Semester 1: Mechanics & Biomechanics Flashcards
What is the multiplication factor for the prefix mega?
10^6
What is the multiplication factor for the prefix kilo?
10^3
What is the multiplication factor for the prefix centi?
10^-2
What is the multiplication factor for the prefix mili?
10^-3
What is the multiplication factor for the prefix micro?
10^-6
Define Scalar quantity
Magnitude only
Define Vector quantity
Magnitude and direction
Give examples of Scalars
Distance Speed Angle Rotation Rate Mass Temperature Energy
Give examples of Vectors
Displacement Velocity Angular Displacement Angular Velocity Force Momentum Acceleration
Conversion of degrees celsius to kelvin?
Add 273
Define speed
Rate of change of distance travelled
Define velocity
Rate of change of displacement
What is the equation used to calculate average velocity?
Average velocity (m/s) = change in displacement / time
Define acceleration
Rate of change of velocity
What is the equation used to calculate average acceleration?
Average acceleration (m/s^2) = change in velocity (m/s) / time taken (s)
What is the term given when change in velocity is negative?
Deceleration
What two effects do forces have on an object?
Change the position and deform the shape
What is the SI unit of force?
Newton
Define static in the context of mechanics
Forces and moments acting upon objects that are either stationary or have a constant velocity i.e. not accelerating
Define static equilibrium in the context of mechanics
A static object with no resultant force (or moment) acting on it
Define translational equilibrium in the context of mechanics
A static equilibrium achieved along straight lines, where the sum of all the external forces along the direction of each axis equals 0 and therefore no resultant force acts upon the object
What is Newton’s Third Law?
To every action there is an equal and opposite reaction
Define mass
Quantity of matter of which a body is composed
Define weight
Force of gravity acting upon a body
What is the SI unit of mass?
Kilogram
What is the SI unit if weight?
Newton
Define density
Mass per unit volume
What is the greek character for density?
Rho, ρ
What is the SI unit of density?
Kg/m^3
If mass changes proportional to volume and vice versa. What will happen to density of a material if mass or volume where to change?
Density of a material remains constant. If mass of an object varies then the volume of the object will change proportionally.
Define gravity
Acceleration due to gravitational attraction between two bodies
What is the equation used to calculate weight?
Weight (N) = mass (kg) X acceleration due to gravity (9.81 m/s^2)
What is the force of the Earth’s gravitational field?
9.81 m/s^2 (sometimes approximated to 10m/s^2)
Where does the centre of mass lie when an individual is standing upright?
Lower abdomen
Where does the centre of mass lie when an individual is bent over?
Lie out with the body in front of the pelvis
Define pressure
Force exerted per unit area
What is the equation used for calculating Pressure?
Pressure (Pascals or N/m^2) = Force (N) /Area (m^2)
Define a moment
Tendency of a force to produce a rotation about an axis (Centre of rotation)
What is another term for moment?
Torque
What is the SI unit for moment?
Newton meters (N m)
Define moment arm
The perpendicular distance from an axis (centre of rotation) to the line of action of a force
What is the equation used to calculate the moment of a force?
Moment, M (N m) = Force (N) X Moment arm (m)
Define rotational equilibrium
Sum of all external moments acting about the axes equal 0
Define the effort arm of a lever system
The length of the line that passes through the fulcrum and is perpendicular to the effort force
Define the resistance arm of a lever system
The length of the line that passes through the fulcrum and is perpendicular to the resistance force
If in a Lever system the effort arm is greater than the resistance arm is the system considered mechanically advantaged or disadvantaged?
Mechanical advantage
If in a Lever system the effort arm is smaller than the resistance arm is the system considered mechanically advantaged or disadvantaged?
Mechanical disadvantage
Define mechanical advantage in a lever system
Magnitude of the force required to overcome a given resistance force is smaller than the magnitude of the resistance force
Define mechanical disadvantage in a lever system
Magnitude of the force required to overcome a given resistance force is larger than the magnitude of the resistance force
In the human body are muscles typically mechanically advantaged or disadvantages in the context of a lever system
Typically disadvantaged because magnitude of the force required to overcome a given resistance force is larger than the magnitude of the resistance force
How is mechanical advantage in the context of a lever system calculated?
As a ratio of the effort arm to the resistance arm
Therefore, if greater than 1 the system is deemed to be at a mechanical advantage
What is the equation used to calculate the mechanical advantage of a lever system?
Mechanical advantage = Effort arm / Resistance arm
Define a first class lever with examples
Fulcrum is located between the effort and the resistance e.g. scissors, crowbar and see-saw
Define a second class lever with examples
Resistance is located between the effort and the fulcrum e.g. wheelbarrow, nutcracker
Do first class lever systems work at a mechanical advantage or disadvantage?
Either mechanical advantage or disadvantage
Do second class lever systems work at a mechanical advantage or disadvantage?
Always a mechanical advantage
Define a third class lever with examples
Effort is located between the fulcrum and the resistance e.g. fishing rod and tweezers
Do third class lever systems work at a mechanical advantage or disadvantage?
Always a mechanical disadvantage
What is the most common lever class seen in the human body?
Third class
What is the unit of pressure?
Pascals or N m^-2
What are the four types of tissue groups?
