JPS6411291B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a hip dislocation diagnostic device. One of the major goals in hip surgery is to restore and maintain lost hip joint afferentity. Many treatments have been tried for this purpose, but none of them are objective or quantitative, and rely on past experience or intuition.
The therapeutic effect was also insufficient. In particular, surgery for hip dislocation is often performed on children or young children, and if the treatment effect is insufficient as a result of the surgery, it is often difficult for the infant or child to undergo reoperation. A method or device for displaying the dislocation force of the hip joint is desired. The present invention meets such demands, and includes:
The purpose of the present invention is to provide a device that can quantitatively and objectively diagnose hip joint dislocation. This invention also examines the degree of afferentity, which is a barometer of the therapeutic effect in hip dislocation surgery, the state of contact pressure distribution on the contact surface of the hip joint, and when performing treatments such as varus osteotomy and pelvic osteotomy. It is an object of the present invention to provide a hip dislocation diagnostic device that can quantitatively grasp the magnitude of dislocation force and the state of change in contact pressure distribution. This invention achieves the above object by performing mechanical analysis of the hip joint using a rigid spring model. Specifically, the method for analyzing nonlinear problems in solid mechanics using a rigid spring model, which was invented by Tadahiko Kawai, one of the inventors of this application,
No.) was used to diagnose hip joints. The present invention also provides means for acquiring positional data of a contact line between the pelvic acetabulum of the hip joint and the femoral head from a cross-sectional image in a longitudinal section in the femoral axial direction; Based on the obtained contact line position data and data on the resultant force of the load applied to the femoral head, the acetabulum on the pelvic side of the hip joint and the femoral head on the femoral side are made into rigid bodies that do not distort due to stress, and the capsular ligament. are respectively replaced with an element model of a dislocation prevention spring, and in the cross section of the element model, the area of the acetabulum and the femoral head along their contact line is divided by finite plane elements, and the divided On each planar element boundary,
Assuming a vertically resisting spring, the friction between the elements along the boundary is zero, the displacement of the acetabulum is zero, and the displacement of the head-side plane element is only in two directions within the plane. means for calculating the equivalent strain energy stored in the spring from the relative displacement in the two directions using the displacement parameter of the center of gravity; calculating the stress applied to each of the springs from the energy; means for detecting a spring being generated; and assuming the disconnection of said spring, again;
means for calculating equivalent strain energy stored in the remaining spring from the relative displacement in the two directions using parameters of the center of gravity of the planar element; and a calculation loop for calculating the stress applied to the remaining spring from the energy; A means for obtaining the final stress of each spring by repeating the process until no spring is applied with force or a predetermined number of times; and a display means for displaying the calculation process by each of the above means or the stress distribution of the spring at the contact line. This aims to achieve the above objectives. The present invention also provides means for acquiring positional data of a contact line between the pelvic acetabulum of the hip joint and the femoral head from a cross-sectional image in a longitudinal section in the femoral axial direction; Based on the obtained contact line position data and data on the resultant force of the load applied to the femoral head, the acetabulum on the pelvic side of the hip joint and the femoral head on the femoral side are made into rigid bodies that do not distort due to stress, and the capsular ligament. are respectively replaced with element models of a rigid body or a joint capsular ligament dislocation prevention spring that does not cause distortion due to stress on the acetabulum on the pelvic side and the femoral head on the pelvic side of the hip joint, and in the longitudinal section of the element model, the Divide the area along the contact line between the acetabulum and the femoral head using finite plane elements, and assume a spring that resists vertically on the boundary edge of each of the divided plane elements, and friction between the elements is zero, displacement of the acetabulum is zero,
