Diagnostic technique for joint implant with metal friction pair

FIELD: medicine.

SUBSTANCE: invention refers to medical equipment tests, namely to production tests of joint implants with a metal friction pair the state of which is assessed in the course of testing with using electric (electrically resistive) diagnostic techniques. The diagnostic technique for joint implants with the metal friction pair consisting in the fact that the implant is mounted in a test bench loaded with axial force; a lubricant layer is formed between surfaces of the implant components, and the physical characteristics of the surface layer of the components in the friction zone are measured. Small AC current is passed through the friction zone of the implant; a temporary function of complex impedance of the implant tribocoupling is recorded; it uses its active and reactive component parameters to show an actual thickness of the lubricant layer and a lubricant type prevailing in the tribocoupling and a friction regimen. The actual technical condition of the joint implant tribocoupling is assessed by a ratio of the time intervals when the active part of the complex impedance is more than the reactive part to the total measurement time.

EFFECT: invention provides shortening the test time, assessing the real time of the contact of the friction surfaces, increasing the produced valid signal power and noise stability, in obtaining the objective initial diagnostic information from the friction zone in order to predict a durability of the joint implant with the metal friction pair.

5 dwg

 

The invention relates to the field of testing of medical equipment, namely to production testing issue joint endoprosthesis with a metal bearing couple, a condition in which the test process is evaluated by applying electric (electroresistive) methods of diagnosis.

From the existing prior art discloses the method of diagnosis of hip arthroplasty with a metal bearing couple. Method for the diagnosis of hip arthroplasty with a metal bearing couple is that the endoprosthesis is fixed in the test bench, load axial force, form a lubricating layer between the surfaces of the components of the endoprosthesis and determine the physical characteristics of the surface layer of components in the friction zone. Axial force is applied perpendicular to the surface of the prosthesis is passed through the friction zone of the endoprosthesis small value stable electric current, caused by a current register and is proportional to the electrical resistance to a voltage drop in the friction zone in the form of the time function, the parameters fluctuations which estimate the actual friction in the endoprosthesis. Against time the integrity of the lubricating layer is determined by the time function of the resistance to General lie�neither the measurements assess the actual technical state of the elements of triborate parts of the prosthesis in the process of testing (see RF patent №2435551, IPC A61F 2/32, publ. 2011).

The disadvantage of this method is that the measurement of DC does not provide the necessary sensitivity and speed of measurement, as the processes occurring at the micro level in the friction zone, have a very low duration. Thus, the accuracy of diagnosing the above method is limited.

The problem to be solved by the invention is to improve the quality of diagnosis by obtaining a greater quantity and quality of information from the zone of friction triborate of the prosthesis joint.

This is achieved in that in the method of diagnosing joint endoprosthesis with a metal friction pair, which consists in that the endoprosthesis of the hip or shoulder joint is fixed to the test bench, load axial force, form a lubricating layer between the surfaces of components of the implant and determine the physical characteristics of the surface layer of components of the implant joint, unlike the prototype is passed through the friction zone of the endoprosthesis small value alternating electric current, caused by a current register and is proportional to the total electric with�rotellini the voltage drop in the friction zone in the form of the time function, in the parameters fluctuations which assess the actual technical condition of triborate of the prosthesis joint.

The technical result obtained by the implementation of the described invention, is to reduce the test time, the assessment of the real-time contact interaction of surfaces of friction, to increase the capacity allocated to the desired signal, its noise immunity and in the formation of an objective source of diagnostic information from the zone of friction to predict the longevity of the prosthesis joint with metal bearing couple.

The invention is illustrated by drawings. Fig.1 is a diagram of the contacting surfaces of the prosthesis when the liquid friction. Fig.2 is a schematic diagram of the contacting surfaces of the prosthesis under mixed friction. Fig.3 is a diagram of the contacting surfaces of the prosthesis, with the boundary friction mode. Fig.4 is illustrated the essence of the diagnostic parameter. Fig.5 shows a diagram of a device for carrying out the method.

The method is as follows. The joint endoprosthesis, consisting of a metal glenoid bowl 3 legs and 1 with femoral head 2, installed in a test stand, which is a container 6 made of non-conductive mate�IALA and filled with a dielectric liquid 4, separating the contacting surface of the prosthesis joint. Under a load when testing lubricating fluid is extruded from the zone of friction, changes its thickness and there is a change of mode of friction from liquid to mixed and boundary. The resistance of the contact area is defined by the expression (1)

where Z(t) - total impedance, Ohms;

R(t) is the resistance in Ohms;

X(t) is the reactance in Ohms.

