Method for measuring angle of knee joint

Abstract

The present invention relates to a method for measuring an angle of a knee joint, the method comprising the steps of: (a) measuring thigh rotation data and calf rotation data according to a calibration operation of a knee joint by inertial sensor modules respectively installed on a thigh and a calf; (b) calculating a calibration value for axis alignment with a global coordinate system by using the thigh rotation data and the calf rotation data measured in step (a); (c) measuring thigh rotation data and calf rotation data according to an actual motion of the knee joint by the inertial sensor modules; and (d) calculating and displaying, on a screen, a rotation angle of the calf relative to the thigh on the basis of the thigh rotation data and the calf rotation data measured in step (c), wherein the rotation angle is calculated by reflecting the calibration value in the thigh rotation data and the calf rotation data measured in step (c). The method allows for an angle of a knee joint to be measured with only a simple configuration.

Description

Method for measuring knee joint angle

[0001] The present invention relates to a method for measuring the angle of a knee joint, and more specifically, to a method for measuring the angle of a knee joint capable of measuring the rotational angle around three axes on the knee joint.

[0002] Measuring the rotation of the three axes of the knee joint is crucial in the fields of surgery and rehabilitation. Even if the surgical or rehabilitation process requires rotation of only one of the three axes, being able to measure rotation of all three axes allows for the exclusion of indirect influences from the other two axes, thereby obtaining more accurate values.

[0003] For example, knee arthroplasty is a surgical procedure that replaces a knee joint damaged by degeneration with an artificial joint to alleviate pain and restore joint function; it is classified into total knee arthroplasty (TKA) and partial knee arthroplasty (PKA) depending on the extent of articular surface resection.

[0004] In such knee replacement surgery, it is necessary to be able to precisely measure the angles of the three axes on the knee joint to accurately determine the cutting position and angle of the articular surface for artificial joint insertion. This not only helps prevent excessive wear and misalignment of the joint and allows the patient to recover a natural range of motion (ROM), but also helps adjust plans and strategies during the postoperative rehabilitation process by acquiring range of motion angle data.

[0005] As another example, in the case of anterior cruciate ligament (ACL) reconstruction, it is a surgery that restores joint stability by reconstructing the ligament using graft tissue when the anterior cruciate ligament, a major stabilizing structure of the knee joint, is damaged.

[0006] In anterior cruciate ligament (ACL) reconstruction, accurately measuring the rotation of the three axes of the knee joint during surgery allows for adjustment to ensure the transplanted ligament maintains the correct tension and also secures joint stability.

[0007] In particular, rotational stability is one of the key roles of the anterior cruciate ligament, and failure to properly assess it can increase the risk of joint instability or re-injury due to improper reconstruction. Furthermore, continuously monitoring knee angles during rehabilitation allows for the evaluation of range of motion (ROM) and balance, enabling the design of an appropriate rehabilitation program.

[0008] Currently, goniometers, robotic navigation systems, and CT are being applied as real-time knee angle measurement methods.

[0009] Goniometers are a traditionally used method, but they cannot measure angles of multiple axes simultaneously, and because they are a manual measurement method, significant errors can occur between users.

[0010] Although robotic navigation systems provide relatively high precision, they are burdensome to patients due to the invasive method of implanting markers into the bone, and there are problems such as delayed surgery time caused by the complexity of their operation.

[0011] While CT provides high-resolution images, it has the disadvantage of limiting repetitive use due to radiation exposure and making it impossible to take scans during surgery.

[0012] Accordingly, the present invention was devised to resolve the above-mentioned problems, and aims to provide a method for measuring the angle of a knee joint that can measure the angle of a knee joint with only a simple configuration.

[0013] The above objective is achieved according to the present invention by a method for measuring the angle of a knee joint, comprising: (a) a step of measuring thigh rotation data and calf rotation data according to a calibration operation of the knee joint by an inertial sensor module installed on the thigh and calf, respectively; (b) a step of calculating a calibration value for axis alignment into a global coordinate system using the thigh rotation data and calf rotation data measured in step (a); (c) a step of measuring thigh rotation data and calf rotation data according to an actual movement of the knee joint by the inertial sensor module; and (d) a step of calculating and displaying the rotation angle of the calf relative to the thigh on a screen based on the thigh rotation data and calf rotation data measured in step (c), wherein the calibration value is reflected in the thigh rotation data and calf rotation data measured in step (c).

