Femur Bones Essay

1.Introduction

Bones are rigid organs that help remain internal structure of vertebrates and the femur is the largest bone in human. Femurs can withstand approximately ten times body weight in static but we can easily break them in dynamic situations. There are many types of bone fractures, but still can be classified roughly by the force directions and causes.

Transverse fracture: a fracture at a right angle to the bone's axis.

Oblique fracture: a fracture in which the break has a curved or Comminuted frac- ture in which the bone fragments into several pieces.

Spiral fracture: a fracture in a spiral shape when the bone is twisted.

Impacted fracture: fractures whose ends are driven into each other, also known as a buckle fracture.

The fractures are also closely related to bone material. There are different types of bones and wide range of properties for the same type of bone among different peo- ple. Femur bones are consist of two type, cortical bone and cancellous bone. Corti- cal bone is significantly higher in density and Young’s modulus (Dieter Christian Wirtz et al., 2000; Critical evaluation of known bone material properties to realize anisotropic FE-simulation of the proximal femur). Cancellous bone is porous, thus lower in both density and Young’s modulus. In the femur, cancellous bone mainly distributes in upper extremity and lower extremity while cortical bone consist mainly the middle shaft bone. Femur bone is light and strong which is hardly bro- ken in static state. However in many high speed impact situations femur is likely broken. The FEA(finite element analysis) method helps apply different kinds of load and force on to the femur model and reveal detail information of it.

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2. Material and Methods

Although bone is...

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...bone. But the max shear stress reaches 38MPa near the knee part and it’s be- long to the cancellous bone area. Fig. 4.3 shows the close up look at the max- imum part. Cancellous bone is weak but luckily the area is so small that it could probably cause a tiny local trau- ma rather than a large-scale bone fail- ure. And according to bone remodeling theory the osteoblasts may strengthen this area after many times of loads.

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But it is not enough, because we know when objects are taking torque as bending, the front and back near-sur- face region would take most normal stresses. So it is necessary to inspect these two areas to be safe.

From diagram 4.4 and 4.5 we can see the biggest stress occurs in the lower shaft which is really near the knee joint. The two max stresses reach 166MPa and

Fig 4.2 Shear stress in X-Z plane.

Fig. 4.3 Close-up look at maximum shear stress.