Orthopedic Biomechanics Presentation PDF

Orthopedic biomechanics The basic types of tissues in the body Connective tissues Bone Highly vascular calcified connective tissue Function of bone mechanical Biological...

Orthopedic biomechanics The basic types of tissues in the body Connective tissues Bone Highly vascular calcified connective tissue Function of bone mechanical Biological Attachment for Protect internal Reservoir for Upright posture muscle, tendons, hematopoietic organs minerals ligaments Bone Bone components Bone matrix Bone cells Bone covering Bone Bone matrix Bone matrix Organic Inorganic water component component Ca Collagen type I Hydroxyapatite crystals Proteoglycans and glycoproteins Bone Bone cells Bone Bone covering Bone Bone formation Bone Levels of structure Bone Structural unit of bone (osteon)  Bone which is a calcified osteoid tissue is formed of: Premature bone cells, Osteoblasts (bone-forming cells), Osteocytes (mature bone cells) and Osteoclasts (bone-eating cells).  the interface between the 'fibers' (osteons) and extraosteonal bone matrix, The osteons, or haversian systems, are apparent as the structural units of bone. The haversian canals are in the center of the osteons, which form the main branches of the circulatory network in bone. Each osteon is bounded by a cement line. One osteon is shown extending from the bone (×20). Bone Bone Bone remodeling  Bone remodeling Bone remodeling occurs in response to forces applied through physical activity. During growth and throughout the life, there is a continuous and highly regulated process of bone resorption and bone formation. This process is called Bone Remodeling due to balance in activities between osteoclasts and osteoblasts. During bone growth; Bone Remodeling starts by bone resorption or destruction by osteoclasts activity at the endosteum in order to increase bone marrow and create longitudinal tubular channel. This is followed by bone formation and deposition under the periosteum (subperiosteal area) by osteoblasts activity in order to help in growth of bone width and increase in the thickness of the shaft. However, the growth of bone length is the responsibility of epiphyseal cartilage plate. In the healthy bone, if the bone is subjected to repetitive loads, small damage develops within and between the osteons. If the damage is not excessive, bone remodeling regain normal bone around microdamage. If the damage is more excessive than bone remodeling, fracture occurs. Bone Types of bone Trabecular arrangement in long bone  Trabecular arrangement in short bone When the load is transmitted from the vertebra above to the vertebra below, it's not equally distributed over 2 parts but it affects mainly on anterior bony block (70% - 80%) and less effect will be on the posterior bony ring (20% - 30%). The load is transmitted from the superior end plate of vertebra to the inferior end plate by the way of 2 paths: 1) Cortical shell, and 2) Cancellous core.  The strength of the trabeculae differs according to the direction of load. If the load is in the longitudinal direction to the vertebral bodies (from down to upward), it was found that vertebral bodies bear more than two times as strong as if the load is applied in the transverse direction (lateral to medial or anterior to posterior direction). That is because the major orientation of the trabecular architecture in the vertebra is vertical (axial). Bone Long bone (femur) Bone Bone Irregular bone (vertebra) Types of bone Behavior of bone under various loading modes Behavior of bone under various loading modes Behavior of bone under various loading modes Tension Behavior of bone under various loading modes Compression Behavior of bone under various loading modes Bending Behavior of bone under various loading modes Bending Behavior of bone under various loading modes Shear Behavior of bone under various loading modes Torsion Stress-strain curve  Stress-strain curve Fracture toughness = Energy expenditure Is the total area under stress strain curve and it is the work required to fracture the material (total energy before failure) Young’s modulus (E) Stiffness in the linear part of the curve E= stress/strain Stress-strain curve Which one has higher fracture toughness? Factors affecting the Stress-strain curve Loading characteristics Mechanical properties of bone Structural properties of bone Factors affecting the Stress-strain curve Loading characteristics The direction of applied load Type of load Loading rate Amount of applied load Factors affecting the Stress-strain curve Loading characteristics The direction of applied load Bone withstand longitudinally applied load more than transversely applied load ✓Bone is anisotropic material ✓Haversian system orientation provides maximum strength along its long axis Factors affecting the Stress-strain curve Loading characteristics The direction of applied load Factors affecting the Stress-strain curve Loading characteristics Type of load Bone resists compressive load more than tensile load more than shear. Tension is more destructive than compression Factors affecting the Stress-strain curve Loading characteristics Loading rate Bone resists rapid loading > slow loading 1-No time for stress to dissipate inside bone. 2- No time for chemical bonds to be ruptured. 