[0014] Here, rotation around the knee joint may include flexion and extension around the pitch axis of the local coordinate system based on the knee joint, adduction and abduction around the yaw axis of the local coordinate system, and internal rotation and external rotation around the roll axis of the local coordinate system.

[0015] In addition, the thigh rotation data and the calf rotation data measured in steps (a) and (c) above can be defined as quaternions.

[0016] And, in step (a) above, the calibration operation includes bending and extension operations and adduction and abduction operations; the thigh rotation data measured in step (a) above includes a thigh bending quaternion in a bent state according to the bending and extension operations and a thigh extension quaternion in an extended state according to the bending and extension operations; and the calf rotation data measured in step (a) above may include a calf bending quaternion in a bent state according to the bending and extension operations, a calf extension quaternion in an extended state according to the bending and extension operations, and a calf abduction quaternion in an abduction state according to the adduction and abduction operations.

[0017] And, the above step (b) comprises: (b1) a step of calculating a relative rotation value of bending from an extension state to a bending state using the thigh flexion quaternion, the thigh extension quaternion, the calf flexion quaternion, and the calf extension quaternion; (b2) a step of calculating a first axis alignment value for aligning the axis of rotation of the bending motion in the local coordinate system with the pitch axis in the global coordinate system using the axis of rotation and the angle of rotation of the relative rotation value of bending; (b3) a step of calculating a relative rotation value of abduction from an extension state to an abduction state using the thigh extension quaternion, the calf extension quaternion, and the calf abduction quaternion; and (b4) a step of calculating a second axis alignment value for aligning the axis of rotation of the abduction motion in the local coordinate system with the yaw axis in the global coordinate system using the axis of rotation and the angle of rotation of the relative rotation value of abduction; The above thigh extension quaternion, the above calf extension quaternion, the above first axis alignment value, and the above second axis alignment value can be calculated as the calibration value.

[0018] And, the above first axis alignment value is a mathematical formula

[0019]

[0020] ( is the above-mentioned first axis alignment value, and is the rotation angle of the first axis alignment value above, and is defined as the axis of rotation of the first axis alignment value; and the rotation angle and axis of rotation of the first axis alignment value are each mathematical formula

[0021]

[0022] ( is the axis of rotation of the above bending relative rotation value, and the (is the pitch axis of the above global coordinate system) can be calculated.

[0023] And, the above bending relative rotation value is a mathematical formula

[0024]

[0025] ( is the above bending relative rotation value, and The above thigh extension quaternion, is the above thigh flexion quaternion, and is the above calf extension quaternion, and It can be calculated by the above calf flexion quaternion.

[0026] And, the above second axis alignment value is a mathematical formula

[0027]

[0028] ( is the above second axis alignment value, and is the rotation angle of the above second axis alignment value, and is defined as the axis of rotation of the second axis alignment value; and the rotation angle and axis of rotation of the second axis alignment value are each mathematical formula

[0029]

[0030] ( is the axis of rotation of the above external rotation relative rotation value, and the It can be calculated by the yaw axis of the above global coordinate system.

[0031] And, the above external rotation relative rotation value is a mathematical formula

[0032]

[0033] ( is the above bending relative rotation value, and The above thigh extension quaternion, is the above thigh flexion quaternion, and is the above calf extension quaternion, and is the above-mentioned calf flexion quaternion, and It can be calculated by the above calf abduction quaternion.

