MEMS-IMU-based auxiliary navigation method for measuring attitude of needle entry point of intramedullary nail

Abstract

The invention relates to the field of inertial navigation and the technical field of medical treatment, in particular to an auxiliary navigation method for measuring the posture of an intramedullary nail entry point based on an MEMS-IMU (Micro-electromechanical System-Inertial Measurement Unit). According to the method, attitude measurement and updating are carried out on the intramedullary nail guide needle only by means of MEMS-IMU gyroscope and accelerometer sensing data which are acquired in real time, and a digital low-pass filter is adopted to suppress interference acceleration in an operation and carry out static detection on a carrier. Attitude iteration updating is carried out through the angular velocity after the zero offset error is removed, and horizontal attitude angle correction is carried out by using the gravitational acceleration component in the acceleration, so that the error drift of the attitude angle is effectively inhibited, and an attitude measurement result meeting the orthopedic surgery navigation measurement precision requirement is finally output. The device and the method have the advantages of electromagnetic interference resistance, low cost, simplicity in operation and real-time calculation, can provide stable and reliable intramedullary nail guide needle posture information support for doctors, assist the doctors in finding an ideal intramedullary nail insertion direction more accurately, and have important clinical significance.

Description

Technical Field

[0001] The invention relates to the fields of inertial navigation and medical technology, and in particular to an auxiliary navigation method for measuring the posture of an intramedullary nail insertion point based on MEMS-IMU. Background Art

[0002] Intramedullary nail fixation can maintain the axial stability of the fracture site, protect the growth environment of the bone, and reduce damage to the blood vessels and soft tissues at the fracture site. It is currently recognized as the best solution for proximal femoral fracture fixation. Anatomical studies have shown that the ideal intramedullary nail insertion point in proximal femoral intramedullary nail fixation is the apex of the greater trochanter of the femur and close to the mid-axis of the femoral neck. The ideal intramedullary nail insertion direction is 5 degrees outward along the axis of the femoral shaft. However, in actual surgery, doctors usually lack a reference direction for intramedullary nail insertion and can only insert the needle according to their own clinical experience, and then check and evaluate according to the results of imaging fluoroscopy. If the needle insertion direction is not selected properly, it is necessary to remove the needle and then reinsert it. The increase in the number of needle insertions will prolong the operation time and increase the probability of splitting at the needle insertion site or failure of fracture reduction.

[0003] Intramedullary nail insertion point assisted navigation technology allows doctors to find the ideal intramedullary nail insertion direction at one time. Considering clinical needs, this navigation technology should meet the characteristics of real-time interaction, convenient operation, low cost, reliable measurement accuracy and anti-electromagnetic interference. Currently, the most widely used orthopedic surgical navigation technology usually adopts electromagnetic navigation or optical navigation. Among them, electromagnetic navigation is easily affected by electromagnetic interference from other surgical equipment and affects measurement accuracy. Optical navigation is expensive, complicated to operate, and easily causes line of sight obstruction and changes doctors' operating habits. Both cannot achieve good clinical application in intramedullary nail insertion point assisted navigation.

[0004] MEMS-IMU has the characteristics of miniaturization, low cost and low power consumption, and is usually combined with magnetometers for navigation. Since there is usually a lot of electromagnetic interference in the operating room environment, the reliability of magnetometers is limited, and combined navigation is rarely used in the medical field. In order to avoid electromagnetic interference from surgical instruments during intramedullary nail fixation, only MEMS-IMU can be used to measure the attitude information of the intramedullary nail guide needle in real time, thereby realizing auxiliary navigation of the intramedullary nail insertion point. However, the gyroscope angular velocity measurement value inevitably contains zero bias drift and random noise. Over time, these errors will gradually accumulate at each integration, causing the attitude measurement results to deviate from the true value. Although the acceleration measurement value can be used to correct the horizontal attitude angle (i.e., pitch angle and roll angle), thereby limiting the error accumulation to a certain extent, it is impossible to effectively feedback and correct the yaw angle error because it cannot sense the change in the yaw direction. This limitation makes it difficult for the system to maintain the long-term accuracy of the yaw angle when it does not include auxiliary sensors such as magnetometers.

