Design method of bone-integrating prosthesis connector stem

Abstract

The application discloses a design method of a bone-integrated prosthesis connector handle body, and belongs to the technical field of the prosthesis connector. The method comprises the following steps: calculating the elastic modulus data of the bone according to the bone density data of the image data; calculating the bone strain energy density after the bone-integrated prosthesis connector handle body is implanted according to the image data, the elastic modulus data of the bone and the diameter of the bone-integrated prosthesis connector handle body; judging whether the bone strain energy density after the bone-integrated prosthesis connector handle body is implanted is within an acceptable range; calculating the maximum principal stress of the bone-integrated prosthesis connector handle body under the current diameter, and judging whether the maximum principal stress is less than the material fatigue strength; and outputting the size design of the bone-integrated prosthesis connector handle body if yes. The design method of the bone-integrated prosthesis connector handle body can make the bone-integrated prosthesis connector handle body keep the press-fitting and the fatigue strength, and the stress shielding degree is as low as possible.

Description

Technical Field

[0001] This invention relates to the field of prosthetic connector technology, and in particular to a design method for a skeletal integrated prosthetic connector stem. Background Technology

[0002] Stress shielding effect is an adverse effect that occurs when a metal implant is inserted into the human body. Because the elastic modulus of the metal is higher than that of human bone, when the same external load is applied, most of the stress on the bone is borne by the metal, resulting in insufficient stress on the bone and subsequent bone resorption.

[0003] Osseointegrated prosthetic connectors are percutaneous implants. The portion implanted within the medullary cavity integrates with the bone tissue, achieving connection and load transfer between the residual limb and the prosthesis, thereby enabling anatomical and functional reconstruction of the residual limb. Since this implant is intended for medullary cavity implantation, initial pressure fitting establishes stability within the medullary cavity. Biological fixation is achieved through the osseointegration design of the outer surface. Therefore, the implant must initially be pressure-fitted to the medullary cavity, and the outer envelope design must closely conform to the shape of the medullary cavity. However, this close fit results in a significant stress shielding effect on the bone.

[0004] To address the aforementioned issues, some products have adopted corresponding solutions, such as replacing the implant material with a low-modulus one, making the outer surface structure porous, or using topological methods, such as ridges, to replace surface contact with bone and reduce the contact area. The ideal effect of a osseointegrated prosthetic connector stem is to maintain press-fit and fatigue strength while minimizing stress shielding. However, research has found that the performance of existing osseointegrated prosthetic connector stems is not ideal and needs improvement. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a design method for the handle of an osseointegrated prosthesis connector, so that the stress shielding degree of the osseointegrated prosthesis connector handle is minimized while maintaining press fit and fatigue resistance.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for designing a osseointegrated prosthetic connector stem, the osseointegrated prosthetic connector stem being implanted into a patient's bone shaft medullary cavity, comprising a solid rod portion and an osseointegrated layer covering the outer surface of the solid rod portion, the method comprising:

[0008] Step 1: Obtain imaging data of the patient's skeletal structure;

[0009] Step 2: Based on the image data, obtain the patient's internal diameter of the bone shaft, external diameter of the bone shaft, and bone mineral density data;

[0010] Step 3: Calculate the elastic modulus of bone based on the bone density data;

[0011] Step 4: Select the initial diameter of the osseointegrated prosthesis connector handle;

[0012] Step 5: Calculate the bone strain energy density after implantation of the osseointegrated prosthesis connector stem based on the image data, bone elastic modulus data, and diameter of the osseointegrated prosthesis connector stem.

[0013] Step 6: Determine whether the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is within an acceptable range. If so, proceed to the next step.

[0014] Step 7: Calculate the maximum principal stress of the osseointegrated prosthesis connector handle at the current diameter, and determine whether the maximum principal stress is less than the material fatigue strength. If so, output the size design of the osseointegrated prosthesis connector handle.

[0015] Furthermore, step 6 includes:

[0016] If not, the diameter of the osseointegrated prosthesis connector handle is reduced by a fixed value before proceeding to step 5.

[0017] Furthermore, in step 2, the bone mineral density data ρ is obtained by converting the Hu value in the image data, and the calculation formula is as follows:

[0018] ρ = 0.0405 + 0.000918HU.