[0034] And, the thigh rotation data and the calf rotation data measured in step (c) above are defined as a thigh rotation quaternion and a calf rotation quaternion, respectively; The above step (d) comprises: (d1) calculating a measured relative rotation value from the extension state based on the thigh extension quaternion and the calf extension quaternion to the rotation in step (c) using the thigh extension quaternion, the calf extension quaternion, the thigh rotation quaternion, and the calf rotation quaternion; (d2) calculating a first alignment quaternion in which the measured relative rotation value is aligned with the pitch axis in the global coordinate system using the first axis alignment value; (d3) calculating a pitch rotation value from which the pitch axis rotation in the global coordinate system is extracted from the first alignment quaternion; (d4) calculating a second alignment quaternion in which the first alignment quaternion is aligned with the yaw axis in the global coordinate system using the second axis alignment value; (d5) calculating a third alignment quaternion by aligning the second alignment quaternion with the pitch rotation value using the pitch rotation value; and (d6) the third alignment It may include a step of calculating a rotation angle based on the three axes of the global coordinate system from the quaternion.

[0035] According to the above configuration, the present invention provides a method for measuring the angle of a knee joint that can measure the angle of a knee joint with only a simple configuration.

[0036] FIG. 1 is a diagram illustrating the three axes of knee joint rotation, and

[0037] FIG. 2 is a diagram showing an example of the configuration of a knee joint angle measurement system according to an embodiment of the present invention, and

[0038] FIG. 3 is a flowchart illustrating a method for measuring the angle of a knee joint according to an embodiment of the present invention, and

[0039] FIGS. 4 to 8 are drawings for explaining the measurement process according to the knee joint angle measurement method according to an embodiment of the present invention.

[0040] The present invention relates to a method for measuring the angle of a knee joint, comprising: (a) a step of measuring thigh rotation data and calf rotation data according to the calibration operation of the knee joint by inertial sensor modules installed on the thigh and calf, respectively; (b) a step of calculating a calibration value for axis alignment into a global coordinate system using the thigh rotation data and calf rotation data measured in step (a); (c) a step of measuring thigh rotation data and calf rotation data according to the actual movement of the knee joint by the inertial sensor modules; and (d) a rotation angle of the calf relative to the thigh calculated and displayed on a screen based on the thigh rotation data and calf rotation data measured in step (c), wherein the calibration value is reflected in the thigh rotation data and calf rotation data measured in step (c).

[0041] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the present invention, and the present invention is defined only by the scope of the claims.

[0042] The terms used in this specification are for describing embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. The terms "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other components in addition to the components mentioned. Throughout the specification, the same reference numerals refer to the same components, and "and / or" includes each of the mentioned components and all combinations of one or more. Although terms such as "first," "second," etc., are used to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another. Therefore, the first component mentioned below may be the second component within the technical scope of the invention.

[0043] Unless otherwise defined, all terms used herein (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0044] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0045] Figure 1 is a diagram illustrating the three axes of knee joint rotation.

[0046] Referring to Figure 1, the three rotation axes in the local coordinate system defined at the center of the knee joint can be classified as the pitch axis, yaw axis, and roll axis, respectively.

[0047] Rotation of the knee joint around the pitch axis is defined as flexion and extension, rotation of the knee joint around the lumbar axis is defined as adduction and abduction, and rotation of the knee joint around the roll axis is defined as internal rotation and external rotation.

[0048] FIG. 2 is a diagram showing an example of the configuration of a knee joint angle measurement system according to an embodiment of the present invention.

[0049] Referring to FIG. 2, the knee joint angle measuring system according to an embodiment of the present invention may be configured to include a first inertial sensor module (110), a second inertial sensor module (120), and an angle measuring terminal (200).

[0050] According to an embodiment of the present invention, the first inertial sensor module (110) and the second inertial sensor module (120) may each be mounted on the thigh and calf of a subject to measurement, respectively. In one embodiment, as shown in FIGS. 4 and 5, the first inertial sensor module (110) may be mounted on one area of ​​the thigh, and the second inertial sensor module (120) may be mounted on one area of ​​the calf.

[0051] The first inertial sensor module (110) and the second inertial sensor module (120) are exemplified by having nine or more degrees of freedom (DOF), such as 3 axes of gyroscope, 3 axes of acceleration, and 3 axes of magnetometer, thereby measuring the rotation of the thigh and calf.

[0052] In one embodiment, the first inertial sensor module (110) and the second inertial sensor module (120) can transmit measured data to an angle measuring terminal (200) via a short-range communication network (300), for example, Bluetooth.

