Biomechanics Flashcards
multiplication factor of the prefix ‘mega’
10 to the power 6
multiplication factor of the prefix ‘giga’
10 to the power 9
multiplication factor of the prefix ‘micro’
10 to the power -6
multiplication factor of the prefix ‘nano’
10 to the power -9
what is the importance of reference frames and coordinate systems?
reference frames allow us to describe all positions and directions in biomechanics.
positions within the reference frame are related by a particular coordinate system
2 types of co-ordinate system
rectangular co-ordinate system
polar co-ordinate system
describe the rectangular co-ordinate system
also known as the Cartesian co-ordinate system.
consists of 3 axes at right angles to one another (x, y and z axes)
describe the polar co-ordinate system
uses a length and an angle to describe positions
define a plane
a flat surface, which has zero-thickness so is therefore 2D
list 3 facts about planes
- two planes can be at right angles to one another
- 3 planes, but no more, can mutually be at right angles, like at the corner of a cube
- a straight line is formed where 2 planes cross each other
name the 3 planes of the body
coronal/frontal plane - side to side
sagittal plane - front to back
transverse - horizontally through
describe the difference between linear and rotary motion
linear motion is motion in a straight line
rotary motion is motion about a central axis
objects can undergo either type of motion or both at the same time
what is a vector quantity and how does it differ from a scalar quantity
a vector is a quantity that has a magnitude and direction, however a scalar is a quantity that only has magnitude
list examples of vector quantities
displacement
velocity
acceleration
force
list examples of scalar quantities
distance
speed
temperature
what is the difference between ‘distance’ and ‘displacement’
distance is a scalar quantity, and is the actual distance travelled between 2 points
displacement is a vector quantity, and is the straight-line distance between 2 points with a defined direction
what is the difference between ‘speed’ and ‘velocity’
speed is a scalar quantity, and is the rate of change of distance travelled
velocity is a vector quantity, and is the rate of change of displacement
what is the equation for average velocity
change in displacement/time (metres per second)
define the term ‘acceleration’
the rate of change of velocity
define the term ‘deceleration’
the rate of change of velocity on slowing down (it will be a negative value)
what is the equation for average acceleration
change in velocity/time (metres per second squared)
what 2 effects can a force have on an object
- change the position of the object in space
2. deform the shape of the object
what is the unit of force
the Newton (N)
i.e. 1 kg per metre per second squared
it is an SI derived unit
define the term ‘statics’
the branch of mechanics dealing with forces and moments acting on objects at rest or moving with constant velocity i.e. not accelerating
define the term ‘static equilibrium’
an object which is static with no resultant force (or moment) acting on it is said to be in static equilibrium
what is the first condition of static equilibrium
the sum of all the external forces acting on an object is zero
define the term ‘translational equilibrium’
a more specific way of describing the first condition of static equilibrium; static equilibrium along straight lines
what is Newton’s III Law
to every action, there is an equal and opposite reaction
what forces are included in a free body diagram
all external forces (and moments) acting on a body, including those due to gravity, friction forces and reaction forces
describe the difference between ‘mass’ and ‘weight’
Mass (m) is a scalar quantity, and is the quantity of matter of which a body is composed (unit = kg)
Weight (W) is a vector quantity, and is the force of gravity acting on a body (unit = N)
define ‘density’
density is equal to the mass per unit volume
give the equation for density
density (ρ) = mass/volume (unit = kg per metre cubed)
what is gravity?
the acceleration due to gravitational attraction between 2 bodies. Gravity results in a body having a weight
what is the equation for calculating the weight of a body
Weight (W) = mass (m) x gravity (g) unit = N
what is the difference between ‘centre of mass’ and ‘centre of gravity’
a ‘centre of mass’ is a point in an object where all the mass of an object can be assumed to act.
a ‘centre of gravity’ is a point in an object where all the weight of an object can be assumed to act.
a centre of gravity will only exist in an object in a gravitational field. where both a centre of mass and a centre of gravity exist, they will be coincidental.
define ‘pressure’
the force exerted per unit area
equation for pressure
Pressure (P) = Force (F)/Area (A)
unit = Newton per metre squared (Pa)
define the term ‘moment’
the moment of a force is the tendency of a force to produce a rotation about an axis.
it is the product of the applied force and the moment arm.
the moment arm is the length of the line that passes through the centre of rotation and is perpendicular to the line of action of the force.
equation for finding the moment of a force
Moment = force x moment arm
M = F x d (unit = N m )
what is the second condition of static equilibrium
the sum of all external moments acting on a body must be equal to zero
define the term ‘rotational equilibrium’
a more specific way of describing the second condition of static equilibrium; static equilibrium about an axis
what is a ‘lever’
a lever is a simple system, where a rigid bar pivots on a fulcrum (i.e. a hinge) and is acted on by an effort force and a resistance force.