3- No time for energy inside bone to be released. Factors affecting the Stress-strain curve Loading characteristics Loading rate Factors affecting the Stress-strain curve Loading characteristics Loading rate Factors affecting the Stress-strain curve Loading characteristics Amount of applied load Wolf’s law: bone formed when needed and resorbed when not needed Factors affecting the Stress-strain curve Loading characteristics Amount of applied load At regular exercises or controlled cyclic loading increase BMC to 150% (1.5 times) contraction of the muscle will help in deposition of calcium Exercise threshold: is the upper limit of exercises beyond which bone BMC does not increase but decreases. Factors affecting the Stress-strain curve Loading characteristics Amount of applied load Use: regular exercises increase BMC to 150% (1.5 times) Disuse: BMC decreases than normal after 42 days without load. Factors affecting the Stress-strain curve Loading characteristics Amount of applied load Factors affecting the Stress-strain curve Mechanical properties of bone Mineral to collagen ratio Bone porosity and density Compact and cancellous bone Age Factors affecting the Stress-strain curve Mechanical properties of bone Mineral to collagen ratio Increased ratio Decrease collagen, Increase minerals Hypermineralization (e.g. osteoporosis) Brittle bone, low plastic deformation Decrease energy absorbing capacity Factors affecting the Stress-strain curve Mechanical properties of bone Bone porosity and density Porosity: state of being porous. Density: mass of bone material per unit volume Factors affecting the Stress-strain curve Mechanical properties of bone Compact and cancellous bone Factors affecting the Stress-strain curve Mechanical properties of bone Age Factors affecting the Stress-strain curve structural properties of bone Bone architecture Cross section area Length of bone Action of skeletal Muscle Joint structure Weak point of bone Factors affecting the Stress-strain curve structural properties of bone Bone architecture Hollow tubular structure Mass is distributed away from the center Bone resists and distributes stresses more than solid structure Factors affecting the Stress-strain curve structural properties of bone Bone architecture Factors affecting the Stress-strain curve structural properties of bone Bone CSA Bone strength increases by increasing the cross-sectional area Factors affecting the Stress-strain curve structural properties of bone Bone length Longer bone has high bending moment Factors affecting the Stress-strain curve structural properties of bone Action of skeletal muscle Muscles act as guy wires Factors affecting the Stress-strain curve structural properties of bone Action of skeletal muscle Muscles act as guy wires Factors affecting the Stress-strain curve structural properties of bone Joints Joints are points of stress relief Factors affecting the Stress-strain curve structural properties of bone Weak point of bone Pathomechanics of bone Pathomechanics of bone Osteonecrosis Fracture Osteoporosis Latin “fractura” to Death of bone Increase porosity, break cell due to absent decrease bone mass. Occurs if loads or deficient blood Increase with exceeds bone ability supply advancing age to withstand force Pathomechanics of bone Fractures  Possible fracture patterns due to various Pathomechanicsloading of bone modes Fractures Tension Compresion Bending Shear Torsion Combined Pathomechanics of bone Fractures Fracture due to tension Pathomechanics of bone Fractures Fracture due to compression Pathomechanics of bone Fractures Fracture due to compression Pathomechanics of bone Fractures Fracture due to bending Pathomechanics of bone Fractures Fracture due to bending Pathomechanics of bone Fractures Fracture due to shear Pathomechanics of bone Fractures Fracture due to shear Pathomechanics of bone Fractures Fracture due to torsion Pathomechanics of bone Repetitive load cycles Fractures Fatigue Fracture Failure at load below Microdamage ultimate (microcracks) stress Remodeling Repeating process fails load to repair Pathomechanics of bone Fractures Fatigue Fracture