[0053] An angle measuring terminal (200) according to an embodiment of the present invention receives data measured by a first inertial sensor module (110) and a second inertial sensor module (120) through a communication network (300), and can measure the angle of a knee joint based on the received data.

[0054] In one embodiment, the angle measuring terminal (200) may be implemented in the form of an information processing device such as a computer or a laptop, and the angle measuring process described below may be performed through a program installed on the angle measuring terminal (200).

[0055] FIG. 3 is a flowchart illustrating a method for measuring the angle of a knee joint according to an embodiment of the present invention.

[0056] Referring to FIG. 3, the first inertial sensor module (110) and the second inertial sensor module (120) are mounted on the thigh and calf of a subject to measurement. The method for measuring the angle of a knee joint according to an embodiment of the present invention may include a calibration process (S10) and a real-time measurement process (S20).

[0057] To explain the calibration process according to an embodiment of the present invention, first, the subject of measurement performs a knee joint calibration operation (S11), and in this process, thigh rotation data and calf rotation data are measured by the first inertial sensor module (110) and the second inertial sensor module (120), respectively (S12).

[0058] Here, thigh rotation data and calf rotation data measured by the first inertial sensor module (110) and the second inertial sensor module (120) are transmitted to an angle measuring terminal (200) via a communication network (300).

[0059] The angle measuring terminal (200) calculates a calibration value for axis alignment into a global coordinate system using thigh rotation data and calf rotation data received through a communication network (300).

[0060] In an embodiment of the present invention, an angle measuring terminal (200) uses thigh rotation data and calf rotation data by defining rotation around the knee joint as a quaternion.

[0061] To explain the calibration process according to an embodiment of the present invention in more detail, the calibration operation is exemplified by including the bending and extension operation shown in FIG. 4 and the adduction and abduction operation shown in FIG. 5.

[0062] FIG. 4(a) is a drawing showing the extended state during bending and extension movements, and FIG. 4(b) is a drawing showing the bent state during bending and extension movements. Also, FIG. 5(a) is a drawing showing the extended state as illustrated in FIG. 4(a), and FIG. 5(b) is a drawing showing the state rotated from the extended state to the abduction state.

[0063] According to the calibration operation as described above, the thigh rotation data may include a thigh flexion quaternion in a flexed state according to the flexion and extension movements, and a thigh extension quaternion in an extended state according to the flexion and extension movements.

[0064] And, the calf rotation data may include a calf flexion quaternion in a flexed state according to flexion and extension movements, a calf extension quaternion in an extended state according to flexion and extension movements, and a calf abduction quaternion in an abduction state according to adduction and abduction movements.

[0065] As described above, when thigh rotation data and calf rotation data are received, a first axis alignment value and a second axis alignment value are calculated as calibration values ​​(S14, S16). Here, the first axis alignment value is a value for aligning the rotation axis of the bending motion in the local coordinate system with the pitch axis in the global coordinate system, and the second axis alignment value is a value for aligning the rotation axis of the abduction motion in the local coordinate system with the yaw axis in the global coordinate system.

[0066] First, the process of calculating the first axis alignment value is explained as follows: using the thigh flexion quaternion, thigh extension quaternion, calf flexion quaternion, and calf extension quaternion, the relative rotation value of the bend from the extension state to the bend state is calculated (S13).

[0067] Referring to FIG. 6, as illustrated in FIG. 6(a), the thigh flexion quaternion (F1), thigh extension quaternion (F0), calf flexion quaternion (T1), and calf extension quaternion (T0) are defined as quaternions in a local coordinate system centered on the knee joint, which does not correspond to the global coordinate system.

[0068] To align to the global coordinate system, first, as shown in Fig. 6 (b), the thigh extension quaternion is aligned to the global coordinate system, which can be expressed as [Equation 1].

[0069] [Mathematical Formula 1]

[0070]

[0071] And, as shown in Fig. 6 (c), if the thigh bending quaternion is aligned with the global coordinate system, it can be expressed as [Equation 2].

[0072] [Mathematical Formula 2]

[0073]

[0074] Here, the relative bending rotation value from the extended state to the bent state in the global coordinate system , that is, the change in rotation of the calf can be expressed as [Equation 3].

