MSK midterm feb 14

biomechanics

the application of mechanics to the study of the structure and function of biological systems

human biomechanics

how forces act on the musculoskeletal system to produce posture and movement, and how tissues react to these forces

3 kind of mechanics

rigid body mechanics, deformable body mechanics, fluid mechanics

rigid body mechanics

cannot be deformed, but realistically some deformation may occur i.e bones and limb segments

2 subdivisons of rigid body mechanics

statics and dynamics

static

forces acting on bodies that are at rest or static equilibrium

dynamic

study of bodies in motion, subdivided into kinematics and kinetics

which laws defines static equilibrium?

newtons first and third law

newtons first law (inertia)

rigid body will remain at rest unless an unbalanced net force acts on it

newtons third law

every action has an equal and opposite reaction

which law defines dynamics?

newtons second law

newtons second law

acceleration is inversely proportional to the mass of the body

kinematics

study of motion without analyzing the forces causing the motion

motion

analyzed by displacement, velocity, and time

3 classifications of motion

translational, rotational, general

translational motion

straight or curved lines

rotational motion

circular motion around an axis of rotation

general motion

any combination of rotational or translational motion

kinetics

study of forces that cause or affect the motion of a body

2 classifications of forces

internal and external

external forces

applied to an object and act in contact with the object

internal forces

exist within the object and act to hold the object together in the presence of external forces

kinetic chain

combination or series of joint movements that make up a larger movement

2 types of kinetic chains

open and closed

force

• newtons second law

• contact forces or field forces

  • represented by vectors (magnitude, direction, position/point of application)

moment

• bending or turning action created when a force is applied to the lever arm and one end of the lever arm is fixed

  • m = force x perpendicular distance between line direction of force and axis of rotation

torque

• type of moment that results in twisting or rotation

• created by single force or pair of parallel forces acting on a body in opposite directions

• m = force x perpendicular distance between line direction of force and axis of rotation

• m = force x perpendicular distance between 2 forces

forces can be classified into 2 categories

orientation or effect

orientation forces

• normal

• tangential

• moment

• torque

• coplanar

• colinear

• concurrent

  • parallel, force couple

effect forces

• tensile

• compressive

• shear

• friction

• bending

  • torsion

normal force

• perpendicular to contact surface

• includes gravitational force

tangential force

acts on an object in the direction of a tangent to the shape or path of the object

• ie shear

friction force

• resists motion between 2 bodies in contact and sliding against one another

• amount of friction depends on surface quality and finish

bending and tension

• moment creates bending if the applied force is great enough

• torque creates torsion

coplanar forces

forces occurring in the same 2d plane but not along the same line

colinear forces

2 or more forces acting along the same line

concurrent forces

2 or more forces that act or intersect at a single common point but in tensile or compressive directions

parallel forces

2 or more forces that run in a parallel direction to each other

parallel: force couple

variation or parallel force where 2 equal but opposite forces cause only rotation around an axis

levers

rigid structure or body part that pivots at a fulcrum and converts linear force into rotation

fulcrum

axis of rotation

moment arm

perpendicular distance between axis of rotation and direction of force

first class lever

fulcrum lies between effort force and load

• ie seesaw

second class lever

fulcrum lies at one end, load lies between effort force and fulcrum

• ie ankle

third class lever

fulcrum lies at one end, load lies at the other with effort force between them

• ie shovel

lever arm

rigid structure or body part that pivots at a fulcrum and when force is transmitted through the lever, rotation occurs at the fulcrum

moment arm

perpendicular distance from axis of rotation and the line of direction of applied force

moment and torque are

vectors because they have magnitude and direction

magnitude of torque depends on

amount of force applied, length of moment arm, angle of force applied

center of gravity

point around which the body or body segment is balanced in every direction

• for solid objects, average position of all points in the object

• for the body, is about the belly button anterior to s2

rear wheel placement of wheelchairs affects

cog, propulsion efficiency, and rear stability of the frame

increase stability by

enlarging base of support

greater surface area contact =

lower pressure per square unit

4 types of body tissues

epithelial, muscular, nervous, connective

connective tissue

• supports and binds tissues and organs in their location

• diverse and varies in structure and function

• extracellular matrix and a few cells

types of connective tissue

• specialized (bone and cartilage)

• proper (regular dense, irregular dense, and loose)

fibroblasts

connect tissue

chondrocytes

cartilage

osteoblasts

bone growth cells

osteocytes

• majority of bone cells

• imprisoned in lacunae

• mechanoreceptor

osteoclasts

bone resorbing cells

3 kinds of extracellular matrix

ground substance, macromolecules, fibers

ground substance

• gel like

• resists compression and absorbs shock

• medium for molecular substances to travel between capillaries and cells

2 types of macromolecules

proteoglycans and glycoproteins

proteoglycans

structural integrity

glycoproteins

binding and adhesion

3 types of fibers

collagen, elastin, reticulum

collagen

• provides tensile strength

• resists longitudinal stress, shear and other forces

• most common

• triple helix structure

elastin

• elastic like properties

• found in skin, lungs, BV

• resists deformational forces with elastic recoil and stretch

• made by fibroblasts

reticulum

inelastic

cartilage

• withstands compressive forces

• collagen and high proteoglycan

bone and tendon

• resist tensile forces

• high collagen fiber and low proteoglycan

dermis

• resists tensile forces

• moderate compression

• accommodates stretching

• collagen and elastin fiber content and low proteoglycan

proteoglycans are made of

glycosaminoglycan (gag) and protein

gag and protein

hydrate matrix, stabilize collagen, resist compressive forces

hyaluronic acid

not technically a proteoglycan but is hydrophilic and abundant in loose hydrated connective tissue

type i collagen

• 80-90% of all collagen

• includes skin, tendon, bone, vasculature, and organs

type ii collagen

cartilage

fibroblasts

collagen is made by

loose ct

• largely proteoglycans

• few collagen and elastin

  • loose arrangement

dense ct in fascia, capsule, and dermis

• woven network

• mostly collagen and some elastin

• impact resistant

dense ct in tendons and ligaments

• parallel fibers

• mostly collagen and some elastin

  • powerfully resistant to axial loading

edema

• excessive accumulation of fluid within interstitial spaces

• problem with fluid distribution, not an excess of fluid

3 types of edema

localized, generalized, dependent

localized edema

limited to site of injury

generalized edema

uniform distribution of fluid in interstitial spaces

dependent edema

fluid accumulates in gravity dependent areas (ie pitting)

hydrostatic pressure and osmosis

how does water move between tissues?

hydrostatic pressure

• generated by pressure of fluid within or outside capillary

• usually water flows out of capillaries

osmosis

• generated by protein in blood plasma or interstitial fluid

• usually water flows into capillaries

hydrostatic pressure

caused by increased BP, vascular malfunction

oncotic pressure

caused by acute injury, inflammation, or malnutrition

bone shapes

flat, short, irregular, long

long bones are composed of

diaphysis, metaphasis, epiphysis, and epiphyseal plate

2 types of bone

compact and spongy

compact bone

• 85% of skeleton

• typically exterior

• haversian system

spongy bone

• 15% of skeleton

• typically interior and ends

• contains bone marrow

• less complex, lamellae lay in plates or bars called trabeculae

• more porous

• larger SA

periosteum

double layered ct surrounding all bone

haversian system

• compact bone

• highly organized into units called osteons that have a central canal surrounded by concentrically arranged lamellae

• solid and strong