CN112656552B - Wireless portable force line track measurement system in unicondylar knee joint replacement operation - Google Patents
Wireless portable force line track measurement system in unicondylar knee joint replacement operation Download PDFInfo
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- 238000005259 measurement Methods 0.000 title claims abstract description 24
- 210000000629 knee joint Anatomy 0.000 title claims abstract description 14
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- 238000004364 calculation method Methods 0.000 claims description 16
- 238000013150 knee replacement Methods 0.000 claims description 16
- 230000015654 memory Effects 0.000 claims description 15
- 238000005070 sampling Methods 0.000 claims description 14
- 230000006835 compression Effects 0.000 claims description 12
- 238000007906 compression Methods 0.000 claims description 12
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- 125000006850 spacer group Chemical group 0.000 claims description 8
- 238000003860 storage Methods 0.000 claims description 5
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- 230000009466 transformation Effects 0.000 claims description 3
- 238000011065 in-situ storage Methods 0.000 claims 1
- 239000011257 shell material Substances 0.000 description 11
- 238000001356 surgical procedure Methods 0.000 description 11
- 238000010586 diagram Methods 0.000 description 9
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- 125000004122 cyclic group Chemical group 0.000 description 2
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- 210000005067 joint tissue Anatomy 0.000 description 2
- 210000003127 knee Anatomy 0.000 description 2
- 238000002324 minimally invasive surgery Methods 0.000 description 2
- 230000001575 pathological effect Effects 0.000 description 2
- 210000002303 tibia Anatomy 0.000 description 2
- 210000001519 tissue Anatomy 0.000 description 2
- 210000000689 upper leg Anatomy 0.000 description 2
- 208000004550 Postoperative Pain Diseases 0.000 description 1
- 206010053476 Traumatic haemorrhage Diseases 0.000 description 1
- 206010003246 arthritis Diseases 0.000 description 1
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- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2/38—Joints for elbows or knees
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2/46—Special tools or methods for implanting or extracting artificial joints, accessories, bone grafts or substitutes, or particular adaptations therefor
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- Health & Medical Sciences (AREA)
- Orthopedic Medicine & Surgery (AREA)
- Transplantation (AREA)
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- Force Measurement Appropriate To Specific Purposes (AREA)
Abstract
The invention relates to a wireless portable force line track measuring system in a unicondylar knee joint replacement operation, which mainly comprises two parts, wherein one part is a data acquisition, processing and wireless transmitting module, and the other part is a data receiving and real-time displaying module. And the data acquisition, processing and wireless transmission module. It mainly comprises: the system comprises a customized pressure sensor array, an analog-digital converter, a multipath analog switch, an algorithm hardware implementation circuit and a system-in-package chip based on a special control logic and interface chip and a radio frequency transmitting chip. The force line trajectory measurement algorithm comprises a pressure maximum point coordinate determination algorithm based on least squares fitting and trajectory fitting. The invention can measure the line of force track generated on the outer shell of the prosthesis by the distal end of the femoral prosthesis in the unicondylar knee joint replacement operation in real time, thereby judging whether the prosthesis is suitable in position.
Description
Technical Field
The invention belongs to the technical field of medical electronics and electronic system integration, and particularly relates to a wireless portable force line track measurement system in unicondylar knee joint replacement.
Background
The knee joint is subjected to pressure for a long time, so that the knee joint is easy to wear and hurt, and osteoarthritis can be seriously developed. It is expected that the number of patients with gonarthritis will increase exponentially over the next few decades. The most common knee joint surgical treatments include total knee replacement surgery (total knee arthroplasty, TKA), high tibial osteotomy (high tibial osteotomy, HTO), and unicondylar knee replacement surgery (unicondylar knee arthroplasty, UKA). It was counted that by 2035, knee replacement surgery may be performed more than 300 tens of thousands of times per year worldwide. The unicondylar knee replacement surgery is a minimally invasive surgery compared to total knee replacement surgery, so that the surgery can be generally performed with less invasiveness due to more protection in terms of bones and tissues, so as to reduce intraoperative traumatic bleeding and postoperative pain and accelerate the clinical recovery rate. The improvement of the unicondylar knee prosthesis and the improvement of the surgical auxiliary tool lead the success rate of the unicondylar knee replacement operation to be improved.
The traditional implanted prosthesis position detection method is finite element analysis, but because the finite element analysis of the bone joint needs to scan all joint tissues and prosthesis models, and the unicondylar knee joint replacement operation is a minimally invasive operation, finite element pressure scanning modeling can not be carried out on all the prostheses and the joint tissues in the operation, so the model accuracy is not high. And the finite element analysis has large data volume and high computational complexity, so that the finite element analysis is impractical to be used for real-time measurement in the unicondylar knee replacement operation.