[0075] [Mathematical Formula 3]

[0076]

[0077] Here, the axis of rotation of the relative bending rotation value becomes the axis of rotation of the bending / extension motion.

[0078] When the bending relative rotation value is calculated as described above, the first axis alignment value is calculated using the rotation axis and rotation angle of the bending relative rotation value (S14).

[0079] As previously explained, the first axis alignment value is a value for aligning the rotation axis of the bending motion in the local coordinate system with the pitch axis in the global coordinate system, and can be conceptually represented as shown in (d) of FIG. 6.

[0080] In an embodiment of the present invention, the first axis alignment value is calculated using [Equation 4] as an example.

[0081] [Mathematical Formula 4]

[0082]

[0083] Here, is the first axis alignment value, and is the rotation angle of the first axis alignment value, and is the axis of rotation of the first axis alignment value. Here, the rotation angle and axis of rotation of the first axis alignment value can be calculated through [Equation 5], respectively.

[0084] [Mathematical Formula 5]

[0085]

[0086] Here, is the axis of rotation of the bending relative rotation value, and is the pitch axis of the global coordinate system.

[0087] Meanwhile, to explain the process of calculating the second axis alignment value, as shown in FIG. 7 (a), the thigh extension quaternion (F0), calf extension quaternion (T0), and calf abduction quaternion (F2) are defined as quaternions in a local coordinate system centered on the knee joint, which does not coincide with the global coordinate system.

[0088] To align to the global coordinate system, first, as shown in Fig. 7(b), the thigh extension quaternion is aligned to the global coordinate system, which can be expressed as [Equation 6].

[0089] [Mathematical Formula 6]

[0090]

[0091] Here, the relative rotation value of the rotation from the extension state to the rotational state in the global coordinate system That is, the change in rotation of the calf can be expressed as [Equation 7].

[0092] [Mathematical Formula 7]

[0093]

[0094] Here, the axis of rotation of the full relative rotation value becomes the axis of rotation of the external rotation movement.

[0095] When the external rotation relative rotation value is calculated as described above, the second axis alignment value is calculated using the rotation axis and rotation angle of the external rotation relative rotation value (S16).

[0096] As previously explained, the second axis alignment value is a value for aligning the rotation axis of the external rotation motion in the local coordinate system with the yaw axis in the global coordinate system, and can be conceptually represented as shown in (c) of FIG. 7.

[0097] In an embodiment of the present invention, the second axis alignment value is calculated using [Equation 8] as an example.

[0098] [Mathematical Formula 8]

[0099]

[0100] Here, is the second axis alignment value, and is the rotation angle of the second axis alignment value, and is the rotation axis of the second axis alignment value.

[0101] And, the rotation angle and rotation axis of the second axis alignment value can be calculated through [Equation 9], respectively.

[0102] [Mathematical Formula 9]

[0103]

[0104] Here, is the axis of rotation of the external rotation relative rotation value, and is the yaw axis of the above global coordinate system.

[0105] As described above, when the first axis alignment value and the second axis alignment value are calculated, the first axis alignment value, the second axis alignment value, and the thigh extension quaternion and calf extension quaternion are stored as calibration values, and the calibration process is terminated.

[0106] Meanwhile, once the calibration value is calculated through the calibration process, that value is applied when the actual knee joint angle is measured.

[0107] First, the subject performs knee joint exercises while the first inertial sensor module (110) and the second inertial sensor module (120) are mounted on the thigh and calf, respectively, as in the calibration process, and the angle of the knee joint is measured in real time during the knee joint exercises.

[0108] Then, during the knee joint movement process, thigh rotation data and calf rotation data corresponding to the knee joint movement are measured by the first inertial sensor module (110) and the second inertial sensor module (120) and transmitted to the angle measuring terminal (200).

[0109] Here, thigh rotation data and calf rotation data are defined as thigh rotation quaternions and calf rotation quaternions, as in the calibration process.

[0110] Then, using the thigh extension quaternion and calf extension quaternion stored as calibration values ​​and the thigh rotation quaternion and calf rotation quaternion according to knee joint movement, the relative rotation value measured from the thigh extension quaternion and calf extension quaternion to the rotation according to the knee joint movement of the subject in an extension state based on the thigh extension quaternion and calf extension quaternion is calculated (S22).