[0019] Furthermore, in step 3, the formula for calculating the elastic modulus E of bone is as follows:

[0020] E3790ρ 3 .

[0021] Furthermore, in step 4, the inner diameter of the bone shaft is selected as the diameter of the handle of the osseointegrated prosthesis connector, which is used as the upper limit value of the handle diameter.

[0022] Alternatively, step 4 may include:

[0023] Step 41: Calculate the stem diameter D when the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is within the lower limit of the acceptable range. s ;

[0024] Step 42: Select the inner diameter of the bone shaft and the D s The smaller of the two is the diameter of the handle of the osseointegrated prosthesis connector, which serves as the upper limit of the handle diameter.

[0025] Furthermore, in step 5, the formula for calculating the bone strain energy density Ui after implantation of the osseointegrated prosthesis connector stem is as follows:

[0026]

[0027] F i =E i I i

[0028] I i =πD i 4 / 64

[0029] Where γ is Poisson's ratio, E is the elastic modulus of bone, r0 is the outer diameter of the bone shaft, I is the moment of inertia of the bone section, and F... i M represents the bending stiffness of the handle of the osseointegrated prosthesis connector, M represents the bending moment experienced by the bone tissue, and E represents the bending stiffness of the handle. i For the elastic modulus of the handle of the osseointegrated prosthesis connector, I i D is the moment of inertia of the cross section of the handle of the osseointegrated prosthesis connector. i This refers to the current diameter of the handle of the osseointegrated prosthesis connector.

[0030] Furthermore, the method also includes:

[0031] Based on the image data and bone elastic modulus data, a skeletal model of the bone shaft to be implanted is established, and the bone strain energy density U0 is calculated when the handle of the osseointegrated prosthesis connector is not implanted under a pre-given load value.

[0032] At this point, in step 6, the acceptable range is greater than 0.25U0.

[0033] Furthermore, the formula for calculating the bone strain energy density Uo when the osseointegrated prosthesis connector handle is not implanted is as follows:

[0034]

[0035] Where γ is Poisson's ratio, E is the elastic modulus of bone, r0 is the outer diameter of the bone shaft, I is the moment of inertia of the bone section, and M is the bending moment caused by daily loads on the bone tissue.

[0036] Furthermore, in step 7, the dimensional design includes the diameter of the solid rod and the thickness of the osseointegration layer. The current diameter of the osseointegrated prosthesis connector handle is used as the diameter of the solid rod, and the intramedullary diameter minus the diameter of the solid rod is divided by 2 to obtain the thickness of the osseointegration layer.

[0037] Furthermore, the patient's skeletal structure includes the femur, tibia, humerus, ulna, radius, or phalanges.

[0038] The present invention has the following beneficial effects:

[0039] The design method of the osseointegrated prosthesis connector handle of the present invention determines the optimal size design of the osseointegrated prosthesis connector handle, so that while maintaining press fit and fatigue resistance, the stress shielding degree of the osseointegrated prosthesis connector handle is reduced as much as possible, the strain energy density is increased, and the bone resorption problem caused by stress shielding is greatly reduced, so that the osseointegrated prosthesis connector can achieve long-term stability. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the design method of the osseointegrated prosthesis connector handle of the present invention.

[0041] Figure 2 This is a schematic diagram showing the state of the osseointegrated prosthesis connector stem after implantation into the medullary cavity, where (a) is a stem diameter of D. S (b) is a sectional view of the handle with a diameter of D. Si A sectional view;

[0042] Figure 3 This is a stress diagram of the handle of the osseointegrated prosthesis connector of the present invention, wherein (a) is the handle diameter D. S The stress diagram, (b) shows the stress of the handle with diameter D. Si The stress diagram. Detailed Implementation

[0043] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0044] This invention provides a design method for the handle of a bone-integrated prosthesis connector, such as... Figure 1-3 As shown, the osseointegrated prosthesis connector handle (the handle material can be titanium alloy, etc.) is implanted into the patient's bone shaft medullary cavity, including a solid rod M and an osseointegrated layer P covering the outer surface of the solid rod M. The method includes:

[0045] Step 1: Obtain imaging data of the patient's skeletal structure;

[0046] In this step, imaging data of the bone shaft of the stem of the osseointegrated prosthesis connector to be implanted in the patient is acquired; the bone shaft may include the femur, tibia, humerus, ulna, radius, or phalanges. In the figure, N represents the cortical bone layer of the medullary cavity of the bone shaft.