Unlike conventional finite element analysis methods that build pressure models based on shape and materials, in unicondylar knee replacement surgery, the force line trajectory on the upper surface of the prosthetic spacer shell is also a key indicator for determining the position of the prosthesis, so that measuring the force line trajectory in real time with a sensor-based measuring device is an effective method. To date, there are mainly two types of sensor-based measuring devices that can be used to measure the force line trajectories in unicondylar knee replacement surgery. One is a robotic-assisted measurement device that helps the bone surgeon program the hands and improves the accuracy of implant positioning. However, doctors using robotic surgical auxiliary measurement systems need to receive specialized training, and are more complex and expensive to use. In addition, due to its large size, it is inconvenient to use during surgery. Another is a portable wireless force line track measurement system, and the closest prior art CN 109758274a to the present invention discloses a method and a system for measuring the force line track of the distal femur relative to the prosthetic pad in the unicondylar knee joint replacement, wherein the hardware system mainly comprises an array pressure sensor, a data transmission and interface circuit, a radio frequency transceiver and a PC. The track measurement algorithm mainly uses two least square fitting, wherein the first least square fitting is used for obtaining pressure distribution data and coordinates of pressure maximum points, in the scheme, the pressure maximum points are considered to be contact points, and the second least square fitting is performed to obtain a final force line track. The method can acquire the motion track of the femoral prosthesis relative to the prosthesis pad in real time, and compare the acquired track with the standard track, and mount the femoral prosthesis, the prosthesis pad and the tibial prosthesis by taking the acquired track as a reference to determine the mounting position and the angle. However, the disadvantage is that the system has low integration, high power consumption, and high speed and accuracy.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a wireless portable force line track measurement system in a unicondylar knee joint replacement operation, which can collect pressure distribution data of a distal end of a femoral prosthesis relative to a prosthesis pad in an operation process of a patient, process the data into force line track data on hardware, send the force line track data to a data recorder in a wireless transmission mode after coding and packaging, and finally transmit the force line track data to a personal computer end for storage and real-time display so as to help a doctor judge whether the position of the prosthesis is proper in the operation process. The invention can greatly improve the system integration level, reduce the system volume, reduce the system power consumption and reduce the board-level circuit interference by designing the special control logic and interface chip and carrying out system-level packaging with the radio frequency transmitting chip.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
The utility model provides a wireless portable unicondylar knee joint replacement intra-operative power line track measurement system, includes data acquisition processing and wireless transmission module and digital receiving and display module, its characterized in that:
the data acquisition processing and wireless transmitting module comprises:
the pressure sensor array is arranged in the prosthesis pad, and is used for measuring the pressure distribution of the concave surface of the prosthesis pad in real time and outputting a resistance value;
The multi-path analog switch scans and polls each pressure sensor at a set frequency, and when a certain array point is selected, the resistance value of the array point is converted into an analog voltage value in a resistance voltage division mode;
an analog-to-digital converter that converts the measured analog voltage value into a digital voltage value;
The algorithm hardware implementation circuit is used for converting pressure distribution data into force line track data by a hardware least square fitting algorithm;
The system-level packaging chip is used for configuring a system working mode, controlling the whole working flow of the system and wirelessly transmitting the power line track data;
the digital receiving and displaying module receives and displays the force line track data in a wireless mode.
The least square fitting algorithm comprises the following steps:
firstly, simplifying an upper surface model of a prosthesis gasket into a part of a spherical surface, and after pressure distribution data are obtained, taking the pressure as a function of coordinates, and performing fitting according to the following formula:
F＝ax2+by2+cz2+dx+ey+m
f represents a pressure value, x, y and z represent spherical three-dimensional coordinates, coefficients a, b, c, d, e and m of a polynomial are obtained by scanning to obtain a point value of a pressure sensor array, the polynomial is fitted in the coordinate range of x, y and z to obtain pressure distribution, and the pressure maximum is obtained by a method of obtaining an extreme value;
Using the maximum pressure point as a contact point, fitting the contact point to a trajectory, wherein coordinate translation and compression transformation are used to reduce the degree of morbidity of the coefficient matrix when solving the function extremum:
Wherein the method comprises the steps of Representing the coordinates of the sampling points after translation, x i representing the coordinates of the sampling points before translation, i=0, 1 … n, n representing the number of sampling points, the compression formula of the coordinates of the sampling points is as follows:
Wherein the method comprises the steps of Represents the coordinates after compression, p represents the compression coefficient, and r represents the number of fits.
The algorithm realized by the algorithm hardware realization circuit comprises a pressure maximum point positioning algorithm and a track fitting algorithm, wherein the core algorithms of the two parts are least square fitting algorithms, and in the least square fitting algorithm, the core is
Ax＝y
Wherein A is a coefficient matrix with dimension of N multiplied by N, x is a vector to be solved, y is a known constant vector, the coefficient matrix A is decomposed into two matrices by using an LU matrix decomposition method, wherein one is an upper triangular matrix U, all elements below a diagonal line in the upper triangular matrix U are equal to 0, the other is a lower triangular matrix L, and all elements above the diagonal line in the lower triangular matrix L are equal to 0, and then the upper formula is converted into:
LUx＝y
continuing to convert into:
Lk＝y
finally, the method is converted into the following steps:
Ux＝k
k is an intermediate solution result matrix.
