L2 - Joints and Biomechanics of Materials Flashcards
Name the planes of joint movement.
Place the movements of the shoulder in each plane.
- Frontal (coronal) plane: abduction and adduction
- Sagittal plane: flexion/extension
- Transverse plane: medial/lateral rotation
See NDC p.6 for illustration
Name the axis of human movement.
- name
- what movement
- perpendicular to which plane
- X = axis perpendicular to sagittal plane
–> flexion and extension - Z = axis perpendicular to frontal plane
–> abduction and adduction - Y = axis perpendicular to transverse plane
–> medial and lateral rotation
See NDC p.7 for illustration
What is the degrees of freedom?
The number of planes within which a joint moves.
ex: uniaxial joint moves in 1 plane (elbow)
See NDC p.9-10 for examples
Name the 2 types of human joints.
How much movement do they provide?
- Synarthroses = little movement
- Diarthroses = more movement
Name the synarthroses joints in the body.
What connects what?
- Synostoses = Bone fused to bone
- Synchondroses = Bone to bone by cartilage
- Syndesmoses = Bone to bone by fibrous connective tissue
See NDC p.12 for illustration
Describe synostoses.
- type of joint
- what connects what
- example
Synarthroses = little movement
Bone fused to bone
ex: Skull sutures
See NDC p.12 for illustration
Describe synchondroses.
- type of joint
- what connects what
- example
Synarthroses = little movement
Bone to bone by cartilage
ex: costochondral joints
See NDC p.12 for illustration
Describe syndesmoses.
- type of joint
- what connects what
- example
Synarthroses = little movement
Bone to bone by fibrous connective tissue
ex: middle radioulnar joint
See NDC p.12 for illustration
Diarthroses = synovial joints.
Name the main structures for synovial joints. (5)
- Articular Cartilage : usually hyaline
- Synovial Fluid
- Synovial Membrane
- Joint (Articular) Capsule
- Ligaments
See NDC p.13 for illustration
What is the function of synovial fluid in diarthroses? (synovial joints)
Lubricates the joint to permit smooth motion.
See NDC p.13 for illustration
What is the function of the joint capsule in diarthroses? (synovial joints)
Proprioception!
It contains joint receptors critical to movement.
See NDC p.13 for illustration
What is the function of the ligaments in diarthroses? (synovial joints)
They RESTRICT movement at the joint.
- too tight = lack of movement
- too loose = too much movement
See NDC p.13 for illustration
Name the mechanical classification of synovial joints + examples
- Uniaxial: hinge and pivot
- Biaxial: condyloid, ellipsoid
- Triaxial: ball and socket, saddle
- No rotation: gliding/plane or sliding
See NDC p.14 for illustration
Name the uniaxial synovial joints. * special name
- Hinge : Ginglymus
- Pivot : Trochoid
See NDC p.14-16 for illustration
Describe the movement of the uniaxial hinge (Ginglymus) joint.
Name examples.
Convex surface articulates with concave surface
Examples: ulnohumeral, interphalangeal
See NDC p.14-15 for illustration
Describe the movement of the uniaxial pivot (trochoid) joint.
Name examples.
Rotation of one bone on another (longitudinal axis)
Examples: proximal radioulnar joint, atlantoaxial joint
See NDC p.14,16 for illustration
Name the biaxial synovial joints.
Describe their overall movement.
- Condyloid
- Ellipsoid
Convex surface fits into concave surface of similar shape
Describe the movement of the biaxial condyloid joint.
Name examples. (1)
Spherical convex surface + shallow concave surface
Examples: metacarpal phalangeal joints
See NDC p.14,17 for illustration
Describe the movement of the biaxial ellipsoid joint.
Name examples. (1)
Flat convex surface + deep concave surface
Examples: radiocarpal joint
See NDC p.14,17 for illustration
Name the triaxial synovial joints.
- Ball and socket
- Saddle
Describe the movement of the triaxial ball and socket.
Name examples. (2)
Spherical head fits into a concave depression
Examples:
1. glenohumeral joint of shoulder
2. femoral head into acetabulum of hip
See NDC p.14,18 for illustration
Describe the movement of the triaxial saddle joint.
Name examples. (1)
Convex and concave surfaces fit together like a saddle
Example: trapeziometacarpal joint of thumb
See NDC p.14,19 for illustration
Describe the movement of the gliding synovial joint.
Name examples. (3)
Articular surfaces that slide on each other.
No rotation.
Examples:
1. tarsal bones
2. inter-carpal joints
3. articular processes of the vertebrae
Name the synovial joint movements.