Epithelial
Muscle
Connective
Nervous
What is the most abundant tissue type in the human body?
Connective tissue
What is the role of connective tissue in the human body?
It is specialised to protect and support the body and its organs, connect and hold them together and to transport substances throughout the body.
What are the four main types of connective tissue?
Bone, Articular Cartilage, Tendon and Ligament
What are the hardest tissues in the human body?
Dentine and Enamel, followed by bone
What are the main types of bone?
Flat bones, Long bones, Short bones, Irregular bones and Sesamoid bones
What cells form bone?
Osteocytes
What makes up the non-cellular organic component of bone?
Type I Collagen fibres (95%) in a jelly-like ground substance (5%)
What percentage of the dry weight of bone is non-cellular organic and inorganic?
Non-cellular organic: 25-30%
Inorganic: 65-70%
What makes up the inorganic component of bone?
Calcium phosphate crystals
What is the difference between compact and cancellous bone types?
Compact (Cortical) - forms the outer layer of bones and is dense.
Cancellous (Spongy) - forms the inner part of bones and has a characteristic mesh-like structure which align themselves in the direction that will best support the load.
What is the basic structural unit in compact bone?
Haversian system
Explain the structure of the Haversian system?
A small central channel called the Haversian canal which contains blood vessels and nerve fibres. Bone tissue surrounding the canal are arranged in layers called lamellae. Cavities between the lamellae known as lacunae, which contain osteocytes. The osteocytes are connected to the Haversian canal and other lacunae by channels called canaliculi.
Where do the blood vessels and nerves run in bone?
Haversian canal
What are the layers surrounding the Haversian canal called?
Lamellae
Where are osteocytes located in bone?
Lacunae
What is the main difference between the microstructure of cortical and cancellous bone?
Cortical bone arranged via the Haversian system
Cancellous bone has no need for Haversian canals as blood vessels pass through marrow filled spaces
What is the basic structural unit in cancellous bone?
Trabeculae
Define tension
When the load is acting to stretch a material
Define compression
When the load is acting to compress the material
Define stress
Force per cross-sectional area
What is the SI unit for Stress?
N m^-2
What is the equation used to calculate Stress?
Stress = Force / Area
Define strain
Change in length divided by the original length
What is the relationship between stress and strain for cortical bone?
Stress increases with increasing strain
What are the two regions of a stress-strain curve called?
- Elastic region
2. Plastic region
What marks the division between the elastic and plastic regions of the stress-strain curve?
Yield point
How are the yield strain and yield stress determined from the stress-strain curve?
Strain at the yield point is termed yield strain
Stress at the yield point is termed yield stress
Define Elastic behaviour
Occurs in the elastic region of the stress-strain curve. The amount of stress is directly proportional to the amount of strain. When a load is removed the material will return to its original shape and size.
Define Plastic behaviour
Occurs in the plastic region of the stress-strain curve. A small increase in stress leads to a large amount of bone deformation. When a load is removed the material is permanently deformed.
What is the stress and strain at which bone fractures on the stress-strain curve called?
The ultimate strain and ultimate stress
What is Young’s modulus?
A constant that can be used to calculate stress or strain.
What is the equation for calculating Young’s modulus?
Young’s Modulus = Stress / Strain
What is the SI units for Young’s modulus?
N m^-2
What does a low Young’s modulus tell you about the flexibility of the material?
Very flexible
What does a high Young’s modulus tell you about the flexibility of the material?
Very stiff
Define a shear loading?
Two forces acting in opposite directions causing layers within a material to slip
Arrange the following from highest to lowest ultimate strength (the point at which stress from a loading force causes the bone to fracture) in cortical bone?
- Tension
- Compression
- Shear
- Compression
- Tension
- Shear
Define Ultimate strength of bone
The point at which stress from a loading force causes the bone to fracture
What are the two types of bending loading?
Cantilever
Three-point
Define Cantilever bending loading
One end of the object is fixed and the load is applied to the other end causing it to bend
Define Three-point bending loading
Three forces are applied to the object causing it to bend
What is the neutral axis of an object undergoing bending loading?
The axis along which no deformation occurs
How does the loading differ on either side of the neutral axis when an object undergoes bending loading?
On one side of the neutral axis the material is elongated and on the other it is compressed. The strain is at its maximum at the surfaces since elongation and compression is greatest there.
What features of long bones maximises their strength to weight ration?
Long bones are hollow with strong cortical bone forming the outer layer. The bone is able to resist torsional stress without being too thin (liable to breaking) or too heavy (no increase in ability to withstand torsional stress).
What is Wolff’s Law?
Bone is laid down where needed and resorbed where not needed.
How does bone change in response to stress?
Lays does collagen fibres and mineral salts to strengthen the bone.
How does bone respond to inactivity?
Bone atrophy occurs in which bone tissue is resorption. .
Define stress shielding?
When the load is carried by a plate rather than the bones itself causing unstressed bone to resorbed.
What happens to bone at the site of the screws when internal fixation via an onlay device takes place?
The bone will strenghten as a greater load is carried at these sites, and bone hypertrophy will occur.
Define a fatigue/stress fracture
A fracture resulting from the repeated application of a load that is smaller than the ultimate strength of the bone
What is the common mechanism of injury resulting in a fatigue/stress fracture?
