FEA on Assembled Fractured Human Femur Bone with and without Hydroxyapatite: Analytical Essay

Abstract

Femur, also called thighbone or hind leg in human body supports the maximum weight of the body under loading conditions. In this present work, the fractured femur bone is reconstructed using DICOM files obtained from Computed Tomography scan images using software’s 3D slicer and blender. In accordance with the crack, prosthetic plate was modeled in Unigraphics NX 11.0 version. The plate is then assembled with the fractured femur bone using Assembly module of the Unigraphics NX 11.0 version. Then Static structure Finite element Analysis was performed on the Assembly for different prosthetic plate materials like SS316L, Alumina, Nylon, Titanium, PMMA and PEEK with and without Hydroxyapatite(HA) coating on the prosthetic plate . It was proved in this work that best results are obtained with HA-coated prosthetic plate material that means the bone healing will be much faster when prosthetic plated are coated with Hydroxyapatite.

Keywords: Femur bone, DICOM files, Prosthetic plate, hydroxyapatite (HA), FEA

1. Introduction

By measurement, femur bone is longest bone in human body and supports the weight of body and allows motion to the leg. Fractures in femur bone are caused due to large force, impact loads, accidents, falls from high altitudes, and disease in the bone. Femur fractures that are simple, short cracks in the bone usually do not require surgery, but sever impact fracture, partial fracture, completely displaced fracture need to treat the bone using prosthetic implants. Fracture management products include a wide variety of devices including wires, pins, screws, plates, spinal fixation devices, and artificial ligaments. The types of prosthetic plates from early stages to the present day of implantation surgeries are Compression plate (CP), Dynamic compression plate (DCP), Limited- contact dynamic compression plate (LC-DCP), Point contact fixator (PC-Fix), Less invasive stabilization system (LISS), Locking compression plate (LCP), Precontoured LCP.

1.1 Materials available for prosthetic plates manufacturing

Biomaterial is defined as “A nondrug substance suitable for inclusion in systems which augment or replace the function of bodily tissues or organs. There are different biomaterials that are used to make these prosthetic plates like metals, polymers, composites, and ceramics. Mostly Stainless steel is used in orthopedic implants for temporary fixation plates because of its widely availability and cost-effectiveness. These plates are removed after the healing process is completed. Titanium is also used as a prosthetic implant which is stronger and lighter in weight compared to stainless steel. Polymers are also used in the form of implants and medical devices to replace and restore the function of damaged parts. Examples of polymers and composites are Polymethyl-methacrylate (PMMA), Polylactic acid (PLA), Polyglycolic acid (PGA). Alumina and hydroxylapatite (HA) come under the category of bioceramics. But this materials cannot be used directly as implants due to its low mechanical strength and low fracture toughness. But these materials can be used in the form of coatings and in mixed ratios with other biomaterials.

To develop the 3D models of bones CT or MRI data is collected. CT or MRI data is saved in the form of DICOM files and is used in CAD software to develop the models.

1.2 Reconstruction of bone using 3D Slicer

The collected DICOM files with slice thickness of 0.6mm were imported into this software. By enabling the volume rendering feature we can observe the visualization of the files on the slicer window in 4 views i.e., axial view, three dimension view, sagittal view, and coronal view as shown in fig2.1.A preset selection of CT bones was selected and it can be observed that in the three-dimensional view, only bones were visualized removing all the other unwanted material which is shown in fig 2.2

Fig 2.1 3D slicer window showing 4 views

Fig 2.2. Preset selection

After this, cropping was done by using the crop volume module. Here the cropping was done to get the right femur bone of the image. The cropped new volume is shown in figure 2.3.

Fig 2.3. Cropped volume

From the obtained CAD model it was observed that the model is with a lot of obstructions, irregularities, and discontinuous as it is already gone for a prosthesis with implantations. So to obtain the best model without any errors, paint effect was used in editor module. After using the paint effects the best 3D cad model of right femur is as shown in figure 2.4. This obtained model was saved in STL file format as to import the model into blender. The obtained model was with some errors and the surface achieved was rough. To remove this, software called Blender was used.

Fig 2.4 Showing 3D CAD model of the right femur after using paint effect

2.2 Finishing the femur model using Blender

The obtained model from 3D slicer was imported into Blender to remove the discontinuous shapes and errors and to obtain a good surface finish which is shown in figure 2.5 from the selection mode, the continuous and inverted links were selected by vertex selection and the inverted links were deleted to obtain an error-free femur bone without any obstructions which are shown in figure 2.6 (a) & (b).

Fig 2.5 Blender window with imported STL file of the right femur bone

Fig 2.6 Showing (a) inverted links (b) obtained model without errors

(c) Final 3D CAD model of right femur with the good surface finish

After applying the smoothening option from object modifiers, the final 3D CAD model of the femur with the good surface finish is shown in figure 2.6(c).

2.3 Initiation of fracture on the femur bone

Partial fracture was initiated for further study on the analysis of fractured femur bone. The fracture was generated in NX by removing the part material from the shaft of the femur bone as shown in figure 2.7

3. Fractured femur bone analysis

The fractured femur bone was inserted into the static structural module and the material properties of the femur bone were assigned from references [2] and[18].

