Thomopoulos handout - Page 1 1 Orthopaedic Biomechanics...

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Unformatted text preview: Page 1 1 Orthopaedic Biomechanics Steve Thomopoulos, Ph.D. Assistant Professor Orthopaedic Surgery & Biomedical Engineering 2 Lecture Outline Why study the biomechanics of bone, cartilage, and tendon/ligament? Bone, cartilage, tendon / ligament Structure Biomechanics Tissue engineering for orthopaedic tissues 3 The Joint 4 5 Why study the strength of bone, cartilage, and tendon/ligament? Primary function of all of these tissues is to transmit loads in very complex ways Bone: bending, compression, torsion Cartilage: friction/shear, compression Tendon/ligament: tension, torsion If we want to engineer replacements, we must understand the mechanical behavior 6 Osteoporosis.so what? Motivation: Bone Decreased bone mass Increased risk of fracture Decreased bone strength Page 2 7 Osteoporotic / age- related fractures Lifetime risk of fracture after age 50: 1/3 women, 1/8 men Spine - 500,000 annually in U.S. Hip - 250,000 Wrist - 250,000 8 Motivation: Tendon/Ligament Tendinosis.so what? Repetitive activity Tendon tear Tendon degeneration 9 10 11 Arthritis.so what? Motivation: Cartilage Decreased cartilage thickness Increased pain Increased friction 12 Osteoarthritis affects an 20.7 million Americans Typically after age 45 Women are more commonly affected than men Osteoarthritis is characterized by the breakdown of the joint's cartilage Osteoarthritis Page 3 13 14 Motivation: Interfaces Tendon-to-bone insertion heals poorly Rotator cuff repair Flexor tendon repair Anterior cruciate ligament reconstruction 15 Why do repairs fail so frequently? Re-connecting two very different materials Modulus of bone is two orders of magnitude larger than modulus of tendon Tendon is relatively extensible Bone is relatively brittle Stress concentrations will arise at the interface and the connection will be at risk for failure 16 17 Mechanical Properties Structure (organization) Composition (material) 18 Bone Structure and Biomechanics Page 4 19 Loading Modes 20 21 St iffness K ~E I /L 2 Moment M(Nm) Mid-Deflect ion (mm) Bone Material Properties Bending 22 23 Cortical Bone Material Properties Modulus (GPa) Ultimate Strength (MPa) Compression 17 205 Tension 135 Shear 3.3 71 Titanium (Ti-6Al-4V) 100 1250 Steel (316 SS) 200 850 24 Mechanical Properties Structure (organization) Composition (material) Page 5 25 Tendon Structure and Biomechanics Tendon structural hierarchy Fibril Fiber 26 27 Tendon tissue structure collagen organization 28 Tendon Mechanical Properties 29 Tendon Mechanical Properties - Hysteresis 30 Elastic mechanical properties behavior can be defined by one variable k : stiffness (structure) E : Youngs modulus (material) Page 6 31 Viscous mechanical properties behavior can be defined by one variable m : structural property : viscosity (material) ....
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Thomopoulos handout - Page 1 1 Orthopaedic Biomechanics...

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