Biomechanics in Human Body

االنسان فيجسم االحيائية الميكانيكية

Mechanics

Statics deal with nonmoving parts (equilibrium).

Dynamics deal with moving systems

Kinematics Describes motion and includes consideration of time, displacement, velocity, acceleration and mass.

Kinetics Describes forces that

cause motion of a body

Mechanics-study of forces and motions for the body.

Basic Biomechanics

• Biomechanics-apply mechanics to the structure and function of the human body.

Is the scientific study of the mechanics of biological systems.

Engineering(Mechanics)

Anatomy Physiology

Biomechanics

Applications Biomechanics

- Improved the performance ( Human movement)- Preventing or treating injury- Design prosthesis & orthosis or artificial limb

Biomechanics• Biomechanics is be used to:

–To understand the biomechanical analysis (motion) (Gait cycle) (for normal and patient human).

–To understand function of vascular system in order to analysis the fluid biomechanics (blood flow).

–To analysis the biomechanics of : soft tissue (muscle) hart tissue (bones).

–To model these systems to aid in the design of prosthetic devices (e.g. artificial artery or artificial limb)

Principles associated to biomechanical analysis

• Density• Momentum• Velocity• Time• Acceleration• Deceleration• Mass• Inertia• Dimensions• Viscosity

• Balance and stability• Centre of gravity• Elasticity• Forces (action & reaction)• pressure• power• Bending moment• Torque moment

• Friction• Wear

Biomechanical principles associated with basic movement patterns

forcesacceleration and decelerationNewtons lawsfriction

StoppingRunning

forces (action/ reaction)motion (straight line)momentumfriction

General Motion

Most movements arecombination of both

• Newton’s First Law–Law of inertia

• Newton’s Second Law–Law of Acceleration

• Newton’s Third Law–Law of Action and

Reaction

Linear motion

Angular motion

JOINTREACTIO

NFORCES

LoadsThe external forces that act on the body impose loads that affect the internal structures of the body.

First class lever

There are 3 classes of levers.

Second class lever Third class lever

Humans moves through a system of levers

First Class Levers

Up and down movement of the head about the atlas joint.

First Class Levers

Using a crowbar to move a rock.

First Class Levers

Using a hammer to pull out a nail.

First Class Levers

A see-saw.

Second Class Levers

The movement of the foot when walking.(the calf muscle provides the effort and

the ball of the foot is the pivot)

Second Class Levers

Opening a bottle with a bottle opener

Second Class Levers

Pushing a wheel barrow.

Third Class Levers

Biceps curl.

Levers• The mechanical advantage of levers may be

determined using the following equations:Mechanical advantage =

ResistanceForceor

Mechanical advantage =Length of force arm

Length of resistance arm

Bitting Force

Dog bite = 1,410 N 2.5

Lion bite down with 5,533 N 10

Boxer can punch with 10,528 N 18

• Human female bite = 360 N• Human male bite = 564 N

Biomechanics of the denture

• Continuity Equation:• mass in = mass out outin uAuA

Assumptions- Laminar Flow- Newtenian fluid- Incompressible fluid- Single phase

Du

Re

Fluid biomechanics (blood flow).Vascular Biomechanics

Q = ((P1-P2)..R4)/(8.µ.L)

Atherosclerosis

Blood viscosity0.0035 kg/m.s

Blood density1060 kg/m3

Atherosclerosis

Velocity PathlinesSteinman, 2000

Wall Shear Stress ContoursAugst et al, 2007 Jamalian Ardakani, 2010

In healthy vessels, tw is low (~ 15-20 dynes/cm)

Velocity Pathlines

Model 1 (peak of systole) Model 1 (peak of diastole)

Bone Biomechanics (Hard tissue)

• Bone is anisotropic material (modulus is dependent upon the direction of

loading).• Bones are:

strongest in compression.weakest in shear.

• Ultimate Stress at Failure Cortical Bone Compression < 212 N/m2

Tension < 146 N/m2

Shear < 82 N/m2

Mechanical Properties of Bone

return to original shape after fracture

Ductile or BrittleDepends on age and rate at which it is loaded

- Younger bone is more ductile- Bone is more brittle at high speeds

Bending

Type of Loading

TorsionAxial LoadingCompressionTension

Fracture Mechanics

•Bending load:– Compression strength greater

than tensile strength– Fails in tension

Tension

Compression

Stress Freein the middle

Bending of a Long, Solid Bone:

Save weight & keep strength:

Tension

Compression

Bending of a Long, Hollow Bone: =M . y / I

I = .(R4-r4)/4

Biomechanics Bone fixation

External fixation

Internal fixation

Biomechanics of External Fixation

• Number of Pins– Two per segment– At least 3 pins

IM Nails (Rod)• Stiffness is high

proportional to the 4th power.

Biomechanics of Internal Fixation

Plate Fixation• Functions of the plate Compression Neutralization Buttress

Biomechanics of Internal Fixation

Bending moment = F x DF = Force

D

D = distance from force to implant

F = Force

D

The bending moment for the plate is greater due to the force being applied over a larger distance

IM Nail

Plate

Biomechanical principlessimilar to those of external fixators

Stress distribution

Osteoarthritis may result from wear and tear on the joint

The medial (inside) part of the knee is most commonly affected by osteoarthritis. 

• Moving surfaces of the knee are metal against plastic

Treatment or Total Knee Replacement

UHMWPE

Structural Alignment

Hyperextension

Genu Valgum (knock kneed)

Genu Varum (Bowlegged)

Biomechanics of Flat Foot

Gait Cycle

Swing Phase

Stance Phase

Heel Strike Midstance Toe off

Biomechanics of motion of human body

To design artificial lower limb

Ground reaction force (by force plate “platform”)

1.3 W

Hip, knee, and ankle joint centers lie along a

common axis.

-Socket alignment-Static alignment-dynamic alignment

Biomechanics of motion of human body

(Interface pressure sensor between socket and skin)

Numerical Study of Prosthetic Socket

Numerical Study of Prosthetic Socket

Theoretical Part

-Stress- Max. Normal Stress- Max. Shear Stress- Von Mises stress

- Deformation- Linear- Angular

-Fatigue ratio-Strain energy-Failure index-Safety factor

Contours of Deformation Distribution

Contours of Equivalent Von Mises Stress Distribution

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