The effort force and resistance force produce moments acting about the fulcrum.
in a lever system, what is the ‘effort arm’
the length of the line that passes through the fulcrum (i.e. the centre of rotation) and is perpendicular to the effort force
in a lever system, what is the ‘resistance arm’
the length of the line that passes through the fulcrum (i.e. the centre of rotation) and is perpendicular to the resistance force
when is a lever system said to be working at a ‘mechanical advantage’
when the magnitude of the effort force required to overcome the resistance force is smaller than the resistance force
i.e. when the effort arm is LONGER than the resistance arm
when is a lever system said to be working at a ‘mechanical disadvantage’
when the magnitude of the effort force required to overcome the resistance is larger than the resistance force
i.e. when the effort arm is SHORTER than the resistance arm
what is the equation for calculating the mechanical advantage of a lever system
MA = effort arm/resistance arm
> 1 indicates mechanical advantage
< 1 indicates mechanical disadvantage
list the 3 types of lever system
1st class lever: fulcrum is located between the effort force and resistance force. can work at either MA or MD
2nd class lever: resistance force is located between the fulcrum and the effort force. always works at MA because the effort arm is always longer.
3rd class lever: effort force is located between the fulcrum and the resistance force. always works at MD because the effort arm is always shorter.
list the 4 types of tissue within the body
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue
what is the role of connective tissue
protects and supports the body and its organs
connects and holds organs together
transport substances throughout the body
list 4 types of connective tissue
bone tissue
articular cartilage
tendons
ligaments
what does the non-cellular organic component of bone consist of
very strong collagen fibres embedded in a jelly-like matrix called ground substance. makes the bone flexible but resist stretching.
what does the cellular inorganic component of bone consist of
calcium phosphate crystals. makes the bone hard and rigid.
describe the composition of compact bone
compact bone is the outer layer and has a dense structure.
basic structural unit - haversian system. lots of longitudinal units arranged in columns.
bone tissue arranged in lamellae - concentric circles around a central canal.
central channel - haversian canal, which contains blood vessels and nerve fibres.
small cavities between lamellae - lacunae, which contain osteocytes.
Canaliculi - link each osteocyte to the Haversian canal and to other lacunae. Nutrients are carried from the blood vessels along these.
Collagen fibres interconnect layers of lamellae.
Each Haversian system is surrounded by ground substance.
describe the composition of cancellous bone
cancellous bone is the inner part and has a spongy mesh-like structure.
basic structural unit - trabeculae. a lattice of branching sheets and columns.
similar structure to haversian system - lamellae layers with lacunae inbetween containing osteocytes and connected by canaliculi.
don’t have haversian canals. they are not needed because blood vessels can pass through the lattice of trabeculae, and supply nutrients to the osteocytes through the canaliculi.
define the term ‘tensile loading’
a material is loaded in tension - acts to stretch the material like in a rope.
define the term ‘compressive loading’
a material is loaded in compression - acts to compress the material like in the supporting column of a building.
define the term ‘stress’
the force per cross-sectional area
equation for stress
stress = force/area (unit N per metre squared)
define the term ‘strain’
the change in length divided by the original length (no units - ratio)
what is Young’s modulus and give the equation
the ratio of stress to strain, where they are directly proportional. i.e. the initial part of a stress-strain curve where they are directly proportional.
Young’s modulus is a constant.
