Semester 1: Mechanics & Biomechanics Flashcards
(403 cards)
1
Q
What is the multiplication factor for the prefix mega?
A
10^6
2
Q
What is the multiplication factor for the prefix kilo?
A
10^3
3
Q
What is the multiplication factor for the prefix centi?
A
10^-2
4
Q
What is the multiplication factor for the prefix mili?
A
10^-3
5
Q
What is the multiplication factor for the prefix micro?
A
10^-6
6
Q
Define Scalar quantity
A
Magnitude only
7
Q
Define Vector quantity
A
Magnitude and direction
8
Q
Give examples of Scalars
A
Distance Speed Angle Rotation Rate Mass Temperature Energy
9
Q
Give examples of Vectors
A
Displacement Velocity Angular Displacement Angular Velocity Force Momentum Acceleration
10
Q
Conversion of degrees celsius to kelvin?
A
Add 273
11
Q
Define speed
A
Rate of change of distance travelled
12
Q
Define velocity
A
Rate of change of displacement
13
Q
What is the equation used to calculate average velocity?
A
Average velocity (m/s) = change in displacement / time
14
Q
Define acceleration
A
Rate of change of velocity
15
Q
What is the equation used to calculate average acceleration?
A
Average acceleration (m/s^2) = change in velocity (m/s) / time taken (s)
16
Q
What is the term given when change in velocity is negative?
A
Deceleration
17
Q
What two effects do forces have on an object?
A
Change the position and deform the shape
18
Q
What is the SI unit of force?
A
Newton
19
Q
Define static in the context of mechanics
A
Forces and moments acting upon objects that are either stationary or have a constant velocity i.e. not accelerating
20
Q
Define static equilibrium in the context of mechanics
A
A static object with no resultant force (or moment) acting on it
21
Q
Define translational equilibrium in the context of mechanics
A
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
22
Q
What is Newton’s Third Law?
A
To every action there is an equal and opposite reaction
23
Q
Define mass
A
Quantity of matter of which a body is composed
24
Q
Define weight
A
Force of gravity acting upon a body
25
What is the SI unit of mass?
Kilogram
26
What is the SI unit if weight?
Newton
27
Define density
Mass per unit volume
28
What is the greek character for density?
Rho, ρ
29
What is the SI unit of density?
Kg/m^3
30
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.
31
Define gravity
Acceleration due to gravitational attraction between two bodies
32
What is the equation used to calculate weight?
Weight (N) = mass (kg) X acceleration due to gravity (9.81 m/s^2)
33
What is the force of the Earth's gravitational field?
9.81 m/s^2 (sometimes approximated to 10m/s^2)
34
Where does the centre of mass lie when an individual is standing upright?
Lower abdomen
35
Where does the centre of mass lie when an individual is bent over?
Lie out with the body in front of the pelvis
36
Define pressure
Force exerted per unit area
37
What is the equation used for calculating Pressure?
Pressure (Pascals or N/m^2) = Force (N) /Area (m^2)
38
Define a moment
Tendency of a force to produce a rotation about an axis (Centre of rotation)
39
What is another term for moment?
Torque
40
What is the SI unit for moment?
Newton meters (N m)
41
Define moment arm
The perpendicular distance from an axis (centre of rotation) to the line of action of a force
42
What is the equation used to calculate the moment of a force?
Moment, M (N m) = Force (N) X Moment arm (m)
43
Define rotational equilibrium
Sum of all external moments acting about the axes equal 0
44
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
45
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
46
If in a Lever system the effort arm is greater than the resistance arm is the system considered mechanically advantaged or disadvantaged?
Mechanical advantage
47
If in a Lever system the effort arm is smaller than the resistance arm is the system considered mechanically advantaged or disadvantaged?
Mechanical disadvantage
48
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
49
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
50
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
51
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
52
What is the equation used to calculate the mechanical advantage of a lever system?
Mechanical advantage = Effort arm / Resistance arm
53
Define a first class lever with examples
Fulcrum is located between the effort and the resistance e.g. scissors, crowbar and see-saw
54
Define a second class lever with examples
Resistance is located between the effort and the fulcrum e.g. wheelbarrow, nutcracker
55
Do first class lever systems work at a mechanical advantage or disadvantage?