[0005] Based on this, there is an urgent need for an auxiliary navigation method for measuring the attitude of the intramedullary nail insertion point based on MEMS-IMU, which can update and correct the attitude angle under the premise of using only gyroscope and accelerometer sensor data, suppress the error drift of the attitude angle (especially the yaw angle), and meet the measurement accuracy requirements of the surgical scene while resisting electromagnetic interference. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide an auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU, which can realize the updating and correction of the posture angle under the premise of using only the sensing data of the gyroscope and accelerometer, effectively suppress the error drift of the posture angle (especially the yaw angle), meet the measurement accuracy requirements of the surgical scene while resisting electromagnetic interference, and provide doctors with stable and reliable posture information support.

[0007] The objective of the present invention is achieved through the following technical solution: An auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU, the method comprising the following steps:

[0008] Step S100: Fix the developing plate horizontally on the surface of the proximal femur of the affected side to take a medical fluoroscopic image;

[0009] Step S200: Record the reading α1 of the center position of the developing board, and the reading of the ideal needle insertion direction on the developing board is α2;

[0010] Step S300: Place the attitude measurement system horizontally on the developing board, align the system heading with the center scale direction of the developing board, start the attitude measurement system, and use the MEMS-IMU-based intramedullary nail insertion point attitude measurement method to measure the pitch angle θ of the center position of the developing board relative to the reference coordinate system. init , Roll Angle Yaw angle

[0011] Step S400: epidermal incision, assembling the posture measurement system and the intramedullary nail guide needle, and the system heading is consistent with the direction of the intramedullary nail guide needle;

[0012] Step S500: Using the MEMS-IMU-based intramedullary nail insertion point posture measurement method to measure the intramedullary nail guide needle at t k The pitch angle θ relative to the reference coordinate system at the moment k , Roll Angle and yaw angle Subtract θ in step S300 respectively init , Get the posture information θ of the intramedullary nail guide needle relative to the center position of the imaging plate k '、

[0013] Step S600: Adjust the intramedullary nail guide needle. When the yaw angle of the intramedullary nail guide needle relative to the center of the imaging plate is Equal to (α1-α2) degrees, pitch angle θ k When ′ is equal to 0 degrees, it is the ideal direction for intramedullary nail insertion;

[0014] Step S700: insert the intramedullary nail guide needle and confirm with fluoroscopy.

[0015] Furthermore, the developing board is a protractor device used in medical fluoroscopic images, which is composed of a high-density marker and a plastic substrate, and is used to clearly display angle scales and position references under fluoroscopic images. The reading of the developing board increases in a clockwise direction.

[0016] Furthermore, the posture measurement system is an execution body of the MEMS-IMU-based posture measurement method, including a processor, a memory, a MEMS-IMU sensor, and a display device, and is used to acquire and process sensor data in real time and output posture measurement results.

[0017] Furthermore, the method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU suppresses the interference acceleration component caused by external force in the acceleration through a digital low-pass filter, and performs static detection on the carrier; a standard Kalman filter model is constructed with angular velocity zero bias as the state quantity, and according to the result of static detection, the model is divided into dynamic and static cases, and corresponding observation equations are established respectively, and the zero bias error is estimated with the angular velocity zero bias measurement value as the observation quantity; the angular velocity is used to iteratively update the posture quaternion after removing the zero bias error estimate, and the horizontal inclination angle is corrected by the posture quaternion according to the gravity acceleration component in the acceleration, and finally the corrected posture quaternion is converted into Euler angle for real-time output.

[0018] Furthermore, the method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU has the following specific steps:

[0019] Step 1: At fixed time intervals t s The acquisition includes the gyroscope output angular velocity and the accelerometer output acceleration f b Sensor data;

[0020] Step 2: Construct the auxiliary coordinate system n′, defined by the angular velocity Unit quaternion obtained by integral recursive update Represents the spatial rotation of the carrier coordinate system b relative to the auxiliary coordinate system n′, and defines the unit correction quaternion represents the spatial rotation of the auxiliary coordinate system n′ relative to the reference coordinate system n, so t k-1The spatial rotation of the carrier coordinate system b relative to the reference coordinate system n is expressed in unit quaternion express:

[0021]

[0022] Step 3: Place t k Gyroscope angular velocity collected at all times Convert to quaternion increment Δq gyr form:

[0023]

[0024] Step 4: Increment Δq via quaternion gyr Unit quaternion To update:

[0025]

[0026] Step 5: Normalize to get unit quaternion

[0027]