The algorithm hardware implementation circuit comprises an LU matrix decomposition module and a solving module, wherein the solving module is used for final result calculation, the LU matrix decomposition module is used for coefficient matrix decomposition calculation, and the LU matrix decomposition module mainly comprises the following parts:
The two Dynamic Random Access Memories (DRAMs) are off-chip structures and are used for storing the pressure distribution data sent by the analog-to-digital converter, and the pressure distribution data cannot be directly stored on-chip due to the large quantity of the pressure distribution data. The method is realized by DDR2 on an FPGA development board and works in a ping-pong mode, namely, the output data in one DRAM becomes the input data of the other DRAM, so that the data throughput of the system is improved;
The data acquisition control module is used for controlling data transmission between the DRAM and the computing array, and the algorithm hardware is used for realizing that the working clock of a circuit part is far larger than the clock of the analog-to-digital converter, so that intermediate data needs to be buffered, the data acquisition control module comprises a state machine and 3 asynchronous FIFO memories FIFO_ W, FIFO _R and FIFO_M with different functions, the asynchronous FIFO memories are respectively used for buffering data written into the computing array, buffering data read out of the computing array and temporarily storing intermediate computing result data, a coefficient matrix is decomposed into a plurality of sub-matrices which can be stored and operated on a chip, and according to the space sequence of the sub-matrices in the coefficient matrix, namely the space sequence from top to bottom and the space sequence from left to right, the state machine controls a circulation structure to traverse all the sub-matrices in an iteration space;
The two memory control modules respectively control the two DRAMs to buffer data which need to be buffered due to different processing speeds and process data streams with different bit widths; the DRAM, the analog-to-digital converter and the algorithm hardware realize circuit have different working speeds and different data bit widths, so that the two memory control modules are needed;
The computing array module comprises 64 processing units working in parallel and three buffers used for buffering data used for storage, data used for computation and data used for transmission respectively, wherein the three buffers work in parallel, and data can be computed while intermediate computing results are stored and transmitted, so that the matrix decomposition rate is improved, among the 64 processing units, only one divider is used by the processing unit PE_0 due to the fact that a great amount of hardware resources are needed by the divider in hardware implementation and the speed is slower, and the rest processing units perform reciprocal operation by utilizing the computing results of the PE_0;
and the LU control module is used for controlling the overall workflow of the calculation array module, and comprises data interaction of three internal buffers and calculation processes of 64 processing units.
The input data of the processing unit pe_0 is a 16-bit floating point number, so that the data width of the off-chip memory, i.e. the two DRAMs, is 16 x 64 bits in order for all the processing units to operate in parallel.
The number of the processing units in the solving module is the same as that of the processing units in the LU matrix decomposing module, the input data of each processing unit in the solving module corresponds to the output data of each processing unit in the LU matrix decomposing module one by one, the data from the LU matrix decomposing module is used as the input data of the solving module, and the calculated force line track data is sent to the radio frequency transmitting chip based on the SPI interface.
The system-level packaging chip consists of two special integrated circuit chips, one is a control logic chip and an interface chip, the control logic chip is manufactured by adopting a TSMC 65nm CMOS technology process, the area of a tube core is 1.351mm multiplied by 1.351mm, the working flow of the system is controlled, the working mode of the system is configured, the radio frequency transmitting chip and the analog-digital converter are configured through an SPI protocol, pressure distribution data are read from the analog-digital converter through a serial interface, the data are transmitted to the radio frequency transmitting chip based on a custom data transmission protocol, in an idle stage, namely, no data acquisition and transmission are needed, the chip consumes about 0.031mA current under a 1.1V power supply, and consumes 0.076mA current under the working mode, and besides a system working flow control circuit and an interface circuit, a linear feedback shift register circuit is arranged in the chip and used for generating random data and cyclic redundancy check, so that the anti-interference capability of the transmitted data is improved, and the 8b/10b coding circuit is increased to ensure stable direct current balance due to excessive transmission pressure distribution data and uneven data distribution, and the tolerance to errors is improved and the channel bandwidth utilization rate is maximized; the other is a radio frequency transmitting chip, which mainly comprises a digital baseband circuit, a transmitter circuit, a power management circuit and a crystal oscillator.
The system-in-package chip packages two special integrated circuit chips together in a square flat pin-free package mode, the area of the packaged chips is 8.4mm multiplied by 8.4mm, 88 pins are provided in total, in the packaging process, in order to reduce signal interference, the intersection of signal wires is reduced as much as possible in the design of the chip pin arrangement direction, the distance between key signal pins and external pins is as short as possible, so that interference noise is reduced, the transmission quality of radio frequency signals is ensured, and the radio frequency output pins of the packaged chips are as close to four corners of the chips as much as possible.
The pressure sensor array senses different pressures at different positions on the upper surface of the outer shell of the prosthesis pad, the pressure sensor comprises a flexible pad, a pressure sensing layer, an isolation layer, a circuit layer and a gum layer from top to bottom, the pressure sensor is adhered in the prosthesis pad through the gum layer, and a lead contact surface of the array pressure sensor is connected with the multi-channel analog switch for the multi-channel analog switch to scan and poll an array point.
The system workflow comprises an idle mode and a transmitting mode, and the radio frequency transmitter can be started only when the wireless transmitting power line track data is needed, so that the power consumption is reduced.