Youngs modulus = stress/strain
what does Young’s modulus give an indication of
how flexible or stiff a material is -
a small Young’s modulus means that a small amount of stress will produce a large strain - it is flexible.
a large Young’s modulus means that a large amount of stress is needed to produce a small strain - it is stiff.
other than tension and compression, what types of loading can bone undergo?
shear loading
bending loading
torsional loading
what is ‘shear loading’
two forces acting in opposite directions tend to cause layers within the material to slip or shear.
bone is strongest in what type of loading?
compression, then tension, then shear
are fractures caused by shear loading common?
no, they are relatively rare, surprisingly
what is ‘bending loading’
loads are applied to a structure that tend to cause the structure to bend
name 2 common types of bending loading and explain them
- cantilever bending:
one end of the object is fixed and a load is applied to the other end causing the object to bend. - three point bending:
3 forces are applied to the object
what is the ‘neutral axis’ in bending loading
when an object is bent, one side is in tension and the other side is in compression.
between the two sides of the structure there is a neutral axis along which no deformation occurs.
when a bone is subjected to a large bending load, will it tend to fracture on the tension side or the compression side?
the tension side - bone is stronger in compression than tension
what is ‘torsional loading’
a bone is twisted about its longitudinal axis. occurs when one end of the bone is fixed and the other end is twisted.
when a structure is subjected to a torsional load, where is the most distortion in this structure, and explain this phenomena
the outer surface is most distorted, with the centre not being distorted.
the centre of a bar is a neutral axis, therefore the core only carries a small proportion of the torsional load
what property of bone maximises its strength-to-weight ratio and explain
hollow structure, with strong cortical bone forming the outer layer.
if the same quantity of bone was used to construct a completely solid structure, the bone would be smaller in diameter and less able to resist torsional loads
what is a combined loading
the presence of more than one type of loading, which results from the irregular geometry of bones
describe the influence of muscle action on the distribution of stress within bone
Loads applied by muscles when they contract alters the stress distribution of bone.
Muscles often contract to alter the stress distribution in bone rather than the cause movement. If a muscle contracts and produces a compressive load on a bone, it will eliminate any tensile forces acting on the bone.
Since bones are stronger in compression than tension, this is desirable
describe the influence of exercise and weightlessness on bone mineralisation
Generally, bone is laid down where needed (exercise) and resorbed when not needed (weightlessness)
- Wolff’s Law
what is a ‘fatigue fracture’
A fracture resulting from repeated application of a load smaller than the ultimate strength of the bone aka. stress fractures, march fractures
describe the influence of age-related changes on the biomechanics of bone
Children -
more bone tissue formation than resorption.
greater proportion of collagen than young adults, so bones are more flexible.
Young adults
- balanced bone formation and resorption.
Older adult
- bone resorption begins to exceed formation. bones are slightly weaker but significantly more brittle.
what does the greater proportion of collagen mean for children’s bones?
more susceptible to fracture - greenstick fractures.
an incomplete fracture where one side of the bone is bent and the other side is buckled.
what are the 3 types of cartilage in the body
- hyaline cartilage (articular cartilage)
- elastic cartilage
- fibrocartilage
what is the role of articular cartilage in synovial joints
articular cartilage is adapted to:
withstand very large loads,
cushions the bones
provides a smooth, lubricated bearing surface with minimal wear
shock absorbs, and reduces contact stress
what is the general composition of articular cartilage
an organic matrix of non-cellular material, interspersed with cells and fluid
what composes the ‘organic matrix of non-cellular material’ in articular cartilage
collagen fibrils,
which are enmeshed in a concentrated solution of proteoglycans (protein-based molecule contributing to the mechanical properties of articular cartilage)
what composes the ‘interspersing cells’ in articular cartilage
chondrocytes,
which secrete and maintain the organic matrix
what composes the ‘interstitial fluid’ in articular cartilage
water
describe the structure of articular cartilage
divided into 3 zones according to the orientation of chondrocytes and collagen fibres.
Superficial tangential zone:
- tight collagen fibres running parallel to articular surface
- oblong chondrocytes parallel to articular surface
Middle zone:
- less tight collagen but still broadly running parallel to surface
- high density of proteoglycans
- circular chondrocytes, randomly distributed
Deep zone:
- large bundles of collagen anchored in underlying bone tissue, acting as the attachment of cartilage to bone
- columns of chondrocytes aligned perpendicular to the line dividing articular cartilage and underlying bone
what is the ‘tidemark’ when describing the structure of articular cartilage
the interface between the articular cartilage and the thin layer of calcified cartilage that lies below the deep zone
list 3 basic mechanical properties that articular cartilage exhibits
- viscoelastic behaviour
- creep
- stress relaxation
define the term ‘viscoelastic’
describes the mechanical behaviour of articular cartilage.
it means that when a load is applied, it will return to its original shape, like an elastic material, but the response isn’t immediate.
