Biomechnics unit 3 Biomech of the lower limb - deck 3 Flashcards
What is the most important function of the patella ?
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)
The lever arm of the quadriceps femoris muscle (the effort lever) is dependent on what?
The position of the patella
What is the position of the patella dependent on ?
The amount of knee flexion-extension.
At full extension of the knee what happens to the quadriceps tendon and therefore the lever arm of the quadriceps femoris muscle?
The quadriceps tendon is displaced anteriorly, lengthening the effort lever arm considerably
Describe what happens to the position of the patella as the knee flexes and then describe what happens to the
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)
What happens to the lever arm of the quadriceps femoris muscle if the patella is removed (patellectomy) and state the subsequent compensation required
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.
What is the function of menisci of the knee?
- 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
Over what are do the menisci distribute the force ?
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)
If the menisci are removed what happens to the force distribution in the knee joint ?
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.
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.
What type of joint is the ankle joint ?
A hinged synovial joint
What 3 bones form the ankle joint ?
It is formed by formed the distal ends of the tibia and fibula and the talus
Name the 3 articulations which make up the ankle joint
- Tibiotalar (between the tibia and the talus)
- The fibulotalar (between the fibula and the talus)
- The distal tibiofibular (between the distal ends of the tibia and fibula).
What are the two distinctive bony prominences on the lateral and medial sides of the ankle joint called?
The lateral and medial malleolus respectively
What bones are the medial and lateral malleolus part of ?
- The lateral malleolus is the distal end of the fibula
- The medial malleolus is the distal end of the tibia.
Is the ankle joint intrinsically stable?
Yes just like the hip
The ankle joint is intrinsically stable - explain why it requires additional stability and state what provides this additional stability
- 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
What are the 3 most important ankle ligaments to know about which provide additional stability to the ankle joint ?
- The anterior inferior talofibular ligament
- The medial ligament - (also called the deltoid ligament)
- The lateral ligament
Think - LAM
In what plane does motion of the ankle joint primarily occur in ?
The sagittal plane
Note doesn’t mention motion in other planes so assume only motion in
What is the axis of rotation of the ankle joint formed by?
The axis of rotation corresponds approximately to the line joining the lateral malleolus and the medial malleolus
About the axis of rotation of the ankle joint what 2 movements occur ?
- Dorsiflexion (toes move upwards - flexion of ankle joint)
- Plantarflexion (toes move downwards extension of ankle joint - planting themselves into the ground).
What is the range of motion in degrees of flexion and extension of the ankle joint ?
- 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
What is the range of motion of the ankle joint required for walking ?
10 degrees of dorsiflexion to 15 degrees plantarflexion.
What is the foot comprised of ?
It is a very complex structure consisting of:
- 26 bones
- 57 synovial joints
- Numerous ligaments and tendons
Why is the foot such a complex structure ?
Because of its diverse functional requirements it needs to be able to fulfil
What are the functional requirements of the foot?
- It needs to adapt to a variety of ground surfaces and still maintain a stable and secure contact
- It is required to distribute and absorb loads to avoid injury
- It must transmit loads between the ground and the rest of the body.
What 3 parts can the foot be split up into ?
- Hindfoot
- Midfoot
- Forefoot
What bones does the hindfoot consist of ?
The talus and the calcaneus (os calcis)
What bones does the midfoot consist of ?
The cuboid, medial, intermediate and lateral cuneiforms and the navicular bone
What bones does the forefoot consist of?
The metatarsals and phalanges
Define what the subtalar joint is
This is the articulation between the talus and the calcaneus bones
Describe the position of the axis of rotation of the subtalat joint
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
What movements does the subtalar joint allow?
Inversion and eversion of the foot
(important to note that inversion and eversion are movements of the foot and not the ankle joint)
Describe what inversion and eversion of the foot is
- 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)
What is the range of motion in degrees of the subtalar joint ?
It can be inverted by 20 degrees and everted by 5 degrees.
During walking what is the range of motion in degrees required from the subtalar joint ?
6 degrees
What is the two-way arched structure of the foot formed by?
It is formed from the bones of the foot and kept in place by strong ligaments
Describe the two-way arched structure of the foot
- 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.
What is the longitudinal arch of the foot supported by ?
The plantar fascia
What are the attachments of the plantar fascia ?
It extends from the calcaneus to attach to the plantar aspect of the proximal phalanges
What is the plantar fascia ?
A heavy ligamentous structure
What causes the plantar fascia to elongate ?
When it is loaded
What is the function of the plantar fascia ?
It acts as a cable between the heel and toes and as a shock absorber.
During standing the bones of the longitudinal arch and the plantar fascia function like what?
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.
Describe what happens to the plantar fascia when the toes are dorsiflexed?
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.