Either mechanical advantage or disadvantage
56
Do second class lever systems work at a mechanical advantage or disadvantage?
Always a mechanical advantage
57
Define a third class lever with examples
Effort is located between the fulcrum and the resistance e.g. fishing rod and tweezers
58
Do third class lever systems work at a mechanical advantage or disadvantage?
Always a mechanical disadvantage
59
What is the most common lever class seen in the human body?
Third class
60
What is the unit of pressure?
Pascals or N m^-2
61
What are the four types of tissue groups?
Epithelial
Muscle
Connective
Nervous
62
What is the most abundant tissue type in the human body?
Connective tissue
63
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.
64
What are the four main types of connective tissue?
Bone, Articular Cartilage, Tendon and Ligament
65
What are the hardest tissues in the human body?
Dentine and Enamel, followed by bone
66
What are the main types of bone?
Flat bones, Long bones, Short bones, Irregular bones and Sesamoid bones
67
What cells form bone?
Osteocytes
68
What makes up the non-cellular organic component of bone?
Type I Collagen fibres (95%) in a jelly-like ground substance (5%)
69
What percentage of the dry weight of bone is non-cellular organic and inorganic?
Non-cellular organic: 25-30%
| Inorganic: 65-70%
70
What makes up the inorganic component of bone?
Calcium phosphate crystals
71
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.
72
What is the basic structural unit in compact bone?
Haversian system
73
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.
74
Where do the blood vessels and nerves run in bone?
Haversian canal
75
What are the layers surrounding the Haversian canal called?
Lamellae
76
Where are osteocytes located in bone?
Lacunae
77
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
78
What is the basic structural unit in cancellous bone?
Trabeculae
79
Define tension
When the load is acting to stretch a material
80
Define compression
When the load is acting to compress the material
81
Define stress
Force per cross-sectional area
82
What is the SI unit for Stress?
N m^-2
83
What is the equation used to calculate Stress?
Stress = Force / Area
84
Define strain
Change in length divided by the original length
85
What is the relationship between stress and strain for cortical bone?
Stress increases with increasing strain
86
What are the two regions of a stress-strain curve called?
1. Elastic region
| 2. Plastic region
87
What marks the division between the elastic and plastic regions of the stress-strain curve?
Yield point
88
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
89
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.
90
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.
91
What is the stress and strain at which bone fractures on the stress-strain curve called?
The ultimate strain and ultimate stress
92
What is Young's modulus?
A constant that can be used to calculate stress or strain.
93
What is the equation for calculating Young's modulus?
Young's Modulus = Stress / Strain
94
What is the SI units for Young's modulus?
N m^-2
95
What does a low Young's modulus tell you about the flexibility of the material?
Very flexible
96
What does a high Young's modulus tell you about the flexibility of the material?
Very stiff
97
Define a shear loading?
Two forces acting in opposite directions causing layers within a material to slip
98
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
99
Define Ultimate strength of bone
The point at which stress from a loading force causes the bone to fracture
100
What are the two types of bending loading?
Cantilever
| Three-point
101
Define Cantilever bending loading
One end of the object is fixed and the load is applied to the other end causing it to bend
102
Define Three-point bending loading
Three forces are applied to the object causing it to bend
103
What is the neutral axis of an object undergoing bending loading?
The axis along which no deformation occurs
104
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.
105
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).
106
What is Wolff's Law?
Bone is laid down where needed and resorbed where not needed.
107
How does bone change in response to stress?
Lays does collagen fibres and mineral salts to strengthen the bone.
108
How does bone respond to inactivity?
Bone atrophy occurs in which bone tissue is resorption. .
109
Define stress shielding?
When the load is carried by a plate rather than the bones itself causing unstressed bone to resorbed.
110
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.
111
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
112
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.
113
Describe the balance between bone tissue formation and resorption in children.
More bone tissue formation in children allowing for growth and development.
114
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.
115
What type of fractures are common in children due to excessive bending or torsion of the bones?
Green stick fractures.
116
How is cancellous bone tissue affected by ageing?