Compared with the prior art, the invention has the beneficial effects that: the force line fitting speed is higher, the force line track fitting precision is higher, the system power consumption is lower, the system integration level is higher, and the size is smaller.
Drawings
FIG. 1 is a schematic illustration of the force line trajectory of the present invention.
FIG. 2 is an overall framework of a system to which the present invention is applied.
FIG. 3 is a flow chart of the system of the present invention.
FIG. 4 is a schematic diagram of a custom pressure sensor array for use in the present invention, wherein (a) is a front view, (b) is a side view, and (c) is an equivalent circuit diagram.
Fig. 5 is a microscopic view of the dedicated control logic and interface chip of the present invention.
Fig. 6 is a schematic diagram of a system-in-package chip according to the present invention.
Fig. 7 is a distribution diagram of a simplified prosthetic spacer model and array points of the present invention.
FIG. 8 is a graph showing the relative pressure profile of the upper surface of a prosthetic spacer according to the present invention.
FIG. 9 is a graph of the pressure maximum point versus force line trace of the present invention.
Fig. 10 is a schematic diagram of an LU matrix decomposition circuit according to the present invention.
FIG. 11 is a schematic diagram of a solution module circuit according to the present invention.
FIG. 12 is a diagram of a system test platform according to the present invention.
Fig. 13 is a schematic view of the appearance and structure of the actual product of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples.
As shown in fig. 1, the good force line trajectory is smooth and centered on the prosthetic pad, e.g., in the safe area shown, based on the surgeon's experience. Poor force lines have significant bending and vibration or deflection to the prosthetic pad edges due to improper materials or improper prosthetic placement. The safe zone of the trajectory covers the middle zone, which is about 10mm in height and is about 5mm from the upper and lower boundaries of the prosthetic pad, respectively.
As shown in fig. 2, the system comprises two parts: the first part is a data acquisition processing and wireless transmitting module, which mainly comprises a sensor array, an analog-to-digital converter, a multiplexing switch, an algorithm hardware realizing circuit, a system-in-package chip, an amplifier and the like. The pressure sensor array is arranged in the prosthesis pad, the pressure distribution of the concave surface of the prosthesis pad is measured in real time, and the resistance value is output; the multi-path analog switch scans and polls each pressure sensor at a set frequency, and when a certain array point is selected, the resistance value of the array point is converted into an analog voltage value in a resistance voltage division mode; the analog-to-digital converter converts the measured analog voltage value into a digital voltage value; the algorithm hardware realizes a circuit hardware least square fitting algorithm, and pressure distribution data are converted into force line track data; the system-in-package chip configures a system working mode, controls the whole working flow of the system and wirelessly transmits the power line track data. The second part is a digital receiving and displaying module with a radio frequency circuit, an intermediate frequency circuit and a digital baseband circuit, the digital receiving and displaying module receives and displays the force line track data in a wireless mode, and the force line track data can be sent to a personal computer through a universal serial bus interface to be displayed in real time.
The system-level packaging chip is an important component of the invention, controls the working flow of the system, configures the working mode of the system, acquires, transmits and wirelessly transmits the line-of-force track data, and consists of two special integrated circuit chips. One of the chips is a control logic and interface chip, and the other is a radio frequency transmitting chip, and the radio frequency transmitting chip mainly comprises a digital baseband circuit, a transmitter circuit, a power management circuit and a crystal oscillator. The system-in-package chip can be used for controlling the working flow of a system, configuring the working mode of the system, transmitting data and wirelessly transmitting.
As shown in fig. 3, the workflow of the system is divided into two phases: the first phase is the configuration phase. The second phase is the process and transfer data phase, and the system has two modes: an idle mode and a data transmission mode, which form a cycle. The time period of the idle mode may be externally configurable in different scenarios where the system may operate at different speeds, meaning that the duty cycle of the system may also be configurable. The duration of the transmission data pattern depends on the amount of data transmitted. Since the power consumption of the system is mainly from the radio frequency transmitter, it only works for a short time in each sampling and transmission period, and thus the system power consumption can be saved.
The pressure sensor array senses different pressures at different locations on the upper surface of the housing of the prosthetic pad, as shown in fig. 4, where diagram (a) shows a top view of the pressure sensor array customized for the system, the sensor array has twenty active sensor sensing pressure cells, which corresponds to twenty piezoresistors as shown in diagram (c). The pressure sensor comprises a flexible pad, a pressure sensing layer, an isolation layer, a circuit layer and a back adhesive layer from top to bottom, wherein the back adhesive layer is adhered in the prosthesis pad, the shell material of the prosthesis pad is soft, the external pressure can be applied to deform the prosthesis pad, the sensor array is used for increasing the deformation degree of the shell of the prosthesis pad through a soft cushion, and the internal pressure sensor array can sense different pressures at different positions of the sensor array. The sensor sensing pressure units are distributed in the sensing layer shown in the figure (b). The flexible circuit board interface of the sensor array has 22 leads connecting 20 sensing pressure cells within the sensor and two more common lines. The sensor is applied with pressure, the common line is connected with a power supply, the pressure change of the point is measured in a resistor voltage division mode, and the lead contact surface of the array type pressure sensor is connected with a plurality of analog switches for the plurality of analog switches to scan and poll the array point. The pressure measurement range for each sensor array point is 0N to 80N, within which the pressure applied by the physician during the procedure is. At a specific working temperature (namely body temperature), the measurement error including nonlinearity and offset is not more than 1N, the accuracy and linearity of the sensor also accord with the standard of a force line track measurement system, and in practical application, the sensor array is completely sealed in the prosthesis pad shell, and no direct contact exists between the sensor and human tissues. Therefore, there is no special requirement for the material of the sensor array. In the working process, the multipath analog switch polls the interface of the scanning sensor at a certain frequency, when a certain array point is selected, the resistance value of the array point is converted into a voltage value in a resistance voltage division mode, and then the voltage value is converted into a digital signal by using an analog-digital converter for subsequent processing.
