Skeletal and Passive Tissues Presentation (SCIE 12941 Module 2)

Mechanical Loads Chapter 3; pages 70-74  Direction of Tissue Loading 1. Compression 2. Tension 3. Shear 4. Torsion Compression “Squishing” Vertebrae during upright posture Act upon longitudinal axis Tension Opposite of Compr...

Mechanical Loads Chapter 3; pages 70-74  Direction of Tissue Loading 1. Compression 2. Tension 3. Shear 4. Torsion Compression “Squishing” Vertebrae during upright posture Act upon longitudinal axis Tension Opposite of Compression “Pulling apart” Muscles produce tension that pulls at the attachment of bone Act upon longitudinal axis Shear Combination of compressive and tensile forces “Sliding” Force acts parallel to surface  Torsion Structure “twists” along its longitudinal axis Fractures to tibia in football and skiing (foot is fixed) Spiral Fracture  Tissue Loading When loaded, tissue develops resistance to the external load Resistance depends upon the properties of the tissue (size, shape, volume, mass, area, etc.) Stress Manner in which the force is distributed Force divided by the surface area over which the force is applied  Stress The same force, applied to a small surface produces larger stress than when applied to a larger surface Likelihood of injury is related to magnitude and direction of stress caused by blow Vertebral Column  Strain Deformation Change in shape Not always perceptible when exposed to external loads Tensile load = tensile strain Compressive load = compressive strain Shear load = shear strain  Stress, Strain & Injury Direct relationship between stress and strain Consequence of this relation in tissue determines the tissue’s susceptibility to injury  A Reminder about Material Mechanics… Material mechanics assumes homogeneity of material Does this directly apply to human tissue? Tissue = structure, not a material  Stress-Strain or Load-Deformation Curve S L T o R E a S d S Deformation STRAIN  Stiffness Stress (Load) / Strain (Deformation) Bone = greatest stiffness in human tissue Skin has the least Tendon, ligament, cartilage and muscle fall in between Stress (Load) Strain (Deformation) Loading Configuration and Likelihood to Fracture  Bending More complicated form of loading Compressive stress on one side Tensile stress on the opposite  Three-Point Bending Force acts perpendicular to longitudinal axis Failure occurs along middle point of force application  Four-Point Bending Failure occurs at the weakest point between the two inner forces Weakness: – Change in shape – Change in direction Human Body Example Bone Structure, Load Tolerance and Fractures Skeletal Considerations for Movement Chapter 4; pages 88-104 Chapter 5; pages118-135  Purpose of Bone ▪ Protect vital organs ▪ Mineral storehouse ▪ Bone marrow (hematopoiesis) ▪ Levers for movement  Gross Structure of Bone ▪ Major building blocks ▪ Calcium carbonate, calcium phosphate, collagen and water ▪ CaC and CaP ~60-70% of dry bone weight ▪ Stiffness ▪ Compressive Strength ▪ Tensile Strength  Structural Organization ▪ Relative percentage of bone mineralization varies with age and specific bones ▪ ↑ Porous = ↓ Calcium Phospate and Calcium Carbonate (mineral tissue) ▪ Low Porosity (5-30% non-mineralized tissue) = Cortical, Compact Bone ▪ High Porosity (30-90% non-mineralized tissue) = Cancellous, Spongy or Trabecular Bone  Porosity ▪ Pores = Cavities (caves, holes) ▪ Directly affects mechanical characteristics of bone tissue ▪ Cortical bone = higher mineral content, therefore stiffer so withstands greater stress (stronger!) ▪ Cancellous bone = lower mineral content, therefore withstands greater strain ▪ Strain = deformation or change in shape  Bone Type Locations Cancellous: high porosity Found where the bone needs to help “absorb” forces or be able to withstand some strain, or change in shape Cortical: low porosity Found where bone needs to be able to withstand greater stress  Bone Architecture ▪ Bone function determines structure ▪ Shafts of long bones, outer coverings of flat and irregular bones = cortical content ▪ Vertebrae = high cancellous content Bone Strength Responds to Force! ▪ Cancellous bone develops depending on the forces that will act upon it ▪ High versus Low ▪ Loading along the length of the bone ▪ Loading perpendicular to the bone  Anisotropic ▪ Both cortical and cancellous bone exhibit