FINITE ELEMENT ANALYSIS OF FEMORAL INTRAMEDULLARY NAILING

Journal for Research | Volume 02 | Issue 10 | December 2016 ISSN: 2395-7549

Finite Element Analysis of Femoral Intramedullary Nailing Mohd. Shahjad A. Sheikh PG Student Department of Mechanical Engineering ACET Nagpur, Maharashtra, India.

Prof. A. P. Ganorkar Assistant Professor Department of Mechanical Engineering ACET Nagpur, Maharashtra, India.

Prof. R. N. Dehankar Assistant Professor Department of Mechanical Engineering ACET Nagpur, Maharashtra, India.

Abstract Biomechanics is the application of mechanical principles on the living organisms and utilizing the principles of physics, simulation and study of biomechanical structures are carried out. Finite Element Method is one of the widely accepted tools for modeling the biomechanical structures. The femur is the only bone located within the human thigh. It is both the longest and the strongest bone in the human body, extending from the hip to the knee. The method most surgeons use for treating femoral shaft fractures is intramedullary nailing. During this procedure, a specially designed nailing is inserted into the marrow canal of the femur. The rod passes across the fracture to keep it in position. An intramedullary nail can be inserted into the canal either at the hip or the knee through a small incision. It is screwed to the bone at both ends. This keeps the nail and the bone in proper position during healing. The Femur bone is modelled using 3-D Scanner and analysis is carried out in an ANSYS environment.

The fracture fixation nailing is modelled using the commercially available Solidworks CAD software. The stress distribution at the fractured site of the femur is obtained when the system is subjected to compressive loadings along with healing stages. The effects of the use of different biomaterials for the nailing on the stress distribution characteristics are also investigated.

Intramedullary nails are usually made of titanium. They come in various lengths and diameters to fit most femur bones. But the titanium is very costly metal. Hence the cost of surgery is more. Therefore aim to find best alternative metal in low cost.

Keywords: Marrow canal, intramedullary nailing, Stress distribution _______________________________________________________________________________________________________ I.

INTRODUCTION

Since the past few decades, the research in the multidisciplinary studies has grown rapidly. The experts from various fields exchange knowledge and work cohesively to find solutions to exigent issues. Biomedical Engineering is one of the multidisciplinary studies where medical practitioners (physicians) and engineers (physicists) share a common platform. Fitness of a patient has been always the topmost priority to any medical practitioner. Accurate diagnosis and exact treatments by the specialist doctors are now becoming a normal practice due to an advent of modern tools and techniques. Mechanical engineers can contribute in the field of biomechanics through their knowledge of classical mechanics, material science, fluid mechanics, computer-aided design (CAD), Finite Element Analysis (FEA) etc. Therefore, advancement of biomechanics is a conglomeration and integration of multiple disciplines, involving the application of mathematics, principles of physics and engineering methodologies to the biological systems.

Biomedical Engineering: Biomedical engineering is the scholarly use of engineering expertise to analyze and solve multifaceted problems in the biology and the medicine, which offers the improved health standards. Biomechanics is one of the many academic sub-disciplines of biomedical engineering. It involves the precise description of human movement and the study of the causes of human movement.

Biomechanics is thus defined as the study of the movement of living things using the science of mechanics. Mechanics is a branch of physics that is concerned with the description of motion and how forces create motion. Forces acting on living things can create motion; however excessive forces may overload tissues, causing injury. Biomechanics, using the principles of solid and fluid mechanics, offers to investigate the effects of energy and forces on biological systems. It provides conceptual and mathematical tools to model and predict the mechanical behavior of any living system. Thus, biomechanics has been enhanced by the research work of mathematicians, engineers, physicists, biologists and physicians.

Human Skeleton System: The human skeleton is the internal framework of the body. It is composed of 270 bones at birth – this total decreases to 206 bones by adulthood after some bones have fused together. Skeletal system is the system of bones, associated cartilages and joints All rights reserved by www.journalforresearch.org

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Finite Element Analysis of Femoral Intramedullary Nailing (J4R/ Volume 02 / Issue 10 / 001)

of human body. Together these structures form the human skeleton. Skeleton can be defined as the hard framework of human body around which the entire body is built. Almost all the hard parts of human body are components of human skeletal system.