The pressure sensors can select different numbers and arrangement modes according to functional requirements, distinguish the pressure distribution inside and outside the prosthesis, and can adopt a transverse arrangement mode; if desired, measuring the trajectory of the prosthesis over the tibia may be achieved by arranging more than two sensors longitudinally. The matrix sensor array can also be directly used inside, and the sensor array needs to meet two indexes 1, measurement precision 2 and measurement range.
As shown in FIG. 5, the control logic and interface chip are manufactured by adopting TSMC 65nm CMOS technology, the die area is 1.351mm multiplied by 1.351mm, the working flow of the system is controlled, the working mode of the system is configured, the radio frequency transmitting chip and the analog-to-digital converter are configured through SPI protocol, the pressure distribution data is read from the analog-to-digital converter through a serial interface, and the data is transmitted to the radio frequency transmitting chip based on a self-defined data transmission protocol. The measurement result shows that in the idle stage, namely without any data acquisition and transmission, the chip consumes about 0.031mA current under a 1.1V power supply, and in the working mode, 0.076mA current is consumed, and besides a system workflow control circuit and an interface circuit, a linear feedback shift register circuit is arranged in the chip and is used for generating random data and cyclic redundancy check, so that the anti-interference capability of transmission data is improved, and the transmission pressure distribution data is too much and the data distribution is uneven, so that an 8b/10b coding circuit is increased to ensure stable direct current balance, improve tolerance to errors and maximize the channel bandwidth utilization rate.
As shown in fig. 6, since the unicondylar knee replacement surgery is a minimally invasive surgery, the system integration is highly required. In the case of limited peripheral space, it is valuable to reduce the external components and system size of the chip. Therefore, the square flat pin-free packaging mode is used for packaging two special chips together, so that the complexity of designing a printed circuit board and the signal transmission noise can be reduced, and the system integration level can be improved. After packaging, the chip area is 8.4mm×8.4mm, and 88 pins are total. In the packaging process, in order to reduce the interference of signals, the intersection of signal lines should be reduced as much as possible in the design of the chip pin arrangement direction, and the distance between the key signal pins and the external pins should be as short as possible to reduce the interference noise. In order to ensure the transmission quality of the radio frequency signals, the radio frequency output pins of the packaged chip should be as close to the four corners of the chip as possible.
As shown in fig. 7, the prosthetic spacer model is simplified by the size of the prosthetic spacer previously scanned, considered as part of a sphere. The prosthetic spacer is evenly distributed with 20 sensor array points and is subjected to pressure when a doctor swings the femoral prosthesis of a patient, thereby generating deformation. Because the deformation degree of the upper surface of the prosthesis gasket shell at different positions is different, the pressure sensor array points at different positions in the prosthesis gasket shell can also receive different forces. The point of greatest deformation, i.e. the point of greatest pressure, will be considered the point of contact.
As shown in fig. 8, a first least squares fit may yield a pressure versus coordinate relationship, resulting in a pressure profile. The solving process is thatIn the minimum, F (x i,yi,zi) is a function value, S (x i,yi,zi) is an observation value, and the function relation between the pressure and the coordinates at a certain moment can be obtained by solving the function relation of F= -0.0001231x 2+0.0001388y2+0.06639z2 -0.02874 x+0.00185y+0.36z+4.432. From the above equation, the pressure profile of FIG. 8 can be obtained, with different color depths representing different pressures.
As shown in fig. 9, the contact points are then fitted to a trajectory using the maximum pressure point as the contact point. In order to obtain accurate and high value trajectories, the present invention uses an improved least squares fit. The least squares fitting algorithm steps are as follows: firstly, simplifying an upper surface model of a prosthesis gasket into a part of a spherical surface, and after pressure distribution data are obtained, taking the pressure as a function of coordinates, and performing fitting according to the following formula:
F＝ax2+by2+cz2+dx+ey+m
f represents a pressure value, x, y and z represent spherical three-dimensional coordinates, coefficients a, b, c, d, e and m of a polynomial are obtained by scanning to obtain the point value of the pressure sensor array, the polynomial is fitted in the x, y and z coordinate range to obtain pressure distribution, and the pressure maximum is obtained by a method of obtaining an extreme value.