Means for calculating the equivalent strain energy stored in the spring from the relative displacement in the two directions using a displacement parameter of the center of gravity of the planar element under the condition that the displacement of the femoral head side planar element is only in two directions within the plane. Calculate the stress applied to each of the springs from the energy, detect the spring that generates the maximum tensile force among these springs, assume that the spring is cut, and use the parameters of the center of gravity of the planar element again. Then, the equivalent strain energy stored in the remaining spring is calculated from the relative displacement in the two directions, and the calculation loop for calculating the stress applied to the remaining spring from this energy is continued until the tension is no longer applied to the spring, or until a predetermined value is reached. The above object is achieved by: means for repeatedly determining the final stress of each spring; and display means for displaying the calculation process by each means or the stress distribution of the spring at the contact line. Embodiments of the present invention will be described below with reference to the drawings. First, a general mechanical analysis method using the above-mentioned rigid spring model used in the hip joint dislocation diagnosis device according to the present invention will be explained. First, as shown in Figures 1 and 2,
As new planar elements, two types of springs Kd and Ks that resist normal force and shear force, and two rigid triangular plates 1 and 2 are assumed. It is assumed that these rigid triangular plates 1 and 2 do not undergo internal deformation due to stress, and these two triangular plates 1 and 2 are subject to normal stress and shear stress that are continuously distributed on the contact interface 53. They are connected by two types of resisting springs Kd and Ks. The displacement of an arbitrary point P (x, y) on the triangular plate is expressed by the displacement of the center of gravity, that is, three components: a parallel displacement component (UV) and a rotational displacement component (Θ). Now, let the displacement of any point P on the triangular plate be 〓U〓 _V〓 ;U〓V〓〓 ^t ,
Letting the displacement of the center of gravity be 〓U〓V〓Θ _I ; U ₂ V ₂ Θ ₂ 〓 ^t ,
The following relational expression is obtained. U=Q・U _i (1) On the other hand, the relative displacement vector P'P'' ---→ after the deformation of point P is given by the following formula: δ=M・ (2) Here, the superscript - indicates a component of the local coordinate system set on the element boundary side. Now, let R be the coordinate transformation matrix in the global coordinate system and the local coordinate system, and the following relationship holds true between R and U. U=R・U (3) Here, l ₃₅ is the length between sides 35. To summarize the above equation, the relative displacement vector δ of point P after deformation is expressed as follows using the displacement U _i of the center of gravity. δ=M・R・Q・U _i =B・U _i (B=M・R・Q) (4) Next, in order to determine the spring constant, a virtual strain component corresponding to the relative displacement component is defined as follows. Here, h ₁ h ₂ indicates the length of a perpendicular line drawn from the center of gravity G ₁ G ₂ of the triangular plate element to the boundary surface of each element. (See Figure 3) ε={ε _d γ _s }=1/h ₁ +h ₂ {δ _d δ _s }=1/hδ (5) Now, the surface force (stress) per unit area on each element boundary ) as follows. From the above results, the spring constants are determined as follows. (i) Spring constant in plane strain state Now, assume a spring as follows. σ _o =K _d・δ _d τ _S =K _S・δ _S (9) Therefore, the spring constant can be obtained as follows. (ii) Spring constant in plane stress state It can be obtained as follows in the same way as in the case of plane strain. Note that the spring constant shown here is for convenience only and has no mathematical reason in a strict sense. In order to accurately know the displacement, it is desirable to estimate the spring constant from experimental values and actual measured values. Now, let us briefly write the relationship between surface force (stress) and relative displacement as follows. σ=D・δ (12) σ=σ _o τ _S 〓 ^t (stress) δ=δ _o δ _S 〓 ^t (relative displacement) D=[K _a O O K _s ] (spring matrix) From the above, after deformation The potential energy stored in the distributed spring system between two elements is given by the following equation. V=1/2∫ _l35 〓 ^t Dδds = 1/2U ^t _i ∫ _l35 (B ^t DB) dsU _i (13) Therefore, the stiffness matrix K for each spring element is obtained from the minimum potential energy theorem.