- Spin
- Roll/Rotation
- Glide (or slide)
Most movement is a combination
Describe the movement of spin.
- Rotary motion
- Fixed axis
- No translation
–> tires spinning in ice = rotation but not advancing
ex: neck
See NDC p.21 for illustration
Describe the movement of roll.
- Rotary motion
- New point of contact
- Translation
–> tires spines and grip ground = advancing
See NDC p.21 for illustration
Describe the movement of glide.
Linear or translatory motion
–> hit the brakes, no rotation but still advancing
See NDC p.21 for illustration
Combination of roll and glide
What is the instant center of rotation?
Does it change?
The theoretical axis of rotation for the joint at any given position.
It refers to a point in a moving body (or system) at any given instant, where the velocity of that point is zero.
Changes since joint movement is rotation as well as gliding.
See NDC p.22-23 for illustration
Concave VS Convex
Concave = dent (cave)
–> ex: acetabulum
Convex = bump
–> ex: humeral head
What is the concave-convex rule?
Name an example.
Concave moves on convex = concave bone slides (translation) in the same direction as the roll (rotation)
If the bone with the concave surface moves on the convex surface, the concave articular surface glides in the same direction as the bone segment’s roll.
ex: thumb metacarpophalangeal (MCP) joint
–> when proximal phalange (concave) bends, it translates downwards as well
See NDC p.24-25 for illustration
What is the convex-concave rule?
Name an example.
Convex moves on concave = convex bone slides (translation) in the opposite direction as the roll (rotation)
If the bone with the convex joint surface moves on the bone with the concave surface, the convex surface glides in the direction opposite the bone rolling
motion.
ex: thumb abduction at carpometacarpal (CMC) joint
–> thumbs rolls out (rotation) and convex surface glides in (translation)
See NDC p.26-27 for illustration
What is the radius of curvature?
Describes the amount of curvature of a joint surface.
It is the length of the radius of a circle of the same curvature.
Radius of curvature is similar in both articular surfaces = much tighter congruent fit
See NDC p.28 for illustration
What is a closed packed position? (4)
- joint surface
- ligaments
- capsule
- joint
Point of exact congruency where:
1. Joint has maximum area of surface contact
2. Ligaments are under tension
3. Capsule is taut (taut = stretched or pulled tight; not slack)
4. Joint is compressed
ex: PIP joint
See NDC p.29 for illustration
What is an open packed position? (4)
- joint surfaces
- ligaments
- capsule
- movement
- Joint surfaces are incongruent
- Ligaments are more slack
- Capsule is more slack
- Greater ease for accessory movement
See NDC p.30 for illustration
What is active movement VS passive movement?
Active movement = motion done with muscles
Passive movement = motion done without muscles
–> this motion = arc of motion
What is the function of evaluating passive movement?
Evaluating the health of the joint, ligaments.
How far can the joint move regardless of muscle.
What is the joint end feel?
Resistance to movement at end of passive joint range of motion (pushing the joint through the arc of motion).
How far can the joint move regardless of movement?
What are the types of end feel?
- Hard end feel
- Soft end feel
- Empty end feel
What is a hard and feel?
When does this happen?
Bone on bone contact.
ex:
- Trauma
- Arthritic surfaces have degraded
What is a soft end feel?
When does this happen?
Soft tissue approximation.
–> joint can’t be pushed further because of contact with other part of body
ex:
Huge bicep stops elbow flexion during active movement.
Brachioradialis makes contact with biceps = soft end feel
What is an empty end feel?
When does it occur?
Not able to reach end point
ex: ligament rupture
What is stress?
Describe it.
- Force Applied to Deform a Structure
- Force is perpendicular to the area
What is the formula for stress?
What is the variable?
What is the unit?
Formula : σ = F/A
–> Force per unit area experienced by the material
Where:
F=Applied Force
A=Area Over Which Force Applied
Variable : σ (sigma)
Unit : Newton/m2
See NDC p.34 for illustration
What are the types of stress?
- Compressive stress (Compression)
–> falling on an outstretched hand - Tensile stress (Tension)
What is shear stress?
What is the formula?
Created by a force that is parallel not perpendicular to the area.
Shear force refers to a force that acts parallel or tangential to the surface of a material, causing one layer or part of the material to slide or deform relative to an adjacent layer
Shear stress = Shear Force/Area
–> Unit: Newton/m2
See NDC p.38 for illustration
What is strain?
Resulting deformation of a material from force.
It can be perpendicular or parallel.
See NDC p.37 for illustration
What is the formula for strain?
