Describe the Ankle
- In the upright posture, the ankle is the region that bears all body weight as it is transferred to the foot.
- Centre of gravity of the body passes just in front.
- Instability of this region will lead to a fall (with a tendency to fall forwards)
- Layer of bones and muscles shifts from vertical to horizontal axes
- Injuries occur regularly either as sprains or fractures
- Arteries, motor nerves and tendons enter the foot turning forwards
- Veins, sensory nerves and lymphatics exit the foot turning upwards.
As the long tendons of muscles change direction from verticle to horizontal, what is there a risk of?
- There is a risk of bow-stringing during movement
- Various retinacula (crural fascia) strap these down to prevent bowstringing of tendons.
Why is the foot important?
It sub-serves 2 functions equally
- It supports body weight
- It is integral to the lower limb as an organ of locomotion
- The 2 functions are antagonistic to each other
What are the design requirements for a versatile foot and ankle joint?
Support body weight:
- Establishes a Broad-base for bearing body weight
- Must be robust to take all body weight
- Must be stable when weight bearing
- Absorb shocks when landing
To Underpin Movements
- Must be loose to permit displacement of the joint
- Must be stable when moving
- Must permit movements on flat, sloping and uneven surfaces.
- Must be light in weight
Capability to Generate Force
- Must be able to lift body weight during initiation of movement
Describe the Ankle Joint
- Formed by articulation of the leg with the foot
- 3 bones are involved - 2 bones of the leg, 1 bone of the foot
- Leg bones: tibia and fibula
- Foot bone: talus
What are the articulatory surfaces of the ankle joint?
- Tibia: contributes 2 articulatory surfaces:
1) Superior articulatory surface
2) Medial articulatory surface
- Fibular: contibutes 1 articulatory surface: 1) Lateral
- Talus: contributes 3 surfaces
What are the malleoli?
Distinguished by a pair of bony prominences in the medio-lateral plane.
These prominences are known as malleoli (pl)
Medial malleolus - distal end of tibia
Lateral malleolus - distal end of fibula
Malleoli are key landmarks in distal superficial venous drainage of lower limb
What deepens the articulatory surfaces?
The Distal Posterior Tibial :Ligament - thus further stabilising the joint.
The joint is further strengthened by a transverse tibio-fibular ligament
What type of joint is the Ankle joint?
Hinge Synovial joint
The axis of rotation in this hinge is not fixed.
It changes between extremes of plantarflexion and dorsiflexion.
It is therefore a rolling-hinge synovial joint
What is the difference between the Ankle Joint and the Sub-talar joint?
In some literature, the articulations of the talus with the calcaneus are included in the ankle joint.
To note the distinction between the ankle joint proper and sub-talar joints, sub-talar joints are formed by articulation of the talus with the calcaneus.
Describe the Division of Labour within the Ankle Joint
- Weight bearing surfaces: tibia, talus
- Joint stabilising surfaces: medial malleolus, lateral malleolus, distal tibio-fibular ligament (posteriorly) and transverse tibio-fibular ligament
last two ligaments deepen articulating surfaces tightening joint
Describe the Arches of the Foot
- A segmented structure such as the foot can hold up wieght only if built in the form of an arch
- The foot has 3 arches - present at birth
- 2 Main arches running antero-posteriorly
- 1 Transverse arch running medio-laterally
- Medial Longitudinal Arch:
- Lateral Longitudinal Arch
- Transverse Arch
Describe the Tarsal bones
- n = 7
- Markedly different in dize
- Irregular, cuboidal in shape
- Each bone has 6 surfaces
- These surfaces characterise each of the tarsals
Describe the Talus
- It is the only bone of the foot involved in the ankle joint
- It is the second largest tarsal bone
- No muscular attachments
- Yes, ligamentous attachments
- It forms the axis of rotation of the ankle joint
- It lies between the distal end of the leg and upper surface of the calcaneum
- Its long axis is directed forwards and medially
- Its long axis is in the antero-medial plane (oblique)
Describe the Dorsal Surface of Body of Talus
- It is the surface that articulates with the leg
- Its shape is reminiscent of a pulley
- Also known as the trochlear
- It is wider in front than behind (posteriorly much narrower)
Describe the Plantar Surface of Body of Talus
- Articulates with calcaneus
- It forms talo-calcaneal joint(s)
- Talo-calcaneal joints are also known as sub-talar joints
- This articulation is more complex when compared with that of the dorsal surface
Describe the Subtalar Joint (Talo-Calcaneal Joint)Uni
- It occurs by articulation of the talus with the calcaneus
- Uniaxial hinge joint
- The talus and calcaneous articulate at two points - one anteriorly and one posteriorly
- These articulations are separated by a deep groove, that runs antero-laterally, the tarsal canal.
