Biomechanics of Bones
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This document provides an overview of bone biomechanics. It discusses the composition and types of bones, as well as their main functions of protecting organs and supporting the body. Bones are made up of collagen fibers and bone cells. There are two types of bone tissue: cortical bone and cancellous bone. Bones can be categorized into four basic shapes: long bones, short bones, flat bones, and irregular bones. The document then covers the mechanical properties of bone, explaining that bone has high compressive but low tensile strength. It analyzes the biomechanics of bone in terms of stress, strain, elasticity, plasticity, and failure points. In summary, the document provides a comprehensive review of bone composition, structure,
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Biomechanics of Bones
- 1. 1 BIOMECHANICS OF BONES Farhod Turaev Warsaw University of Technology
- 2. Contents 2 Introduction The Skeleton System Types of the Bones Composition of Bones Functions of Bones Bone Biomechanics
- 3. Introduction 3 Bone tissue, or osseous tissue, - a type of connective tissue used in forming bones. Bones protect the vital organs and help support the body. Bone is composed mainly of collagen, or ossein, fibers, and bone cells called osteocytes. There are two types of bone tissue, referred to as cortical bone and cancellous bone.
- 4. The Skeleton System 4 299 bones (baby), 209 bones (adults) 4 basic shapes
- 5. Types of the Bones 5 4 basic shapes: Long bones (femur)
- 6. Types of the Bones 6 4 basic shapes: Short bones (wrist, ankle)
- 7. Types of the Bones 7 4 basic shapes: Flat bones (skull, scapula)
- 8. Types of the Bones 8 4 basic shapes: Irregular bones (vertebrae)
- 11. Mechanical properties of bone 11 Relatively hard; Lightweight; Composite material; high compressive strength of about 170 MPa (1800 kgf/cm²); poor tensile strength of 104–121 MPa; very low shear stress strength (51.6 MPa).
- 12. Basic Biomechanics Material Properties Elastic-Plastic Yield point Brittle-Ductile Toughness Independent of Shape! Structural Properties Bending Stiffness Torsional Stiffness Axial Stiffness Depends on Shape and Material!
- 13. Basic Biomechanics Force, Displacement & Stiffness Force Slope Stiffness = Force/Displacement Displacement
- 14. Basic Biomechanics Force Area Stress = Force/Area L Strain Change Height ( L) / Original Height(L0)
- 15. Basic Biomechanics Stress-Strain & Elastic Modulus Stress = Force/Area Elastic Modulus = Stress/Strain Strain = Change in Length/Original Length ( L/ L0)
- 16. Basic Biomechanics Elastic Modulus (GPa) of Common Materials in Orthopaedics Stainless Steel Titanium Cortical Bone Bone Cement Cancellous Bone UHMW-PE 200 100 7-21 2.5-3.5 0.7-4.9 1.4-4.2
- 17. Basic Biomechanics Elastic Deformation Plastic Deformation Energy Elastic Plastic Force Energy Absorbed Displacement
- 18. Basic Biomechanics Elastic • • • • • Plastic Failure Stiffness-Flexibility Yield Point Failure Point Brittle-Ductile Toughness-Weakness Yield Force Stiffness Displacement
- 20. Basic Biomechanics Load to Failure Continuous application of force until the material breaks (failure point at the ultimate load). Common mode of failure of bone and reported in the implant literature. Fatigue Failure Cyclical subthreshold loading may result in failure due to fatigue. Common mode of failure of orthopaedic implants and fracture fixation constructs.
- 21. Basic Biomechanics Material properties of bones: Anisotropic Mechanical properties dependent upon direction of loading Viscoelastic Stress-Strain character dependent upon rate of applied strain (time dependent).
- 22. Bone Biomechanics Bone is anisotropic - its modulus is dependent upon the direction of loading. Bone is weakest in shear, then tension, then compression. Ultimate Stress at Failure Cortical Bone Compression Tension Shear < 212 N/m2 < 146 N/m2 < 82 N/m2
- 23. Bone Biomechanics Bone is viscoelastic: its forcedeformation characteristics are dependent upon the rate of loading. Trabecular bone becomes stiffer in compression the faster it is loaded.
- 24. Bone Mechanics Bone Density Subtle density changes greatly changes strength and elastic modulus Density changes Normal aging Disease Use Disuse Cortical Bone Trabecular Bone Figure from: Browner et al: Skeletal Trauma 2nd Ed. Saunders, 1998.