ε =∆L/L
Strain = change in length of material / resting length of material
Where: ∆L=change in the length of the structure
L=resting length of a structure
Variable : ε (epsilon)
See NDC p.38 for illustration
What is a stress-strain curve?
What do they examine? (3)
Graph of stress according to strain.
They examine how materials:
1. Change with age
2. React to different forces
3. React to everyday stresses
See NDC p.39 for illustration
Name the regions of the stress-strain curve.
- Toe region
- Elastic region
- Plastic region
- Failure
See NDC p.40 for illustration
Describe the toe region of the stress-strain curve.
Initial un-crimping of fibers.
See NDC p.40 for illustration
Describe the elastic region of the stress-strain curve.
Stress vs strain relationship is linear.
Material returns to original length when load (applied force) removed.
See NDC p.40 for illustration
Describe the plastic region of the stress-strain curve.
Structure does not return to original length when load removed.
See NDC p.40 for illustration
Describe the failure of the stress-strain curve.
Applied force continues beyond the plastic region.
The material will break.
See NDC p.40 for illustration
Describe the yield point in the stress-strain curve.
- between what regions
- other name
- what
Yield point = elastic limit : elastic region –> plastic region
Stress level at which a material begins to permanently deform.
See NDC p.42 for illustration
Describe the ultimate strength in the stress-strain curve.
- between what regions
- other name
- what
Ultimate strength = failure point : plastic region –> failure
Largest stress a material withstands before failure.
See NDC p.42 for illustration
What is the elasticity modulus?
What is it represented by?
The slope of the straight line (elastic region) of a stress-strain curve.
Represented by the symbol E.
See NDC p.43 for illustration
What does a higher or lower elasticity modulus indicate?
Higher value of E (slope) = stiffer material (ex: glass)
Lower value of E (slope) = looser material
What is a ductile material?
Describe the stress-strain curve of a ductile material.
Describes a material that deforms plastically before failure.
Stress-strain relationship is a curve: Material yields with continued increase in the applied load
It reaches the failure zone = it breaks at the ultimate strength point
See NDC p.45-46 for illustration
What is brittle material?
Describe the stress-strain curve of a brittle material.
Describes a material that fails before plastic deformation.
Linear stress-strain relationship
It doesn’t reach the plastic region = it breaks at the yield point.
See NDC p.45,47 for illustration
See NDC p.48 for stress-strain graphs of brittle and ductile materials.
:)
What is Poisson’s ratio?
The ratio of lateral strain over axial strain
ν= -lateral strain/axial strain
Example: A material is pulled (tension) during testing and the diameter and length change
–> axial strain increases (↑ length) and lateral strain decreases (↓ width)
See NDC p.49-50 for illustration
What does fatigue testing determine?
How many loading cycles (load-unload) at a given load a material can withstand before failing.
What is fatigue life?
Nb of loading cycles that a material can withstand at a given stress level.
What is the influence of loading rates on materials?
Most materials subjected to a higher number of loading cycles will fail at a stress lower than their ultimate strength
–> ex: bending a paperclip until it breaks
What is a viscoelastic material?
Do humans have viscoelastic materials?
Materials that demonstrate a TIME DEPENDENT behavior to loading.
–> fluid like component
Most human biological materials (eg. tendon) exhibit
viscoelastic behaviour.
What is viscocity?
How do viscous fluids move?
Viscocity = “gooeyness” of a material.
High viscosity fluid flows more slowly.
What is stress relaxation?
Name an example.
The reduction of stress within a material over time as
the material is subject to constant deformation.
–> progressive reduction of stress overtime
ex: an orthosis keeps the wrist extended = wrist stress decreases
See NDC p.55-56 for the stress-strain curve
What is creep?
Name an example.
The continued deformation of material over time as
the material is subjected to a constant load.
–> active force pushing on it
ex: an elastic band with a weight = looser after 1 week
See NDC p.55,57 for the stress-strain curve
What is the neutral axis in bending?
The location where a beam experiences zero stress.
See NDC p.59 for illustration
What are the types of stress at play in bending?
Stress on one side of the neutral axis is compression and on the other side is tension.
See NDC p.59 for illustration
What is torsion?
What type of stress does it generate?
A twisting force.
Torsion generates shear stress that are distributed over the entire structure
Name the types of bone fractures and what forces are at play.
- Transverse : tension
- Oblique : compression
- Butterfly : bending
- Spiral : torsion
See NDC p.61 for illustration
What is an isotropic material?
Isotropic material properties do not depend on the direction of loading.
Example: glass
What is an anisotropic material?
Anisotropic material properties DO depend on the direction of loading.
Example: bone, tendons, ligaments
–> bicep is dependent on the direction of loading