[0028] Step 6: Convert the accelerometer output acceleration f b According to quaternion The described spatial rotation is transferred to the auxiliary coordinate system n′:

[0029]

[0030] Step 7: Use the cutoff frequency f d A second-order Butterworth low-pass filter with a frequency of 0.1 Hz is used for f n′ Filtering is performed to retain only the gravity acceleration component, that is, the DC component. The filter output value is recorded as

[0031] Step 8: According to t k-1 Time-corrected quaternion The described spatial rotation is transferred to the reference coordinate system n:

[0032]

[0033] Step 9: Normalize to get the unit acceleration vector

[0034]

[0035] Step 10: The specific force unit vector [0,0,1] corresponding to the gravitational acceleration sensed by the accelerometer in the reference coordinate system n is obtained from The spatial rotation to [0,0,1] corresponds to the correction quaternion The quaternion increment Δq that should be updated cor ; According to the basic concept of quaternion, the quaternion increment Δq is expressed in the form of trigonometric function cor :

[0036]

[0037] Among them, from The rotation axis u to [0,0,1] can be obtained by After normalization, we get the unit rotation axis from The rotation angle α to [0,0,1] is The angle between the z-axis component of and the z-axis of the carrier coordinate system

[0038] Step 11: Increment Δq via quaternion cor Correction Quaternion To update:

[0039]

[0040] Step 12: Normalize to get unit-corrected quaternion

[0041]

[0042] Step 13: Perform static detection on the MEMS-IMU carrier;

[0043] Step 14: Use standard Kalman filter to calculate the gyroscope angular velocity To perform real-time zero bias estimation, the model selects the gyroscope angular velocity deviation [b x b y b z ] T As the state variable x k , select the angular velocity zero bias measurement value as the observation value z k ; The system state space model is:

[0044] x k =x k-1 +w k

[0045] z k =H k x k +v k

[0046] E{w k}=E{v k}=0

[0047] E{w k w k T =Q k

[0048] E{v k v k T = R k

[0049] In static condition, directly use As the observed quantity z k , the observation matrix H = I3; in the dynamic case, the quaternion Convert to posture array Using cutoff frequency f d A second-order Butterworth low-pass filter of 0.1 Hz is used as well as Filter them separately and record the filter output as and According to the derived observation z k use Observation Matrix

[0050] The standard Kalman filter algorithm is used for prediction and update:

[0051]

[0052] Step 15: In t k+1 During the iterative update process at time , the gyroscope angular velocity should remove the zero bias estimate, which is recorded as

[0053]

[0054] Step 16: Update the unit quaternion

[0055]

[0056] Step 17: Convert the Quaternion Convert to attitude angle expression output:

[0057] θ k =sin -1 (2(q2q3+q0q1))

[0058]

[0059] Among them, θ k , Represents t kThe pitch angle, roll angle and yaw angle of the intramedullary nail guide needle relative to the reference coordinate system n at this moment.

[0060] Furthermore, in step 13: the MEMS-IMU carrier is subjected to static detection, and the specific technical scheme is as follows: using the cutoff frequency f d A 0.5 Hz second-order Butterworth low-pass filter is used to filter out the noise caused by the handheld moving surgical equipment during the operation. and f b The fast motion signal and high frequency noise in the filter are recorded as and judge and Is the absolute difference less than the threshold T? ω and f b and Is the absolute difference less than the threshold T? f ,If these two conditions are met at the same time, the sensor is considered to be in a stationary state.

[0061] The beneficial effects of the present invention are as follows: the present invention proposes an auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU, which measures and updates the posture of the intramedullary nail guide needle only by relying on the real-time collected MEMS-IMU gyroscope and accelerometer sensor data, wherein a digital low-pass filter is used to suppress the interference acceleration during surgery and to perform static detection on the carrier, and a Kalman filter is used to estimate the angular velocity zero bias in real time. The posture is iteratively updated by removing the angular velocity after the zero bias error, and the horizontal posture angle is corrected using the gravity acceleration component in the acceleration, thereby effectively suppressing the error drift of the posture angle, and finally outputting the posture measurement result that meets the measurement accuracy requirements of orthopedic surgery navigation. The present invention has the advantages of anti-electromagnetic interference, low cost, simple operation, and real-time calculation, and can provide doctors with stable and reliable intramedullary nail guide needle posture information support, assisting doctors to more accurately find the ideal intramedullary nail insertion direction, and has important clinical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art or ordinary technicians, other drawings can be obtained based on these drawings without paying creative work.

