Biomechanics Unit 3 Flashcards
what are the 3 segments of the lower limb
thigh
- femur
leg
- tibia
- fibula
foot
- 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
circumduction
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
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.]
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
hindfoot:
- talus and the calcaneus (os calcis)
midfoot:
- cuboid, medial, intermediate and lateral cuneiforms and the navicular.
forefoot:
- 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
Electromyography
- 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
hip
- 15° extension to 30° flexion
knee
- few degrees extension to 70° flexion
ankle
- 15° plantarflexion [extension] to 10° dorsiflexion [flexion]
when is the peak flexion/extension in the hip joint, knee joint and ankle joint during walking
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.
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]
