PTY1016 Mechanics Biological Tissues (2024) PDF

PTY1016 Foundation of Physiotherapy: Movement Biomechanics Basic Concepts of Mechanics of Biological Tissues Alan Wong, PhD, MPH [email protected] Kinetic Concepts Forces Gravity Muscles Externally ap...

PTY1016 Foundation of Physiotherapy: Movement Biomechanics Basic Concepts of Mechanics of Biological Tissues Alan Wong, PhD, MPH [email protected] Kinetic Concepts Forces Gravity Muscles Externally applied resistances Friction Types of Forces on Musculoskeletal System The manner by which forces or loads are most frequently applied to the musculoskeletal system is shown. The combined loading of torsion and compression is also illustrated. Neumann, D. A. (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier. Basic Mechanics Concepts – (1) Stress Stress (σ) is a physical quantity. The stress is the force per unit area applied to the material. Basic Mechanics Concepts – (2) Strain Stresses lead to strain (or deformation). Putting pressure on an object causes it to stretch. Strain is a measure of how much an object is being stretched. Stress and Strain Elastic Modulus Stress divided by strain is defined as the modulus of elasticity an indicator of an object's likelihood to deform when a force is applied. Page 17 Basic Mechanics Concepts – Stress-Strain Curves Ref: Nihat Özkaya and Margareta Nordin. Fundamentals of Biomechanics: Equilibrium, Motion, and Deformation. 2nd ed. Springer; 1999. Tensile Stress-Strain Response There are 3 distinct regions in the stress- strain curve: Initial linearly elastic region where slope = elastic modulus (E). Intermediate region – exhibit yielding & nonlinear elasto- plastic material behaviour. Final region – exhibits linear plasticity where slope = strain hardening modulus. In biological tissues: Dunleavy, K., & Kubo Slowik, A. (2019). Therapeutic exercise prescription. Elsevier, chapter 1. In biological tissues: Dunleavy, K., & Kubo Slowik, A. (2019). Therapeutic exercise prescription. Elsevier, chapter 1. Stress-strain Relationship The stress-strain relationship of an excised ligament that has been stretched to a point of mechanical failure (disruption). Neumann, D. A. (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier. Viscoelasticity All connective tissues are viscoelastic materials, i.e. fluid-like component to their behaviour Viscosity – material's resistance to flow (a fluid property) High-viscosity fluids (e.g., honey) flow slowly. Lower-viscosity fluids (e.g., water) flow quickly. Decreases with temperature and slowly applied loads Elasticity – material’s ability to return to its original length or shape after the removal of deforming load. Length changes or deformations are proportional to applied forces/loads. Depend on connective tissue’s collagen and elastin content and organization. When stretched, work is done (= force x distance) and energy in stretched material increases. Oatis, C. A. (2016). Kinesiology: The Mechanics and Pathomechanics of Human Movement. (3rd ed.). New York: Wolters Kluwer. Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Time- and rate-dependent properties Viscoelastic materials deform under either tensile or compressive forces, but return to their original state after removal of the force Creep Stress-relaxation Strain-rate sensitivity Hysteresis Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis.  Time- and rate-dependent properties of dense connective tissues. A. Creep: When the tissue is loaded to a fixed force level, and length is measured, the latter increases with time (T0 to T1) and the tissue recovers its original length in a nonlinear manner (T1 to T0). (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer-Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Creep Progressive strain (deformation) of a material when under a constant load over time. A phenomenon of viscoelasticity, and therefore common in human tissue. What are some examples for clinical practice?  Time- and rate-dependent properties of dense connective tissues. B. Force or stress-relaxation: If the tissue is stretched to a fixed length and held there, the force needed to maintain this length will decrease with time. (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer-Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Stress Relaxation Stress relaxation is the reduction of stress within a material over time as the material is subjected to a constant deformation. When applying and maintaining a fixed displacement, or strain, the resisting force (from which stress is calculated) can be measured as a function of time. Stress generally decreases with time and hence the label “relaxation.”  Both creep and stress relaxation are important behaviors in biological soft tissue.  What are some examples of stress relaxation in human movement?  