Continuous periods of strenuous physical activity, as frequency of repetition occurs too fast thus not allowing the appropriate remodelling process.
Describe the balance between bone tissue formation and resorption in children.
More bone tissue formation in children allowing for growth and development.
How does proportion of collagen in children’s bones differ from that of adults?
There is more collagen in the bones of children allowing for greater flexibility.
What type of fractures are common in children due to excessive bending or torsion of the bones?
Green stick fractures.
How is cancellous bone tissue affected by ageing?
There is thinning of the bone due to resorption of the transverse and longitudinal trabecular.
What are the three types of cartilage?
Hyaline, elastic and fibrocartilage.
Name an example of hyaline cartilage in the human body?
The articular surfaces of synovial joints and the tip of the nose.
Name an example of elastic cartilage in the human body?
The external ear and the epiglottis.
Name an example of fibrocartilage in the human body?
Symphysis pubis and the intervertebral discs.
What is the role of chondrocytes?
Manufacture, secrete and maintain the organic matrix which is mainly made up of collagen.
What is the name and function of the of protein that collagen fibrils are enmeshed in?
Proteoglycans.
What are the three zones of articular cartilage?
Superficial tangential, middle and deep.
Describe the structure of the superficial tangential zone?
Collagen fibrils are tightly packed and parallel to the articular surface. Chondrocytes are oblong and their longitudinal axis are parallel to the articular surface.
Describe the structure of the middle zone?
Collagen fibrils (though still broadly parallel to the articular surface) are more random in placement to accommodate proteoglycans. The chondrocytes are round and randomly distributed.
Describe the structure of the deep zone?
The collagen fibrils are arranged in large fibre bundles that are anchored to the bone tissue connecting the articular cartilage to the bone. Chondrocytes are in loose columns perpendicular to the line that divides the articular cartilage and the underlying bone.
What is the interface between the articular cartilage and the calcified cartilage beneath it called?
The Tidemark
How is articular cartilage attached to bone?
Via the bundles of collagen fibrils in the deep layer attaching the articular cartilage to the underlying bone tissue.
How can one describe the mechanical behaviour of articular cartilage?
Viscoelastic.
Define viscoelastic mechanical behaviour.
Response of the material varies according to length of time load is applied and the rate at which the load is applied.
What are the two main characteristics of viscoelastic materials?
Creep and stress relaxation.
Define creep in the context of viscoelastic mechanical behaviour.
Creep is an increase in strain under a constant stress. Continuing lengthening of a material over time when a constant load is applied.
Define stress relaxation in the context of viscoelastic mechanical behaviour?
Stress relaxation is a reduction in stress under a constant strain. Caused by the rearrangement of atoms in the atomic structure of the material.
Why does the amount of stress required to maintain deformation in stress relaxation diminish over time?
During the initial deformation fluid is expelled for the articular cartilage. Fluid moving over a solid matrix will create friction, so more stress will be required to cause deformation. After a certain amount of time (once the fluid has reached equilibrium) there will be no friction due to the flow of fluid. This will reduce the amount of stress required to maintain deformation.
What are the two factors that effect the lubrication of a synovial joint?
The magnitude of the load on the joint pressing the two surfaces together and the length of time that this load is maintained.
What are the three types of lubrication?
Elastohydrodynamic lubrication; Boosted lubrication; Boundary lubrication
What factors determine the dominant type of lubrication?
Variations in the loading in different parts of the joint; and variation in anatomy.
Define elastohydrodynamic lubrication.
It occurs when two surfaces one of which is deformable are lubricated by a film of fluid as they move relative to one another.
What are the two ways in which surfaces can move relative to one another in the context of elastohydrodynamic lubrication?
Slide over each other (this is called hydrodynamic lubrication); they can also move closer together (known as squeeze film lubrication.
Describe how the pressure is distributed between two soft surfaces in the context of lubrication.
Pressure distribution is increased over the deformed surface as a consequence the magnitude of the pressure is decreased and the film remains relatively thick. This is elastohydrodynamic lubrication.
Explain how boosted lubrication works?
When two articulating surfaces are squeezed together the fluid will be pushed towards the edges of the joint. The resistance to the sideways flow of lubricant becomes greater the the resistance to the flow of small molecules (such as water) into the articular cartilage. This leaves behind a viscous gel that is able to support large loads.
What type of lubrication occurs when fluid film is completely depleted?
Boundary lubrication
In the human synovial joint what protein coats the articular surface when the fluid film is completely depleted?
Lubricin
What is the structure called when lubricant molecules attach themselves chemically to the surfaces of joints? What are the properties of this structure?
Boundary layer - low sheer strength - offering a lower friction than the bare surfaces.
How does the arrangement of collagen fibre differ in tendons and ligaments?
In tendons the fibres are arranged in parallel as they need to withstand large loads in one direction. In ligaments the collagen fibres are interwoven and branched as (though they need to withstand a large load primarily in one direction) they need to withstand smaller loads in other direction.
What is the normal physiological range of joint displacement at the knee?
Around 4mm the ligament remains undamaged. Beyond 4mm to 7mm the loading will result in injury as the collagen fibres progressively rupture leading to more joint pain and joint instability. Beyond 7mm the anterior cruciate ligament will fail.
