Kab Chapter 2: Skeletal Considerations for Movement PDF

Skeletal Considerations for Movement Prepared By Mr. ST. Hashona 2  Chapter 2 Skeletal Considerations for Movement...

Skeletal Considerations for Movement Prepared By Mr. ST. Hashona 2  Chapter 2 Skeletal Considerations for Movement 3  LEARNING OBJECTIVES 1. Define how the mechanical properties of a structure can be expressed in terms of its stress–strain relationship. 2. Define stress, strain, elastic region, plastic region, yield point, failure point, and elastic modulus. 3. Identify the elastic region, yield point, plastic region, and failure point on a stress–strain curve. 4. Describe the difference between elastic and a viscoelastic material. 5. Differentiate between brittle, stiff, and compliant materials. 6. List the functions of bone tissue that makes up the skeletal system 7. Describe the composition of bone tissue and the characteristics of cortical and cancellous bone. 8. Identify the types of bones found in the skeletal system and describe the role each type of bone plays in human movement or support. 4  LEARNING OBJECTIVES 9. Describe how bone tissue forms and the differences between modeling and remodeling. 10. Discuss the impact of activity and inactivity on bone formation. 11. Define osteoporosis and discuss the development of osteoporosis. 12. Discuss the strength and stiffness of bone as well as bone’s anisotropic and viscoelastic properties. 13. Define the following types of loads that bone must absorb and provide an example to illustrate each load on the skeletal system: compression, tension, shear, bending, and torsion. 14. Describe stress fractures and other common injuries to the skeletal system and explain the load causing the injury. 15. Describe the types of cartilage and their function in the skeletal system. 16. Describe the function of ligaments in the skeletal system. 5  LEARNING OBJECTIVES 17. Describe all of the components of the diarthrodial joint, factors that contribute to joint stability, and examples of injury to the diarthrodial joint. 18. List the seven different types of diarthrodial joints and provide examples of each one. 19. Describe the characteristics of the synarthrodial and amphiarthrodial joint and provide an example of each. 20. Define osteoarthritis and discuss the development of osteoarthritis. 6 Measuring the Mechanical Properties of Body Tissues 7  BASIC STRUCTURAL ANALYSIS Stress and strain The force applied to deform a structure and the resulting deformation is referred to as stress and strain, respectively. Stress–strain curve: The graph relating stress to strain. A stress–strain analysis can be used to discern how a material changes with age, how materials react to different force applications, and how a material reacts to lack of everyday stress. A stress–strain analysis can be performed with pulling force (tension), pushing force (compression), or shear force (a push or pull along the surface of the material). Deformation or strain is also scaled to the initial length of the structure being tested. That is, the deformation caused by the applied stress is compared with the initial, or resting, length of the material, when no force is applied. 8  A stress–strain analysis can be performed with pulling force (tension), pushing force (compression), or shear force (a push or pull along the surface of the material). Stress is defined as the force per unit area. The force is applied perpendicular to the surface of the structure over a predetermined area. The unit in which a force is measured is the newton (N). The unit of area is the square meter. Deformation or strain is also scaled to the initial length of the structure being tested. That is, the deformation caused by the applied stress is compared with the initial, or resting, length of the material, when no force is applied. 9  Types of Materials Elastic In this type of material, a linear relationship exists between the stress and strain. That is, when the material is deformed by the applied force, the amount of deformation is the same for a given amount of stress. When the applied load is removed, the material returns to its resting length as long as the material did not reach its yield point. In an elastic material, the mechanical energy that was stored is fully recovered 10  Viscoelastic These structures have nonlinear or viscous properties in combination with linear elastic properties. The combination of these properties results in the magnitude of the stress being dependent on the rate of loading, or how fast the load is applied. Nearly all biological materials, such as tendon and ligament, show some level of viscoelasticity. 