Biomechnics unit 3 Biomech of the lower limb - deck 3

Question 1

What is the most important function of the patella ?

Answer 1

To assist knee extension by increasing the lever arm of the quadriceps femoris muscle it does this by displacing the quadriceps tendon

Pic shows a close-up of the knee joint whilst standing with the knee flexed. The quadriceps femoris provides the effort force required to maintain the knee joint’s position, overcoming the resistive force, the ground reaction force, produced by the weight of the body acting behind the knee. (I think the lever arm is the small 2 sided arrow)

Question 2

The lever arm of the quadriceps femoris muscle (the effort lever) is dependent on what?

Answer 2

The position of the patella

Question 3

What is the position of the patella dependent on ?

Answer 3

The amount of knee flexion-extension.

Question 4

At full extension of the knee what happens to the quadriceps tendon and therefore the lever arm of the quadriceps femoris muscle?

Answer 4

The quadriceps tendon is displaced anteriorly, lengthening the effort lever arm considerably

Question 5

Describe what happens to the position of the patella as the knee flexes and then describe what happens to the

Answer 5

As the knee flexes the contribution of the patella to the length of the lever arm decreases as the patella sinks into the intercondylar notch. At full flexion, the patella is located in the intercondylar notch where it contributes little to the effort arm (lever arm of the quadriceps femoris muscle)

Question 6

What happens to the lever arm of the quadriceps femoris muscle if the patella is removed (patellectomy) and state the subsequent compensation required

Answer 6

If the patella is removed (patellectomy), the lever arm is reduced (pic). To compensate for this the force produced by the quadriceps muscle must increase considerably (by up to 30% at full extension) in order to provide the required turning moment.

Question 7

What is the function of menisci of the knee?

Answer 7

• They act as force distributors and shock absorbers between the femur and the tibia
• The menisci also make the flat top of the tibia slightly concave which aids stability. - secondary function

Question 8

Over what are do the menisci distribute the force ?

Answer 8

Over nearly the entire surface of the tibial plateau (Figure 25A). Since the force is distributed over a large area the stress in the articular cartilage and underlying bone tissue is small (remember stress is equal to the force divided by area)

Question 9

If the menisci are removed what happens to the force distribution in the knee joint ?

Answer 9

The force becomes concentrated in the area of contact between the tibia and femur (Fig B). This increases the stress in the joint tissues and will increase the likelihood of wear and joint damage. In fact there is approximately a three fold increase in stress when the menisci are removed.

Question 10

Appreciate this:

If the menisci are damaged they have no capacity to heal because there is only a blood supply to their outer edges. Tears in the menisci can obstruct the motion of the knee and cause it to jam. Injured knees with part or all of the menisci removed (a meniscectomy) may still function adequately but the articulating surfaces are more likely to be damaged and there is a significantly increased likelihood of the development of degenerative osteoarthritis. For this reason, if possible, the menisci are preserved after injury.

Question 11

What type of joint is the ankle joint ?

Answer 11

A hinged synovial joint

Question 12

What 3 bones form the ankle joint ?

Answer 12

It is formed by formed the distal ends of the tibia and fibula and the talus

Question 13

Name the 3 articulations which make up the ankle joint

Answer 13

1. Tibiotalar (between the tibia and the talus)
2. The fibulotalar (between the fibula and the talus)
3. The distal tibiofibular (between the distal ends of the tibia and fibula).

Question 14

What are the two distinctive bony prominences on the lateral and medial sides of the ankle joint called?

Answer 14

The lateral and medial malleolus respectively

Question 15

What bones are the medial and lateral malleolus part of ?

Answer 15

• The lateral malleolus is the distal end of the fibula
• The medial malleolus is the distal end of the tibia.

Question 16

Is the ankle joint intrinsically stable?

Answer 16

Yes just like the hip

Question 17

The ankle joint is intrinsically stable - explain why it requires additional stability and state what provides this additional stability

Answer 17

• It requires additional stability because of the high loads that the ankle must withstand
• This is provided by the ligaments that surround the joint and to a smaller extent by the surrounding muscles

Question 18

What are the 3 most important ankle ligaments to know about which provide additional stability to the ankle joint ?

Answer 18

1. The anterior inferior talofibular ligament
2. The medial ligament - (also called the deltoid ligament)
3. The lateral ligament

Think - LAM

Question 19

In what plane does motion of the ankle joint primarily occur in ?