[0063] Figure 1 is a coronal anatomical schematic diagram of the proximal femur in an embodiment of the present invention;

[0064] Figure 2 This is a schematic diagram of the process of auxiliary navigation of the intramedullary nail insertion point in an embodiment of the present invention;

[0065] Figure 3 Schematic diagram of the structure of the method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU in an embodiment of the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0067] Example:

[0068] Figure 1 FIG. 1 is a coronal anatomical diagram of the proximal femur in an embodiment, wherein the numbers in the figure are: developing plate 1, developing plate center position 2, femoral shaft axis 3, and ideal needle insertion direction 4. Figure 1 As shown, the ideal intramedullary nail insertion point and direction is to insert the needle from the apex of the greater trochanter of the femur, close to the middle axis of the femoral neck, and 5 degrees outward along the axis of the femoral shaft. Since the femoral shaft axis 3 is an imaginary central axis and is not visible during the actual operation, a developing plate device visible in medical fluoroscopic images is used. The posture measurement system is combined with the intramedullary nail guide needle, and the posture information of the intramedullary nail guide needle relative to the developing plate is measured in real time by the posture measurement system, so as to determine the ideal intramedullary nail insertion direction.

[0069] Figure 2 The flowchart of the auxiliary navigation of the intramedullary nail insertion point in one embodiment includes the following steps:

[0070] Step S100: Fix the developing plate 1 horizontally on the surface of the proximal femur of the affected side to take a medical perspective image;

[0071] Step S200: Record the reading α1 of the center position 2 of the developing board, and the reading of the ideal needle insertion direction 4 on the developing board is α2;

[0072] Step S300: Place the attitude measurement system horizontally on the developing board, align the system heading with the center scale direction of the developing board, start the attitude measurement system, and use the MEMS-IMU-based intramedullary nail insertion point attitude measurement method to measure the pitch angle θ of the center position of the developing board relative to the reference coordinate system. init , Roll Angle Yaw angle

[0073] Step S400: epidermal incision, assembling the posture measurement system and the intramedullary nail guide needle, and the system heading is consistent with the direction of the intramedullary nail guide needle;

[0074] Step S500: Using the MEMS-IMU-based intramedullary nail insertion point posture measurement method to measure the intramedullary nail guide needle at any time (denoted as t k The pitch angle θ relative to the reference coordinate system at the moment k , Roll Angle and yaw angle Subtract θ in step S300 respectively init , Get the posture information θ of the intramedullary nail guide needle relative to the center position of the imaging plate k '、

[0075]

[0076] Step S600: Adjust the intramedullary nail guide needle. When the yaw angle of the intramedullary nail guide needle relative to the center of the imaging plate is Equal to (α1-α2) degrees, pitch angle θ k When ′ is equal to 0 degrees, it is the ideal direction for intramedullary nail insertion;

[0077] Step S700: insert the intramedullary nail guide needle and confirm with fluoroscopy.

[0078] It should be noted that the developing board described in this embodiment is a protractor device used in medical fluoroscopic images, which may be composed of a high-density marker and a plastic substrate, and is used to clearly display the angle scale and position reference under the fluoroscopic image, and the developing board reading increases in a clockwise direction. The posture measurement system described in this embodiment is the execution subject of the posture measurement method based on MEMS-IMU, and may be composed of a processor, a memory, a MEMS-IMU sensor, a display device, etc., and is used to acquire and process posture data in real time and output measurement results. The intramedullary nail insertion point posture measurement method based on MEMS-IMU described in steps S300 and S500 of this embodiment has a structural principle diagram as shown in FIG. Figure 3 As shown, the specific steps include:

[0079] Step 1: Parameter initialization, in this embodiment, includes setting the initial parameters of the attitude quaternion, the Butterworth low-pass filter, and the Kalman filter;

[0080] Step 2: At fixed time intervals t s The acquisition includes the gyroscope output angular velocity and the accelerometer output acceleration f b of sensor data.