3.1 Meshing

The meshing of the fractured femur bone was done with Element type triangular and element size of 5mm

Fig 2.7Fracture on femur shaft

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3.2 Boundary conditions

The lower part of the femur bone was fixed and two forces on the upper part of the femur were assigned.

Force 1: 750N, 150, 0 and Force 2: -150N, -50N, 0

Force 1 is the total body weight of the person which is acting downwards when the person is standing and force 2 is the reaction force which acting in the opposite direction as shown in fig 3.1

Fig 3.1Boundary conditions

3.3 Results of fractured bone analysis

Static structural analysis is carried out and it was noted that the maximum stresses are acting on the shaft at the initiation of fracture for the boundary conditions that are considered and the total deformation was seen maximum on head of the femur bone. The results are as shown below figure 3.2

Fig 3.2 Fractured bone (a) Maximum principal stress (b) Equivalent stress (c) Total deformation

4. Assembly for fractured bone and prosthetic plate

In this work, prosthetic plate of LCP type is modeled and assembly is done as shown in figure 4.1

Fig 4.1 Assembly of the femur and prosthetic plate

5. Assembly analysis

Edge size meshing was generated at the crack by using same mesh sizing as of fractured bone and the boundary conditions are kept same as of fractured bone. Analysis of the assembly was carried out by changing the material properties of prosthetic plates, from references [2], [17], [19], and [20]. The results of stresses and deformation of prosthetic plate materials SS316L, alumina, titanium, PEEK are as shown in fig 5.1 to 5.4.

5.1 Analysis results of fractured bone with SS316L prosthetic plate

Fig 5.1 Maximum principal stress, Equivalent stress, Total deformation of fractured bone with SS316L plate

5.2 Analysis results of fractured bone with Alumina prosthetic plate

Fig 5.2Maximum principal stress, Equivalent stress, Total deformation of fractured bone with Alumina plate

5.3 Analysis of results of fractured bone with Titanium prosthetic plate

Fig 5.3Maximum principal stress, Equivalent stress, Total deformation of fractured bone with Titanium plate

5.4 Analysis results of fractured bone with PEEK prosthetic plate

Maximum principal stress, Equivalent stress, Total deformation of fractured bone with PEEK plate

The results of stresses and deformation of prosthetic plate materials with HA-coated on SS316L, alumina, titanium, PEEK are as shown in fig 5.5 to 5.8.

5.5 Analysis results of fractured bone with HA-coated SS316L

Maximum principal stress, Equivalent stress, Total deformation of fractured bone with HA-coated SS316L plate

5.6 Analysis of results of fractured bone with HA-coated Titanium

Maximum principal stress, Equivalent stress, Total deformation of fractured bone with HA-coated Titanium plate

5.7 Analysis results of fractured bone with HA-coated Alumina

Maximum principal stress, Equivalent stress, Total deformation of fractured bone with HA-coated Alumina plate

5.8 Analysis results of fractured bone with HA-coated PEEK

Maximum principal stress, Equivalent stress, Total deformation of fractured bone with HA coated PEEK plate

6. Results and Discussions

It was observed that for HA coated Prosthetic plates stresses are been increased and deformations are reduced. The maximum stresses were acting on the plate which means that the bone was not taking the load. The decrease in the deformations means that the load-bearing capacity was increased by the plates which are affixed to the bone. The obtained maximum stresses and deformations are tabulated as shown in table 6.1 and 6.2

Table 6.1 Equivalent stress, Maximum principle stress, and total deformation of fractured bone with Prosthetic plates of different materials

• Equivalent Stress
• (Pa) Max principle stress
• (Pa) Total deformation
• (m)

1. SS316L 1.1985e8 6.7819e7 0.0017282
2. Alumina 1.322e8 09.5249e7 0.0017076
3. Titanium 2.436e8 2.3294e8 0.0016636
4. PEEK 6.9348e7 5.0685e7 0.001858

Table 6.2 Equivalent stress, Maximum principle stress and total deformation of fractured bone with HA coated Prosthetic plates of different materials

• HA Coated plates Equivalent stress
• (Pa) Max principle stress
• (Pa) Total deformation
• (m)

1. SS316L 6.0371e8 4.9614e8 0.0015459
2. Alumina 6.5522e8 5.364e8 0.0013172
3. Titanium 1.7232e8 1.1508e9 0.00094946
4. PEEK 1.908e8 1.8263e8 0.0015637

7. Conclusions and future scope

7.1 Conclusions:

• Construction of femur bone was successfully done using 3D Slicer and Blender software’s from DICOM files or CT scan data
• Analysis was carried out with different prosthetic plate materials without HA coating to the assembled fracture femur bone.
• Same procedure was carried out with 0.3mm hydroxyapatite (HA) coated on different base prosthetic plate material.
• From the results it was concluded that for HA coated plates the stresses were increased and were acting on the plate, taking the maximum load.
• It was concluded that deformations were decreased and so that the healing can be obtained with less time duration.

7.2 Future scope

Fibers and other composite materials can be used as prosthetic plates in future which should be tested clinically.

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