11 Biomechanical Characteristics of Bone 12  BONE TISSUE FUNCTION The skeleton consists of approximately 20% of total body weight. The skeletal system is generally broken down into axial and appendicular skeletons. Bone tissue performs many functions: 1. Support The skeleton provides significant structural support and can maintain a posture while accommodating large external forces, such as those involved in jumping. 2. Attachment sites Bones provide sites of attachment for tendons, muscles, and ligaments, allowing for the generation of movement through force applications to the bones through these sites. 13. 3. Leverage The skeletal system provides the levers and axes of rotation about which the muscular system generates the movements. 4. Other functions Three additional bone functions are not specifically related to movement: protection, storage, and blood cell formation. The bones protect the brain and internal organs. 14 COMPOSITION OF BONE TISSUE 15. Bone is composed of a matrix of inorganic salts and collagen, an organic material found in all connective tissue. The inorganic minerals, calcium and phosphate, along with the organic collagen fibers, make up approximately 60% to 70% of bone tissue. Water constitutes approximately 25% to 30% of the weight of bone tissue. Bone cells are referred to as osteocytes. The two types of these cells are referred to as osteoblasts and osteoclasts. These cells are responsible for remodeling bone. Osteoclasts are the cells that break down bone and convert calcium salts into a soluble form that passes easily into the blood. Osteoblasts produce the organic fibers on which the calcium salts are deposited. A balance in the activities of these two cells maintains a constant bone mass 16  MACROSCOPIC STRUCTURE OF BONE Bone is composed of two types of tissue: cortical bone and cancellous bone. Cortical Bone Cortical bone is often referred to as compact bone and constitutes about 80% of the skeleton. Cortical bone looks solid, but closer examination reveals many passageways for blood vessels and nerves. The exterior layer of bone is very dense and has a porosity less than 15% (48). Porosity is the ratio of pore space to the total volume; when porosity increases, bone mechanical strength deteriorates. Small changes in porosity can lead to significant changes in the stiffness and strength of bone 17  Cancellous Bone The bone tissue interior to cortical bone is referred to as cancellous or spongy bone. Cancellous bone is found in the ends of the long bones, in the body of the vertebrae, and in the scapulae and pelvis. It has a lattice-like structure with a porosity greater than 70%. Although quite rigid, is weaker and less stiff than cortical bone, and is not as dense as cortical bone because it is filled with spaces. Trabeculae=flat pieces of bone that serve as small beams between the spaces. The trabeculae adapt to the direction of the imposed stress on the bone, providing strength without adding much weight. Collagen runs along the axis of the trabeculae and provides cancellous bone with both tensile and compressive resistance. 18 Anatomical Classification of Bones 19  BONE FORMATION Ossification, Modeling, and Remodeling Ossification is the formation of bone by the activity of the osteoblasts and osteoclasts. In fetuses, the cartilage is slowly replaced through this process so that at the time of birth, many of the bones have been at least partially ossified. Long bones grow from birth through adolescence through activity at cartilage plates located between the shaft and the heads of the bones. Epiphyseal plates expand as new cells are formed and the bone is lengthened until the thicknesses of the plates diminish to reach ossification. Modeling occurs during growth to create new bone as bone resorption and bone formation occur at different locations and rates to change the bone shape and size. In growing bone, bone properties are related to the growth-related demands on size and to changes in tensile and compressive forces acting on the body.. In the process of resorption, old bone tissue is broken down and digested by the body. This process is not the same in all bones or even in a single bone 20  Physical Activity and Inactivity and Bone Formation Bones require mechanical stress to grow and strengthen. Bones slowly add or lose mass and alter form in response to alterations in mechanical loading Physical Activity: physical activity is an important component of the development and maintenance of skeletal integrity and strength. Bone tissue must have a daily stimulus to maintain health. Inactivity: Bone loss after a decrease in the activity level may be significant. When under loaded in conditions such as fixation or bed rest, bone mass is