[0111] Here, the measured relative rotation value can be calculated using [Equation 3], and is calculated by applying the thigh rotation quaternion and calf rotation quaternion to the F1 and T1 values.

[0112] Then, using the first axis alignment value, the measured relative rotation value is aligned with the pitch axis in the global coordinate system to calculate the first alignment quaternion (S23). Here, the first alignment quaternion can be calculated through [Equation 10].

[0113] [Mathematical Formula 10]

[0114]

[0115] Here, is a first-ordered quaternion, and is the measured relative rotation value.

[0116] Then, a pitch rotation value is calculated from the first alignment quaternion, in which the pitch axis rotation in the global coordinate system is extracted (S24). Here, the pitch rotation value can be defined as [Equation 11].

[0117] [Mathematical Formula 11]

[0118]

[0119] Here, is the pitch rotation value, and is the pitch axis rotation angle in the global coordinate system in the first alignment quaternion.

[0120] Then, using the second axis alignment value, the first alignment quaternion is aligned to the yaw axis in the global coordinate system to produce the second alignment quaternion (S25). Here, the second alignment quaternion can be produced through [Equation 12].

[0121] [Mathematical Formula 12]

[0122]

[0123] Here, is a second-ordered quaternion.

[0124] Then, the second aligned quaternion can be aligned with the pitch rotation value using the pitch rotation value to produce the third aligned quaternion (S26). Here, the third aligned quaternion It can be calculated through [Mathematical Formula 13].

[0125] [Mathematical Formula 13]

[0126]

[0127] When the third alignment quaternion is calculated as described above, the rotation angles based on the three axes of the global coordinate system can be calculated from the third alignment quaternion (S28). In one embodiment, the rotation angles can be calculated by converting the third alignment quaternion into Euler angles, so that the angles based on each rotation axis in the global coordinate system can be calculated.

[0128] The rotation angle calculated in this way can be displayed on the monitor (not shown) of the angle measuring terminal (200), and as shown in FIG. 7, the rotation angle based on each axis can be displayed using the femoral image and the tibia image.

[0129] Although some embodiments of the present invention have been illustrated and described, those skilled in the art will understand that modifications can be made to these embodiments without departing from the principles or spirit of the invention. The scope of the invention will be defined by the appended claims and their equivalents.

[0130] [Explanation of the symbol]

[0131] 110: 1st inertial sensor module 120: 2nd inertial sensor module

[0132] 200 : Angle measuring terminal 300 : Communication network

[0133] The present invention is applicable to the field of inertial sensors for measuring knee joints.

Claims

1. Regarding the method for measuring the angle of the knee joint, (a) A step in which thigh rotation data and calf rotation data are measured according to the calibration motion of the knee joint by inertial sensor modules installed respectively on the thigh and calf; (b) a step of calculating a calibration value for axis alignment into a global coordinate system using the thigh rotation data and calf rotation data measured in step (a) above; and (c) a step in which thigh rotation data and calf rotation data according to the actual movement of the knee joint are measured by the inertial sensor module above; (d) A method for measuring the angle of a knee joint, characterized in that the angle of rotation of the calf relative to the thigh is calculated and displayed on a screen based on the thigh rotation data and the calf rotation data measured in step (c), wherein the calibration value is reflected in the thigh rotation data and the calf rotation data measured in step (c).

2. In Paragraph 1, A method for measuring the angle of a knee joint, characterized in that the rotation around the knee joint includes flexion and extension around the pitch axis of a local coordinate system based on the knee joint, adduction and abduction around the yaw axis of the local coordinate system, and internal rotation and external rotation around the roll axis of the local coordinate system.

3. In Paragraph 2, A method for measuring the angle of a knee joint, characterized in that the thigh rotation data and the calf rotation data measured in step (a) and step (c) are defined as quaternions.

