Biomechanics Unit 3

Question 1

what are the 3 segments of the lower limb

Answer 1

thigh
- femur

leg

• tibia
• fibula

foot

• tarsals
• metatarsals
• phalanges

Question 2

the hip is a ball and socket joint - what does the joint consist of

Answer 2

the ball consists of the head of the femur which fits into the socket-shaped acetabulum of the pelvic girdle

Question 3

what are the directions of movement possible at the hip joint

Answer 3

flexion - extension
abduction - adduction
internal rotation - external rotation
circumduction

Question 4

what helps make the hip joint intrinsically stable

Answer 4

surrounded by a very strong articular joint capsule
several ligaments
several large, strong muscles

Question 5

what is the range of movement in the hip joint

Answer 5

flexion = 0-140 degrees
extension = 0-20 degrees
[sagittal plane]

abduction = 0-30 degrees
adduction = 0-25 degrees
[frontal plane]

external rotation = 0-90
internal rotation = 0-70
[transverse plane]

Question 6

when is there less external and internal rotation possible in the hip join

Answer 6

when the hip is extended due to restrictions of soft tissue

Question 7

in walking, what is the greatest plane of movement

Answer 7

sagittal plane

with about 30 degrees flexion and 15 degrees extension

Question 8

what range of movement is required from the hip to stand up and sit down

Answer 8

110° of flexion-extension, 20° of abduction-adduction and 15° of rotation

Question 9

when standing up on TWO legs what is important to remember

Answer 9

normally no muscles active at the hip joint.

to calculate the hip joint force we only need to consider the external forces present.

Question 10

what are the external forces present acting of the pelvis

Answer 10

the weight of the upper body acting downwards

2 reaction forces, 1 at each hip joint, acting upwards

Question 11

what is the percentage break down of weight of each body part

Answer 11

70% of weight = head, arms and trunk

15% = each leg

[30% = both legs]

Question 12

when standing up on TWO legs what is the expected forces acting at the 2 hip joints

Answer 12

forces acting on hip joints are vertical and equal to half the upper body weight.

e.g. upper body weight = 560N, then would expect 280N acting on each hip joint

Question 13

during unilateral stance, what is acting to stabilise the position of the body

Answer 13

the abductor muscle group

Question 14

during unilateral stance, what are the forces acting on the 1 hip joint

Answer 14

acting downwards:
- the weight of the lower limb

acting vertically upwards on the foot:

• the abductor muscle force
• the joint force at the hip
• the ground reaction force

Question 15

for calculating forces on a hip joint during unilateral stance

Answer 15

example Q in the notes page 118

Question 16

the forces acting on a hip during unilateral stance is approx 4.5 times the weight go the upper body - why is this

[bilateral stance was approx 0.5 times]

Answer 16

Most of the increase is due to the contraction of the hip abductor muscles which is required to stabilise the hip

effectively pulls the two sides of the hip joint together and this greatly increases the force at the hip joint.

Question 17

what are the 2 articulations of the knee joint

Answer 17

tibiofemoral (between the proximal surface of the tibia and the distal surface of the femur)
[accounts for most movement of the knee]

patellofemoral (between the patella and the distal surface of femur)
[assists movement]

Question 18

what is the proximal surface of the tibia covered in and whats its function

Answer 18

covered with menisci
- 2 crescent pieces of fibrocartilage

act as load distributors and shock absorbers

Question 19

what are the femoral condyles covered by

Answer 19

articular cartilage

Question 20

where are the cruciate ligaments located

Answer 20

in the intercondylar notch

Question 21

what is the patella

Answer 21

largest sesamoid bone (a bone found in a tendon)

located in tendon of the quadriceps femoris muscle

Question 22

where is the stability of the knee joint mainly derived from

Answer 22

the ligaments

ACL and PCL

• limit forward and backward sliding of the femur on the tibia
• limit hyperextension

Medial collateral ligament
- prevents abduction

Lateral collateral ligament
- prevents adduction

[The quadriceps muscle also aids stability as do the menisci, especially during rotation.]

Question 23

the knee is generally considered to behave like a hinge joint - by why is there some debate about this

Answer 23

A hinge always rotates about the same axis

This is not true for the knee joint - its axis of rotation changes as it flexes and extends

Question 24

consider the knee joint in the sagittal plane

- what is its centre of rotation?

Answer 24

centre of rotation moves in a semi-circle pattern

pattern arises because the femoral condyles are not perfectly circular and due to restrictions imposed by the knee ligaments

Question 25

what do deformities of the knee joint surfaces cause

Answer 25

the centre of rotation to follow more complex patterns.