[Table] Next, the case where the above method is applied to diagnosis using a hip dislocation diagnosis device will be explained. As shown in FIG. 4, the acetabulum 4 on the pelvis side of the hip joint 3 and the femoral head 6 on the femur 5 side are connected to rigid bodies 4A and 6A that do not cause distortion due to stress, as shown in FIG. The joint capsular ligament 7 is replaced with an element model of a dislocation prevention spring 7A, and in the axial longitudinal section of the femur 5 of the element model, the area along the contact line of the rigid bodies 4A and 6A is shown in FIG. Assume that the element is divided into finite plane elements as shown in , and there is a spring Kd that resists vertically on the boundary edge of the divided plane element, and the friction between the elements along the boundary edge is zero, that is, the spring Ks. The shape of the contact line is determined under the conditions that the constant is zero, the roller 8 exists between the rigid bodies 4A and 6A, the displacement of the rigid body 4A is zero, and the displacement of the rigid body 6A side is only in two directions within the longitudinal section. and the load P (resultant force of all loads) applied to the femoral head 6 as a known number, calculate the equivalent strain energy stored in the spring Kd from the relative displacement in the two directions using the displacement parameter of the center of gravity of the planar element, Find the stress applied to each spring Kd from the energy; detect the spring that generates the maximum tensile force among these springs, assume that the spring is cut, and use the parameters of the center of gravity of the planar element again. Then, calculate the equivalent strain energy stored in the remaining other springs from the relative displacement in the two directions,
The calculation loop for determining the stress applied to the remaining springs from the energy is repeated until there are no more springs under tension or a predetermined number of times to determine the final stress of each spring Kd. As mentioned above, if the displacement on the rigid body 4 side is zero,
u ₂ , v ₂ , and θ ₂ in equation (14) are each zero,
Also, since M ₁ is also zero, the components of the load P applied to each plane element in the X direction and Y direction are (15)
It becomes like the expression. P _X1 = K ₁₁ u ₁ + K ₁₂ v ₁ (15) P _Y1 = K _{12 u 1} + K ₂₂ v ₁ Therefore, the value _of P equal to the directional component. This is shown as the following equation. _X1 =K ₁₁ +K ₁₁ +…)u ₁ +(K ₁₂ +K ₁₂ +…)v _{1 Y1} =K ₁₂ +K ₁₂ +…)u ₁ +(K ₂₂ +K ₂₂ +…)v ₁ (16) (Superscript ,... indicates the stiffness of each element.) Here, the above K ₁₁ , K ₁₂ and K ₂₂ are from Table 1,
Also, _X1 and _Y1 are the X-direction and Y-direction components of the load P, and since both are known quantities, the displacements _u1 and _v1 can be found from equation (16). By substituting the obtained u ₁ and v ₁ into the above equation (12), the stress σ of each spring Kd can be obtained. At the contact surface between the acetabulum 4 and the femoral head 6, there should be only compressive force and no tensile force, so
If there is a spring that is generating a tensile force among the springs, the spring that is generating the maximum tensile force is detected, and it is assumed that the acetabulum 4 and the femoral head 6 are not in contact when the spring is cut, that is, the spring is cut. , Under these new conditions, create the spring stiffness matrix shown in Table 1 again, and use equation (16) as before to calculate the displacement u ₁ ,
Find v ₁ , then find the stress of each spring from equation (12). If a tensile force is present among the determined stresses, the calculation loop is repeated again until there are no more springs to which the tensile force is applied, or until a predetermined number of times, and the final stress of each spring is determined. The calculation loop is repeated up to a predetermined number of times and then terminated to prevent the program from running out of control when the calculation is performed on a computer. In reality, such a hip joint does not exist. In the actual procedure, as shown in FIGS. 6 and 10, from an X-ray photograph (cross-sectional image) of the hip joint 3, a digitizer 8 is used to examine the hip joint 3.
, that is, the peripheral shape of each element x,
Read the y coordinate into the computer 9, then input the integration point (the contact point between the roller 8 and the dislocation prevention spring 7A) into the computer 9 along the line of contact between the acetabulum 4 and the femoral head 6 in the cross section, and then calculate the load P. Input from digitizer 8. The calculator 9 calculates, based on the positional data of the contact line obtained by the digitizer 8 and the load P, the acetabulum 4 on the pelvis side and the femoral head 6 on the femoral side of the hip joint 3 into a rigid body that does not cause distortion due to stress. 4A, 6A, and the joint capsular ligament 7 are replaced with element models of the dislocation prevention spring 7A, respectively, and in the longitudinal section of the element model, the area along the contact line of the acetabulum and the femoral head is transformed into a finite plane element. Assuming that there is a spring Kd that resists vertically on the boundary side of each divided planar element, the friction between the elements along the boundary side is zero, the displacement of the acetabulum 4 is zero, and the femoral head Means for calculating the equivalent strain energy stored in the spring Kd from the relative displacement in the two directions using the displacement parameter of the center of gravity of the plane element under the condition that the displacement of the side plane element is only in two directions within the plane; A means for determining the stress applied to each of the springs Kd from the energy and detecting the spring producing the maximum tensile force among these springs; assuming that the spring is cut, and again using the parameters of the center of gravity of the planar element; and means for calculating the equivalent strain energy stored in the remaining spring from the gross body displacement in the two directions; and a calculation loop for calculating the stress applied to the remaining spring from the energy until no spring is under tension, or means for determining the final stress of each spring by repeating it a predetermined number of times;
It is equipped with The calculator 9 calculates and creates a stiffness matrix for each spring according to equation (14) or (15), obtains displacement u ₁ and v 1 from equation (16), and then calculates the displacement u 1 and v ₁ from equation (16) based on equation (12). Find the stress in each spring. Judgment of the presence or absence of the tensile force...The computer 9 repeats the cutting of the spring and the calculation, and when the calculation converges, the compressive stress of each spring is displayed on the graphic display 10 as shown in FIG. 7, for example.