State two functions of the joints in the lower limb.
Two functions of the joints in the lower limb are weight bearing and movement.
What are the ball and socket in the hip joint?
The head of the femur and the acetabulum of the pelvic girdle respectively.
How many direction of rotation are there at the hip joint?
Three: flexion and extension, abduction and adduction, and internal and external rotation.
What is circumduction in the hip joint?
When the femur is able to move in a circle relative to the pelvis.
Describe the structure of the synovial joint?
The surfaces of the bones are covered in articular cartilage. The joints are enclosed by the fibrous joint capsule forming the synovial cavity. This is filled with synovial fluid which lubricates and provides articular cartilage with nutrients.
Why is the hip joint intrinsically stable?
The joint is surrounded by a strong joint capsule and several ligaments. These are in turn are surrounded by strong muscles. This and the ball and socket shape of the joint all contribute to the intrinsic stability of the hip joint.
In which plane does the hip joint have the greatest range of motion?
The sagittal plane.
What is the range of motion of the hip joint in the sagittal plane?
Flexion 0 - 140 degrees. Extension 0 - 20 degrees.
What is the range of motion of the hip joint in the frontal plane?
Abduction 0 - 30 degrees. Adduction 0 - 25 degrees.
What is the range of motion of the hip joint in the transverse plane?
External rotation 0 - 90 degrees. Internal rotation 0 - 70 degrees.
Why is rotation limited when the hip joint is extended?
This is due to restriction of soft tissue.
What range of motion is required to stand up and sit down?
110 degrees of flexion-extension; 20 degrees of abduction-adduction and 15 degrees of rotation.
When taking into consideration the frontal plane, are there any active muscles when a bilateral stance is taken?
No
Which three external forces ac ton the pelvis during a bilateral stance?
The weight of the upper body acting downwards and two reaction forces one at each hip joint acting upwards.
What proportion of total body weight is the upper body (head, arms and trunk - HAT)?
70%
What proportion of total body weight is the lower limbs?
30% (15% per leg)
What are the four forces acting on the hip joint during a unilateral stance?
The weight of the lower limb acting downwards; the abductor muscle force, the joint force at the hip and the ground reaction force acting vertically upwards on the foot.
What is the largest joint in he body?
The knee joint.
Which articulation of the knee accounts the greatest amount of movement?
Tibio-femoral articulation.
What are the purposes of the menisci on the proximal surface of the tibia?
Shock absorption and load distribution. They aid stability due to their concave shape.
What is the smooth anterior depression between the femoral condyles called?
Trochlea.
What is deep posterior between the femoral condyles called?
The intercondylar notch
What is the role of the cruciate ligaments of the knee?
Limits forward and backwards sliding of the femur on the tibia; limits hyperextension.
What are the roles of the medial and lateral collateral ligaments of the knee?
Prevent abduction and adduction respectively.
How much longer is the medial femoral condyle than the lateral femoral condyle?
1.7 cm longer.
Describe the mechanism by which the knee flexes and extends?
Screw - home mechanism.
The tibia rotates internally during flexion and the tibia rotates externally during extension.
What is the range of motion of the knee in the sagittal plane?
A few degree of extension to about 140 degrees of flexion.
When is the range of movement of the knee in the frontal plane at its maximum?
At about 30 degrees flexion; but abduction and adduction is only a few degrees.
When is the range of movment of the knee in the transverse plane at its maximum?
At about 90 degrees flexion where external rotation ranges from 0 - 45 degrees and internal rotation ranges from 0 - 30 degrees.
What is the function of the menisci?
Force distribution and shock absorbers.
What effect does a meniscectomy have on the stress of the knee joint?
Force is no longer distributed; but concentrated in areas of contact increasing stress in the knee joint.
Why do the menisci have only a limited capacity to heal?
They only have a blood supply to their outer third.
What are the three points of articulation in the ankle joint?
Fibulotalar, tibiotalar and distal tibiofibular.
What are the three most important ligaments that contribute to the stability of the ankle joint?
Anterior-inferior talofibular ligament, the medial ligament and the later ligament.
What is the range of movement of the ankle joint in the sagittal plane?
45 degrees (made up of 10 - 20 degrees dorsiflexion and 25 - 35 degrees of plantarflexion).
What is the most common sprain of the ankle?
The partial tear of the anterior - inferior talofibular ligament.
What bones form the hindfoot?
The talus and the calcaneus.
What bones form the midfoot?
The cuboid, the navicular and the medial, intermediate and lateral cuneiforms.
What bones form the forefoot?
The phalanges and the metatarsals.
Where does the subtalar joint articulate?
Between the talus and the calcaneous.
At what position in the oblique axis does the joint articulate?
At 42 degrees.
At what position in the medial and midline of the food does the joint articulate?
At 16 degrees.
What movement does the subtalar joint facilitate and to what degree?
Eversion (5 degrees) and inversion (20 degrees).
What are the functions of the plantar fascia?
Extends from the calcaneous to attach to the plantar aspects of the proximal phalanges. Acts as a cable between the heel and toes and as a shock absorber.