Question 26

consider the knee joint in 3 dimensions | - what is the mechanism of movement of the joint?

Answer 26

screw-home mechanism - follows a spiral motion - as knee flexes the tibia rotates internally - as knee extends the tibia rotates externally

Question 27

what is the spiral motion of the knee joint caused by

Answer 27

the different sizes of the lateral and medial femoral condyles [medial condyle is about 1.7cm longer than the lateral condyles]

Question 28

what is the range of motion at the knee joint

Answer 28

flexion = 0-140 degrees extension = 5 degrees [sagittal plane] external rotation = 0-45 internal rotation = 0-30 [transverse plane]

Question 29

what is the motion needed at the knee joint to preform activities of daily living

Answer 29

motion in the sagittal plane from full extension to about 115 degrees of flexion about 10 degrees of rotation in the transverse plan

Question 30

how is the range of motion in the transverse plane in the knee dependant on amount of flexion and extension at the knee

Answer 30

The range of motion in the transverse plane is almost zero at full extension, increases with flexion to a maximum at around 90° of flexion and reduces with further flexion

Question 31

what is the function of the patella

Answer 31

to increase the lever arm of the quadriceps femoris muscle | - this assists knee extension

Question 32

what is the relationship between the quadriceps tendon, the patella and knee flexion

Answer 32

lever arm of the quadriceps femoris muscle is dependent on the position of the patella the position of the patella is dependant on the degree of knee flexion-extension

Question 33

what is the relationship between the quadriceps tendon, the patella and knee flexion - at full extension - as the knee flexes - at full flexion

Answer 33

At full extension - quadriceps tendon is displaced anteriorly, lengthening the effort lever arm considerably As the knee flexes - patella sinks into the intercondylar notch - contribution to length of lever arm decreases At full flexion - patella is located in the intercondylar notch where it contributes little to the effort arm

Question 34

what happens if the patella is removed [patellectomy]

Answer 34

lever arm is reduced To compensate for this the force produced by the quadriceps muscle must increase

Question 35

what is the function of the menisci

Answer 35

act as force distributors and shock absorbers between the femur and the tibia. distribute the force over nearly the entire surface of the tibial plateau

Question 36

what happens to the pressure in a tibia with menisci and a tibia without

Answer 36

With menisci - force is distributed over a large area - stress in the articular cartilage and underlying bone tissue is small Without menisci - force is no longer distributed - concentrated in the area of contact between the tibia and femur - increases stress in joint and likelihood of wear and tear - 3 times increase in stress when menisci are removed

Question 37

why are menisci removed when damaged

Answer 37

have no capacity to heal and there is only a blood supply on the outer edges [surgery called a meniscectomy]

Question 38

what are the 3 articulations of the ankle joint | [hinge joint]

Answer 38

tibiotalar (between the tibia and the talus) the fibulotalar (between the fibula and the talus) distal tibiofibular (between the distal ends of the tibia and fibula).

Question 39

what makes the medial and the lateral malleoulus

Answer 39

lateral - distal end of the fibula medial - distal end of the tibia

Question 40

the ankle joint is intrinsically stable due to the arrangement of the bones - why does it need additional stability? - what provides it?

Answer 40

because of the high loads that the ankle must withstand, additional stability is necessary provided by ligaments: 1 - anterior inferior talofibular ligament 2 - the medial ligament 3 - the lateral ligament

Question 41

what is the range of motion of the ankle joint

Answer 41

Dorsiflexion = 10-20 degrees [flexion of the ankle joint - toes move upwards] Plantarflexion = 25-35 degrees [extension of the ankle joint - plant toes on the ground] range of motion in an individual is around 45 degrees greatest range is in the sagittal plane

Question 42

where is the axis of rotation located in the ankle joint

Answer 42

corresponds approximately to the line joining the lateral and medial malleolus

Question 43

what is the most common injury to the ankle

Answer 43

sprained ankle - partial tear of the anterior inferior talofibular ligament resulting from a sudden adduction of the foot whilst the ankle is plantarflexed.

Question 44

what are the 3 parts of the foot

Answer 44

hindfoot: - talus and the calcaneus (os calcis) midfoot: - cuboid, medial, intermediate and lateral cuneiforms and the navicular. forefoot: - metatarsals and phalanges.