And when the extremum of the solving function is solved, the coefficient matrix has high probability of being a pathological matrix, namely, very small disturbance can bring very large interference to the solving result, and the practicability of the solving result is reduced. Factors affecting the pathological degree of the coefficient matrix are the distance between the sampling point and the origin, and the order of magnitude difference of coordinates between the sampling points. Coordinate translation and compression transformation are applied to reduce the ill-condition degree of the coefficient matrix.
Wherein the method comprises the steps ofRepresenting the coordinates of the sampling points after the translation, x i (i=0, 1 … n) represents the coordinates of the sampling points before the translation, and n represents the number of sampling points. The sample point coordinate compression formula is as follows:
Wherein the method comprises the steps of Represents the coordinates after compression, p represents the compression coefficient, and r represents the number of fits.
The algorithm can be used for obtaining a real-time maximum pressure point and a real-time track map. Basically meets the requirements of the unicondylar joint replacement operation.
According to the foregoing, the overall algorithm of the present invention is divided into two parts, namely, a pressure maximum point positioning algorithm and a trajectory fitting algorithm, and the core algorithms of the two parts are both least squares fitting algorithms, in which the core is ax=y. This is a linear solution problem, where A is a coefficient matrix of dimension N, x is the vector to be solved, and y is a known constant vector. The invention has the purpose of converting pressure distribution data into force line track data by the least square fitting algorithm hardware, thereby improving the force line track fitting calculation speed, reducing wireless transmission data and reducing power consumption. The invention decomposes the coefficient matrix A by utilizing the LU matrix decomposition method, fully utilizes the characteristic that a hardware circuit can perform parallel calculation, and improves the calculation speed. The LU matrix decomposition method is integrally divided into two steps: the coefficient matrix a decomposition process and the solution vector x process, wherein most of the computation time is spent on the coefficient matrix a decomposition process. The coefficient matrix A is decomposed by dividing the coefficient matrix A into two matrices, one of which is an upper triangular matrix U, and all elements below the diagonal in the matrix U are equal to 0. The other is a lower triangular matrix L in which all elements above the diagonal are equal to 0. The above equation can thus be converted into:
LUx＝y
continuing to convert into:
Lk＝y
finally, the method is converted into the following steps:
Ux＝k
k is an intermediate solution result matrix.
On the basis, the algorithm hardware implementation circuit comprises an LU matrix decomposition module and a solving module, wherein each part comprises 64 processing units working in parallel, and the LU matrix decomposition module is used for carrying out coefficient matrix decomposition calculation (namely, dividing a coefficient matrix A into an upper triangular matrix U and a lower triangular matrix L). The solution module is used for final result calculation (i.e., lk=yux=k).
As shown in fig. 10, the LU matrix decomposition module mainly includes the following parts:
The two dynamic random access memories DRAM are realized by DDR2 on the FPGA development board and work in a ping-pong mode, namely the output data in one DRAM becomes the input data of the other DRAM, so that the data throughput can be obviously improved.
The data acquisition control module controls data transmission between the DRAM and the computing array and comprises a state machine, and the state machine controls the loop structure to traverse all the submatrices in the iteration space. Because the clock frequency of the off-chip memory is different from that of the FPGA, the data acquisition controller is provided with 3 asynchronous FIFO memories of FIFO_ W, FIFO _R and FIFO_M with different functions, and the three FIFOs are respectively used for caching data written into the computing array, caching data read out of the computing array and temporarily storing intermediate computing result data.
The two memory control modules respectively control the two DRAMs which execute ping-pong operation outside the chip and process different bit width data streams.
The computing array module comprises 64 processing units which are used for caching data used for storage, data used for calculation and buffers used for transmission respectively, the three buffers are used for parallel operation, data can be calculated while intermediate calculation results are stored and transmitted, matrix decomposition rate is improved, and among the 64 processing units, as the divider is more complex than the adder and the multiplier, more hardware resources are occupied, the operation speed is slower, only one divider is used for the processing unit PE_0, and the other processing units perform reciprocal operation by using the calculation results of the PE_0; since the input data of the processing unit pe_0 is a 16-bit floating point number, the data width of the off-chip memory, i.e., the two DRAMs, is 16×64 bits in order for all the processing units to operate in parallel.
The LU control module is used for controlling the overall workflow of the computing array module, and comprises data interaction of three internal buffers and a computing process of 64 processing units.
As shown in fig. 11, the data from the LU matrix decomposition module is used as input data to the solving module, and the number of processing units in the solving module must be the same as the number of processing units in the LU matrix decomposition module. And the input data of each processing unit in the solving module and the output data of each processing unit in the LU matrix decomposing module are calculated in a one-to-one correspondence mode, and the calculated force line track data is sent to the radio frequency transmitting chip based on the SPI interface.