to be displayed. Here, since the aim of the present invention is to determine the shape of the pressure distribution on the contact surface of the hip joint, the spring constant of each spring may be arbitrary as long as the mutual ratio is kept constant, so the unit contact surface length Assign an appropriate number, such as ``1'', which is convenient for calculations. Arrow F in FIG. 7 indicates the magnitude of the dislocation force, and if this is above a certain level, it is diagnosed that dislocation has occurred. Further, the range indicated by the symbol N indicates that the spring has been cut. During the actual surgery, based on the results shown on the graphic display 10, the shape of the contact surfaces of the rigid bodies 4A and 5A is corrected little by little on the display, and the stress of each spring in the corrected cross section is adjusted as described above. Similarly, determine the shape that will not cause dislocation. That is, simulation is performed using an element model. Therefore, it is no longer necessary to perform a surgery that relies on intuition and closely matches the actual joint, as in the past, and with the help of a computer and display, the ideal shape of the hip joint contact surface can be determined in advance and the surgery performed. . Next, the second part of the hip joint dislocation diagnosis device according to the present invention
An example will be explained. The calculator of this embodiment calculates the equivalent strain energy stored in the spring from the relative displacement in two directions using the displacement parameter of the center of gravity of the plane element, and calculates the stress applied to each spring from the calculated energy. This embodiment is the same as the first embodiment, but differs from the first embodiment in that the spring that has generated the maximum tensile stress is cut, the release force caused by this cutting is borne by the remaining springs, and the resulting incremental stress in the springs is determined. In other words, as shown in Figure 8, after creating the stiffness matrix, calculate the incremental displacement (in the first calculation, the previous displacement is set to zero), calculate the incremental stress of the spring based on this incremental displacement, and calculate the (the previous stress is set to zero for the first time), and the remaining stress of each spring is determined. If there is a tensile force among the calculated stresses, detect the spring that produces the maximum tensile force and its value, calculate the maximum release force of the tension spring as before, and calculate the spring that produces the maximum tensile force. The calculation loop of determining the stiffness matrix of the spring is repeated using the cutting and releasing force as a new load until there are no more springs that are under tension. This embodiment has the advantage that the stress of the spring can be calculated more precisely than the first embodiment, but the calculator for calculation is expensive and the calculation time is slow. It is longer than the first embodiment. Next, a third embodiment of the hip joint dislocation diagnostic apparatus according to the present invention shown in FIG. 9 will be described. In this third embodiment, first, a plurality of longitudinal sections of the hip joint 3 are photographed using a continuous X-ray photographing system, shape data is input from each cross-sectional photograph by a digitizer 8, and based on this, the Alternatively, calculate the stress distribution of each cross section in the same manner as in the second embodiment, then determine the most severe stress distribution cross section from among these cross sections, and if the stress distribution in the most severe stress distribution cross section is unacceptable, The cross-sectional shape is corrected, the corrected shape is input again via the digitizer, and the same calculation loop as in the first or second embodiment is repeated until the stress distribution in the severest stress distribution cross section is acceptable. Repeat this process, and when the stress distribution reaches an acceptable state, analyze the changes in stress distribution in other cross sections due to the shape modification,
If the modified stress distribution including this change is acceptable, the calculation is converged; if it is not, the three-dimensional shape of the structural model is corrected, input is made again by the digitizer 8, and the calculation loop is repeated. , until the modified stress distribution is acceptable. These calculation processes or results are displayed on a graphic display 10 as shown in the figure. In the case of this embodiment, since the corrected shape of the hip joint can be obtained three-dimensionally, there is an advantage that more accurate treatment can be performed. Since the present invention is configured as described above, the contact pressure between the acetabulum and the femoral head 9 in the hip joint, that is, the distribution shape of the stress, can be accurately determined and displayed, and based on this, the ideal shape of the hip joint can be corrected. It has the excellent effect of being able to be carried out using a model and therefore dramatically increasing the therapeutic effect. As a result of analyzing the cross-sectional shapes of hip joints before and after previous hip dislocation treatment surgery by the present inventors using the method and device of the present invention, all cases were consistent with the display results by the device of the present invention, indicating that the surgery was unsuccessful. I was able to find out the cause.