the behaviour is time-dependent - deformation varies depending on how long a load is applied for and the rate of application of the load.
define the term ‘creep’
describes the behaviour a viscoelastic material when it is subjected to a CONSTANT LOAD.
when the load is first applied the material deforms quite rapidly, then continues with slowly (creeping) increasing deformation over time.
explain how ‘creep’ occurs in articular cartilage
due to its viscoelastic properties -
during initial rapid deformation, fluid is rapidly forced out of the articular cartilage. As the amount of fluid remaining diminishes, so the rate of expellation decreases until equilibrium, when outward flow ceases completely.
define the term ‘stress relaxation’
describes the behaviour of a viscoelastic material when it is kept at a CONSTANT DEFORMATION.
the stress in a material reduces over time when it is kept at constant deformation (strain)
explain how ‘stress relaxation’ occurs in articular cartilage
due to its viscoelastic properties -
during initial rapid deformation, interstitial fluid is forced out as the surface layers are compacted. During the stress relaxation phase, no more fluid is being forced out and the fluid within the tissue is redistributed to the surface layers in the cartilage.
what substances contribute to synovial joints having a low coefficient of friction
the combined action of articular cartilage and synovial fluid.
the synovial fluid lubricates the surface of articular cartilage, reducing the contact between the two surfaces and reducing the amount of friction and wear.
what factors determine the method of lubrication of a synovial joint
- magnitude of the load on the joint
2. the length of time the load is maintained
list the 3 main types of lubrication
- elastrohydrodynamic lubrication
- boosted lubrication
- boundary lubrication
explain ‘elastohydrodynamic lubrication’
occurs when two surfaces, one of which is deformable, are lubricated by a film of fluid as they move relative to one another. the fluid of film completely separates the surfaces.
there are 2 ways the surfaces can move relative to one another:
- slide over each other, forming a wedge of lubricant fluid (hydrodynamic lubrication)
- move closer together, pushing lubricant out (squeeze film lubrication)
Due to one or both of the surfaces being deformable, the pressure distribution is increased, therefore the pressure is decreased and the fillm remains relatively thick
explain ‘boosted lubrication’
reduces the depletion of lubricant when 2 surfaces are squeezed together for a prolonged period.
as the size of the gap between articulating surfaces decreases, the resistance to the sideways flow of lubricant becomes greater than the reistance of flow of the small molecules into the articular cartilage.
small molecules (like water) therefore flow into the articular cartilage leaving a thick solvent component of synovial fluid.
explain ‘boundary lubrication’
prevents articular surfaces from coming into direct contact even when lubricant is fully depleted.
lubricant molecules attach themselves chemically to the surface and create a boundary layer.
this offers a lower friction than the bare surfaces.
explain the role of tendons and ligaments
tendons connect muscles to bone
ligaments connect bone to bone
describe the structure and composition of tendons and ligaments
they are dense fibrous connective tissue, containing few cells called fibroblast which are embedded in a collagen matrix
tendons - collagen arranged in parallel (only need to withstand large forces in one direction)
ligaments - collagen not completely parallel (need to withstand smaller forces in other directions)
what is the basic mechanical behaviour of tendons and ligaments
viscoelastic behaviour
how far can the ACL be elongated before it fails completely
7mm
what length of joint displacement is within physiological range and means the ligament will be undamaged
4mm - after this the collagen fibres rupture progressively and lead to instability
name the major bones and joints of the lower limb
bones:
femur, tibia, fibula, tarsals, metatarsals, phalanges
joints:
hip, knee, ankle
describe the anatomy of a synovial joint
the surface of the bones that form a synovial joint are covered with articular cartilage.
enclosed in a tough fibrous sheet - the JOINT CAPSULE
the joint capsule forms the SYNOVIAL CAVITY inside.
the synovial cavity is filled with SYNOVIAL FLUID.
the synovial fluid is produced from the SYNOVIAL MEMBRANE, which lines the inner surface of the capsule.
what are the two functions of synovial fluid
- lubricate joints
2. provide nutrients to the articular cartilage
describe the structure of the hip joint
ball-and-socket shaped synovial joint.
ball - head of femur
socket - acetabulum of pelvic girdle
describe the motion and range of motion of the hip joint
motion occurs in all 3 planes:
flexion (140) / extension (20)
abduction (30) / adduction (25)
external rotation (90) / internal rotation (70)
explain why the force at the hip joint is increased so greatly during unilateral stance compared with bilateral stance
during bilateral stance, there are no active muscles at the hip joint. therefore only external forces need to be considered: the weight of the body acting downwards, and two reaction forces, one at each hip joint, acting upwards.