- 25. Basic Biomechanics Bending Axial Loading Tension Compressio n Bending Compression Torsion Torsion
- 26. Fracture Mechanics Figure from: Browner et al: Skeletal Trauma 2nd Ed, Saunders, 1998.
- 27. Fracture Mechanics Bending load: Compression strength greater than tensile strength Fails in tension Figure from: Tencer. Biomechanics in Orthopaedic Trauma, Lippincott, 1994.
- 28. Fracture Mechanics Torsion The diagonal in the direction of the applied force is in tension – cracks perpendicular to this tension diagonal Spiral fracture 45º to the long axis Figures from: Tencer. Biomechanics in Orthopaedic Trauma, Lippincott, 1994.
- 29. Fracture Mechanics Combined bending & axial load Oblique fracture Butterfly fragment Figure from: Tencer. Biomechanics in Orthopaedic Trauma, Lippincott, 1994.
- 30. Conclusion 30 • Stress-Strain-Strength properties; • Elastic Deformation Analyses; • Plastic Deformation Analyses; • Hardness of the parts; • Resistance of bones.
Editor's Notes
- The human skeletal system is primarily composed of two types of skeletal tissue, bones and cartilage. Bones provide the framework for the human body and help protect internal organs from trauma.
- They also aid in red blood cell production, store minerals, and support movement. Cartilage keeps the bones connected, helps them move, and prevents friction damage at the ends of joined bones. It provides flexible support and shaping in external structures like the nose and ears as well as internal structures, such as the wind pipe.The skeletal system includes all the bones of the body plus joints where they attach to each other. Skeleton system protects internal organs and provides a framework, allows standing upright and moving. Skeleton system stores minerals that a body needs to function properly and produce blood cells.The skeletal system is made up 206 different bones which come in 4 basic shapes.
- Long bones are characterized by a shaft, the diaphysis, that is much longer than it is wide. They are made up mostly of compact bone, with lesser amounts of marrow, located within the medullary cavity, and spongy bone. Most bones of the limbs, including those of the fingers and toes, are long bones.
- Short bones are roughly cube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. The bones of the wrist and ankle are short bones.
- Flat bones are thin and generally curved, with two parallel layers of compact bones sandwiching a layer of spongy bone. Most of the bones of the skull are flat bones.
- Irregular bones do not fit into the above categories. They consist of thin layers of compact bone surrounding a spongy interior. By the name, their shapes are irregular and complicated. Often this irregular shape is due to their many centers of ossification or because they contain bony sinuses. The bones of the spine, Pelvis, and some bones of the skull are irregular bones.
- The majority of bone is made of the bone matrix. It is composed primarily of inorganic hydroxyapatite and organic collagen. Bone is formed by the hardening of this matrix around entrapped cells. When these cells become entrapped from osteoblasts they become osteocytes.It is much less dense and comparatively weaker than cortical bone tissue, cancellous tissue serves an important purpose. There are two kinds of bone marrow. Red bone marrow is almost completely made up of specialized cells that make the majority of the body's red and white blood cells, and platelets.
- This image shows trabecular bone structure in the lower spine of a young adult compared to an osteoporotic elderly adult. When a child is born, all of the bone marrow in his body is typically red bone marrow.As a person grows older, more and more red bone marrow is replaced by yellow bone marrow, which is made mostly of fat. During times of extreme starvation, the body will use these fat stores, and, in some cases, the yellow marrow can change back into red marrow if needed. Roughly half of all marrow in an adult's body is yellow.
- Let’s talk about Mechanical properties.The primary tissue of boneis a relatively hard and lightweight composite material. It is mostly made up of a composite material incorporating the mineral calcium phosphate in the chemical arrangement termed calcium hydroxyl apatite (this is the osseous tissue that gives bones their rigidity) and collagen, an elastic protein which improves fracture resistance. It has relatively high compressive strength of about 170 MPabut poor tensile strength of up to 121 MPa and very low shear stress strength (51.6 MPa), meaning it resists pushing forces well, but not pulling or torsional forces. While bone is essentially brittle, it does have a significant degree of elasticity, contributed chiefly by collagen. All bones consist of living and dead cells embedded in the mineralized organic matrix that makes up the osseous tissue.