[Brief explanation of the drawing]

Figures 1 and 2 are plan views showing a rigid spring model for explaining the underlying principle of the hip dislocation diagnostic device according to the present invention, and Figure 3 shows numerical values on elements in calculations based on the same principle. A plan view, FIG. 4 is a schematic sectional view showing the shape of the hip joint, and FIG.
Cross-sectional view of the hip joint shown in the figure replaced with an element model, No. 6
The figure is a flowchart of the first embodiment of the hip dislocation diagnosis device according to the present invention, Figure 7 is an explanatory diagram showing an example of calculation results shown on a graphic display, and Figures 8 and 9 are the same. FIG. 10 is a flowchart showing the operation of the second and third embodiments, and a block diagram showing the hip dislocation diagnostic apparatus according to the present invention. 1, 2...plane element, 3...hip joint, 4...acetabulum, 4A, 6A...rigid body, 5...femur, 6...
Bony head, 7... Joint capsular ligament, 7A... Dislocation prevention spring, 8... Digitizer, 9... Calculator, 10...
...Graphic display, kd...spring.

Claims (1)

[Scope of Claims] 1. Means for acquiring positional data of a contact line between the pelvic acetabulum of the hip joint and the femoral head from a cross-sectional image in a longitudinal section in the axial direction of the femur; Based on the data on the position of the contact line and the resultant force of the load applied to the femoral head obtained by the method, the acetabulum on the pelvic side of the hip joint and the femoral head on the femoral side are made into rigid bodies that do not cause distortion due to stress, and joints. Replace the capsular ligament with an element model of a dislocation prevention spring, and in the longitudinal section of the element model, divide the area of the acetabulum and the femoral head along their contact line with finite plane elements,
Assuming a spring that resists vertically on the boundary edge of each of the divided planar elements, the friction between the elements along the boundary edge is zero, the displacement of the acetabulum is zero, and the displacement of the cephalic plane element is within the plane. means for calculating equivalent strain energy stored in the spring from the relative displacement in the two directions using displacement parameters of the center of gravity of the planar element under the conditions of only two directions; and a stress applied to each of the springs from the energy. means for determining which spring is producing the maximum tensile force among these springs;
Assuming that the spring is cut, calculating the equivalent strain energy stored in the remaining spring from the relative displacement in the two directions, again using the parameters of the center of gravity of the planar element; means for calculating the final stress of each of the springs by repeating a calculation loop for calculating the stress applied to the springs until there are no more tensioned springs or a predetermined number of times; calculation process by each of the above means or the stress of the spring at the contact line; A dislocation diagnostic device for a hip joint, comprising: a display device for displaying distribution; 2. Means for acquiring position data of a contact line from a cross-sectional image including a contact line between the pelvic acetabulum of the hip joint and the femoral head in a longitudinal section in the axial direction of the femur; and the contact line obtained by this means. Based on the data on the position of , and in the longitudinal section of the element model, divide the region of the acetabulum and the femoral head along their contact line with finite plane elements, and
Assuming a spring that resists vertically on the boundary edge of each of the divided planar elements, the friction between the elements along the boundary edge is zero, the displacement of the acetabulum is zero, and the displacement of the cephalic plane element is within the plane. means for calculating equivalent strain energy stored in the spring from the relative displacement in the two directions using displacement parameters of the center of gravity of the planar element under the conditions of only two directions; and a stress applied to each of the springs from the energy. means for determining the tensile force of the spring producing the maximum tensile force among these springs, and calculating from this the maximum releasing force that the spring has; assuming that the tensile force spring is cut, the maximum releasing force is a new load applied to the femoral head, and means for determining the incremental displacement of the planar element due to this load and the incremental stress applied to each spring other than the cut spring in the same manner as above; In addition, we calculate the stress of each spring by adding it to or a predetermined number of times to obtain the final stress of each spring; and a display device that displays the calculation process by each of the means or the stress distribution of the spring at the contact line. Dislocation diagnostic device.