There is thinning of the bone due to resorption of the transverse and longitudinal trabecular.
117
What are the three types of cartilage?
Hyaline, elastic and fibrocartilage.
118
Name an example of hyaline cartilage in the human body?
The articular surfaces of synovial joints and the tip of the nose.
119
Name an example of elastic cartilage in the human body?
The external ear and the epiglottis.
120
Name an example of fibrocartilage in the human body?
Symphysis pubis and the intervertebral discs.
121
What is the role of chondrocytes?
Manufacture, secrete and maintain the organic matrix which is mainly made up of collagen.
122
What is the name and function of the of protein that collagen fibrils are enmeshed in?
Proteoglycans.
123
What are the three zones of articular cartilage?
Superficial tangential, middle and deep.
124
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.
125
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.
126
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.
127
What is the interface between the articular cartilage and the calcified cartilage beneath it called?
The Tidemark
128
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.
129
How can one describe the mechanical behaviour of articular cartilage?
Viscoelastic.
130
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.
131
What are the two main characteristics of viscoelastic materials?
Creep and stress relaxation.
132
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.
133
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.
134
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.
135
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.
136
What are the three types of lubrication?
Elastohydrodynamic lubrication; Boosted lubrication; Boundary lubrication
137
What factors determine the dominant type of lubrication?
Variations in the loading in different parts of the joint; and variation in anatomy.
138
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.
139
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.
140
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.
141
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.
142
What type of lubrication occurs when fluid film is completely depleted?
Boundary lubrication
143
In the human synovial joint what protein coats the articular surface when the fluid film is completely depleted?
Lubricin
144
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.
145
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.
146
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.
147
State two functions of the joints in the lower limb.
Two functions of the joints in the lower limb are weight bearing and movement.
148
What are the ball and socket in the hip joint?
The head of the femur and the acetabulum of the pelvic girdle respectively.
149
How many direction of rotation are there at the hip joint?
Three: flexion and extension, abduction and adduction, and internal and external rotation.
150
What is circumduction in the hip joint?
When the femur is able to move in a circle relative to the pelvis.
151
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.
152
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.
153
In which plane does the hip joint have the greatest range of motion?
The sagittal plane.
154
What is the range of motion of the hip joint in the sagittal plane?
Flexion 0 - 140 degrees. Extension 0 - 20 degrees.
155
What is the range of motion of the hip joint in the frontal plane?
Abduction 0 - 30 degrees. Adduction 0 - 25 degrees.
156
What is the range of motion of the hip joint in the transverse plane?
External rotation 0 - 90 degrees. Internal rotation 0 - 70 degrees.
157
Why is rotation limited when the hip joint is extended?
This is due to restriction of soft tissue.
158
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.
159
When taking into consideration the frontal plane, are there any active muscles when a bilateral stance is taken?
No
160
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.
161
What proportion of total body weight is the upper body (head, arms and trunk - HAT)?
70%
162
What proportion of total body weight is the lower limbs?
30% (15% per leg)
163
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.
164
What is the largest joint in he body?
The knee joint.
165
Which articulation of the knee accounts the greatest amount of movement?
Tibio-femoral articulation.
166
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.
167
What is the smooth anterior depression between the femoral condyles called?
Trochlea.
168
What is deep posterior between the femoral condyles called?
The intercondylar notch
169
What is the role of the cruciate ligaments of the knee?
Limits forward and backwards sliding of the femur on the tibia; limits hyperextension.
170
What are the roles of the medial and lateral collateral ligaments of the knee?
Prevent abduction and adduction respectively.
171
How much longer is the medial femoral condyle than the lateral femoral condyle?
1.7 cm longer.
172
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.
173
What is the range of motion of the knee in the sagittal plane?
A few degree of extension to about 140 degrees of flexion.
174
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.
175
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.
176
What is the function of the menisci?
Force distribution and shock absorbers.
177
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.
178
Why do the menisci have only a limited capacity to heal?
They only have a blood supply to their outer third.
179
What are the three points of articulation in the ankle joint?
Fibulotalar, tibiotalar and distal tibiofibular.
180
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.
181
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).
182
What is the most common sprain of the ankle?