Time- and rate-dependent properties of dense connective tissues. C. Hysteresis: As the tissue is loaded and unloaded, some energy is dissipated through tissue elongation and heat release. (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer-Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Hysteresis When force is applied (loaded) and removed (unloaded) to a structure, the resulting load- deformation curves do not follow the same path. Not all of the energy gained as a result of the lengthening work (force x distance) is recovered during the exchange from energy to shortening work. Some energy is lost, usually as heat.  Time- and rate-dependent properties of dense connective tissues. D. If the tissue is loaded rapidly, more energy (force or stress) is required to deform the tissue. (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer- Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Strain-rate sensitivity Most tissues behave differently if loaded at different rates. When a load is applied rapidly, the tissue is stiffer, and a larger peak force can be applied to the tissue than if the load was applied slowly. The subsequent stress-relaxation also will be larger than if the load was applied slowly. Creep will take longer to occur under conditions of rapid loading. What are some examples of clinical applications? Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. PTY1016 Foundation of Physiotherapy: Movement Biomechanics Biomechanics of the Bone, Joint and Soft Tissues Alan Wong, PhD, MPH, BPhty(Hons) [email protected] Biological Tissues Biological tissues can be classified as : Hard – e.g. bone, teeth. Soft – Tendons, ligaments, joint capsules, skin, muscles, articular cartilage. Page Fracture Bone fractures heal by forming bone callus at the site of fracture. When a bone is fractured, blood pours into the injured area to form a clot. This is known as a fracture haematoma and its role is to act as a provisional scaffold for migration of cells and a source of growth factors released by the haematopoietic cells trapped in the haematoma. These growth factors induce the migration and proliferation of osteoblasts, fibroblasts and mesenchymal cells, which form a type of granulation tissue around each fracture end, thus forming a bridge between the separated ends. In the first week of injury, the granulation tissue gives rise to islands of cartilaginous procallus, also known as soft callus , to anchor the broken ends together. Within two to three weeks, through a process known as endochondral ossification, the soft callus is slowly converted to a hard bony framework to further stabilise the connection between the separated ends. Between four to 16 weeks, the callus is remodelled so that the cartilaginous structure converts to calcified bone matrix and the bone is shaped to return towards the near-normal shape and function, including clear separation of the medullary cavity from the compact bone. The most important factors that influence bone healing include blood supply, mechanical stability, the location of the injury and bone loss due to age-associated changes or the extent of trauma to the bone. Patient diet also has an impact on the quality of formed bone; for example, nutritional deficiencies in calcium and vitamin D or loss of capacity to absorb calcium through procedures such as gastric bypass. Medication prescribed, such as bisphosphonates, also affects a patient's Tomkins, Z. (2020). Applied Anatomy & Physiology : an interdisciplinary approach. capacity to generate good-quality bone. Elsevier, pp. 279-304. Bone Tissue Bone is the primary structural element of the human body Supports and protects the internal organ. Assists movement: Sites for muscle attachment Facilitates muscle actions and body movement Mineral “bank”: Reservoir for calcium deposit to maintain homeostasis of blood calcium Blood cell production: Hemopoiesis (red marrow) Energy storage: Adipose tissue (yellow marrow) Page Types of the Bones Patton, K. T., & Thibodeau, G. A. (2019). Anatomy & physiology ([Adapted International edition].). Elsevier, chapter 11. Long Bone Patton, K. T., & Thibodeau, G. A. (2019). Anatomy & physiology ([Adapted International edition].). Elsevier, chapter 11. Flat and other bones Patton, K. T., & Thibodeau, G. A. (2019). Anatomy & physiology ([Adapted International edition].). Elsevier, chapter 11. Composition of the Bone Biologically, bone is a connective tissue which binds together various structure of the body. Mechanically, bone is a composite material with various solid and fluid phases. Bone contains inorganic components which makes it hard and rigid and organic components which provide the flexibility. https://in.pinterest.com/pin/773000723516028291/ Composition of the Bone There are two types of bone tissue: Cortical or compact bone tissue is a dense material forming outer shell (cortex) of bones. Cancellous, trabecular, or spongy bone tissue consists of thin plates (trabeculae) in a loose mesh structure enclosed by the cortical bone. Bones