4. In Paragraph 3, In step (a) above, the calibration operation includes bending and extension movements, and adduction and abduction movements; The thigh rotation data measured in step (a) above According to the above bending and extension movements, the thigh flexion quaternion in the bent state, and It includes a thigh extension quaternion in an extended state according to the above bending and extension movements; The calf rotation data measured in step (a) above A calf flexion quaternion in a flexed state according to the above flexion and extension movements, and According to the above flexion and extension movements, the calf extension quaternion in an extended state, and A method for measuring the angle of a knee joint characterized by including an abducted calf quaternion in an abducted state according to the above adduction and abduction movements.

5. In Paragraph 4, The above step (b) (b1) A step of calculating a relative rotation value of bending from an extended state to a bent state using the thigh flexion quaternion, the thigh extension quaternion, the calf flexion quaternion, and the calf extension quaternion, and (b2) a step of calculating a first axis alignment value to align the axis of rotation of the bending operation in the local coordinate system with the pitch axis in the global coordinate system using the axis of rotation and the angle of rotation of the relative bending value, and (b3) A step of calculating a relative abduction rotation value from the extended state to the abduction state using the thigh extension quaternion, the calf extension quaternion, and the calf abduction quaternion, and (b4) A step of calculating a second axis alignment value to align the axis of rotation of the external rotation operation in the local coordinate system with the yaw axis in the global coordinate system using the axis of rotation and the angle of rotation of the external rotation relative rotation value; A method for measuring the angle of a knee joint, characterized in that the thigh extension quaternion, the calf extension quaternion, the first axis alignment value, and the second axis alignment value are calculated as the calibration value.

6. In Paragraph 5, The above first axis alignment value is a mathematical formula ( is the above-mentioned first axis alignment value, and is the rotation angle of the first axis alignment value above, and is defined as the rotation axis of the above-mentioned first axis alignment value; The rotation angle and rotation axis of the first axis alignment value above are each mathematically formulated ( is the axis of rotation of the above bending relative rotation value, and the A method for measuring the angle of a knee joint characterized by being calculated by (which is the pitch axis of the global coordinate system).

7. In Paragraph 6, The above bending relative rotation value is a mathematical formula ( is the above bending relative rotation value, and The above thigh extension quaternion, is the above thigh flexion quaternion, and is the above calf extension quaternion, and A method for measuring the angle of a knee joint characterized by being calculated by the above-mentioned calf flexion quaternion.

8. In Paragraph 5, The above second axis alignment value is a mathematical formula ( is the above second axis alignment value, and is the rotation angle of the above second axis alignment value, and is defined as the axis of rotation of the second axis alignment value; and the rotation angle and axis of rotation of the second axis alignment value are each mathematical formula ( is the axis of rotation of the above external rotation relative rotation value, and the A method for measuring the angle of a knee joint characterized by being calculated by the yaw axis of the above-mentioned global coordinate system.

9. In Paragraph 8, The above external rotation relative rotation value is a mathematical formula ( is the above bending relative rotation value, and The above thigh extension quaternion, is the above thigh flexion quaternion, and is the above calf extension quaternion, and is the above-mentioned calf flexion quaternion, and A method for measuring the angle of a knee joint characterized by being calculated by the above-mentioned calf abduction quaternion.

10. In Paragraph 5, The thigh rotation data and the calf rotation data measured in step (c) above are defined as a thigh rotation quaternion and a calf rotation quaternion, respectively; The above (d) step (d1) a step of calculating a measured relative rotation value from the extension state based on the thigh extension quaternion and the calf extension quaternion to the rotation in step (c) using the thigh extension quaternion, the calf extension quaternion, the thigh rotation quaternion and the calf rotation quaternion, and (d2) a step of calculating a first alignment quaternion in which the measured relative rotation value is aligned with the pitch axis in the global coordinate system using the first axis alignment value, and (d3) A step of calculating a pitch rotation value from which the pitch axis rotation in the global coordinate system is extracted from the first alignment quaternion, and (d4) A step of calculating a second aligned quaternion in which the first aligned quaternion is aligned with the yaw axis in the global coordinate system using the second axis alignment value, and (d5) A step of calculating a third alignment quaternion by aligning the second alignment quaternion with the pitch rotation value using the pitch rotation value, and (d6) A method for measuring the angle of a knee joint, characterized by including the step of calculating a rotation angle based on three axes of the global coordinate system from the third alignment quaternion.

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