The partial tear of the anterior - inferior talofibular ligament.
183
What bones form the hindfoot?
The talus and the calcaneus.
184
What bones form the midfoot?
The cuboid, the navicular and the medial, intermediate and lateral cuneiforms.
185
What bones form the forefoot?
The phalanges and the metatarsals.
186
Where does the subtalar joint articulate?
Between the talus and the calcaneous.
187
At what position in the oblique axis does the joint articulate?
At 42 degrees.
188
At what position in the medial and midline of the food does the joint articulate?
At 16 degrees.
189
What movement does the subtalar joint facilitate and to what degree?
Eversion (5 degrees) and inversion (20 degrees).
190
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.
191
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.
192
What term is given to the biomechanics of normal walking (locomotion)?
Reciprocal gait.
193
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.
194
What is the term given to the period in the gait cycle when both feet are in contact with the ground?
Double support.
195
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.
196
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.
197
Which lower limb joint has the greatest range of motion during reciprocal gait?
Knee joint.
198
When does the peak amount of dorsiflexion occur during the gait cycle?
Heel off.
199
What is the range of motion at the hip joint during reciprocal gait?
15 degrees extension to 30 degrees flexion.
200
When does the peak amount of hip extension occur during the reciprocal gait cycle?
Shortly before toe off.
201
When does the peak amount of hip flexion occur during the reciprocal gait cycle?
Mid swing to ensure a long step.
202
What is the range of motion at the knee joint during reciprocal gait?
Few degrees of extension to 70 degrees of knee flexion.
203
When does the peak amount of knee flexion occur during the reciprocal gait cycle?
Swing phase to allow the limb to clear the ground.
204
What is the range of motion at the ankle joint during reciprocal gait?
15 degrees plantar-flexion to 10 degrees dorsiflexion.
205
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.
206
When does the peak amount of ankle dorsiflexion occur during the reciprocal gait cycle?
Heel off.
207
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.
208
What are the four articulations of the shoulder ?
Glenohumeral, Acromioclavicular, Sternoclavicular and Scapulothoracic (bone-on-muscle)
209
Name the bone-on-muscle articulation in the shoulder joint
Scapulothoracic
210
Which thick cartilaginous structure provides stability in the glenohumeral joint?
Glenoid Labrum
211
Name the four rotator cuff muscles
Supraspinatus, Infraspinatus, Teres Minor and Subscapularis
212
Name the shallow depression in which the humeral head rests
Glenoid fossa
213
The acromioclavicular joint is an articulation between which two bones?
Scapula and Clavicle
214
Which ligaments help stabilise the acromioclavicular joint?
Superior and Inferior acromioclavicular ligaments along with the Coracoclavicular ligament which limits upward movement of the clavicle
215
Which two muscles lie on the anterior surface of the scapula and separates it from the posterior thorax?
Subscapularis and Serratus Anterior
216
Which muscle is responsible for preventing scapula 'winging'?
Serratus anterior
217
Which of the rotator cuff muscles act to medially rotate the humerus?
Subscapularis
218
What is the insertion of the subscapularis muscle ?
Lesser tubercle of the humerus
219
Name the ligament about whose attachment the clavicle rotates during elevation and depression
Costoclavicular Ligament
220
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
221
What is the most common type of shoulder dislocation?
Anterior dislocation of the glenohumeral articulation
222
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
223
Which three articulations form the elbow joint?
Humeroradial, Humeroulnar and the Proximal Radioulnar
224
Describe the surfaces involved in the humeroradial articulation
Capitellum of the distal (lateral) humerus and the head of the radius
225
Describe the surfaces involved in the humeroulnar articulation
Trochlear of the distal (medial) humerus and the reciprocally shaped trochlear fossa of the proximal ulnar
226
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
227
What is the range of movement of the elbow joint?
140deg of flexion and 0deg of extension
228
Which elbow articulation facilitates the rotation movement of pronation and supination?
Proximal radioulnar
229
What name is given to the ligamentous sling which binds the radius to the ulnar?
Annular ligament
230
What is the range of supination and pronation of the forearm?