resorbed, resulting in reduced bone mass and thinning. The skeletal system senses changes in load patterns and adapts to carry the load most efficiently using the least amount of bone mass. 21  Osteoporosis A disease of increasing bone fragility that is initially subtle, affecting only the trabeculae in cancellous bone, but leads to more severe examples in which one might experience an osteoporotic vertebral fracture just opening a window or rising from a chair. Bone fragility depends on the ultimate strength of the bone, the level of brittleness in the bone, and the amount of energy bone can absorb. The symptoms of osteoporosis often begin to appear in elderly individuals, especially postmenopausal women. Osteoporosis may begin earlier in life, however, when bone mineral density decreases. When bone deposition cannot keep up with bone resorption, bone mineral mass decreases, resulting in reduced bone density accompanied by loss of trabecular integrity. The exact causes of osteoporosis are not fully understood, but the condition has been shown to be related to genetics, hormonal factors, nutritional imbalances, and lack of exercise 22 Mechanical Properties of Bone 23  STRENGTH AND STIFFNESS OF BONE The strength can be evaluated by examining the relationship between the load imposed (external force) and the amount of deformation (internal reaction) occurring in the material. The strength in weight-bearing bones lies in their ability to resist bending by being stiff. Strength The strength of bone or any other material is defined by the failure point or the load sustained before failure. The overall ability of bone to bear a load depends on having sufficient bone mass with adequate material properties as well as fiber arrangement that resist loading possibilities in different directions. Stiffness Stiffness, or the modulus of elasticity, is determined by the slope of the load deformation curve in the elastic response range and is representative of the material’s resistance to load as the structure deforms. 24  STRENGTH AND STIFFNESS OF BONE Anisotropic Characteristics Bone tissue is an anisotropic material, which means that the behavior of bone varies with the direction of the load application. The differences between the properties of the cancellous and cortical bone contribute to the anisotropy of bone. Viscoelastic Characteristics Bone is viscoelastic, meaning that its response depends on the rate and duration of the load. At a higher speed of loading, bone is stiffer and tougher because it can absorb more energy to failure the more rapidly it is loaded. A bone loaded slowly fractures at a load that is approximately half of the load handled by the bone at a fast rate of loading 25 LOADS APPLIED TO BONE 26  Cartilage Cartilage is a firm, flexible tissue made up of cells called chondrocytes surrounded by an extracellular matrix. The two main types of cartilage=articular or hyaline cartilage and fibrocartilage. Articular cartilage Covers the articulating ends of the bones in freely moving. Is an avascular substance consisting of 60% to 80% water and a solid matrix composed of collagen and proteoglycan. Collagen is a protein with the important mechanical properties of stiffness and strength. 27. FIBROCARTILAGE Acts as an intermediary between hyaline cartilage and the other connective tissues. Fibrocartilage is found where both tensile strength and the ability to withstand high pressures are necessary, such as in the intervertebral disks, the jaw, and the knee joint. A fibrocartilage structure is referred to as an articular disc, or meniscus. 28  LIGAMENTS A ligament is a short band of tough fibrous connective tissue that binds bone to bone and consists of collagen, elastin, and reticulin fibers. Provides support in one direction and often blends with the capsule of the joint. Ligaments can be capsular, extracapsular, or intra-articular. Capsular ligaments are simply thickenings in the wall of the capsule, much like the glenohumeral ligaments in the front of the shoulder capsule. Extracapsular ligaments lie outside the joint itself. The collateral ligaments found in numerous joints are extracapsular (i.e., fibular collateral ligament of the knee). Intra-articular ligaments, such as the cruciate ligaments of the knee and the capitate ligaments in the hip, are located inside a joint. 