What effects does dorsiflexing the toes have on the plantar-fascia and the longitudinal arches?
Plantar-fascia is put under tension and the two ends of the foot are drawn together raising the longitudinal arches.
What term is given to the biomechanics of normal walking (locomotion)?
Reciprocal gait.
Define a stride in terms of gait cycle?
Two steps one taken by each lower limb. It starts with the initial heel contact of one limb and ends with the next initial heel contact of the same limb.
What is the term given to the period in the gait cycle when both feet are in contact with the ground?
Double support.
What happens to the duration of double support as the speed of locomotion increases?
It decreases until eventually there is no double support. This is the transition from walking to running.
What is the sequence of events that characterise the reciprocal gait cycle?
Heel contact, foot flat, mid stance, heel off, toe off and mid swing.
Which lower limb joint has the greatest range of motion during reciprocal gait?
Knee joint.
When does the peak amount of dorsiflexion occur during the gait cycle?
Heel off.
What is the range of motion at the hip joint during reciprocal gait?
15 degrees extension to 30 degrees flexion.
When does the peak amount of hip extension occur during the reciprocal gait cycle?
Shortly before toe off.
When does the peak amount of hip flexion occur during the reciprocal gait cycle?
Mid swing to ensure a long step.
What is the range of motion at the knee joint during reciprocal gait?
Few degrees of extension to 70 degrees of knee flexion.
When does the peak amount of knee flexion occur during the reciprocal gait cycle?
Swing phase to allow the limb to clear the ground.
What is the range of motion at the ankle joint during reciprocal gait?
15 degrees plantar-flexion to 10 degrees dorsiflexion.
When do the two main peaks of plantar-flexion occur during the reciprocal gait cycle?
The first occurs at foot flat and the second shortly after toe off.
When does the peak amount of ankle dorsiflexion occur during the reciprocal gait cycle?
Heel off.
What forms the characteristic double hump appearance in the ground reaction vectors recorded by force platforms.
The first peak is due to the deceleration of body mass as the weight is transferred onto the foot. The second peak is due to the foot pushing off the ground.
What are the four articulations of the shoulder ?
Glenohumeral, Acromioclavicular, Sternoclavicular and Scapulothoracic (bone-on-muscle)
Name the bone-on-muscle articulation in the shoulder joint
Scapulothoracic
Which thick cartilaginous structure provides stability in the glenohumeral joint?
Glenoid Labrum
Name the four rotator cuff muscles
Supraspinatus, Infraspinatus, Teres Minor and Subscapularis
Name the shallow depression in which the humeral head rests
Glenoid fossa
The acromioclavicular joint is an articulation between which two bones?
Scapula and Clavicle
Which ligaments help stabilise the acromioclavicular joint?
Superior and Inferior acromioclavicular ligaments along with the Coracoclavicular ligament which limits upward movement of the clavicle
Which two muscles lie on the anterior surface of the scapula and separates it from the posterior thorax?
Subscapularis and Serratus Anterior
Which muscle is responsible for preventing scapula ‘winging’?
Serratus anterior
Which of the rotator cuff muscles act to medially rotate the humerus?
Subscapularis
What is the insertion of the subscapularis muscle ?
Lesser tubercle of the humerus
Name the ligament about whose attachment the clavicle rotates during elevation and depression
Costoclavicular Ligament
What are the normal range of movement of the shoulder joint?
Forward flexion and Abduction is about 180deg
Backward extension is about 60deg
Adduction is about 75 deg
What is the most common type of shoulder dislocation?
Anterior dislocation of the glenohumeral articulation
What is the equation used to calculate the mechanical advantage of a fully extended arm?
MA = (Distance from the acromium to the point of application of the external force, DF) / (Distance from the acromium to the point of application of the resultant resistance force, DR)
MA= 50cm /5cm = 10
Therefore, the magnitude of the resistance force must be 10 times that of the applied force to avoid dislocation
Which three articulations form the elbow joint?
Humeroradial, Humeroulnar and the Proximal Radioulnar
Describe the surfaces involved in the humeroradial articulation
Capitellum of the distal (lateral) humerus and the head of the radius
Describe the surfaces involved in the humeroulnar articulation
Trochlear of the distal (medial) humerus and the reciprocally shaped trochlear fossa of the proximal ulnar
Describe the axis of rotation of the elbow joint
It passes through the middle of the trochlear and is roughly parallel to the line joining the lateral and medial epicondyles of the humerus
What is the range of movement of the elbow joint?
140deg of flexion and 0deg of extension
Which elbow articulation facilitates the rotation movement of pronation and supination?
Proximal radioulnar
What name is given to the ligamentous sling which binds the radius to the ulnar?
Annular ligament
What is the range of supination and pronation of the forearm?
70 deg pronation and 80deg supination
What structures contribute to the side-to-side stability of the olecranon process?
Two collateral ligaments - medial resisting elbow abduction and lateral slightly contributing to resisting elbow adduction
Which two structures resist elbow adduction?
Anconeus muscle (origin on lateral epicondyle of the humerus and inserts into the olecranon and superior portion of the ulnar shaft) and to a lesser extent the lateral collateral ligament of the elbow
How are the eight carpal bones arranged?