[0081] Step 3: Due to the angular velocity Contains random noise, zero-speed bias and other errors, and only relies on angular velocity The attitude quaternion obtained by integral recursion update cannot express the spatial rotation relationship between the carrier coordinate system b and the reference coordinate system n. Therefore, the auxiliary coordinate system n′ is constructed and defined by the angular velocity Unit quaternion obtained by integral recursive update Represents the spatial rotation of the carrier coordinate system b relative to the auxiliary coordinate system n′, and defines the unit correction quaternion represents the spatial rotation of the auxiliary coordinate system n′ relative to the reference coordinate system n, so t k-1 The spatial rotation of the carrier coordinate system b relative to the reference coordinate system n is expressed in unit quaternion express:

[0082]

[0083] Step 4: Place t k Gyroscope angular velocity collected at all times Convert to quaternion increment Δq gyr form:

[0084]

[0085] Step 5: Increment Δq via quaternion gyr Unit quaternion To update:

[0086]

[0087] Step 6: Normalize to get unit quaternion

[0088]

[0089] So far, we have obtained t k The unit attitude quaternion of the carrier coordinate system b relative to the auxiliary coordinate system n′ at this moment

[0090] Step 7: Convert the Accelerometer Output Acceleration f b According to quaternion The described spatial rotation is transferred to the auxiliary coordinate system n′:

[0091]

[0092] Step 8: To suppress the disturbance acceleration caused by rapid motion, use the cutoff frequency f d A second-order Butterworth low-pass filter with a frequency of 0.1 Hz is used for f n′The purpose of filtering is to retain only the gravity acceleration component (DC component). The filter transfer function H(z) is:

[0093]

[0094] Ω is calculated by the following formula:

[0095]

[0096] where f s represents the sampling frequency, which is 100 Hz in this embodiment, and f d represents the cut-off frequency, which is 0.1 Hz in this embodiment, and the filter output value is recorded as

[0097] Step 9: According to t k-1 Time-corrected quaternion The described spatial rotation is transferred to the reference coordinate system n:

[0098]

[0099] Step 10: Normalize to get unit acceleration vector

[0100]

[0101] Step 11: The specific force unit vector [0,0,1] corresponding to the gravitational acceleration sensed by the accelerometer in the reference coordinate system n is obtained from The spatial rotation to [0,0,1] corresponds to the correction quaternion The quaternion increment Δq that should be updated cor According to the basic concept of quaternion, the correction quaternion can be expressed in the form of trigonometric function The quaternion increment Δq cor :

[0102]

[0103] Among them, from The spatial rotation to [0,0,1] corresponds to the quaternion increment Δq cor , unit rotation axis Can be After normalization, the rotation angle α corresponds to The angle between the z-axis component of and the z-axis of the carrier coordinate system

[0104] Step 12: Increment Δq via quaternion cor Correction Quaternion To update:

[0105]

[0106] Step 13: Normalize to get unit-corrected quaternion

[0107]

[0108] So far, we have obtained t k The unit attitude quaternion of the auxiliary coordinate system n′ relative to the reference coordinate system n at this moment

[0109] Step 14: Perform static detection on the MEMS-IMU carrier. The specific technical solution is as follows: Use the cutoff frequency f d A 0.5 Hz second-order Butterworth low-pass filter is used to filter out the noise caused by the handheld moving surgical equipment during the operation. and f b The fast motion signal and high frequency noise in the filter are recorded as and judge and Is the absolute difference less than the threshold T? ω and f b and Is the absolute difference less than the threshold T? f , if these two conditions are met at the same time, the sensor is considered to be in a stationary state. In this embodiment, T ω The value is 2dps, T f The value is 0.5m / s 2 .

[0110] At this point, the static detection of the MEMS-IMU carrier has been completed.

[0111] Step 15: Use standard Kalman filter to calculate the gyroscope angular velocity To perform real-time bias estimation, the model selects the gyroscope angular velocity bias [b x b y b z ] T As the state variable x k , select the angular velocity zero bias measurement value as the observation value z k The system state space model is:

[0112] x k =x k-1 +w k

[0113] z k =H k x k +vk

[0114] E{w k}=E{v k}=0

[0115] E{w k w k T =Q k

[0116] E{v k v k T = R k

[0117] Step 16: If the carrier is in a static state, directly use As the observed quantity z k , the observation matrix H = I3; if the carrier is in a dynamic situation, the quaternion Convert to posture array Using cutoff frequency f d A second-order Butterworth low-pass filter of 0.1 Hz is used as well as Filter them separately and record the filter output as and According to the derived observation z k use Observation Matrix

[0118] Step 17: Use the standard Kalman filter algorithm for prediction and update:

[0119]

[0120] in, That is t k The gyroscope angular velocity zero bias estimate predicted and updated by the standard Kalman filter at all times.