Joints are very important because they make the hard and rigid skeleton allow different types of movements at different locations. If the skeleton were without joints, no movement would have taken place and the significance of human body; no more than a stone.

Femur Bone: Femur is the bone of leg that articulates above with the hip bone to form hip joint and below with the tibia and patella to form the knee joint. It is the longest bone of human body. The femur is responsible to bear the largest percentage of body weight during normal weight bearing activities. Its length is 26% of the person’s total height, a ratio that is useful in anthropology, because it offers a basis for a reasonable estimate of a subject’s height from an incomplete skeleton. Femoral shaft fractures are among the most common major injuries that an orthopedic surgeon will be required to treat. Femoral shaft fracture treatment can be divided into two divisions: External Fixation of Fractures: In this type of operation, metal pins or screws are placed into the bone above and below the fracture site. The pins and screws are attached to a bar outside the skin. This device is a stabilizing frame that holds the bones in the proper position so they can heal.

External fixation is usually a temporary treatment for femur fractures. Because they are easily applied, external fixators are often put on when a patient has multiple injuries and is not yet ready for a longer surgery to fix the fracture. An external fixator provides good, temporary stability until the patient is healthy enough for the final surgery. In some cases, an external fixator is left on until the femur is fully healed, but this is not common.

Fig. 1: External Fixation of Fractures

Internal Fixation of Fractures: In this type of operation, metal plate, nailing or screws are placed into the bone above and below the fracture site. The plate, nailing and screws are attached to a bar inside the skin. Following method of internal fixation as shown below: 1) Plates and Screws: During this operation, the bone fragments are first repositioned (reduced) into their normal alignment.

They are held together with special screws and metal plates attached to the outer surface of the bone as shown in figure 2.3.

Plates and screws are often used when intramedullary nailing may not be possible, such as for fractures that extend into either the hip or knee joints.

2) Intramedullary Nailing: Currently, the method most surgeons use for treating femoral shaft fractures is intramedullary nailing. During this procedure, a specially designed metal rod is inserted into the marrow canal of the femur. The rod passes across the fracture to keep it in position.

An intramedullary nail can be inserted into the canal either at the hip or the knee through a small incision. It is screwed to the bone at both ends as shown in figure 2.3. This keeps the nail and the bone in proper position during healing. Intramedullary nails are usually made of titanium. They come in various lengths and diameters to fit most femur bones.

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Finite Element Analysis of Femoral Intramedullary Nailing (J4R/ Volume 02 / Issue 10 / 001)

Fig. 2: Internal Fixation

II. SELECTION OF MATERIALS The biomaterials I have selected for this study are:  Titanium (Ti-6Al-4V)  stainless steel (S.S-316L)  Cobalt Chrome.

Table – 1 Mechanical Properties of Intramedullary Nailing Material.

Material Titanium (Ti-6Al-4V) Stainless Steel (S.S-316L) Cobalt Chrome

Density (ρ) Kg/m3 4430 8000 8300

Young’s Modulus (E) GPa 895 193 210

Poisson’s Ratio (µ) 0.342 0.30 0.3

III. MODELING AND ANALYSIS OF FEMUR BONE The human femur bone was Scan by 3D Scanner and converted into CAD model is shown in Fig. 3. The analysis of human bone is done by using ANSYS WORKBENCH®.

Fig. 3: CAD Model of Femur Bone

Material Assignments: The file created using the 3D Scanner software is saved in .IGS format. It is imported to the ANSYS software Then generate option is clicked. Now the model is ready for analysis. The imported geometry in ANSYS is shown in Fig. 4. Femur was assumed to be isotropic and linearly elastic and the material properties for the cortical bone.