different strength and stiffness responses to forces applied from different directions ▪ Overall, bone is strongest in resisting compression (along the bone’s length) and weakest in resisting shear (opposite directions) Stress  Types of Bones 206 bones in the human body Divide the skeleton: – Axial – Appendicular  Categories of Bone 1. Short: carpals and tarsals 2. Long: framework of appendicular skeleton 3. Irregular: vertebrae, sacrum, coccyx, maxilla 4. Flat: skull, scapula, sternum, ribs, patella  Bone Development ▪ Cartilaginous model ▪ Ossification proceeds during long bone development via growth plates (physis) ▪ Movement and its related forces during skeletal development influence final skeletal form ▪ Strength also influenced by hormones & diet ▪ Osteoblasts (bone forming) ▪ Osteoclasts (bone resorption)  Bone Growth and Development Bone grows in both Adult Bone length (from Development epiphysis) and ↓ Collagen ↑ “Brittleness” circumference (from Mineral peak typically inside and out) between 25-28 for women, 30-35 for men Cancellous bone particularly effected  Bone Response to “Stress” Bone responds dynamically to the presence or absence of forces Bone density is a function of the magnitude and direction of the mechanical stresses acting upon it (Wolff’s Law) This healthy response is called “Remodelling” Bone mineralization, AND bone strength are a function of the stresses placed on the skeleton  Bone Hypertrophy and Atrophy Hypertrophy due to increases in physical activity or demands of activity (increased mechanical stress) Atrophy due to decreases in physical activity (e.g. Lying in bed, sedentary lifestyle – decreased mechanical stress)  Osteoporosis Bone atrophy Begins as Osteopenia Fractures from Activities of Daily Living (ADL) More problematic post menopausal and with increased age  Fractures ▪ Occurs when applied load exceeds the bone’s ability to withstand the force ▪ Fracture resistance influenced by: ▪ Magniute, duration and rate of applied force ▪ Bone geometry (ie. Cross-section) ▪ Anisotropic effects (loading direction) ▪ Bone porosity ▪ Health and maturity level of person  Fractures ▪ Acute loading (single, large magnitude) ▪ Chronic loading (repeated application, lower magnitude) ▪ Simple (bone ends remain within soft tissue) ▪ Compound (bone ends protrude through skin)  Fracture Types ▪ Avulsions – Tensile loading ▪ Spiral Fractures – bending and torsion ▪ Compression Fractures – rare, ie. Osteoporosis ▪ Greenstick – more flexible, young children ▪ Stress Fractures – repeated, low magnitude ▪ Epiphyseal – fracture of growth plate  Joints and Classification Joints govern our movements Movement capabilities are dependent upon the type of joint Joints are a complex collection of bone, ligaments and capsules, cartilage and finally the muscles that cross them Passive Tissues: Ligaments and Cartilage  Ligament ▪ Connective tissue that joins bones together ▪ Resist excessive movements or dislocations of bones ▪ PASSIVE joint stabilizers ▪ Composed of complex matrix of collagen and ground substance ▪ Dense component = 70% collagen ▪ Bundles organized according to main biomechanical stresses  Ligament Functions ▪ Identified according to: ▪ Bony attachment (coracoacromial) ▪ Gross function (capsule) ▪ Relations to joint (collateral) ▪ Shape (deltoid) ▪ Arrangement with respect to another ligament (cruciate) ▪ Injury classified as a Sprain: 3 categories  Articular Connective Tissue ▪ Tendons (muscle to bone) ▪ Ligaments (bone to bone) ▪ Collagen ▪ Elastic capabilities ▪ Respond to mechanical loads; size dependant on location and purpose ▪ ACL  Articular/Hyaline Cartilage ▪ Dense, white connective tissue ▪ Provides protective lubrication ▪ 1-5mm thick ▪ Covers diarthrodial joints ▪ Purpose: ▪ Spread load (force) over wide area (↓ stress) ▪ ↓ Friction of bone ends on one another  Hyaline Cartilage ▪ Soft ▪ Porous ▪ Hydrated ▪ Specialized cells = Chondrocytes ▪ Embedded in matrix ▪ Matrix = protection and information pertaining to pressure changes ▪ Purpose = maintain and restore cartilage from wear ▪ Density and structure = response to mechanical loads of the joint  During Loading… ▪ Cartilage deforms ▪ Synovial fluid (hydration) “flows” out ▪ “Weeping Lubrication” ▪ Low rate loading = matrix resists the load ▪ High rate loading = fluid resisting the load ▪ Contact stress ↓ up to 50% ▪ ↓ Friction  Articular Fibrocartilage ▪ Fibrocartilaginous discs ▪ Intervertebral discs ▪ Menisci of knee  Purposes of Fibrocartilage ▪ ↑ distribution of force over joint surfaces ▪ Improve fit of articulating surfaces ▪ Limit bone movement ▪ Protection ▪ Lubrication ▪ Shock absorption Joint Architecture and Classification Systems  Joint Architecture Joint categorized based on: ▪ Complexity ▪ Number of axes present ▪ Geometry ▪ Movement capabilities  Classification due to Movement 3 Categories: 1. Immovable 2. Slightly Movable 3. Freely Movable  1. Immovable Joints ▪ Synarthrosis (Syn=togther, arthron=joint) ▪ Fibrous Joint ▪ Can attenuate shock ▪ Permits little to no movement Subcategories a. Sutures b. Syndesmosis  Sub-Categories A. Sutures ▪ Irregular grooves on “sheets” of bone ▪ Tightly connected by fibres continuous with the periosteum ▪ Ossification occurs in adulthood ▪ Only human example is skull  Sub-Categories B. Syndesmosis ▪ “held by bands” ▪ Dense fibrous tissue holds bones together ▪ VERY limited movement ▪ Interosseous membrane (radius & ulna, tibia & fibula)  2. Slightly Movable Joints ▪ Amphiarthrosis (amphi=on both sides) ▪ Cartilaginous joints ▪ Attenuate applied forces ▪ Permit greater motion than synarthrodial Subcategories: a. Synchondrosis b. Symphysis  Sub-Categories A. Synchondrosis ▪ Held together by thin layer of hyaline cartilage ▪ Epiphyseal growth plates ▪ Sternocostal joints  Sub-Categories B. Symphysis ▪ Hyaline cartilage separates a fibrocartilaginous disc from the bones ▪ Pubic Symphysis ▪ Vertebral joints  3. Freely Movable Joints ▪ Diarthorodal and synovial ▪ Slight limitations ▪ 5 Criteria: ▪ Hyaline cartilage ▪ Articular capsule ▪ Synovial membrane ▪ Synovial fluid (fills joint cavity) ▪ Reinforcing ligaments  Sub-Categories Diarthrosis: Classed according to movement capabilities/ architecture: i. Gliding (plane; arthrodial) ii. Hinge (ginglymus) iii. Pivot (screw; trochoid) iv. Condyloid (ovoid, ellipsoidal) v. Saddle (sellar) vi. Ball & Socket (spheroidal)  Variance among Diarthrodial Joints ▪ Vary in structure and capacity to move ▪ Categorized by axes of rotation ▪ One axis = uniaxial, 1 df (degree of freedom) ▪ Two axes = biaxial, 2 df ▪ Three axes = triaxial, 3 df ▪ Nonaxial = limited motion Freely Moveable - Diarthrodial Joint Types: Overview or Gliding Freely Moveable – Diarthrodial Joint types: i. Gliding Joints (Plane Joints) ▪ Articulating surfaces are nearly flat ▪ Movement = non-axial gliding ▪ Intermetatarsal ▪ Intercarpal ▪ Zygapophyseal joints of vertebrae Freely Moveable – Diarthrodial Joint types: ii.Hinge Joints ▪ Convex surface on one end, concave surface on other ▪ Planar movement restricted by STRONG collateral ligaments ▪ Humeroulnar joint ▪ Interphalangeal joints Freely Moveable – Diarthrodial Joint types: iii. Pivot Joints ▪ Rotation is permitted around one axis (uniaxial) ▪ Proximal and distal radioulnar joints ▪ Atlantoaxial joint Freely Moveable – Diarthrodial Joint types: iv. Condyloid Joints ▪ Ovular convex and concave shapes ▪ Biaxial (flexion/extension, abduction/adduction) ▪ 2nd-5th metacarpal joints ▪ Radiocarpal joints Freely Moveable – Diarthrodial Joint types: v. Saddle Joint ▪ Bone surfaces shaped like seat of a horse’s saddle ▪ Biaxial as condyloid, however, greater range of movement ▪ Carpometacarpal of thumb Freely Moveable – Diarthrodial Joint types: vi. Ball & Socket Joint ▪ Surfaces reciprocally convex and concave ▪ Triaxial joint ▪ Hip ▪ Shoulder Joint Architecture and Stability Joint Stability ▪ Stability of a joint refers to its ability to resist dislocation ▪ Dislocation can result in bone, ligament, tendon and muscle damage  Human Joint Stability ▪ Reciprocally shaped articulating surfaces ▪ Surfaces NOT symmetrical ▪ One position of “best fit”; position where joint surface contact is maximum ▪ Close-Packed Position ▪ Reduction of surface area contact = Loose-Packed Position/Open-Packed Position ▪ Specific to each joint  Contact Surface Area ▪ Hip Joint: Deep Socket = ↑ Contact Area ▪ Shoulder Joint: Shallow Socket = ↓ Contact Area  Stability is Determined by… ▪ Shape of articulating surfaces and… ▪ Supporting soft tissue ▪ For example: ▪ Hip and Shoulder versus ▪ Ankle and Wrist versus ▪ Elbow and Knee Hip Joint Wrist Joint Knee Joint Shoulder Joint(s)