[0047] Step 2: Based on the image data, obtain the patient's internal diameter of the bone shaft, external diameter of the bone shaft, and bone mineral density data;

[0048] In this step, the imaging data can primarily be CT data; the bone mineral density data ρ can be obtained by converting the Hu value (bone absorption value to X-rays) from the imaging data. The calculation formula is as follows:

[0049] ρ=0.0405+0.000918HU (1).

[0050] The following is a specific example. In this example, the patient's bone shaft (medullary cavity) inner diameter is 20mm and the bone shaft outer diameter is 30mm. Based on the imaging data, the patient's bone shaft inner diameter ri = 10mm, bone shaft outer diameter r0 = 15mm, and bone mineral density data ρ are obtained.

[0051] Step 3: Calculate the elastic modulus of bone E based on the bone density data ρ;

[0052] In this step, the formula for calculating the elastic modulus E of bone can be as follows:

[0053] E = 3790ρ 3 (2).

[0054] In the example above, the calculated elastic modulus of bone is E = 20 GPa.

[0055] Step 4: Select the initial diameter of the osseointegrated prosthesis connector handle;

[0056] In this step, in one embodiment, the inner diameter ri of the bone shaft can be selected as the diameter D of the osseointegrated prosthesis connector handle. si This serves as the upper limit for the diameter of the handle.

[0057] Alternatively, in another embodiment, step 4 may include:

[0058] Step 41: Calculate the stem diameter D when the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is within the lower limit of the acceptable range. s ;

[0059] Step 42: Select the inner diameter ri / D of the bone shaft si and the D s The smaller of the two is the diameter of the handle of the osseointegrated prosthesis connector, which serves as the upper limit of the handle diameter.

[0060] This embodiment facilitates faster output of the size design of the osseointegrated prosthesis connector handle in subsequent steps.

[0061] Step 5: Calculate the bone strain energy density after implantation of the osseointegrated prosthesis connector stem based on the image data, bone elastic modulus data, and diameter of the osseointegrated prosthesis connector stem.

[0062] In this step, the formula for calculating the bone strain energy density Ui after implantation of the osseointegrated prosthesis connector stem can be as follows:

[0063]

[0064] Furthermore, the F i The calculation formula is as follows:

[0065] F i =E i I i (4)

[0066] Furthermore, the I i The calculation formula is as follows:

[0067] I i =πD i 4 / 64 (5)

[0068] Where y is Poisson's ratio, E is the elastic modulus of bone, r0 is the outer diameter of the bone shaft, I is the moment of inertia of the bone section, and F... i M represents the bending stiffness of the handle of the osseointegrated prosthesis connector, M represents the bending moment experienced by the bone tissue, and E represents the bending stiffness of the handle. i For the elastic modulus of the handle of the osseointegrated prosthesis connector, I i D is the moment of inertia of the cross section of the handle of the osseointegrated prosthesis connector. i This refers to the current diameter of the handle of the osseointegrated prosthesis connector.

[0069] In the example above, the moment of inertia I of the skeleton's cross section i =31893.76mm 4 F i =1.7e8Nmm.

[0070] During their research, the inventors discovered that the direct consequence of stress shielding in bone tissue is bone resorption. The most direct and quantifiable indicator of bone resorption is strain energy density. When the strain energy density is less than a minimum value for bone steady-state, osteoclastosis is initiated, leading to bone resorption. Therefore, the strain energy density of bone can be used to guide the design of the stem.

[0071] Furthermore, the method may also include:

[0072] Based on the image data and bone elastic modulus data, a skeletal model of the bone shaft to be implanted is established, and the bone strain energy density U0 is calculated when the handle of the osseointegrated prosthesis connector is not implanted under a pre-given load value.

[0073] This step can be performed before step 4, specifically as step 3', or it can be included in step 6.

[0074] At this point, in steps 4 and 6, the acceptable range can be greater than 0.25U0. That is, when the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is greater than 0.25U0, bone resorption will not occur.