Proximal row (lateral to medial) - Scaphoid - Lunate - Triquetrum Anterior to Triquetrum - Pisiform Distal row (lateral to medial) - Trapezium - Trapezoid - Capitate - Hamate
What is the insertion point of the flexor carpi ulnaris?
Pisiform
What are the four articulations involved in the wrist joint?
Radiocarpal, midcarpal, carpo-metacarpal and the intercarpal
Which bones are involved in the radiocarpal articulation?
Lunate, Scaphoid with the distal end of the radius
What type of joint id the radiocarpal joint?
Condyloid joint
What is the significance of the triangular-shaped inter-articular disc which occupies the ulnocarpal space?
It is the point of articulation between the distal ulna and the triquetrum
What are the attachments of the triangular-shaped inter-articular disc which occupies the ulnocarpal space?
Apex attached to the styloid process of the ulna and at its base attached to the ulnar notch of the radius
What are the ranges of flexion and extension of the wrist joint?
80-90deg of flexion
70-80deg of extension
Which proportion of the full flexion range is attributed to the midcarpal joint and the radiocarpal joint?
Midcarpal joint 60%
Radiocarpal joint 40%
Which proportion of the full extension range is attributed to the midcarpal joint and the radiocarpal joint?
Midcarpal joint 33% (one third)
Radiocarpal joint 67% (two thirds)
What are the ranges of Abduction and Adduction of the wrist joint?
Abduction 15-20deg
Adduction 35deg
Total range around 50deg
What is the most functional position for an immobilised wrist joint?
Extension fixed at 15deg
List all the joints of the hand
Carpometacarpal joints, Intermetacarpal joints, Metacarpophalangeal joints, Proximal Interphalangeal joints and Distal Interphalangeal joints
What type of joint is the first carpometacarpal joint?
Saddle joint
Where does the first carpometacarpal joint articulate?
Between the Trapezium and and first metacarpal at the base of the thumb
Which joints in the hand share a joint capsule with the carpometacarpal joint?
Intermetacarpal joints
Name an example of a Condyloid joint in the hand
Metacarpophalangeal (MCP) Joints
Which joints form the Knuckles of the hand?
MCP joints
What type of joints are the proximal and distal interphalangeal joints?
Hinge
What is the range of flexion and extension of the various metacarpals?
Second and third metacarpals are basically immobile
Fourth metacarpal permits 10-15deg
Fifth metacarpal permits 20-30deg
What is the maximum amount of flexion permitted by the metacarpophalangeal joints of the fingers?
90deg
What is the maximum amount of flexion permitted by the PIP joints?
100-110deg
What is the maximum amount of flexion permitted by the DIP joints?
90deg
What is the maximum amount of flexion permitted by the metacarpophalangeal joints of the thumb?
30-90deg
What is the maximum amount of extension permitted by the metacarpophalangeal joints of the thumb?
15deg
What is the range of movement of the thumb in the flexion and extension plane?
Flexion 15deg
Extension 20deg
What is the range of abduction of the thumb?
60deg
Where does the flexor digitorum profundus originate?
Anterior aspect of the ulna
How many unfused vertabrae are there in the spine?
24
What type of joints are spinal facet joints?
Synovial
What are two roles of intervertebral discs?
Bearing and distributing loads
Restraining excessive motion
How does the nucleus pulposus differ in the lumbar segments of the spine?
It is located slightly posterior, rather than centrally
Describe the composition of the nucleus puposus
Strongly hydrophilic gel that is enmeshed in a random collagen matrix
Describe the composition of the annulus fibrosus
Tough layer of concentric collagen fibres (lamellae) with alternating orientations of the collagen fibres
What are the two articulations that occur between the rib and the vertabrae?
Head of each rib articulates with the body of the vertabrae and the tubercle of each rib articulates with the transverse process
Which ribs also articulate with the body of the vertabrae above in addition to the two regular articulations?
2-9th ribs
Which spinal region has the greatest flexion-extension range of motion?
Cervical (C4-5) approx 21deg
Which spinal region has the least flexion-extension range of motion?
Thoracic (T9-10) approx 3deg
What is the average maximum range of flexion and extension in the Lumbar spine?
Flexion Avg. 10deg
Extension Avg. 4deg
Does any lateral flexion occur in the first two cervical vertabrae?
No
Does any rotation occur between atlas and the occipital bone of the skull?
No
Between which two vertabrae is there the greatest range of rotation?
C1 and C2
Define translational movement in the context of kinematics
Movement of an object in a straight line with no rotation taking place
Define rotational movement in the context of kinematics
Movement of an object in a circular path with no translation taking place
How many degrees of freedom does a free rigid object have in the context of kinematics?
Three translational degrees of freedom and three rotational degrees of freedom. So six degrees of freedom in total.
What four parameters are used to describe linear motion?
Time, displacement, linear velocity and linear acceleration
What is the difference between average velocity and instantaneous velocity?
Average velocity is the displacement travelled divided by the time taken, whereas the instantaneous velocity is the velocity at an instant in time
On a displacement-time graph what is on the y and x axes?
Y-axis - Displacement
X-axis - Time
How is gradient calculated from a displacement-time graph?
Displacement divided by time taken
How is velocity calculated from a displacement-time graph?