70 deg pronation and 80deg supination
231
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
232
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
233
How are the eight carpal bones arranged?
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Proximal row (lateral to medial)
- Scaphoid
- Lunate
- Triquetrum
Anterior to Triquetrum
- Pisiform
Distal row (lateral to medial)
- Trapezium
- Trapezoid
- Capitate
- Hamate
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234
What is the insertion point of the flexor carpi ulnaris?
Pisiform
235
What are the four articulations involved in the wrist joint?
Radiocarpal, midcarpal, carpo-metacarpal and the intercarpal
236
Which bones are involved in the radiocarpal articulation?
Lunate, Scaphoid with the distal end of the radius
237
What type of joint id the radiocarpal joint?
Condyloid joint
238
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
239
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
240
What are the ranges of flexion and extension of the wrist joint?
80-90deg of flexion
| 70-80deg of extension
241
Which proportion of the full flexion range is attributed to the midcarpal joint and the radiocarpal joint?
Midcarpal joint 60%
| Radiocarpal joint 40%
242
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)
243
What are the ranges of Abduction and Adduction of the wrist joint?
Abduction 15-20deg
Adduction 35deg
Total range around 50deg
244
What is the most functional position for an immobilised wrist joint?
Extension fixed at 15deg
245
List all the joints of the hand
Carpometacarpal joints, Intermetacarpal joints, Metacarpophalangeal joints, Proximal Interphalangeal joints and Distal Interphalangeal joints
246
What type of joint is the first carpometacarpal joint?
Saddle joint
247
Where does the first carpometacarpal joint articulate?
Between the Trapezium and and first metacarpal at the base of the thumb
248
Which joints in the hand share a joint capsule with the carpometacarpal joint?
Intermetacarpal joints
249
Name an example of a Condyloid joint in the hand
Metacarpophalangeal (MCP) Joints
250
Which joints form the Knuckles of the hand?
MCP joints
251
What type of joints are the proximal and distal interphalangeal joints?
Hinge
252
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
253
What is the maximum amount of flexion permitted by the metacarpophalangeal joints of the fingers?
90deg
254
What is the maximum amount of flexion permitted by the PIP joints?
100-110deg
255
What is the maximum amount of flexion permitted by the DIP joints?
90deg
256
What is the maximum amount of flexion permitted by the metacarpophalangeal joints of the thumb?
30-90deg
257
What is the maximum amount of extension permitted by the metacarpophalangeal joints of the thumb?
15deg
258
What is the range of movement of the thumb in the flexion and extension plane?
Flexion 15deg
| Extension 20deg
259
What is the range of abduction of the thumb?
60deg
260
Where does the flexor digitorum profundus originate?
Anterior aspect of the ulna
261
How many unfused vertabrae are there in the spine?
24
262
What type of joints are spinal facet joints?
Synovial
263
What are two roles of intervertebral discs?
Bearing and distributing loads
| Restraining excessive motion
264
How does the nucleus pulposus differ in the lumbar segments of the spine?
It is located slightly posterior, rather than centrally
265
Describe the composition of the nucleus puposus
Strongly hydrophilic gel that is enmeshed in a random collagen matrix
266
Describe the composition of the annulus fibrosus
Tough layer of concentric collagen fibres (lamellae) with alternating orientations of the collagen fibres
267
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
268
Which ribs also articulate with the body of the vertabrae above in addition to the two regular articulations?
2-9th ribs
269
Which spinal region has the greatest flexion-extension range of motion?
Cervical (C4-5) approx 21deg
270
Which spinal region has the least flexion-extension range of motion?
Thoracic (T9-10) approx 3deg
271
What is the average maximum range of flexion and extension in the Lumbar spine?
Flexion Avg. 10deg
| Extension Avg. 4deg
272
Does any lateral flexion occur in the first two cervical vertabrae?
No
273
Does any rotation occur between atlas and the occipital bone of the skull?
No
274
Between which two vertabrae is there the greatest range of rotation?
C1 and C2
275
Define translational movement in the context of kinematics
Movement of an object in a straight line with no rotation taking place
276
Define rotational movement in the context of kinematics
Movement of an object in a circular path with no translation taking place
277
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.