during unilateral stance, abductor muscle activity is required to stabilise the position of the body. there are 4 forces: the weight of the lower limb acting downwards, the abductor muscle force, the joint force at the hip, and the ground reaction force acting upwards.
the contraction of the hip abductor muscles effectively pulls the two sides of the hip joint together and greatly increases the force at the hip joint.
what are the 2 articulations of the knee joint
- tibiofemoral
2. patellofemoral
describe the structure of the proximal surface of the tibia
flat surface and covered with menisci.
menisci are 2 crescent-shaped pieces of fibrocartilage which make the flat surface slightly concave which aids stability and act as load distributors and shock absorbers.
describe the structure of the distal end of the femur
formed by two circular shaped condyles - femoral condyles, which are covered with articular cartilage.
anterior depression between femoral condyles - trochlea.
posterior depression - intercondylar notch (where the cruciate ligaments are lodged)
describe the structure of the patella
it is a sesamoid bone (a bone which is located within a tendon - the quadriceps tendon).
has two posterior smooth surfaces which articulate with each femoral condyle.
what gives the knee joint its stability
anterior and posterior cruciate ligaments -
limit forward and backward sliding of the femur on the tibia and limit hyperextension
medial and lateral collateral ligaments -
lie outside the joint capsule and prevent abduction and adduction.
how does the knee joint’s centre of rotation change in the sagittal plane as it flexes and extends?
it moves in a semi-circular pattern because the femoral condyles aren’t perfectly circular and because of the restrictions due to the knee ligaments
what does the screw-home mechanism of the knee describe
describes the spiral motion of the knee as it flexes and extends when the rotation of the knee is considered in all directions
as the knee flexes, the tibia internally rotates, and as it extends, the tibia externally rotates
describe the range of motion of the knee joint
sagittal plane: flexion (140) / extension (few degrees)
coronal plane: abduction / adduction
(range of motion is dependent on how much the knee is flexed - max at 30 degree flexion)
transverse plane: internal (45) / external rotation (30)
(range of motion increases with flexion - max at 90 degree flexion)
what is the most important function of the patella
increase the lever arm of the quadriceps femoris muscle to assist in knee extension.
explain the function of the menisci
act as force distributors and shock absorbers between the femur and the tibia
what type of joint is the ankle
a hinged synovial joint
list the 3 articulations of the ankle joint
- tibiotalar
- fibulotalar
- distal tibiofibular
what are the bony prominences of the ankle joint
medial malleolus - distal end of tibia
lateral malleolus - distal end of fibula
3 important ligaments of the ankle joint
anterior inferior talofibular ligament
medial ligament
lateral ligament
describe the motion and range of motion of the ankle joint
greatest motion occurs in the sagittal plane
dorsiflexion - flexion of the ankle joint (10-20 degrees)
plantarflexion - extension of the ankle joint (25-35 degrees)
what bones make up each section of the foot
Hindfoot - talus and calcaneus
Midfoot - cuboid, medial intermediate and lateral cuneiforms and navicular
Forefoot - metatarsals and phalanges
what is the subtalar joint
the articulation between the talus and the calcaneus
the subtalar joint permits what type of motion
inversion (20 degrees) and eversion (5 degrees) of the foot
explain the position and function of the plantar fascia
extends from the calcaneus to attach to the plantar aspect of the proximal phalanges.
it supports the longitudinal arch of the foot, and acts as a shock absorber. prevents the vertical force acting downwards at the ankle joint from collapsing the longitudinal arches
define the term ‘reciprocal gait’
the gait commonly used for walking
define the term ‘gait analysis’
the clinical examination of gait
what equipment is found in a gait lab
motion analysis system
force plates
electromyopgrahy equipment
describe a motion analysis system
markers placed on prominent body parts which are then seen by cameras. the system calculates the position of each amrker in 3D, allowing the body to be looked at from any angle on the computer.
describe the gait cycle
gait cycle = one stride = 2 steps, 1 by each lower limb
begins with initial contact of one foot on the ground (heel contact), and ends with the next heel contact of the same foot.
