Biomechanics Unit 3 Flashcards Preview

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Flashcards in Biomechanics Unit 3 Deck (66):

what are the 3 segments of the lower limb

- femur

- tibia
- fibula

- tarsals
- metatarsals
- phalanges


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

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


what are the directions of movement possible at the hip joint

flexion - extension
abduction - adduction
internal rotation - external rotation


what helps make the hip joint intrinsically stable

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


what is the range of movement in the hip joint

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]


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

when the hip is extended due to restrictions of soft tissue


in walking, what is the greatest plane of movement

sagittal plane

with about 30 degrees flexion and 15 degrees extension


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

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


when standing up on TWO legs what is important to remember

normally no muscles active at the hip joint.

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


what are the external forces present acting of the pelvis

the weight of the upper body acting downwards

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


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

70% of weight = head, arms and trunk

15% = each leg

[30% = both legs]


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

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


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

the abductor muscle group


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

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


for calculating forces on a hip joint during unilateral stance

example Q in the notes page 118


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]

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.


what are the 2 articulations of the knee joint

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]


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

covered with menisci
- 2 crescent pieces of fibrocartilage

act as load distributors and shock absorbers


what are the femoral condyles covered by

articular cartilage


where are the cruciate ligaments located

in the intercondylar notch


what is the patella

largest sesamoid bone (a bone found in a tendon)

located in tendon of the quadriceps femoris muscle


where is the stability of the knee joint mainly derived from

the ligaments

- 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.]


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

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


consider the knee joint in the sagittal plane
- what is its centre of rotation?

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


what do deformities of the knee joint surfaces cause

the centre of rotation to follow more complex patterns.


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

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


what is the spiral motion of the knee joint caused by

the different sizes of the lateral and medial femoral condyles

[medial condyle is about 1.7cm longer than the lateral condyles]


what is the range of motion at the knee joint

flexion = 0-140 degrees
extension = 5 degrees
[sagittal plane]

external rotation = 0-45
internal rotation = 0-30
[transverse plane]


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

motion in the sagittal plane from full extension to about 115 degrees of flexion

about 10 degrees of rotation in the transverse plan


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

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


what is the function of the patella

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


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

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


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

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


what happens if the patella is removed [patellectomy]

lever arm is reduced

To compensate for this the force produced by the quadriceps muscle must increase


what is the function of the menisci

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


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

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


why are menisci removed when damaged

have no capacity to heal and there is only a blood supply on the outer edges

[surgery called a meniscectomy]


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

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).


what makes the medial and the lateral malleoulus

lateral - distal end of the fibula

medial - distal end of the tibia


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

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


what is the range of motion of the ankle joint

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


where is the axis of rotation located in the ankle joint

corresponds approximately to the line joining the lateral and medial malleolus


what is the most common injury to the ankle

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


what are the 3 parts of the foot

- talus and the calcaneus (os calcis)

- cuboid, medial, intermediate and lateral cuneiforms and the navicular.

- metatarsals and phalanges.


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

articulation between the talus and the calcaneus

allows the inversion [20 degrees] and eversion [5 degrees] of the foot

6 degrees range when walking


what are the names of the arches in the foot

5 longitudinal arches [extend from the calcaneus along the five sets of tarsals and metatarsals]

1 transverse arch [runs across the foot]


what supports the longitudinal arches

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


how does the plantar fascia support the arches during standing

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


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

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.


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

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


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

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.


what is the equipment found in the gait lab

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

- measures muscle activity


what is the gait cycle equivalent too

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


what does the gait cycle start and end with

starts with - initial contact of one foot on the ground, termed HEEL CONTACT

ends with - next HEEL CONTRACT with the SAME FOOT


what are the 2 phases of the gait cycle

stance phase
- foot is in contact with the ground
- 1st part

swing phase
- foot not in contact with the ground
- 2nd part


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

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


what are the events in reciprocal gait

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


what is the duration of the stance phase and swing phase

heel contact to toe off
= stance phase

toe off to next heel contact
= swing phase


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

the foot hangs down during the swing phase

so the toes will make contact with the ground before the heel


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

the sagittal plane


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

- 15° extension to 30° flexion

- few degrees extension to 70° flexion

- 15° plantarflexion [extension] to 10° dorsiflexion [flexion]


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

- 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.

- 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

- 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.


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

the butterfly diagram


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

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


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

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


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

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]