Answer 19

The sagittal plane

Note doesn’t mention motion in other planes so assume only motion in

Question 20

What is the axis of rotation of the ankle joint formed by?

Answer 20

The axis of rotation corresponds approximately to the line joining the lateral malleolus and the medial malleolus

Question 21

About the axis of rotation of the ankle joint what 2 movements occur ?

Answer 21

1. Dorsiflexion (toes move upwards - flexion of ankle joint)
2. Plantarflexion (toes move downwards extension of ankle joint - planting themselves into the ground).

Question 22

What is the range of motion in degrees of flexion and extension of the ankle joint ?

Answer 22

• The full range of motion is approx 45 degrees
• This is made up of 10 - 20 degrees of dorsiflexion and 25 - 35 degrees of plantarflexion

Question 23

What is the range of motion of the ankle joint required for walking ?

Answer 23

10 degrees of dorsiflexion to 15 degrees plantarflexion.

Question 24

What is the foot comprised of ?

Answer 24

It is a very complex structure consisting of:

• 26 bones
• 57 synovial joints
• Numerous ligaments and tendons

Question 25

Why is the foot such a complex structure ?

Answer 25

Because of its diverse functional requirements it needs to be able to fulfil

Question 26

What are the functional requirements of the foot?

Answer 26

1. It needs to adapt to a variety of ground surfaces and still maintain a stable and secure contact
2. It is required to distribute and absorb loads to avoid injury
3. It must transmit loads between the ground and the rest of the body.

Question 27

What 3 parts can the foot be split up into ?

Answer 27

1. Hindfoot
2. Midfoot
3. Forefoot

Question 28

What bones does the hindfoot consist of ?

Answer 28

The talus and the calcaneus (os calcis)

Question 29

What bones does the midfoot consist of ?

Answer 29

The cuboid, medial, intermediate and lateral cuneiforms and the navicular bone

Question 30

What bones does the forefoot consist of?

Answer 30

The metatarsals and phalanges

Question 31

Define what the subtalar joint is

Answer 31

This is the articulation between the talus and the calcaneus bones

Question 32

Describe the position of the axis of rotation of the subtalat joint

Answer 32

It has an oblique axis positioned at about 42 degrees to the plantar surface and 16 degrees medial to the mid-line of the foot

Question 33

What movements does the subtalar joint allow?

Answer 33

Inversion and eversion of the foot

(important to note that inversion and eversion are movements of the foot and not the ankle joint)

Question 34

Describe what inversion and eversion of the foot is

Answer 34

• Inversion is the inward rotation of the foot so that the plantar surface (the underneath surface) faces medially (inwards).
• Eversion is the outward rotation of the foot so that the plantar surface faces laterally (externally)

Question 35

What is the range of motion in degrees of the subtalar joint ?

Answer 35

It can be inverted by 20 degrees and everted by 5 degrees.

Question 36

During walking what is the range of motion in degrees required from the subtalar joint ?

Answer 36

6 degrees

Question 37

What is the two-way arched structure of the foot formed by?

Answer 37

It is formed from the bones of the foot and kept in place by strong ligaments

Question 38

Describe the two-way arched structure of the foot

Answer 38

• There are five longitudinal arches that extend from the calcaneus along the five sets of tarsals and metatarsals.
• The transverse arch runs across the foot.

Question 39

What is the longitudinal arch of the foot supported by ?

Answer 39

The plantar fascia

Question 40

What are the attachments of the plantar fascia ?

Answer 40

It extends from the calcaneus to attach to the plantar aspect of the proximal phalanges

Question 41

What is the plantar fascia ?

Answer 41

A heavy ligamentous structure

Question 42

What causes the plantar fascia to elongate ?

Answer 42

When it is loaded

Question 43

What is the function of the plantar fascia ?

Answer 43

It acts as a cable between the heel and toes and as a shock absorber.

Question 44

During standing the bones of the longitudinal arch and the plantar fascia function like what?

Answer 44

A truss (a framework to support the body) (Fig) The plantar fascia prevents the vertical force acting downwards at the ankle joint from collapsing the longitudinal arches.

Question 45

Describe what happens to the plantar fascia when the toes are dorsiflexed?

Answer 45

The plantar fascia is put under tension and the two ends of the foot are drawn together raising the longitudinal arches (Fig).

The bones of the foot are thus held together tightly and function as a single unit rather than as separate bones.