when foot is in contact with the ground - stance phase
when foot loses contact with ground - swing phase
when both foot are in contact with ground - double support
list the landmark events of the gait cycle
heel contact foot flat mid stance heel off toe off mid swing
define the term ‘ground reaction force’
the equal and opposite force exerted by the ground
describe the moments acting at the joints of the lower limb during reciprocal gait
Hip:
- after heel contact there is a positive extension moment
- prevents the upper body falling forward
Knee:
- after heel contact there is a small flexion moment
- hamstrings contract the prevent hyperextension of the knee
- changes to extension moment as the quads contract to prevent knee buckling
Ankle:
- plantarflexion moment increases to a peak just before toe off as the triceps surae contracts to push the foot up and off the ground
name the 4 shoulder joint articulations
glenohumeral articulation
acromioclavicular articulation
sternoclavicular articulation
scapulothoracic articulation
describe the structure of the glenohumeral joint
ball-and-socket shaped synovial joint
formed by the humeral head and the glenoid fossa of scapula
what property of the shoulder joint helps to assist stability
a thick cartilaginous rim - GLENOID LABRUM
which muscles and their tendons form the rotator cuff
subscapularis (anterior)
supraspinatus (posterior)
infraspinatus (posterior)
teres minor (posterior)
explain the function of the rotator cuff
the muscles form a cuff of tissue around the joint, and press on the humeral head, preventing any anterior-posterior movement
name the ligament about whose attachment the clavicle rotates during elevation and depression
the costoclavicular ligament
- between the clavicle and 1st rib
why is the scapulothoracic articulation not a joint in the truest sense?
there are no direct bony or ligamentous connections between the scapula and thorax
what separates the anterior scapula from the posterior thorax
2 broad flat muscles - subscapularis and serratus anterior
what is the origin and insertion of the serratus anterior muscle, and give its function
originates - upper 8/9 ribs
insertion - anterior surface of scapula
function - holds scapula against the thorax, preventing ‘winging’ of the scapula, and is a strong abductor
what is the origin and insertion of the subscapularis muscle, and give its function
origin - subscapular fossa
insertion - lesser tubercle of humerus
function - rotator cuff muscle, acts medially to rotate humerus
describe the different possible motions of the shoulder joint
shoulder elevation - movement of the humerus away from the side of the thorax
shoulder depression - movement of the humerus towards to the side of the thorax
elevation and depression are given different names depending on the plane of movement
sagittal plane - forward flexion, backward extension
coronal plane - abduction, adduction
transverse - horizontal flexion, horizontal extension
also - internal/external rotation around the longitudinal axis of humerus
what is the range of forward flexion and backward extension of the shoulder joint
forward flexion - 180 degrees
backward extension - 60 degrees
total range - 240 degrees
what is the range of abduction and adduction of the shoulder joint
abduction - 180 degrees
adduction - 75 degrees
total range - 255
what is the range of internal rotation and external rotation of the shoulder joint
internal rotation - 90 degrees
external rotation - 90 degrees
total range - 180 degrees
what is the range of horizontal flexion and horizontal extension of the shoulder joint
(max at 90 degrees abduction)
horizontal flexion - 135 degrees
horizontal extension - 45 degrees
total range - 180 degrees
what is the most common type of dislocation of the shoulder joint and explain
anterior dislocation
heavy blow to arm when shoulder is abducted and extended horizontally
name the 3 elbow joint articulations
humeroradial articulation -
between the capitulum of humerus and head of radius
humeroulnar articulation -
between trochlea of humerus and trochlear notch of proximal ulna
proximal radioulnar articulation -
between head of radius and radial notch of ulna
describe the type of motions and ranges of motion at the elbow joint
humeroradial and humeroulnar articualtions permit:
flexion (140 degrees) / extension (0 degrees)
proximal radioulnar articulation permits:
pronation (70 degrees) / supination (80 degrees)
describe the function of the annular ligament
binds the radius to the ulna, inside which pronation and supination occur at the elbow joint
discuss the stability of the elbow joint
olecranon process - gives antero-posterior stability
medial and lateral collateral ligaments - give medial and lateral stability
are forces around the elbow joint generally high or low? and explain why
high - up to 2000N, (2.5-3 x body weight)
large muscle forces need to be generated to perform daily activities since the moment arms of the muscles are generally small
what structures form the wrist joint
distal radius
structures in the ulnocarpal space
the carpal bones
proximal ends of the metacarpals
name the carpal bones
scaphoid (some) lunate (lovers) triquetrum (try) pisiform (positions) trapezium (that) trapezoid (they) capitate (cant) hamate (handle)
where is the pisiform bone located
anteriorly to the triquetrum, on the little finger side of the hand - small rounded elevation
the pisiform bone is the insertion point of which muscle
flexor carpi ulnaris
- flexes and adducts the wrist
what forms the radiocarpal joint
articulation between the distal radius and the lunate and scaphoid bones
what type of joint is the radiocarpal joint and what movements does it permit
condyloid joint -
oval-shaped condyle fits into elliptical depression
flexion, extension, abduction, adduction and circumduction
how does the distal ulna articulate with the triquetrum
via a triangular shaped inter-articular disc, occupying the ulnocarpal space.
