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‫‪Biomechanics in‬‬
‫‪Human Body‬‬
‫الميكانيكية االحيائية في جسم االنسان‬
Mechanics-study of forces and motions for the body.
Mechanics
Statics
Dynamics
deal with nonmoving
parts (equilibrium).
deal with moving systems
Kinetics
Describes forces that
cause motion of a body
Kinematics
Describes motion and includes
consideration of time, displacement,
velocity, acceleration and mass.
Basic Biomechanics
• Biomechanics-apply mechanics to the structure
and function of the human body.
Is the scientific study
of the mechanics of
biological systems.
Biomechanics
Engineering
(Mechanics)
Anatomy
Physiology
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
• Balance and stability
• Centre of gravity
• Elasticity
• Forces (action & reaction)
• pressure
• power
• Bending moment
• Torque moment
• Friction
• Wear
• Density
• Momentum
• Velocity
• Time
• Acceleration
• Deceleration
• Mass
• Inertia
• Dimensions
• Viscosity
Biomechanical principles associated with basic movement patterns
Running
forces
(action/ reaction)
motion (straight line)
momentum
friction
Stopping
forces
acceleration
and deceleration
Newtons laws
friction
General Motion
Most movements are
combination of both
Linear
motion
•
•
•
Angular
motion
Newton’s First Law
–Law of inertia
Newton’s Second Law
–Law of Acceleration
Newton’s Third Law
–Law of Action and
Reaction
JOINT
REACTION
FORCES
Loads
The external forces that act on the
body impose loads that affect the
internal structures of the body.
Humans moves through a system of levers
There are 3 classes of levers.
First class lever
Second class lever
Third class lever
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 =
Resistance
Force
or
Mechanical advantage =
Length of force arm
Length of resistance arm
Biomechanics of the denture
Bitting Force
• Human female bite = 360 N
• Human male bite = 564 N
Boxer can punch
with 10,528 N 18
Dog bite = 1,410 N 2.5
Lion bite down
with 5,533 N 10
Fluid biomechanics (blood flow).
Vascular Biomechanics
• Continuity Equation:
• mass in = mass out
  Au    Au
in
out
Q = ((P1-P2)..R4)/(8.µ.L)
Assumptions
- Laminar Flow
- Newtenian fluid
- Incompressible fluid
- Single phase
Re 
Du

Atherosclerosis
Blood density
1060 kg/m3
Blood viscosity
0.0035 kg/m.s
Atherosclerosis
Velocity Pathlines
Steinman, 2000
Wall Shear Stress Contours
Augst 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
Tension
Shear
< 212 N/m2
< 146 N/m2
< 82 N/m2
Mechanical Properties of Bone
Ductile or Brittle
Depends on age and rate at which it is loaded
- Younger bone is more ductile
- Bone is more brittle at high speeds
return to original
shape after fracture
Type of Loading
Bending
Torsion
Axial Loading
Compression
Tension
Fracture Mechanics
•Bending load:
– Compression strength greater
than tensile strength
– Fails in tension
Bending of a Long, Solid Bone:
Tension
Stress Free
in the middle
Compression
Bending of a Long, Hollow Bone:
 =M . y / I
Tension
I = .(R4-r4)/4
Compression Save weight &
keep strength:
Biomechanics Bone fixation
External
fixation
Internal
fixation
Biomechanics of External Fixation
• Number of Pins
– Two per segment
– At least 3 pins
Biomechanics of Internal Fixation
IM Nails (Rod)
• Stiffness is high
proportional to the 4th
power.
Biomechanics of Internal Fixation
Plate Fixation
• Functions of the plate Compression Neutralization Buttress
Bending moment = F x D
F = Force
F = Force
IM
Nail
D
D = distance
from force to
implant
Plate
D
The bending moment
for the plate is greater
due to the force being
applied over a larger
distance
Biomechanical principles
similar 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.
Treatment or Total Knee Replacement
•Moving surfaces of the knee are
metal against plastic
UHMWPE
Structural Alignment
Genu Varum
(Bowlegged)
Genu Valgum
(knock kneed)
Hyperextension
Biomechanics of Flat Foot
Biomechanics of motion of human body
Gait Cycle
Swing
Phase
Stance
Phase
Heel Strike
Midstance
Toe off
To design artificial
lower limb
Ground reaction force (by force plate “platform”)
1.3 W
Biomechanics of motion of human body
-Socket alignment
Hip, knee, and ankle
joint centers lie along a
common axis.
-Static alignment
-dynamic alignment
Numerical Study of Prosthetic Socket
(Interface pressure sensor between socket and skin)
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
Thanks you
for listening