278
What four parameters are used to describe linear motion?
Time, displacement, linear velocity and linear acceleration
279
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
280
On a displacement-time graph what is on the y and x axes?
Y-axis - Displacement
| X-axis - Time
281
How is gradient calculated from a displacement-time graph?
Displacement divided by time taken
282
How is velocity calculated from a displacement-time graph?
Displacement divided by time taken (Gradient)
283
What does the gradient of a displacement-time graph show?
Velocity
284
What is the gradient on a velocity - time graph?
Acceleration
285
Define angular velocity
Angular displacement travelled per second
286
What does the symbol ω represent?
Angular Velocity
287
What does the symbol α represent?
Angular Acceleration
288
What does the symbol θ represent?
Angle in Radians
289
What does the symbol φ represent?
Angle in Degrees
290
What are the SI units for angular velocity?
Radians per second
291
What does the gradient of an Angle-Time graph represent?
Angular Velocity
292
What are the SI units of angular acceleration?
Radians per second squared
293
What is the branch of mechanics concerned with stationary bodies or bodies moving at constant velocity called?
Statics
294
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
295
What does the symbol "m" represent?
Mass
296
What does the symbol "W" represent?
Weight
297
What does the symbol ρ represent?
Density
298
Density of a material always remains ____________
Constant
299
What does the symbol "g" represent?
Acceleration due to gravity
300
What units are equivalent to Newtons?
Kg m s^-2
301
What is the SI unit of friction?
Newton
302
What two factors effect the maximum magnitude of friction force?
1. Texture
| 2. Magnitude of force pressing them together
303
What does the symbol μ represent?
Coefficient of Friction
304
What is the coefficient of friction?
The ratio of friction force to the force acting normally (perpendicular to press the two surfaces together
305
Equation for the coefficient of friction
Friction Force / Force acting normally to the surfaces
306
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.
307
What is the relationship between sliding friction and static friction?
Sliding friction < Static friction
308
What is the relationship between sliding friction and rolling friction?
Rolling friction < Sliding friction
309
How does lubrication effect the rolling friction of an object?
It does not, however it may reduce wear
310
What is the branch of mechanics that concerns itself with the change of motion of objects due to forces?
Kinetics/Dynamics
311
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
312
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
313
Define inertia
Reluctance to accelerate
314
What is the inertia of an object represented by?
Its mass
315
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).
316
Define momentum
It is an expression of the body's persistence to continue in its present state of motion. Calculated by mass x velocity
317
How is momentum calculated?
Momentum (p) = mass (m) x velocity (v)
318
What does the symbol "p" represent?
Momentum
319
What is the units of momentum?
Kg m s^-1 or N s
320
Express a Newton in terms of its equivalent SI units
Kg m s^-2
321
Define torque
tendency of a force to produce a rotation about an axis
322
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.
323
What are the two reasons why muscles mostly act at a force disadvantage?
Range of movement and Speed of movement
324
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
325
What is the equation used to calculate angular acceleration?
α=ω/t
| Angular acceleration = angular velocity/time
326
What is the equation used to find tangential acceleration?
Tangential acceleration = radius x angular acceleration
327
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
328
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
329
What equation is used to calculate the radial acceleration of a rotating body?
Radial acceleration = V^2/r=rω^2
330
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
331
What equation is used to calculate moment of inertia?
M=Iα
| Where, I is mr^2 and α is angular acceleration
332
Define radius of gyration
The distance between the centre of rotation and where the mass of a body is thought to be most concentrated
333
What is the unit of moment of inertia?
Kg m^2
334
What does the symbol "I" represent?
Moment of inertia
335
What does the symbol "k" represent?
Radius of gyration
336
What are the units used for radius of gyration?
Meters
337
What equation links moment of inertia and radius of gyration?
I=mk^2
338
What does the symbol "L" represent?
Angular Momentum
339
What is the equation for angular momentum?
L=Iω
| Where, I is moment of Inertia (I=mk^2) and ω is angular velocity
340
What are the SI units for angular momentum?
Kg m^2 rad s^-1
341
What are the four basic body segment parameters?