As shown in fig. 12, a force line track measurement system experimental platform for the unicondylar knee joint replacement operation is constructed, and the experimental platform consists of a data acquisition processing and transmitting module, a data receiving module and a PC end for data display. In experiments, the tibial prosthesis was fixed and the angle of the femoral prosthesis relative to the tibial prosthesis was varied such that the distal end of the femoral prosthesis produced a line of force trace on the prosthetic pad shell, with the pressure sensor array placed inside the prosthetic pad shell. The pressure applied to the different positions of the prosthesis pad shell is different, and the deformation generated by the different contact points on the prosthesis pad shell is also different, so that the pressure born by the sensor array points at the different positions is also different. The device size of the data acquisition processing and transmitting part is 70mm multiplied by 35mm multiplied by 4mm, the hardware circuit realizes the force line track fitting algorithm, the speed of the system for fitting the force line track is further improved, and the radio frequency transmitter is used for packaging and transmitting the force line track data with smaller data quantity instead of the pressure distribution data, so that the system power consumption is reduced. The data receiving part is mainly a data recorder built based on the existing radio frequency transmitting chip and is mainly used for receiving wireless pressure data. The 400MHz rod antenna in the data recorder is used as a receiving antenna, receives and processes the data, transmits the force line track data to a personal computer end for storage through a USB interface, and displays the maximum pressure point and the force line track in real time.
The system comprises an idle mode and a transmitting mode, and the radio frequency transmitter can be started only when the wireless transmitting power line track data is needed, so that the power consumption is reduced.
The actual product appearance and structure of the invention refer to figure 13, which comprises a pressure test head 11, a neck 12 and a holding handle 14, wherein a display screen 13 is arranged on the holding handle 14, the sensor array is arranged on the pressure test head 11, and the data processing and wireless communication part is arranged on the holding handle 14 to perform signal conversion, noise reduction and other treatments, and meanwhile, the power supply is managed to ensure stable power supply. After the data is processed, some simple information is displayed on the display 13, meanwhile, the data is packed and sent to a receiver outside the body in a wireless communication mode, and the data is displayed on a computer running software. The shape of the compression test head 11 is identical to the shape of the prosthesis to be replaced by the patient. At the same time, a raised slice can be added at the bottom of the pressure test head 11, so as to adapt to different femur and tibia platform gaps. After the thickness is increased, the implanted prosthesis with corresponding model and identical size is matched.
Claims (7)
1. The utility model provides a wireless portable unicondylar knee joint replacement intra-operative power line track measurement system, includes data acquisition processing and wireless transmission module and digital receiving and display module, its characterized in that:
the data acquisition processing and wireless transmitting module comprises:
the pressure sensor array is arranged in the prosthesis pad, and is used for measuring the pressure distribution of the concave surface of the prosthesis pad in real time and outputting a resistance value;
The multi-path analog switch scans and polls each pressure sensor at a set frequency, and when a certain array point is selected, the resistance value of the array point is converted into an analog voltage value in a resistance voltage division mode;
an analog-to-digital converter that converts the measured analog voltage value into a digital voltage value;
The algorithm hardware implementation circuit is used for converting pressure distribution data into force line track data by a hardware least square fitting algorithm;
The system-level packaging chip is used for configuring a system working mode, controlling the whole working flow of the system and wirelessly transmitting the power line track data;
The digital receiving and displaying module receives and displays the force line track data in a wireless mode;
the algorithm realized by the algorithm hardware realization circuit comprises a pressure maximum point positioning algorithm and a track fitting algorithm, wherein the core algorithms of the two parts are least square fitting algorithms, and in the least square fitting algorithm, the core is
Ax＝y
Wherein A is a coefficient matrix with dimension of N multiplied by N, x is a vector to be solved, y is a known constant vector, the coefficient matrix A is decomposed into two matrices by using an LU matrix decomposition method, wherein one is an upper triangular matrix U, all elements below a diagonal line in the upper triangular matrix U are equal to 0, the other is a lower triangular matrix L, and all elements above the diagonal line in the lower triangular matrix L are equal to 0, and then the upper formula is converted into:
LUx＝y
continuing to convert into:
Lk＝y
finally, the method is converted into the following steps:
Ux＝k
k is an intermediate solution result matrix;
the system-level packaging chip consists of two special integrated circuit chips, one is a control logic and interface chip, the control logic and interface chip is manufactured by adopting a TSMC 65nm CMOS technology process, the area of a tube core is 1.351mm multiplied by 1.351mm, the working flow of the system is controlled, the working mode of the system is configured, the radio frequency transmitting chip and the analog-to-digital converter are configured through an SPI protocol, pressure distribution data are read from the analog-to-digital converter through a serial interface, the data are transmitted to the radio frequency transmitting chip based on a custom data transmission protocol, in an idle stage, namely, no data acquisition and transmission are needed, the chip consumes about 0.031mA current under a 1.1V power supply, and consumes 0.076mA current under the working mode, a linear feedback shift register circuit is arranged in the chip except for a system working flow control circuit and an interface circuit, and an 8b/10b coding circuit is added to ensure stable direct current balance, error tolerance is improved, and channel bandwidth utilization rate is maximized; the other is a radio frequency transmitting chip which mainly comprises a digital baseband circuit, a transmitter circuit, a power management circuit and a crystal oscillator;
The system-in-package chip packages two special integrated circuit chips together in a square flat pin-free package mode, the area of the packaged chips is 8.4mm multiplied by 8.4mm, 88 pins are provided in total, in the packaging process, in order to reduce signal interference, the intersection of signal wires is reduced as much as possible in the design of the chip pin arrangement direction, the distance between key signal pins and external pins is as short as possible, so that interference noise is reduced, the transmission quality of radio frequency signals is ensured, and the radio frequency output pins of the packaged chips are as close to four corners of the chips as much as possible.