what are the movements possible at the wrist joint and the range of these movements
flexion (90 degrees) / extension (80 degrees)
abduction (20 degrees) / adduction (35 degrees)
at which articulation of the wrist joint does most flexion occur
midcarpal joint
at which articulation of the wrist does most extension occur
radiocarpal joint
list the principal joints of the hand
carpometacarpal joints
intermetacarpal joints
metacarpophalangeal joints
proximal interphalangeal joints
distal interphalangeal joints
why is the 1st carpometacarpal joint significant
most freely moving - gives the opposable thumb as it is able to flex, extend, adduct and abduct
what type of joints are the carpometacarpal joints (CMCs)?
saddle joints
what type of joints are metacarpophalangeal joints (MCPs)
condyloid joints
what type of joints are the interphalangeal joints (IPs)
hinge joints
discuss the mobility of the metacarpal bones
2nd and 3rd basically immobile
4th and 5th permit small amount of flexion and extension
discuss the mobility of the metacarpophalangeal (MCP) joints
flexion (90 degrees) / extension (depends on ligament laxity)
adduction /abduction
discuss the mobility of the interphalangeal (IP) joints
both distal and proximal only permit flexion-extension
Flexion -
most at PIPs (110 degrees)
DIPs (90 degrees)
Extension -
dependent on ligament laxity
what are the ranges of motion of the thumb
flexion (15 degrees) / extension (20 degrees)
abduction (60 degrees)
small amount of rotation
why do the motions of the hand and wrist interact with each other?
because the main muscles controlling the digits actually are located in the forearm, therefore their distal tendons cross the wrist joint.
as the wrist changes position it alters the length of the tendons crossing it.
name the different regions of the spine
cervical (7 vertebrae)
thoracic (12 vertebrae)
lumbar (5 vertebrae)
sacral (5 fused vertebrae)
coccyx (4 fused vertebrae)
what features do all vertebrae (apart from the first two) have in common?
vertebral body
neural arch
spinal foramen
spinous process
transverse processes
what are the 3 articulating points of each vertebrae
intervertebral disc (between vertebral bodies)
2 facet joints (either side of the vertebral arch)
what are intervertebral discs composed of
an inner nucelus pulposus -
hydrophilic gel in a random collagen matrix. high water content which allows balance when there is high stress
an outer annulus fibrosus -
dense collagen fibres forming layers to resist bending and torsion
describe the anatomy of C1 vertebrae
a.k.a. atlas
- no body
- composed of a ring
describe the anatomy of C2 vertebrae
a. k.a. axis
- has a dens process which protrudes superiorly and allows articulation with the atlas
describe the anatomy of the thoracic vertebrae in relation to the ribs
each thoracic vertebrae is attached to its corresponding rib.
the tubercle of each rib articulate with the transverse process.
the head of each rib articulates with the vertebral body.
why does the lumba spine vertebrae have larger bodies than the other vertebrae?
the lumbar vertebrae are subjected to larger loads
in what region of the spine is flexion-extension greatest and least
greatest - cervical spine
least -thoracic spine
in what region of the spine is lateral bending greatest and least
greatest - cervical (N.B. none between C1/C2)
least - thoracic spine
in what region of the spine is rotation greatest and least
rotation of the spine decreases down the spine
greatest - between atlas and axis
how do loads on the spine vary with positioning of the trunk
prone - 25% erect standing - 100% erect sitting - 130% bent forward standing - 150% relaxed sitting - 200%
why does the load on the spine increase when changing position to sitting
larger moment arm of the upper body mass about the lumbar spine, therefore greater muscle forces needed. as muscle force increase, so does compressive load