are surrounded by a dense fibrous membrane called the periosteum and covers entire bone except for the joint surfaces which are covered by articular cartilage. Spongy Bone vs. Compact Bone: What's the Difference? https://www.pinterest.com/pin/718676053017868345/ Mechanical Properties of the Bone Major factors influencing mechanical behavior of bone: Composition of bone. Mechanical properties of tissues comprising the bone. Size and geometry of bone. Direction, magnitude, and the rate of applied loads. Page 33 Mechanical Properties of the Bone Bone can be characterised as: Nonhomogeneous material as it consists of various cells, organic and inorganic substances with different material properties. Anisotropic (direction dependent) as material properties is different when acted upon in different directions. Viscoelastic (time and rate dependent), e.g., bone can resist rapidly applied load much better than slowly applied loads. Hence, bone is stiffer and stronger at higher strain rates. Page 34 Effects of Anisotropy Stress-strain behavior is dependent on orientation of bone with respect to direction of loading. Page 35 Effects of Anisotropy Table: Mechanical properties for cortical bone Example: Cortical bone Loading Mode Ultimate Strength Has larger ultimate strength (MPa) (ie stronger) and a larger Longitudinal elastic modulus (ie stiffer) in Tension 133 the longitudinal than Compression 193 Transverse transverse direction. Tension 51 Also, it is more brittle (w/o Compression 133 yielding) as compared to bone ELASTIC MODULI, E specimens loaded in longitudinal Longitudinal 17.0GPa direction. Transverse 11.5GPa SHEAR MODULUS,G 3.3GPa An experiment to demonstrate Anisotropic behavior Viscoelastic Property of the Bone Page 25 Comparison of Mechanical Properties Between Cortical and Cancellous Bones Structural Integrity of the Bone Factors affecting integrity of bone: Osteoporosis reduces bone integrity in terms of strength and stiffness by reducing apparent density. Surgery altering normal bone geometry. Bone defects. Screw holes for pins & bone plates can cause stress concentrations on bone. Bone fracture occurs when stresses generated in bone exceeds the ultimate strength of bone. Osteoporosis Osteoporosis is the most epidemic bone disease in older populations. It is characterized by: low bone mass, deterioration of bone micro-architecture, compromised bone strength. It leads to bone fragility and increased risk of fracture under low loads. Biomechanics of Soft Tissues Page 29 Musculoskeletal Soft Tissues Types of soft tissues Articular Cartilage Tendon Ligament Muscle Joint Capsules Skin Others Composition of the Soft Tissues All soft tissues are composite materials. Collagen and elastin fibers made up the main structural elements of soft tissues. Collagen Fibers Collagen fibres are not effective under compression. When stretched, energy is stored in the fiber like a spring. When release, energy returns to the fiber to its unstretched state. Individual fibrils of the collagen fibers are surrounded by a gel-like ground substance, which consists mainly of water. Collagen fibre possesses a two-phase, solid-fluid, or viscoelastic material behavior. Elastin Fibres The noncollagenous tissue components include: Elastin which is another fibrous protein whose material properties resemble the properties of rubber. Elastin and microfibrils form the elastic fibres that are highly extensible and reversible even at high strains. Elastin fibres possess a low-modulus elastic material property, while collagen fibres show a higher-modulus viscoelastic behavior. Collagen vs Elastin Collagen Elastin Found in skin and protective tissue. Found in the connective tissue of elastic structures. 3rd most abundant protein in the body. Less abundant. Generally white. Generally yellow. Gives strength to structures. Provides elasticity to structures. Produced until the ageing process begins. Produced mainly in the fetal period. Viscoelastic Behavior of Biological Tissues In general, the mechanical behavior of biological tissues can be described as viscoelastic. A viscoelastic model comprises: A spring to model the elastic behavior, and A dashpot to model the time dependent behavior. Biomechanics of Muscles and Joints Page 36 Skeletal Muscles Movement of human body segments is achieved as a result of forces generated by skeletal muscles which convert chemical energy into mechanical work. The skeletal muscle is composed of muscle fibres and myofibrils. Muscles exhibit viscoelastic material behaviour. Muscles are viscous in the sense that there is an internal resistance to motion. Muscle Contraction Contraction is a unique ability of the muscle tissue, which is defined as the development of tension in the muscle. In engineering mechanics, contraction implies shortening under compressive forces. In muscle mechanics, contraction can occur as a result of muscle shortening or muscle lengthening, or