2. The wireless portable unicondylar knee replacement intra-operative force line trajectory measurement system of claim 1, wherein the least squares fitting algorithm steps are as follows:
firstly, simplifying an upper surface model of a prosthesis gasket into a part of a spherical surface, and after pressure distribution data are obtained, taking the pressure as a function of coordinates, and performing fitting according to the following formula:
F＝ax2+by2+cz2+dx+ey+m
F represents a pressure value, x, y and z represent spherical three-dimensional coordinates, coefficients a, b, c, d, e and m of a polynomial are obtained by scanning to obtain a point value of a pressure sensor array, the polynomial is fitted in the x, y and z coordinate range to obtain pressure distribution, and the pressure maximum is obtained by a method of obtaining an extremum;
Using the maximum pressure point as a contact point, fitting the contact point to a trajectory, wherein coordinate translation and compression transformation are used to reduce the degree of morbidity of the coefficient matrix when solving the function extremum:
Wherein the method comprises the steps of Representing the coordinates of the sampling points after translation, x i representing the coordinates of the sampling points before translation, i=0, 1 … n, n representing the number of sampling points, the compression formula of the coordinates of the sampling points is as follows:
Wherein the method comprises the steps of Represents the coordinates after compression, p represents the compression coefficient, and r represents the number of fits.
3. The wireless portable unicondylar knee replacement intra-operative force line trajectory measurement system of claim 1, wherein the algorithm hardware implementation circuit comprises two parts, namely an LU matrix decomposition module and a solution module, wherein the solution module is used for final result calculation, the LU matrix decomposition module is used for coefficient matrix decomposition calculation, and the LU matrix decomposition module mainly comprises the following parts:
The two Dynamic Random Access Memories (DRAMs) are off-chip structures and are used for storing pressure distribution data sent by the analog-to-digital converter, the pressure distribution data are realized by DDR2 on an FPGA development board and work in a ping-pong mode, namely, output data in one DRAM becomes input data of the other DRAM, and the data throughput of the system is improved;
The data acquisition control module is used for controlling data transmission between the DRAM and the computing array and comprises a state machine and 3 asynchronous FIFO memories FIFO_ W, FIFO _R and FIFO_M with different functions, which are respectively used for caching data written into the computing array, caching data read out of the computing array and temporarily storing intermediate computing result data, decomposing a coefficient matrix into a plurality of sub-matrixes which can be stored and operated on a chip, and traversing all the sub-matrixes in an iteration space by a state machine control loop structure according to the space sequence of the sub-matrixes in the coefficient matrix, namely the space sequence from top to bottom and from left to right;
The two memory control modules respectively control the two DRAMs to buffer data which need to be buffered due to different processing speeds and process data streams with different bit widths;
The computing array module comprises 64 processing units working in parallel and three buffers used for buffering data used for storage, data used for calculation and data used for transmission respectively, wherein the three buffers work in parallel, and can also calculate data when intermediate calculation results are stored and transmitted, so that the matrix decomposition rate is improved, among the 64 processing units, only the processing unit PE_0 uses a divider, and the rest processing units perform reciprocal operation by using the calculation results of the PE_0;
and the LU control module is used for controlling the overall workflow of the calculation array module, and comprises data interaction of three internal buffers and calculation processes of 64 processing units.
4. The wireless portable unicondylar knee replacement intra-force line trajectory measurement system of claim 3, wherein the input data of the processing unit pe_0 is a 16-bit floating point number, so that the data width of the off-chip memory, i.e., the two DRAMs, is 16 x 64 bits for all processing units to operate in parallel.
5. The wireless portable unicondylar knee replacement in-process force line trajectory measurement system according to claim 3, wherein the number of processing units in the solving module is the same as the number of processing units in the LU matrix decomposing module, input data of each processing unit in the solving module and output data of each processing unit in the LU matrix decomposing module are calculated in one-to-one correspondence, data from the LU matrix decomposing module is used as input data of the solving module, and the calculated force line trajectory data is sent to the radio frequency transmitting chip based on the SPI interface.
6. The wireless portable unicondylar knee replacement in-situ force line trajectory measurement system of claim 1, wherein the pressure sensor array senses different pressures at different positions on the upper surface of the outer shell of the prosthetic spacer, the pressure sensor comprises a flexible pad, a pressure sensing layer, an isolation layer, a circuit layer and a gum layer from top to bottom, the pressure sensor is adhered to the prosthetic spacer through the gum layer, and a lead contact surface of the pressure sensor array is connected with a plurality of analog switches for the plurality of analog switches to scan and poll array points.
7. The wireless portable unicondylar knee replacement intra-operative force line trajectory measurement system of claim 1, wherein the system workflow includes an idle mode and a transmit mode, wherein the radio frequency transmitter is activated only when wireless transmit force line trajectory data is required, reducing power consumption.
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| CN109758274A (en) * | 2019-02-28 | 2019-05-17 | 清华大学 | Measurement method and system of the distal femur relative to prosthese gasket line of force track in single condyle knee replacements |
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