[0075] Furthermore, the formula for calculating the bone strain energy density U0 when the osseointegrated prosthesis connector handle is not implanted is as follows:

[0076]

[0077] Where γ is Poisson's ratio, E is the elastic modulus of bone, r0 is the outer diameter of the bone shaft, I is the moment of inertia of the bone section, and M is the bending moment caused by daily loads on the bone tissue.

[0078] In the example above, based on the maximum bending moment that may be generated during the movement of the femoral end, which is 70 Nm, the loading bending moment M = 70 Nm is set. Substituting into the formula, U0 = 2.45 * e - 2 MPa is obtained. The lower limit of the acceptable range is U = 0.25 * U0 = 0.6125 * e - 2 MPa. In step 5, Ui = 0.09 * e - 2 MPa.

[0079] Substituting U = 0.25U0 into the aforementioned formulas (3)-(5) for calculating Ui, we can calculate D. i This is Ds, thus obtaining Ds = 13.3 mm; since the inner diameter of the skeleton is greater than Ds, Ds is used as the upper limit value of the stem diameter.

[0080] Step 6: Determine whether the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is within an acceptable range. If so, proceed to the next step.

[0081] As an optional embodiment, step 6 may include:

[0082] If not, the diameter of the osseointegrated prosthesis connector handle is reduced by a fixed value before proceeding to step 5.

[0083] In this step, if the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is within an acceptable range, it means that bone resorption will not occur, and the next step can be performed. Otherwise, it means that bone resorption will occur, and the strength of the osseointegrated prosthesis connector stem needs to be reduced. Therefore, the diameter of the osseointegrated prosthesis connector stem is reduced by a fixed value. This fixed value can be flexibly set as needed, such as 1mm, 0.5mm, etc.

[0084] Step 7: Calculate the maximum principal stress of the osseointegrated prosthesis connector handle at the current diameter, and determine whether the maximum principal stress is less than the material fatigue strength. If so, output the size design of the osseointegrated prosthesis connector handle.

[0085] In this step, material fatigue strength refers to the stress value when the material reaches infinite life under high-cycle fatigue. If the calculated maximum principal stress of the handle at the current diameter is less than the material fatigue strength, it means that the size of the handle of the osseointegrated prosthesis connector is large enough and the size design meets the requirements. Otherwise, it means that the size of the handle is too small and the size should be increased.

[0086] The dimensional design may include the diameter of the solid rod M and the thickness of the osseointegration layer N. The current diameter of the osseointegration prosthesis connector handle is used as the diameter of the solid rod M. The thickness of the osseointegration layer N is obtained by subtracting the diameter of the solid rod M from the intramedullary diameter (i.e., the aforementioned inner diameter of the bone shaft) and dividing by 2.

[0087] In the above example, the osseointegrated prosthesis connector stem is implanted into the medullary cavity of the bone model of the segment to be implanted, and then a bending moment is applied to obtain the value of the maximum principal stress. Finite element analysis yields the maximum principal stress when the stem diameter is Dsi, as shown below. Figure 3 In (b), the stress is 63.4 MPa, which is less than the fatigue strength of titanium alloy. Simultaneously, the maximum principal stress for a handle diameter of Ds = 13.3 mm is calculated as follows: Figure 3 The stress in (a) is 62.03 MPa, which is less than the fatigue strength of titanium alloy. Therefore, the handle diameter Ds = 13.3 mm is considered an acceptable result. The diameter of the handle body rod M can be designed to be 13.3 mm, and the thickness of the osseointegrated layer P can be designed to be 3.35 mm. This determines the optimal size design of the handle of the osseointegrated prosthesis connector, ensuring the initial press fit and fatigue strength of the handle of the osseointegrated prosthesis connector, while reducing stress shielding.

[0088] Figure 3 In diagram (a), the maximum principal stress of the Ds shank (thin shank) is represented. Figure 3 (b) shows the maximum principal stress of the Dsi shank (thick shank). As can be seen from the figure, under the same bending moment, the thinner shank... Figure 3 (a) and the thicker stem ( Figure 3 (b) has similar fatigue strength. At this point, you can choose to output this diameter directly, or you can perform a loop calculation to obtain a better solution. The loop calculation method is to continue to reduce the current diameter by a fixed value, such as 0.5mm or 1mm, based on the appropriate gradient of the bone in the selected application area.