it can occur without any change in the muscle length. There are various types of muscle contractions: concentric, eccentric and isometric contractions. Skeletal Joints The human body is both: Rigid in the sense that it can maintain a posture. Flexible in the sense that it can change its posture and move. The flexibility of the human body is due primarily to the joints, or articulations, of the skeletal system. The primary functions of joints: Mobility Stability Classification of Joints Skeletal Joint Classification: Structural Skeletal Joint Classification: Functional Synar-throdial joints (immovable): formed by two tightly fitting bones and do not allow any relative motion of the bones forming them (eg skull). Amphiar-throdial joints (slightly movable): allow slight relative motions, and feature an intervening substance (a cartilaginous or ligamentous tissue) whose presence eliminates direct bone-to-bone contact (eg vertebrae). Diar-throdial joints (freely movable): Varying degrees of relative motion Articular cavities Ligamentous capsules Synovial membranes and fluids Types of Synovial Joints Types of Synovial Joints Examples Glenohumeral joint (ball-and-socket) enables the arm to move in all three planes (triaxial motion): High level of mobility Reduced stability Increase vulnerability of the joint to injuries, such as dislocations. Humeroulnar joint: movement only in one plane (uniaxial motion) more stable Less prone to injuries than the shoulder joint. The extreme case of increased stability is achieved at joints that permit no relative motion between the bones constituting the joint. The contacting surfaces of the bones in the skull are typical examples of such joints. Function of the Articular Cartilage Covers the articulating surfaces of bones at the diarthrodial (synovial) joints. Provides weight bearing surface with low friction and wear. Facilitates the relative movement of articulating bones. Distributes loads over larger contact area due to compliant nature, ie reduces stress applied to bones. Loads acting on the Articular Cartilage During daily activities, articular cartilage is subjected to tensile, shear and compressive stresses. Under tension, cartilage responds by realigning the collagen fibers which carry the tensile loads applied to the tissue. Shear stresses on the articular cartilage are due to frictional forces between the relative movement of articulating surfaces. However, coefficient of friction for synovial joint is very low (about 0.001 – 0.06) and has insignificant effect on the stress resultants. Lifespan Changes of the Joints Joint stiffness in older people. Fibrous joints change first. Changes in symphysis joints may also over in vertebral column (water loss from intervertebral discs) -> loss of disc height and flexibility. Synovial joint loses elasticity. Reduced physical activity may lead to disuse and poor circulation. Importance of regular physical activity and exercises to keep joints functional. Biomechanics of Tendons and Ligaments Page 49 Tendons and Ligaments Tendons and ligaments are fibrous connective tissues. Tendons execute joint motion by transmitting mechanical forces (tensions) from muscles to bones. Unlike muscles, tendons & ligaments are passive tissues, ie. cannot contract to generate forces. Tendons Compared to muscles, tendons are stiffer, have higher tensile strengths, and can endure larger stresses. At joints where space is limited, muscle attachments are via tendons. Enable muscles to transmit forces to bones without wasting energy to stretch tendons. Ligaments Attach articulating bones to one another across a joint. Guide and stabilise skeletal joint movement. Prevent excessive motion. Greater proportion of elastic fibers which account for higher extensibility but lower strength and stiffness. It is also viscoelastic and exhibits hysteresis. Magee, D. J. (2014). Orthopedic physical assessment (Sixth edition.). Elsevier. Comparison of Tendons and Ligaments https://differences.info/tendon-vs-ligament/ Summary Biomechanical principles are foundational to our understanding, description and analysis of human movements. Kinematic is concerned with the description of the movement in terms of time and spatial factors; kinetics is concerned with the forces involved in bringing about the movement. Both linear and angular (rotatory) movements can be interpreted in terms of its kinematics and kinetics. Newton’s laws can be applied in the analysis of human movements; concepts of mass, inertia, displacements, speed and velocity, acceleration, momentum and impulse are important in describing and analyzing movements. Forces acting on the human body can be analyzed and resolved using polygon or parallelogram methods. Human body can be conceptualized in terms of machines, e.g. lever and pulley. Centre of gravity, centre of mass and base of support are central to our understanding of the human body in equilibrium.