Length
Mass
Centre of Mass
Radius of Gyration
342
Define Work
When a force moves its point of application
343
What is the SI unit of Work?
Joules
344
What is the equation to calculate work?
Work = force x distance
345
Define Power
Rate at which work occurs
346
Equation of Power
Work done / Time taken
347
What does the symbol "p" represent?
Power
348
What is the SI unit of power?
Watt, W
349
Define Energy
Capacity to do work
350
What is the SI unit of Energy?
Joules, J
351
What is the equation used to calculate Kinetic Energy? How does this differ in rotary motion?
KE=0.5mv^2
| KE=0.5Iω^2
352
How is the total kinetic energy of a body calculated?
Linear KE + Rotational KE
353
What is the SI unit of Potential Energy?
Joules
354
What is the equation to calculate potential energy?
PE=Wh=mgh
355
State the principle of energy conservation
Energy can be redistributed or changed in to another form but cannot be created nor destroyed
356
Define Kinematics
Study of movement without considering force, it includes translation and rotation
357
What are Orthogonal axes?
Independent axes - changing position on one axis does not result in change on another i.e. Cartesian System
358
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
359
How does apparent surface area effect friction?
They independent from one another
360
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
361
Define Structure
An arrangement of one or more materials in a way that is designed to sustain loads
362
Define Material
A substance that may be used to construct a structure
363
What does the symbol ε represent?
Strain
364
What does the symbol η represent?
Coefficient of Viscosity
365
What does the symbol σ represent?
Stress
366
Define Tensile Force
A force which acts to stretch an object
367
Define Axial Loads
Pure tensile and compressive forces acting along the geometric axis
368
At what point is the relationship between Stress and Strain no longer a directly proportional one?
Proportional Limit (located within the elastic region)
369
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.
370
What occurs once the yield point of a stress-strain curve is surpassed?
Material will undergo increasing elongation (strain) under constant stress
371
What is the stress at the yield point termed?
Yield Strength
372
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
373
Where on the stress-strain curve does the ultimate strength (point U) occur?
Highest point of the curve. Stress here is termed ultimate strength.
374
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.
375
Define brittle
A material that can only sustain limited strain before breaking i.e. glass
376
Define ductile
A material that can deform plastically before breaking i.e. copper
377
What is Hooke's Law?
Up to a certain level of stress (the proportional limit), the strain produced is proportional to the applied stress
378
What is the equation to calculate rigidity?
Young's Modulus X Cross-sectional Area
379
Define Rigidity
Ability to resist axial deformation
380
Define Stiffness
Force required to produce a unit deflection
381
What is the equation to calculate stiffness (K) ?
k = Force/Change in length = (Young's Modulus X Cross-sectional Area)/original length
382
Define flexibility
Deflection under a unit load (inverse of stiffness)
383
What is the equation to calculate flexibility ?
1/k
384
What is the equation for the coefficient of viscosity?
Stress/Strain rate
385
How can Strain rate be calculated?
Change in strain divided by change in time
386
What are the SI units of the coefficient of Viscosity?
Nm^-2 s or Pa s
387
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
388
What does the symbol τ represent?
Shear stress
389
What does the symbol φ represent?
Shear strain
390
What is the equation for Shear stress?
Shearing force / Sheared area
391
What is the SI unit of Shear stress?
Pa
392
Define shear strain
Angle sheared
393
What is the SI unit of Shear strain?
Radians
394
What is the equation for shear strength?
Shear force before material fractures / Sheared area
395
What is the equation of Modulus of Rigidity (G) ?
Shear stress / Shear strain
396
What is the SI unit of the Modulus of Rigidity (G) ?
Pa or N m^-2
397
What is the relationship between shear stress and axial stress?
Shear stress is maximum at 45deg and is half of the axial stress
398
What is the equation used to calculate the maximum shear stress?
Axial stress / 2
399
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
400
Define the bending moment
The internal moment created to balance the externally applied moments hence satisfying static equilibrium
401
Define sagging and hogging in relation to bending loading
Sagging - positive bending movement in upward direction
| Hogging - negative bending movement in downward direction
402
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
403
What are the units for the Polar second moment of area (J)
| ?
m^4