Full impedance when liquid (2) and the semi-liquid lubricant (3) is described by the following expression

where R - resistance lubricant layer, Ohm;

SSM - capacity lubricating layer, Φ;

ω - cyclic frequency of the applied voltage, Hz;

R1 is the resistance of the contact metal to metal, Ohm;

R2 - resistance of the lubricating boundary layer at the friction.

In this case,

where S is the surface area, m2;

d - the distance between the surfaces, m;

ρ is the specific conductivity, Ohm·m;

ε0- electric constant, Φ/y;

εr- the relative permittivity of the medium between the plates.

Analyzing the numerator of the reactive part of the expression (2) we get that

Substituting known values (ε0=8,85·10-12Φ/m; for silicone oils εr=2,2%, ρ=1013Ohm·m) and comparing the active and reactive parts of the impedance, we get

The expression (7) is valid for frequencies whereω>1194,7Hz. Thus, research on frequencies of 103-105Hz the reactance value will be much greater than the value of active resistance.

When the liquid friction of fluctuations in the temporal function of the electrical impedance Z(t) is negligible. During the transition to the semi-liquid friction point contacts occur parts in the friction zone. This leads to a sharp decrease of the reactance of the impedance X(t) and additional fluctuations of the function Z(t). If the condition of the contacting surfaces in the friction zone of the endoprosthesis of inferior quality, the contact surfaces occurs more frequently and the point contacts longer. Such processes occur in the mode of boundary friction when a lubricant is almost forced out of the friction zone and the function of the electrical complex impedance is determined mainly active SOP�the resistance R(t). To the fluctuations of the function Z(t) will also lead to local inhomogeneities of the surface friction (abrasion and hooks, the results of the adhesion interactions of the contacting surfaces, contamination of the lubricant (synovial fluid) and the rheological properties of the lubricant. The articular Cup of the prosthesis 3 is fixed in the holder 5, which is rotated by the actuator 7, simulating the rotational movement of the joint.

Loading is carried out adjustable axial force (the value of which varies depending on the type and size of prosthesis) applied perpendicular to the surface of the base. To create such a load is used as the loading device 13, which allows in manual mode to set the current value of the axial force, the current collector 12 is connected to the leg prosthesis 1, remove a signal is transmitted to the divider 10.

The time function of the voltage divider 10 is proportional to the electrical resistance of the friction zone and reflects the actual process of microconductivity in the friction zone of the endoprosthesis. The voltage divider supplied from the generator 11 and the divider is fed to a digital oscilloscope 8 which in turn is connected to the computer 9. The parameters of the fluctuation of the measured function of resistance Z(t) will characterize the real macro - and microgeometry its�STV contacting surfaces and friction regime as a whole. As a diagnostic parameter is proposed to use the normalized integral time electrical contacting, K, units.

where Tand- time of measurement, C;

nT- the number of segments in tribounit of the prosthesis, corresponding to R(t)-X(t)≥0 at time Tand, ed;

tn(K)i- the start time (the end of) the i-th segment corresponding to the condition R(t)-X(t)≥0, s

Varying from 0 when the liquid lubricant to 1 under boundary lubrication, the parameter K is a statistical estimate of the likelihood of microconductivity in tribounit of the prosthesis joint. Thus, the parameters of active and reactive components of the resistance are judged on the actual thickness of the lubrication layer and dominant in the tribounit the form of lubrication and friction, with respect to the time intervals, in which the active part of the complex impedance of more reactive to total measurement time estimate of the actual technical state of triborate of the prosthesis joint. The difference between the active and reactive components of the contact resistance is determined by the parameter of the normalized integral time electrical contacting K.

According to the obtained value To the conclusion about the mode of friction in the endoprosthesis, the state macro - and microgeometry of contacting de�Aley, about the likelihood of future use of the prosthesis or its rejection. The reference values for implants are determined on the basis of statistical processing of the results of endurance tests for implants of various sizes.

Thus, the technical result obtained by the implementation of the described invention, is to reduce the test time, the assessment of the real-time contact interaction of surfaces of friction, to increase the capacity allocated to the desired signal, its noise immunity and in the formation of an objective source of diagnostic information from the zone of friction to predict the longevity of the prosthesis joint with metal bearing couple.

Method of diagnosing joint endoprosthesis with a metal friction pair, which consists in that the endoprosthesis is fixed in the test bench, load axial force, form a lubricating layer between the surfaces of the components of the endoprosthesis and determine the physical characteristics of the surface layer of components in the friction zone, characterized in that, through the friction zone of the endoprosthesis small value alternating electric current, record the time function of the complex impedance of triborate of the endoprosthesis, the parameters of active and reactive components koto�Oh is judged on the actual thickness of the lubrication layer and dominant in the tribounit the form of lubrication and friction, in this respect the time intervals, in which the active part of the complex impedance of more reactive to total measurement time estimate of the actual technical state of triborate of the prosthesis joint.



 

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