Displacement divided by time taken (Gradient)
What does the gradient of a displacement-time graph show?
Velocity
What is the gradient on a velocity - time graph?
Acceleration
Define angular velocity
Angular displacement travelled per second
What does the symbol ω represent?
Angular Velocity
What does the symbol α represent?
Angular Acceleration
What does the symbol θ represent?
Angle in Radians
What does the symbol φ represent?
Angle in Degrees
What are the SI units for angular velocity?
Radians per second
What does the gradient of an Angle-Time graph represent?
Angular Velocity
What are the SI units of angular acceleration?
Radians per second squared
What is the branch of mechanics concerned with stationary bodies or bodies moving at constant velocity called?
Statics
If we only consider a force’s effect to move an object and not its ability to deform an object what type of mechanics are we referring to?
Rigid body mechanics
What does the symbol “m” represent?
Mass
What does the symbol “W” represent?
Weight
What does the symbol ρ represent?
Density
Density of a material always remains ____________
Constant
What does the symbol “g” represent?
Acceleration due to gravity
What units are equivalent to Newtons?
Kg m s^-2
What is the SI unit of friction?
Newton
What two factors effect the maximum magnitude of friction force?
- Texture
2. Magnitude of force pressing them together
What does the symbol μ represent?
Coefficient of Friction
What is the coefficient of friction?
The ratio of friction force to the force acting normally (perpendicular to press the two surfaces together
Equation for the coefficient of friction
Friction Force / Force acting normally to the surfaces
Define static friction
A force that exists only when motion is about to occur between two surfaces. It is just sufficient to oppose the applied force that is trying to move an object. Once maximum friction is exceeded, motion will begin.
What is the relationship between sliding friction and static friction?
Sliding friction < Static friction
What is the relationship between sliding friction and rolling friction?
Rolling friction < Sliding friction
How does lubrication effect the rolling friction of an object?
It does not, however it may reduce wear
What is the branch of mechanics that concerns itself with the change of motion of objects due to forces?
Kinetics/Dynamics
What is Newton’s first law of motion?
Law of inertia
Every body remains at rest or moving at constant velocity unless it is acted upon by a resultant force
What is Newton’s second law of motion?
Law of acceleration
Acceleration of a body is proportional to the applied force and inversely proportional to its mass
a=F/m
Define inertia
Reluctance to accelerate
What is the inertia of an object represented by?
Its mass
How does a dynamic equilibrium differ from a static equilibrium?
Whereas a static equilibrium the sum of all external forces in the X, Y and Z plane are equal to zero. In a dynamic equilibrium the sum of all the external forces is equal to the resultant force which can be calculated using Newton’s second law (F=ma).
Define momentum
It is an expression of the body’s persistence to continue in its present state of motion. Calculated by mass x velocity
How is momentum calculated?
Momentum (p) = mass (m) x velocity (v)
What does the symbol “p” represent?
Momentum
What is the units of momentum?
Kg m s^-1 or N s
Express a Newton in terms of its equivalent SI units
Kg m s^-2
Define torque
tendency of a force to produce a rotation about an axis
Explain how the Right Hand Grip Rule of Moments is useful
Allows the moment’s positive direction to be determined. By “gripping” the arrow shaft with the right hand and pointing with thumb in direction of arrowhead, your fingers will then point in the positive moment direction.
What are the two reasons why muscles mostly act at a force disadvantage?
Range of movement and Speed of movement
Which equation denotes the relationship between linear velocity and angular velocity?
v=rω
Where, v is linear magnitude of angular velocity directed at a tangent to the circle formed by the motion
What is the equation used to calculate angular acceleration?
α=ω/t
Angular acceleration = angular velocity/time
What is the equation used to find tangential acceleration?
Tangential acceleration = radius x angular acceleration
A body moving at a uniform angular motion has a tangential acceleration of _____.
Zero, since body is rotating at constant angular velocity and acceleration is the rate of change of velocity
What is the difference between tangential acceleration and radial acceleration of a rotating body?
Tangential - represents the linear acceleration directed at a tangent to circle formed by the motion
Radial - acts to maintain the body on its circular path, it is directed from the body to its centre of rotation
What equation is used to calculate the radial acceleration of a rotating body?
Radial acceleration = V^2/r=rω^2
Define moment of inertia
The inertia of a rotating body
The sum of the products of the mass of each particle of the body and the square of its perpendicular distance from the axis of rotation
What equation is used to calculate moment of inertia?
M=Iα
Where, I is mr^2 and α is angular acceleration
Define radius of gyration
The distance between the centre of rotation and where the mass of a body is thought to be most concentrated
What is the unit of moment of inertia?
Kg m^2
What does the symbol “I” represent?
Moment of inertia
What does the symbol “k” represent?
Radius of gyration
What are the units used for radius of gyration?
Meters
What equation links moment of inertia and radius of gyration?
I=mk^2
What does the symbol “L” represent?
Angular Momentum
What is the equation for angular momentum?
L=Iω
Where, I is moment of Inertia (I=mk^2) and ω is angular velocity
What are the SI units for angular momentum?
Kg m^2 rad s^-1
What are the four basic body segment parameters?
Length
Mass
Centre of Mass
Radius of Gyration
Define Work
When a force moves its point of application
What is the SI unit of Work?