- These articulations produce a 3-part joint called the subtalar joint
- The subtalar joint allows side-to-side motion of the foot
Describe the Subtalar Joint
- Allows inversion and eversion of the foot
- Movements allow us to walk on sloping or uneven ground using the sides of our feet
- Under normal conditions the subtalar joint allows about 30o of inversion and 15o of eversion
Describe Dorsi-flexion and Plantar-flexion of the Ankle Joint
- In dorsi-flexion the broader anterior portion of the trochlear of the talus occupies and completely fills the mortise of the joint, achieving the maximum stability of the joint.
- Adjustments at the tibio-fibular syndesmosis contribute to stability in extreme dorsi-flexion, when the malleoli spready apart and the lateral malleolus is everted.
- In plantar flexion the narrow part of the trochlear of the talus occupies the mortise, allowing little rotational movements of abduction and adduction.
- The joint is least stable during plantar flexion
What are neurological root values for Dorsiflexion? And what are the muscles reponsible for Dorsiflexion?
- Fibular division of sciatic (roots L4-5)
- Same root values for the big toe
- Tibialis Anterior: assisted by extensor digitorum longus and extensor hallucis longus
What are the neurological root values of the ankle joint for Plantarflexion? And the muscles?
- Tibial division of Sciatic (Roots S1-2)
- Gastrocnemius and Soleus assisted by Tibialis posterior, flexor hallucis longus, flexor digitorum longus
What is the Medial Ligament of the Ankle Joint?
- Also known as the Deltoid ligament
- Strongest ligament of the ankle joint
- Originates from the apex of the medial malleolus (antero-posterior) and fans dwonwards in a triangular shape to attach to the talus, calcaneus and navicular
- Consists of two sets of fibres; superficial and deep
- The Deltoid ligament is crossed by the tendons of Tibalis Posterior and Flexor Digitorum Longus, further reinforcing the stability of the joint
- Resists inversion
What is the Lateral Ligament of the Ankle Joint?
- Consists of 3 separate bands radiating from the lateral malleolus
- Anterior and posterior fibres pass to the talus
- Intermediate fibres pass to the calcaneum
- Resists eversion
What are common injuries of the foot?
- A fractured ankle normally involves fracture of the tibia, fibula or both
- The ankle joint forms a ring of bones and ligaments
- The medial malleolus is connected to the talus by the deltoid ligement
- The talus is connected to the lateral malleolus by the lateral ligaments
- The fibula is connected to the tibia by the tibio-fibular syndesmoses (ligament) completing the ring.
- The significance is that it is rare to break this ring on only one side.
- Usually an ankle fracture involves damage on both of the medial and lateral aspects of the joint
Describe the Mechanism of Pott's Fracture
- Term loosely applied to a variety of bimalleolar ankle fractures
- Results from forced excessive eversion of the foot.
- Caused by a combined abduction and external rotation.
- This action pulls on the extremely strong medial ligament, often tearing off the medial malleolus.
- The talus then moves laterally, shearing off the lateral malleolus.
- More commonly, this results in breakage of the fibula superior to the tibiofibular syndesmosis
- If the tibia is carried anteriorly, the posterior margin of the distal end of the tibia is also sheared off by the talus
Explain about the Medial Arch
- Formed by the calcaneus, talus, navicular, three cuneiforms and three metatarsals
- The plantar aponeurosis and the plantar calcaneonavicular ligament together with the tibialis anterior and the fibularis longus tendon play major roles in maintaining the integrity of this arch.
- Excessive stretching of the spring ligaments and plantar aponeurosis can result in 'flat feet'.
- Stretching of the ligaments result in the talar head being displaced inferomedially flatrening the medial longitudinal arch and producing some lateral deviation of the foot
How does the foot support the weight of the body?
- The main weight bearing bones on standing are the heel and the heads of the metatarsals.
- The bones of the foot are arranged in the form of two longitudinal arches, the medial and lateral arches, and atransverse half arch (two of which, when the feet are together, form the whole arch).
- The arches are maintained by the interlocking bones, the ligaments of the foot, small (intrinsic) muscles of the foot and the pull of the long tendons of extrinsic muscles (i.e. muscles in the anterolateral and posterior compartments of the leg).
- In the standing position, the arches sink somewhat under the body's weight, the individual bones lock together, the ligaments linking them are at maximum tension and the foot becomes an immobile pedestal.
- As soon as one walks, the weight is released from the arches which unlock and become a mobile lever system in the spring-like actions of locomotion.
For Gait Problems see Notability