[0089] The design method of the osseointegrated prosthesis connector handle of the present invention determines the optimal size design of the osseointegrated prosthesis connector handle, so that while maintaining press fit and fatigue resistance, the stress shielding degree of the osseointegrated prosthesis connector handle is reduced as much as possible, the strain energy density is increased, and the bone resorption problem caused by stress shielding is greatly reduced, so that the osseointegrated prosthesis connector can achieve long-term stability.

[0090] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A design method for the handle of a osseointegrated prosthesis connector, characterized in that, The osseointegrated prosthesis connector stem is used for implantation into the patient's bone shaft medullary cavity, and includes a solid rod and an osseointegrated layer covering the outer surface of the solid rod. The method includes: Step 1: Obtain imaging data of the patient's skeletal structure; Step 2: Based on the image data, obtain the patient's internal diameter of the bone shaft, external diameter of the bone shaft, and bone mineral density data; Step 3: Calculate the elastic modulus of bone based on the bone density data; Step 4: Select the initial diameter of the osseointegrated prosthesis connector handle; Step 5: Calculate the bone strain energy density after implantation of the osseointegrated prosthesis connector stem based on the image data, bone elastic modulus data, and diameter of the osseointegrated prosthesis connector stem. Step 6: Determine whether the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is within an acceptable range. If so, proceed to the next step. Step 7: Calculate the maximum principal stress of the osseointegrated prosthesis connector handle at the current diameter, and determine whether the maximum principal stress is less than the material fatigue strength. If so, output the size design of the osseointegrated prosthesis connector handle. In step 5, the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is measured. The calculation formula is as follows: ； ； ； in, Poisson's ratio, For the elastic modulus data of bone, The outer diameter of the skeletal shaft. Let the moment of inertia of the skeleton's cross section be... Let M be the bending stiffness of the handle of the osseointegrated prosthesis connector, and M be the bending moment caused by daily loads on the bone tissue. The elastic modulus of the stem of the osseointegrated prosthesis connector. The moment of inertia of the cross section of the handle of the osseointegrated prosthesis connector. The current diameter of the handle of the osseointegrated prosthesis connector; The method further includes: Based on the image data and bone elastic modulus data, a skeletal model of the bone shaft to be implanted is established, and the bone strain energy density U0 is calculated when the handle of the osseointegrated prosthesis connector is not implanted under a pre-given load value. At this point, in step 6, the acceptable range is greater than 0.25U0; Bone strain energy density of the osseointegrated prosthesis connector stem when not implanted The calculation formula is as follows: 。 2. The method according to claim 1, characterized in that, Step 6 includes: If not, the diameter of the osseointegrated prosthesis connector handle is reduced by a fixed value before proceeding to step 5.

3. The method according to claim 1, characterized in that, In step 2, the bone mineral density data ρ is obtained by converting the HU value in the image data, and the calculation formula is as follows: 。 4. The method according to claim 3, characterized in that, In step 3, the formula for calculating the elastic modulus E of bone is as follows: 。 5. The method according to claim 1, characterized in that, In step 4, the inner diameter of the bone shaft is selected as the diameter of the handle of the osseointegrated prosthesis connector, which is used as the upper limit value of the handle diameter. Alternatively, step 4 may include: Step 41: Calculate the stem diameter when the bone strain energy density after implantation of the osseointegrated prosthesis connector stem is within the lower limit of the acceptable range. ; Step 42: Select the inner diameter of the bone shaft and the... The smaller of the two is the diameter of the handle of the osseointegrated prosthesis connector, which serves as the upper limit of the handle diameter.

6. The method according to claim 1, characterized in that, In step 7, the size design includes the diameter of the solid rod and the thickness of the osseointegration layer. The current diameter of the osseointegration prosthesis connector handle is used as the diameter of the solid rod, and the intramedullary diameter minus the diameter of the solid rod is divided by 2 to obtain the thickness of the osseointegration layer.

7. The method according to claim 1, characterized in that, The patient's skeletal structure includes the femur, tibia, humerus, ulna, radius, or phalanges.

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