the following examples which are illustrative and should not be construed as limiting the scope of the invention in any manner. Example 1 A fresh cadaveric lower limb which was obtained due to amputation thereof for a malignant tumor was tested. The pressure inside each compartment of the leg was gradually increased by injecting a saline solution into each compartment. Intra-compartmental pressures were measured first with the help of a Stryker intra-compartmental prssure monitoring system. Corresponding readings were then taken using the device of the invention based on dial gauge. It was observed that when intra-compartmental pressure increased, a corresponding increase occurred in the tissue hardness. The measurements obtained using the device of the invention are given in Figure 5. Example 2

The experiment of example 1 was repeated with the difference that instead of a dial gauge probe, a LED-LDR based device was used. The measurement was repeated three times to test the intra-observer reproducibility. The data obtained is given in Figure 6 Example 3

The experiment of example 1 was repeated with two independent observers and the LED-LDR based device to determine inter-observer reproducibility. The data obtained is given in Figure 7.

The above three experiments confirmed that reproducible measurements of tissue hardness are obtained using the device of the invention. Example 4

The contra-lateral normal limbs of 38 subjects with fractures of the forearm bones were measured using the dial gauge based device of the invention. The frequency distribution value curve of the normal tissue hardness of the flexor compartment of a forearm measured using the dial gauge based device of the invention are given in Figure 8. It was observed that in normal limbs, tissue hardness values greater than 3.5 mm were not seen. The absolute values of tissue hardness ranged from 0.2 mm to 3.1 mm with a mean of 1.78 (SE of 0.12). . Example 3

10 (ten) dial gauge based probes were manufactured. It was ensured that all 10 probes were of the same weight. Testing was first done on normal subjects in order to verify their inter-observer and intra-observer reproducibility using the methods of examples 2 and 3. Five centers were selected across India for the testing of the probes. The Centers were Christian Medical College, Vellore, Ganga Hospital₂ Coimbatore, Institute of Orthopaedic Research and Accident Surgery, Madurai, Sion Hospital, Mumbai and M. S. Ramaiah Hospital, Bangalore. For ease of reference these five centers are referred to below as Centers 1 to 5 respectively. Measurements were taken on patients with closed or Type I open fractures of the elbow, forearm or leg in the six centers between the period from August 15, 2001 to November 30, 2001. The protocol followed was as follows:

I. hardness of the osteo-fascial compartment of the injured forearm or leg was measured at i. junction of the proximal third and middle third of the limb ii. junction of the middle third and the distal third of the limb iii. level of the fracture site;

II. hardness of the compartment of the uninjured contralateral limb was also measured at coinciding sites as above;

III. concomitant readings of the intracompartmental pressures were also taken in four of the above five centers. Three of such centers used the manometric technique of Whitesides to measure intracompartmental pressure while one center used an intra-arterial pressure transducer for invasive intracompartmental pressure monitoring.

The number of subjects studied and the data collected are given in Table 1 below:

Data in respect of intracompartmental pressures could not be pooled for analysis since the methods of measurement thereof were different in the centers.

Figure 9 shows the correlation between the intra-compartmental pressure and tissue hardness measured of patients with closed fractures of the limbs obtained in Center 4. A good correlation was noted (Pearson's correlation coefficient r = 0.86, p < 0.01). This suggests that tissue hardness measured non-invasively using the device of the invention from the exterior of the limb could also indicate status of tissue pressure within the osteo-fascial compartment.

The next set of analysis was done to determine whether the device facilitates the actual diagnosis of compartment syndrome. 3 cases from Center 4, and one each from Centers 1 and 5 were found to suffer confirmed compartment syndrome based on clinical features. Fasciotomies were done on the five patients after obtaining due consent. Findings during surgery were compatible with diagnosis of compartment syndrome in all five cases.

Figure 10 shows the intra-compartmental pressure and tissue hardness values of the 3 patients with closed fractures who were treated at Center 4. These three patients had the highest intracompartmental presures (all of which were 30 mm Hg or greater). The two highest values of tissue hardness were also seen in two of these three patients. The third patient had the fourth highest value of tissue hardness. The patient with the third highest value of tissue hardness showed intracompartmental pressure of 26 mm Hg and displayed no other sign of compartment syndrome. Example 6

The ratios of tissue hardness of the injured limb with the tissue hardness of the uninjured limb were also measured since the absolute values of tissue hardness vary from individual to individual. Values and frequency distribution thereof obtained in Centers 1 and 5 and in another Center 6 (Kasturba Medical College, Manipal) are given in Figures 11 to 13.

The data obtained from Center 6 showed that in no patient was the tissue hardness greater than 2.5 and none of the patients had features of compartment syndrome. In Center 1, the majority of patients showed tissue hardness ratios of less than 2. None of the patients with tissue hardness below 3 showed any clinical features of compartment syndrome. This conclusion was also confirmed by results from Center 5.

The conclusions that are drawn are as follows: i. if tissue hardness values exceeds 3; or if ii. tissue hardness ratio of injured to uninjured limb exceeds 3 compartment syndrome is to be expected. If both the above criteria are met, the level of likelihood of compartment syndrome is extremely high and fasciotomy should be considered. Advantages of the invention i. The device of the invention is a simple to use hand held device ii. The values obtained are accurate with satisfactory correlation with values of tissue hardness and intracompartmental pressure. iii. External power sources and complicated and expensive computing means are not required to analyse the data obtained to confirm diagnosis of compartment syndrome.

Claims

We claim

1. A device for the non-invasive measurement of tissue hardness, the said device comprising a housing provided with a user control grip means on one end thereof, a tissue contact probe means protruding through a base piece means out of the said housing at the opposite end to the control grip, said tissue contact probe means being connected to a pressure application means provided inside said housing and movable thereby from a rest position to a measurement position inside said housing on the application of an externally applied predetermined pressure, a measurement and display means provided in the housing and connected to the tissue contact means to measure the displacement thereof on application of pressure.

2. A device as claimed in claim 1 wherein the measurement and display means comprises a dial gauge

3. A device as claimed in claim 1 wherein the predetermined weight of the housing and the measurement means together serve as a linear force

4. A device as claimed in claim 1 wherein the measurement and display means comprises of a light emitting diode connected to a light dependent resistor, the resistance of the light dependent resistor being inversely proportional to the intensity of light falling thereon, the movement of the tissue contact means within the housing on the application of pressure affecting the resistance of the light dependent resistor and thereby its output

5. A device as claimed in claims 1 to 4 wherein the said housing is provided with at least one, preferably two, runner means and at least one, preferably two, corresponding runner guide bar means to limit the movement of the tissue contact probe means to a predetermined distance

6. A device as claimed in claims 1 to 4 wherein the tissue contact probe means comprises of a needle with a rounded tip

7. A device as claimed in any preceding claim wherein the user grip control means comprises of a movable grip.

8. A device as claimed in claim 4 wherein the measurement and display means is provided with an external cover connected to the face of the housing to protect it from damage during non-use

9. A device as claimed in claim 8 wherein the cover comprises of an opaque lid or a transparent material enabling unhindered view of the measurement and display means

0. A device as claimed in claim 5 wherein the housing is provided with two runners means and two corresponding runner guide bars means to limit the movement of the tissue contact probe means to a predetermined distance.