29 Bony Articulations 30  THE DIARTHRODIAL OR SYNOVIAL JOINT Movement potential of a segment is determined by the structure and function of the diarthrodial or synovial joint. The diarthrodial joint provides low-friction articulation capable of withstanding significant wear and tear. Characteristics of the Diarthrodial Joint Covering the ends of the bones is the articular end plate, a thin layer of cortical bone over cancellous bone. On top of the end plate is articular cartilage. Articular cartilage=Offers additional load transmission, stability, improved fit of the surfaces, protection of the joint edges, and lubrication. The capsule, a fibrous white connective tissue made primarily of collagen. o It protects the joint. o The capsule basically defines the joint, creating the interarticular portion, or inside, of the joint, which has a joint cavity and a reduced atmospheric pressure. 31  On the inner surface of the joint capsule is the synovial membrane=(a loose, vascularized connective tissue that secretes synovial fluid into the joint to lubricate and provide nutrition to the joint) The ligaments operate to guide and restrict motion, which defines the normal envelope of passive motion of the joint. Stability of the Diarthrodial Joint Stability in a diarthrodial joint is provided by the ligaments surrounding the joints, the capsule, and the tendons spanning the joint—gravity, and the vacuum in the joint produced by negative atmospheric pressure. 32  Close-Packed versus Loose-Packed Positions o Close-packed position: When the joint position is such that the two adjacent bones fit together best and maximum contact exists between the two surfaces. This is the position of maximum compression of the joint, in which the ligaments and the capsule are tense and the forces travel through the joint as if it did not exist. Examples: (full extension for the knee, extension of the wrist, extension of the interphalangeal joints, and maximum dorsiflexion of the foot). o Loose-packed positions: When there is less contact area between the two surfaces and the contact areas are frequently changing. There is more sliding and rolling of the bones over one another in a loose-packed position. Allows for continuous movement, reducing the friction in the joint. 33 34  Types of Diarthrodial Joints o Plane or Gliding Joint Plane or gliding joint=found in the foot among the tarsals and in the hand among the carpals. Movement at this type of joint is termed nonaxial=it consists of two flat surfaces that slide over each other rather than around an axis. o Hinge Joint Allows movement in one plane (flexion, extension). It is uniaxial. Examples of the hinge joint in the body are the interphalangeal joints in the foot and hand and the ulnohumeral articulation at the elbow. o Pivot Joint Allows movement in one plane (rotation; pronation, supination). It is uniaxial. Pivot joints are found at the superior and inferior radioulnar joint and the atlantoaxial articulation at the base of the skull. 35. o Condylar Joint Allows a primary movement in one plane (flexion and extension) with small amounts of movement in another plane (rotation). Examples are the metacarpals, interphalangeal, metacarpals, and the temporomandibular joint. o Ellipsoid Joint Allows movement in two planes (flexion and extension; abduction and adduction). It is biaxial. Examples of this joint are the radiocarpal articulation at the wrist and the metacarpophalangeal articulation in the phalanges. o Saddle Joint It is found only at the carpometacarpal articulation of the thumb, allows two planes of motion (flexion and extension; abduction and adduction) plus a small amount of rotation. It is similar to the ellipsoid joint in function. 36. o Ball-and-Socket Joint The last type of diarthrodial joint, the ball-and-socket joint, allows movement in three planes (flexion and extension; abduction and adduction; rotation) and is the most mobile of the diarthrodial joints. The hip and shoulder are examples of ball-and-socket joints. Other types of joints o Synarthrodial or Fibrous Joints o Amphiarthrodial or Cartilaginous Joints 37 38  OSTEOARTHRITIS Is a disease characterized by degeneration of the articular cartilage, which leads to fissures, fibrillation, and finally disappearance of the full thickness of the articular cartilage. Starts as a result of trauma to or repeated wear on the joint that causes a change in the articular substance to the point of removal of actual material by mechanical action. This results in diminished contact areas and erosion of the cartilage through development of rough spots in the cartilage. The rough spots develop into fissures and eventually go deep enough that only subchondral bone is exposed. Osteoarthritis can also be created by joint immobilization because the joint and the cartilage require loading and compression to exchange nutrients and wastes. After only 30 days of immobilization, the fluid in the cartilage is increased, and an early form of osteoarthritis develops. o This process can be reversed with a return to activity 39. END 40