[0121] At this point, the gyroscope angular velocity zero bias estimation based on the standard Kalman filter is completed.

[0122] Step 18: In t k+1 During the iterative update process at time , the gyroscope angular velocity should remove the zero bias estimate, which is recorded as

[0123]

[0124] Step 19: Update the unit quaternion

[0125]

[0126] Step 20: Convert the Quaternion Convert to attitude angle expression output:

[0127] θ k =sin -1 (2(q2q3+q0q1))

[0128]

[0129] Among them, θ k , Represents t k The pitch angle, roll angle and yaw angle of the intramedullary nail guide needle relative to the reference coordinate system n at this moment.

[0130] At this point, the entire process of the intramedullary nail insertion point posture measurement method based on MEMS-IMU in this example is completed.

[0131] The present invention proposes an auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU, which measures and updates the posture of the intramedullary nail guide needle only by relying on the real-time collected MEMS-IMU gyroscope and accelerometer sensor data, wherein a digital low-pass filter is used to suppress the interference acceleration during surgery and to perform static detection on the carrier, and a Kalman filter is used to estimate the angular velocity zero bias in real time. The posture is iteratively updated by removing the angular velocity after the zero bias error, and the horizontal posture angle is corrected by using the gravity acceleration component in the acceleration, thereby effectively suppressing the error drift of the posture angle, and finally outputting the posture measurement result that meets the measurement accuracy requirements of orthopedic surgery navigation. The present invention has the advantages of anti-electromagnetic interference, low cost, simple operation, and real-time calculation. It can provide doctors with stable and reliable intramedullary nail guide needle posture information support, assisting doctors to more accurately find the ideal intramedullary nail insertion direction, and has important clinical significance.

[0132] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU, characterized by: The method comprises the following steps: Step S100: Fix the developing plate horizontally on the surface of the proximal femur of the affected side to take a medical fluoroscopic image; Step S200: Record the reading α1 of the center position of the developing board, and the reading of the ideal needle insertion direction on the developing board is α2; Step S300: Place the attitude measurement system horizontally on the developing board, align the system heading with the center scale direction of the developing board, start the attitude measurement system, and use the MEMS-IMU-based intramedullary nail insertion point attitude measurement method to measure the pitch angle θ of the center position of the developing board relative to the reference coordinate system. init , Roll Angle Yaw angle Step S400: epidermal incision, assembling the posture measurement system and the intramedullary nail guide needle, and the system heading is consistent with the direction of the intramedullary nail guide needle; Step S500: Using the MEMS-IMU-based intramedullary nail insertion point posture measurement method to measure the intramedullary nail guide needle at t k The pitch angle θ relative to the reference coordinate system at the moment k , Roll Angle and yaw angle Subtract θ in step S300 respectively init , Get the posture information θ of the intramedullary nail guide needle relative to the center position of the imaging plate k '、 Step S600: Adjust the intramedullary nail guide needle. When the yaw angle of the intramedullary nail guide needle relative to the center of the imaging plate is Equal to (α1-α2) degrees, pitch angle θ k When ′ is equal to 0 degrees, it is the ideal direction for intramedullary nail insertion; Step S700: insert the intramedullary nail guide needle and confirm with fluoroscopy.

2. The auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU according to claim 1 is characterized by: The developing board is a protractor device used in medical fluoroscopic images, which is composed of a high-density marker and a plastic substrate and is used to clearly display angle scales and position references under fluoroscopic images. The reading of the developing board increases in a clockwise direction.

3. The auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU according to claim 1 is characterized by: The posture measurement system is an execution subject of the posture measurement method based on MEMS-IMU, including a processor, a memory, a MEMS-IMU sensor, and a display device, and is used to acquire and process sensor data in real time and output posture measurement results.

4. The auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU according to claim 1 is characterized by: The method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU suppresses the interference acceleration component caused by external force in the acceleration through a digital low-pass filter, and performs static detection on the carrier; A standard Kalman filter model is constructed with angular velocity bias as the state quantity. According to the results of static detection, the model is divided into dynamic and static cases, and the corresponding observation equations are established respectively. The bias error is estimated with the angular velocity bias measurement value as the observation quantity. The angular velocity is used to iteratively update the attitude quaternion after removing the bias error estimate. At the same time, the attitude quaternion is corrected for the horizontal inclination according to the gravity acceleration component in the acceleration. Finally, the corrected attitude quaternion is converted into Euler angle for real-time output.