Joules
What is the equation to calculate work?
Work = force x distance
Define Power
Rate at which work occurs
Equation of Power
Work done / Time taken
What does the symbol “p” represent?
Power
What is the SI unit of power?
Watt, W
Define Energy
Capacity to do work
What is the SI unit of Energy?
Joules, J
What is the equation used to calculate Kinetic Energy? How does this differ in rotary motion?
KE=0.5mv^2
KE=0.5Iω^2
How is the total kinetic energy of a body calculated?
Linear KE + Rotational KE
What is the SI unit of Potential Energy?
Joules
What is the equation to calculate potential energy?
PE=Wh=mgh
State the principle of energy conservation
Energy can be redistributed or changed in to another form but cannot be created nor destroyed
Define Kinematics
Study of movement without considering force, it includes translation and rotation
What are Orthogonal axes?
Independent axes - changing position on one axis does not result in change on another i.e. Cartesian System
What are the two types of collision? What are the similarities and differences between them?
Elastic - kinetic energy conserved
Inelastic - kinetic energy not conserved
Both - momentum is conserved
How does apparent surface area effect friction?
They independent from one another
What are force couples?
Forces which act parallel to the centre of mass of an object in opposing directions and have the same magnitude thus causing rotational movement only
Define Structure
An arrangement of one or more materials in a way that is designed to sustain loads
Define Material
A substance that may be used to construct a structure
What does the symbol ε represent?
Strain
What does the symbol η represent?
Coefficient of Viscosity
What does the symbol σ represent?
Stress
Define Tensile Force
A force which acts to stretch an object
Define Axial Loads
Pure tensile and compressive forces acting along the geometric axis
At what point is the relationship between Stress and Strain no longer a directly proportional one?
Proportional Limit (located within the elastic region)
What is the Elastic limit of a stress-strain curve?
The greatest stress that may be applied to a material before causing any permanent deformation. Beyond this point any further stress will cause the structure to not return to its original size and shape.
What occurs once the yield point of a stress-strain curve is surpassed?
Material will undergo increasing elongation (strain) under constant stress
What is the stress at the yield point termed?
Yield Strength
Describe the Strain Hardening region of the Stress-Strain curve
After maximum strain has occurred during yielding (when a material undergoes strain deformation under constant stress) the material’s atomic structure changes resulting in an increased resistance to further deformation
Where on the stress-strain curve does the ultimate strength (point U) occur?
Highest point of the curve. Stress here is termed ultimate strength.
What occurs after the ultimate point is surpassed in a stress-strain curve?
Stretching occurs with an actual reduction in stress, this is as a result of necking, whereby the cross-sectional area is reduced.
Define brittle
A material that can only sustain limited strain before breaking i.e. glass
Define ductile
A material that can deform plastically before breaking i.e. copper
What is Hooke’s Law?
Up to a certain level of stress (the proportional limit), the strain produced is proportional to the applied stress
What is the equation to calculate rigidity?
Young’s Modulus X Cross-sectional Area
Define Rigidity
Ability to resist axial deformation
Define Stiffness
Force required to produce a unit deflection
What is the equation to calculate stiffness (K) ?
k = Force/Change in length = (Young’s Modulus X Cross-sectional Area)/original length
Define flexibility
Deflection under a unit load (inverse of stiffness)
What is the equation to calculate flexibility ?
1/k
What is the equation for the coefficient of viscosity?
Stress/Strain rate
How can Strain rate be calculated?
Change in strain divided by change in time
What are the SI units of the coefficient of Viscosity?
Nm^-2 s or Pa s
What are the characteristic features exhibited by viscoelastic materials?
Exhibits both viscous behaviour in that it responds to the rate of loading and elastic behaviour in that it returns to its original size and shape after loading is removed
What does the symbol τ represent?
Shear stress
What does the symbol φ represent?
Shear strain
What is the equation for Shear stress?
Shearing force / Sheared area
What is the SI unit of Shear stress?
Pa
Define shear strain
Angle sheared
What is the SI unit of Shear strain?
Radians
What is the equation for shear strength?
Shear force before material fractures / Sheared area
What is the equation of Modulus of Rigidity (G) ?
Shear stress / Shear strain
What is the SI unit of the Modulus of Rigidity (G) ?
Pa or N m^-2
What is the relationship between shear stress and axial stress?
Shear stress is maximum at 45deg and is half of the axial stress
What is the equation used to calculate the maximum shear stress?
Axial stress / 2
What is the equation used to calculate strain of an object segment which is undergoing bending loading?
Strain = Displacement from neutral axis / radius of circle containing neutral axis
- This is the reason the edges of the object furthest from the neutral axis is under the greatest strain and therefore explains why the object will fail at the surfaces rather than within
Define the bending moment
The internal moment created to balance the externally applied moments hence satisfying static equilibrium
Define sagging and hogging in relation to bending loading
Sagging - positive bending movement in upward direction
Hogging - negative bending movement in downward direction
What is the equation used to calculate the maximum moment of an object under bending loading?
Mmax = (Max stress, sigma X second moment of area, I) / Ymax, max displacement from neutral axis
What are the units for the Polar second moment of area (J)
?
m^4
