الميكانيكية الاحيائية في جسم الانسان Biomechanics in Human Body الميكانيكية الاحيائية في جسم الانسان

Mechanics Mechanics-study of forces and motions for the body. 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

Basic Biomechanics Biomechanics-apply mechanics to the structure and function of the human body. Is the scientific study of the mechanics of biological systems.

Applications 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 There are far too may to cover in 4- 5 weeks so go back to the context of striking and still there are a lot.

Biomechanical principles associated with basic movement patterns Running Stopping forces (action/ reaction) motion (straight line) momentum friction 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

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

The movement of the foot when walking. 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 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 Lion bite down with 5,533 N 10 Dog bite = 1,410 N 2.5

Fluid biomechanics (blood flow). Vascular Biomechanics Continuity Equation: mass in = mass out Q = ((P1-P2)..R4)/(8.µ.L) Assumptions - Laminar Flow - Newtenian fluid - Incompressible fluid - Single phase

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 < 212 N/m2 Tension < 146 N/m2 Shear < 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 Following a fracture, ductile material will not conform to original shape after fracture. Brittle will return to original shape after fracture. return to original shape after fracture

Type of Loading Fracture Mechanics Bending Torsion Bending load: Compression strength greater than tensile strength Fails in tension Axial Loading Compression Tension

Bending of a Long, Solid Bone: Tension Compression Stress Free in the middle Bending of a Long, Hollow Bone:  =M . y / I Tension Compression I = .(R4-r4)/4 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 Plate D D D = distance from force to implant 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 To design artificial lower limb 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 -Static alignment -dynamic alignment Hip, knee, and ankle joint centers lie along a common axis.

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

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