Table – 2 Mechanical properties of Femur Bone Material properties Bone Density (ρ) 2000 Kg/m3 Young’s Modulus (E) 12 GPa. Poisson’s Ratio (µ) 0.3

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Finite Element Analysis of Femoral Intramedullary Nailing (J4R/ Volume 02 / Issue 10 / 001)

Fig. 4: Assigning the Material Property of Bones

Meshing: There are several types of meshing such as tetrahedral, pentahedral, hexahedral etc. As the structures of bones are irregular, the femur is meshed by using tetrahedral meshing. Tetrahedral meshing being used because the geometrical shape triangle is suitable for irregular structures. The bone was meshed with tetrahedral elements with a total number of 1,73,821 (2,52,563 nodes).

Fig. 5: Meshing of Femur Bone Model

Boundary Condition: Femur bone is inflexible condition. During analysis geometrical model is subjected to eccentric and concentrate loading conditions. In this boundary condition applied load of 750 Pa applied on the head of femur bone and fixed support is provided at lateral end (lower surface). The boundary conditions given for the femur bone in ANSYS is shown in Fig. 6.

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Finite Element Analysis of Femoral Intramedullary Nailing (J4R/ Volume 02 / Issue 10 / 001)

Fig. 6: Fixed Supports in the Lower Surface and Load at the Head Surface of Femur

Results: Results shows that higher deformation occurs at the head of femur and lowest occur at the lower end. Maximum equivalent stress 67733 Pa and Minimum principle stress is 99.98 Pa. Maximum principle stress is generated at the middle section of the femur.

The equivalent (Von Misses) stress 67733 Pa occurs. Show in figure 7

Fig. 7: Equivalent Stress of Femur Bone

Fig. 8: Directional Deformation of Femur Bone

IV. ANALYSIS OF FRACTURED FEMUR BONE JOINED WITH INTRAMEDULLARY NAILING Bone nailing for the femur bone is modelled by using SOLIDWORKS software. The dimensions for this bone nailing are referred by buying a femur bone nailing made of Ti-6Al-4V. The previous femur bone model is broken into two pieces. They are joined by a screw by using the SOLIDWORKS software. Then the new assembled model is imported to ANSYS software. The same procedure is follow by the previous femur analysis setup. But a change is that, here three materials are being used and so that material properties are assigned for both the materials. Bonded contact with no slip was modelled for bone to bone interfaces. Friction joint is given for joining the screws with the nailing. The frictional coefficient of (Îź=0.2) was taken.

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Finite Element Analysis of Femoral Intramedullary Nailing (J4R/ Volume 02 / Issue 10 / 001)

Fig. 9: Assigning the Material Property of Intramedullary Nailing

The stress distribution and deformation of femur with implant of different material properties for a different weight during normal position. The entire process required a couple of hour. Only static load was applied on the models. The deformation of bone-nailing system in compressive for apply titanium material as shown in Fig 10.

Figure 10: Fixed Supports in the Lower Surface and Load at the Head Surface of Femur

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Finite Element Analysis of Femoral Intramedullary Nailing (J4R/ Volume 02 / Issue 10 / 001)

Fig. 11: Equivalent Stresses on Titanium Nailing Model

Fig. 12: Graphs Shown Finite Element Result for Different Materials.

V. CONCLUSIONS In this study femur bone with simple intramedullary nailing was modelled and analyzed. Three different materials for fabricating intramedullary nailing selected. Analysis was done in the assembled models. Selection of intramedullary nailing material for surgical implants plays a vital role in Femur shaft fracture healing process. Mostly used materials are Titanium. Through this static loading condition and material comparison analysis we have found out the Titanium Implant mechanical properties is better than other material. But also stainless steel material has good stability. Since Ti-6Al-4V material cost more, Titanium cost over the Stainless Steel can be used as an alternative for Re-Engineered Indian femur implant nailing.

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Sandeep Das, Saroj Kumar Sarangi, Pravin P Patil; Finite Element Analysis of Femur Fracture Fixation Plates, International Journal of Basic and Applied Biology, ISSN: 2349-5839 Volume 1, Number 1 (2014) pp. 1-5.

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