FEET Flashcards
PURPOSE OF THE ANKLES AND FEET
- The ankle allows the foot to take up any position in space
- It helps the foot adapt to any irregularities of ground
- The foot has to be pliable to absorb stress and rigid enough to withstand large propulsive forces
- The entire body is affected by the mechanics of the foot, through its influence on the ankle, hip, knee, pelvis and vertebral column
VECTORS OF MOVEMENT OF EACH JOINT IN THE FOOT/ANKLE
o Talo-crural joint = plantar and dorsi flexion
o Sub talar joint = internal / external movement
o Tarsals/midfoot = pronation / supination
ACCESSORY MOVEMENTS OF THE FEET AND ANKLE
o Talo crural – anterior / posterior draw
o Talo navicular = wringing
o Talo cuneiforms – wringing / shear
o Cuneiforms metatarsals = shear
RANGES OF MOVEMENT
o Dorsiflexion = 20
o Plantar flexion = 50
o Inversion = 10
o Eversion = 15
o Pronation = 15-30
o Supination = 45-60
o Toe flexion MTP = 40
o Toe extension MTP = 40
FOOT LOADING DURING GAIT
o Walking = 1.2x bodyweight
o Running = 2x bodyweight
o Jumping from 2 feet = 5x bodyweight
o Standing on tip toes – 2.1x bodyweight
MECHANICAL CONCEPTS INVOLVED IN THE FOOT
- Structural shape allows for adaptation to ground reaction forces
- Talo-crural joint is an example of a 2nd class lever – fulcrum under the ball of the foot
- Concave/convex, roll and slide concept of the talo-crural joint
- Windlass, keystone, staples and beam mid foot mechanical concepts
TALOCRURAL JOINT - MULTIPLE MECHANISMS CONCAVE/CONVEX CONCEPT, SLIDE AND ROLL CONCEPT
- The ankle has a concave (tibia) on convex (talus) roll and slide opposite direction, with the pivot point being in the mid talus
- In both plantar or dorsi flexion, the tibia and talus passively allow movement from the foot. The tibia slides anteriorly on superior talus. Talus rolls posteriorly on calcaneum
- Anticlockwise roll and slide on dorsiflexion
- Clockwise roll and slide on plantarflexion
HOW THE ARCHES OF THE FEET ARE MAINTAINED
The shape of the bones
The tendon of flexor hallucis longus
Strong plantar ligaments
Peroneus longus
FORM AND FORCE CLOSURE OF THE FOOT
- Form closure uses the shape of one bone in relation to bones to provide stability to the surrounding joints
- For mobility to occur further joint compression and stabilisation is required to withstand a vertical load
- Force closure is the term used to describe the other forces such as the ligaments and muscles acting across the joint to create stability
- Superior talus is convex, inferior talus is concave, superior calcaneum is convex, this is a form closure
- The medial and lateral ligaments create force closure
- Don’t forget gravity
HOW THE PLANTAR FASCIA SUPPORTS FOOT FUNCTION
- The plantar fascia increases the stability during weight bearing and locomotion
- Acts like a ligament but is less flexible
- Due to proximity to plantar surface it has greater leverage and shock absorption
- It has limited flexibility, but by being attached to heel and toes only it stabilises and supports the twisting mechanism of arches
NEUROLOGICAL MECHANISMS INVOLVED IN WALKING
o Central control, local control, corrective measures, feedback loops
o Extrapyramidal system – control muscle tone and posture. They maintain postural equilibrium via active adaptation - E.g. hip shift on walking
o Basal ganglia – smooth out motor behaviour and inhibit unwanted movements
o Sensory feedback is via visual, vestibular and proprioceptive mechanisms
o “Predictive or anticipatory postural control is critical for successful execution of any voluntary movement whether it is episodic or rhythmic” Patla 2002
ROLE OF THE TALUS IN LOCOMOTION
- The talus acts as a torque converter, causing rotations of the leg to be converted to inversion and eversion vectors in the foot
- This helps adaptation of the foot to ground reaction forces
- Locking of the talus during toe off create a stable base for weight bearing and propulsion
- The tibia and fibular movement on the talus is a sliding movement which acts in the opposite movement to the talus which rolls on the calcaneum
TALOCRURAL JOINT
- The posterior inferior transverse ligament has a deep portion covered by hyaline cartilage and forms part of the articular surface of talocrural joint
- The vulnerability of the talocrural joint is that it has no direct muscle attachments and its domed/wedge like shape. It is totally dependent on ligamentous support to prevent anterior/posterior displacement of leg on talus, excessive inversion/eversion
SINUS TARSI
- The secret ligament – interosseous talocalcaneal ligament and cervical ligament, this lies in the sinus tarsi
- The space between the talus and the calcaneus is the sinus tarsi
- This space is filled with connective and adipose tissue, richly innervated with mechanoreceptors and free nerve endings
- Important area for proprioception
- Inferior extensor retinacular lies over the lateral aspect of the sinus tarsi
THE ROLE OF THE ARCHES DURING WALKING
- The longitudinal arches (medial and lateral) act like a twisting flexible ruler
- Increased twist on medial arch leads to inversion, whilst decrease twist leads to eversion
- This control on the medial arch allows small joints of the foot to be stabilised during propulsion and intrinsic muscles to produce leverage during propulsion
- This is supported by long and short plantar ligaments and action of tibialis anterior and posterior
- The lateral arch relies on the ‘keystone’ role of the cuboid for stability