Question 45

what is the subtalar joint, what does it allow for and what is the range of motion whilst walking

Answer 45

articulation between the talus and the calcaneus allows the inversion [20 degrees] and eversion [5 degrees] of the foot 6 degrees range when walking

Question 46

what are the names of the arches in the foot

Answer 46

5 longitudinal arches [extend from the calcaneus along the five sets of tarsals and metatarsals] 1 transverse arch [runs across the foot]

Question 47

what supports the longitudinal arches

Answer 47

the plantar fascia - extends from the calcaneus to attach to plantar aspect of the proximal phalanges - acts as a shock absorber

Question 48

how does the plantar fascia support the arches during standing

Answer 48

prevents the vertical force acting downwards at the ankle joint from collapsing the longitudinal arches

Question 49

how does the plantar fascia support the arches when the toes are dorsiflexed

Answer 49

plantar fascia is put under tension 2 ends of the foot are drawn together raising the longitudinal arches bones of the foot are thus held together tightly and function as a single unit rather than as separate bones.

Question 50

reciprocal gait is the 'normal gait' | - what are examples of other gaits

Answer 50

swing-through gait - seen in someone who has a femur # - in this gait crutches are used for support and both legs swing through the crutches landing ahead of the crutches, the crutches are then advanced forward and the process is begun again

Question 51

what does a gait lab analysis and when is this info useful

Answer 51

used to analysis the walking cycle of a person. useful to help determine surgical intervention, to quantify severity of a disorder and determine whether an operation or treatment was successful.

Question 52

what is the equipment found in the gait lab

Answer 52

Motion analysis system - use markers to calculate where body parts are in space and allow movement to be reconstructed by a computer Force plates - measure ground reaction force exerted on the foot Electromyography - measures muscle activity

Question 53

what is the gait cycle equivalent too

Answer 53

one stride - which is equal to two steps; one taken by each lower limb

Question 54

what does the gait cycle start and end with

Answer 54

starts with - initial contact of one foot on the ground, termed HEEL CONTACT ends with - next HEEL CONTRACT with the SAME FOOT

Question 55

what are the 2 phases of the gait cycle

Answer 55

stance phase - foot is in contact with the ground - 1st part swing phase - foot not in contact with the ground - 2nd part

Question 56

what is double support in the gait cycle and what happens to it as people walk quicker

Answer 56

period when both feet are in touch with the ground as the speed increases the duration of double support decreases until eventually there is no period of double support. - transition from walking to running

Question 57

what are the events in reciprocal gait

Answer 57

``` heel contact foot flat mid stance heel off toe off mid swing ```

Question 58

what is the duration of the stance phase and swing phase

Answer 58

heel contact to toe off = stance phase toe off to next heel contact = swing phase

Question 59

what would be wrong in a gait in someone with foot drop

Answer 59

the foot hangs down during the swing phase so the toes will make contact with the ground before the heel

Question 60

what plane does the majority of motion in the reciprocal gait occur

Answer 60

the sagittal plane

Question 61

what is the range of motion at the hip joint, knee joint and ankle joint during walking

Answer 61

hip - 15° extension to 30° flexion knee - few degrees extension to 70° flexion ankle - 15° plantarflexion [extension] to 10° dorsiflexion [flexion]

Question 62

when is the peak flexion/extension in the hip joint, knee joint and ankle joint during walking

Answer 62

hip - peak extension occurs shortly before toe off as the leg is left trailing behind - peak flexion is shortly after mid- swing to ensure a long step. knee - peak flexion is during the swing phase as the knee is flexed to allow the foot to clear the ground as it swings past the other limb ankle - 2 main peaks of plantarflexion; the first at foot flat and the second shortly after toe off - peak amount of dorsiflexion occurs at around heel off as the foot is left trailing behind the rest of the body.

Question 63

what is the name given to the diagram of the change in magnitude and direction of ground reaction force measured by the force plates

Answer 63

the butterfly diagram

Question 64

what causes the 2 characteristic humps of ground reaction force in reciprocal gait

Answer 64

1st hump - due to the deceleration of body mass as the weight is transferred on to the foot 2nd hump - due to the foot pushing off the ground

Question 65

what happens at the hip after heel contract in regards to joint forces and moments

Answer 65

there is a positive extension moment produced by the hip extensors to prevent the upper body falling forward

Question 66

what happens at the knee after heel contract in regards to joint forces and moments

Answer 66

small flexion moment as the hamstrings contract to prevent hyperextension of the knee [changes to an extension moment as the quadriceps contract to prevent the knee from buckling]