Transcript Stiffness
Right ulna and radius in relation to the humerus and carpals Skeleton of the Hand • The carpus (wrist) consists of 8 small bones (carpals) • Two rows of carpal bones • Proximal row - scaphoid, lunate, triquetrum, pisiform • Distal row - trapezium, trapezoid, capitate, hamate • Scaphoid - most commonly fractured • Carpal tunnel - space between carpal bones and flexor retinaculum Copyright 2009 John Wiley & Sons, Inc. Articulations formed by the ulna and radius Metacarpals and Phalanges • Five metacarpals - numbered I-V, lateral to medial • 14 phalanges - two in the thumb (pollex) and three in each of the other fingers • Each phalanx has a base, shaft, and head • Joints - carpometacarpal, metacarpophalangeal, interphalangeal Right wrist and hand in relation to ulna and radius Skeleton of the Lower Limb • Two separate regions 1. A single pelvic girdle (2 bones) 2. The free part (30 bones) Pelvic (Hip) Girdle • Each coxal (hip) bone consists of three bones that fuse together: ilium, pubis, and ischium • The two coxal bones are joined anteriorly by the pubic symphysis (fibrocartilage) • Joined posteriorly by the sacrum forming the sacroiliac joints Copyright 2009 John Wiley & Sons, Inc. Right Hip Bone Copyright 2009 John Wiley & Sons, Inc. Bony Pelvis The Ilium • Largest of the three hip bones • Ilium is the superior part of the hip bone • Consists of a superior ala and inferior body which forms the acetabulum (the socket for the head of the femur) • Superior border - iliac crest • Hip pointer - occurs at anterior superior iliac spine • Greater sciatic notch - allows passage of sciatic nerve Ischium and Pubis • Ischium - inferior and posterior part of the hip bone • Most prominent feature is the ischial tuberosity, it is the part that meets the chair when you are sitting • Pubis - inferior and anterior part of the hip bone False and True Pelves • Pelvic brim - a line from the sacral promontory to the upper part of the pubic symphysis • False pelvis - lies above this line (Fig 8.9b) • Contains no pelvic organs except urinary bladder (when full) and uterus during pregnancy • True pelvis - the bony pelvis inferior to the pelvic brim, has an inlet, an outlet and a cavity • Pelvic axis - path of baby during birth True and False Pelvis Right Lower Limb Copyright 2009 John Wiley & Sons, Inc. Right Femur Patella Copyright 2009 John Wiley & Sons, Inc. Tibia and Fibula Copyright 2009 John Wiley & Sons, Inc. Tibia and Fibula Copyright 2009 John Wiley & Sons, Inc. Skeleton of the Foot - Tarsals, Metatarsals, and Phalanges • Seven tarsal bones - talus (articulates with tibia and fibula), calcaneus (the heel bone, the largest and strongest), navicular, cuboid and three cuneiforms • Five metatarsals - (I-V) base, shaft, head • 14 phalanges (big toe is the hallux) • Tarsus = ankle Copyright 2009 John Wiley & Sons, Inc. Right Foot Arches of the foot Vertebral Segments A-P View Secondary Curves Lateral Vertebral Column Osteology • Typical Vertebrae • Body • Superior and inferior surfaces of body (plateaus) • Thickened around the rim, location of epiphyseal plates • Cartilaginous end-plates • Vertebral Arch • Pedicles, Laminae • Transverse Processes • Spinous Process • Facets – superior articular and inferior articular • Spinal Foramen • Intervertebral Foramen Typical Vertebrae Typical Vertebrae Typical Lumbar Typical Thoracic Typical C BIOMECHANICS 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! Basic Biomechanics Force, Displacement & Stiffness Force Slope = Stiffness = Force/Displaceme nt Displacement Basic Biomechanics Force Area L Stress =Force/Area Strain= L / L0 Basic Biomechanics Stress-Strain & Elastic Modulus Stress Slope = Elastic Modulus Strain Basic Biomechanics Common Materials in Orthopaedics • Elastic Modulus (GPa) • Stainless Steel • Titanium • Cortical Bone • Bone Cement • Cancellous Bone Stress • UHMW-PE Strain 200 100 7-21 2.5-3.5 0.7-4.9 1.4-4.2 Basic Biomechanics • Elastic Deformation Elastic Plastic • Plastic Deformation • Energy Force Energy Absorbed Displacement Basic Biomechanics • • • • • Stiffness-Flexibility Yield Point Failure Point Brittle-Ductile Toughness-Weakness Elastic Plastic Failure Yield Force Stiffness Displacement Stiff Ductile Tough Strong Stiff Brittle Strong Ductile Weak Stress Brittle Weak Strain Flexible Brittle Strong Stress Flexible Brittle Weak Strain Flexible Ductile Weak Flexible Ductile Tough Strong 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 sub-threshold loading may result in failure due to fatigue. • Common mode of failure of orthopaedic implants and fracture fixation constructs. Basic Biomechanics • Anisotropic • Mechanical properties dependent upon direction of loading • Viscoelastic • Stress-Strain character dependent upon upon the speed at which the force is applied 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 Bone Mechanics • Bone Density Cortical Bone • Subtle density changes greatly changes strength and elastic modulus • Density changes • Normal aging • Disease • Use • Disuse Trabecular Bone Figure from: Browner et al: Skeletal Trauma 2nd Ed. Saunders, 1998. Basic Biomechanics • Bending • Axial Loading • Tension • Compression • Torsion Bending Compression Torsion Fracture Mechanics Figure from: Browner et al: Skeletal Trauma 2nd Ed, Saunders, 1998.