5. The auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU according to claim 3 is characterized by: The method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU has the following specific steps: Step 1: At fixed time intervals t s The acquisition includes the gyroscope output angular velocity and the accelerometer output acceleration f b Sensor data; Step 2: Construct auxiliary coordinate system n ′ system, defined by the angular velocity Unit quaternion obtained by integral recursive update Indicates that the carrier coordinate system b is relative to the auxiliary coordinate system n ′ Space rotation of the system, defining the unit correction quaternion Represents the auxiliary coordinate system n ′ The spatial rotation of the system relative to the reference coordinate system n, so t k-1 The spatial rotation of the carrier coordinate system b relative to the reference coordinate system n is expressed in unit quaternion express: Step 3: Place t k Gyroscope angular velocity collected at all times Convert to quaternion increment Δq gyr form: Step 4: Increment Δq via quaternion gyr Unit quaternion To update: Step 5: Normalize to get unit quaternion Step 6: Convert the accelerometer output acceleration f b According to quaternion The spatial rotation described is transferred to the auxiliary coordinate system n ′ Tie: Step 7: Use the cutoff frequency f d A second-order Butterworth low-pass filter with a frequency of 0.1 Hz is used for f n′ Filtering is performed to retain only the gravity acceleration component, that is, the DC component. The filter output value is recorded as Step 8: According to t k-1 Time-corrected quaternion The described spatial rotation is transferred to the reference coordinate system n: Step 9: Normalize to get unit acceleration vector Step 10: The specific force unit vector [0,0,1] corresponding to the gravitational acceleration sensed by the accelerometer in the reference coordinate system n is obtained from The spatial rotation to [0,0,1] corresponds to the correction quaternion The quaternion increment Δq that should be updated cor ; According to the basic concept of quaternion, the quaternion increment Δq is expressed in the form of trigonometric function cor : Among them, from The rotation axis u to [0,0,1] can be obtained by After normalization, we get the unit rotation axis from The rotation angle α to [0,0,1] is The angle between the z-axis component of and the z-axis of the carrier coordinate system Step 11: Increment Δq via quaternion cor Correction Quaternion To update: Step 12: Normalize to get unit-corrected quaternion Step 13: Perform static detection on the MEMS-IMU carrier; Step 14: Use standard Kalman filtering to gyro angular velocity To perform real-time zero bias estimation, the model selects the gyroscope angular velocity deviation [b x b y b z ] T As the state variable x k , select the angular velocity zero bias measurement value as the observation value z k ; The system state space model is: x k =x k-1 +w k z k =H k x k +v k E{w k }=E{v k }=0 E{w k w k T }=Q k E{v k v k T }=R k In static condition, directly use As the observed quantity z k , the observation matrix H = I3; in the dynamic case, the quaternion Convert to posture array Using cutoff frequency f d A second-order Butterworth low-pass filter of 0.1 Hz is used as well as Filter them separately and record the filter output as and According to the derived observation z k use Observation Matrix The standard Kalman filter algorithm is used for prediction and update: Step 15: In t k+1 During the iterative update process at time , the gyroscope angular velocity should remove the zero bias estimate, which is recorded as Step 16: Update the unit quaternion Step 17: Convert the Quaternion Convert to attitude angle expression output: i k =sin -1 (2(q2q3+q0q1)) Among them, θ k , Represents t k The pitch angle, roll angle and yaw angle of the intramedullary nail guide needle relative to the reference coordinate system n at this moment.

6. The auxiliary navigation method for measuring the posture of the intramedullary nail insertion point based on MEMS-IMU according to claim 5 is characterized by: In step 13: static detection of the MEMS-IMU carrier is performed, and the specific technical scheme is as follows: using the cutoff frequency f d A 0.5 Hz second-order Butterworth low-pass filter is used to filter out the noise caused by the handheld moving surgical equipment during the operation. and f b The fast motion signal and high frequency noise in the filter are recorded as and judge and Is the absolute difference less than the threshold T? ω and f b and Is the absolute difference less than the threshold T? f ,If these two conditions are met at the same time, the sensor is considered to be in a stationary state.

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