MSK 12b: bones, joints and muscles of the foot Flashcards
Name all the tarsal bones from proximal to distal
Tarsus (7 bones, proximal foot)
CALCANEUS-heel bone, when standing transmits majority of weight from the talus to the ground. Lateral surface has fibular trochlea which lies between the tendons of fibularis longus and braves, anchoring the evertors. Calcaneal tuberosity on posterior surface for weight-bearing; only medial tubercle contacts ground in standing. Allows levering at ankle to increase efficacy of plantar and dorsi flexion
TALUS-gripped superiorly by the malleoli (trochlea of talus). Only tarsal bone with no muscular or tendinous attachments
NAVICULAR-medial side, just distal to talus. Flattened, boat-shaped bone between head of tales and the 3 cuneiforms. Medial surface projects inferiorly as navicular tuberosity (tendon attachment)
CUBOID-most lateral in the distal row of the tarsus. Anterior to its tuberosity is a groove for tendon of fibularis longus
CUNEIFORMS-medial, intermediate and lateral. Wedge-shaped, each articulates with the navicular posteriorly and the base of the metatarsal anteriorly. Lateral cuneiform also with cuboid. Form the transverse arch
Describe metatarsals and phalanges of the foot
Metatarsus: 5 metatarsals numbered from the medial side. 1st metatarsal is shorter than the others, 2nd is the longest. Each has a base proximally, a shaft, and a head distally. Bases articulate with cuneiform and cuboid, heads with proximal phalanges. Bases of 1st and 5th have tuberosity for tendon attachment, and tuberosity of 5th projects laterally over the cuboid. On plantar surface of 1st are prominent medial and lateral sesamoid bones
Phalanges: 14. Great toe has proximal and distal and the rest have proximal, middle and distal. Each has a base, shaft and head. 1st digit phalanges are short, broad and strong
Calcaneal fracture
Hard fall onto heal may fracture it into several pieces (comminuted). Disrupts subtalar joint so usually disabling
Fracture of talar neck
During severe dorsiflexion e.g. pressing extremely hard on break pedal. May dislocate posteriorly
Fracture of metatarsals
Heavy object falls on foot and common in ballet dancers. Can also be transverse fatigue fractures from repeated stress e.g. excessive walking
If foot suddenly and violent inverted, tuberosity of 5th metatarsal may be avulsed by tendon of fibularis brevis
What type of joint is the ankle (talocrural articulation)?
Hinge-type synovial joint
Articulations of the ankle
Ankle: TIBIA, FIBULA and TALUS
Malleolar mortise: distal ends of tibia and fibula bound by tibiofibular ligaments and bound by hyaline cartilage
Body of talus fits into mortise (wedge-shaped articulating part)
When is the grip of the malleoli tightest on the talus?
Dorsiflexion-as when descending a steep slope
So this is when the ankle is most stable
Joint capsule of ankle
Thin anteriorly and posteriorly, but supported by strong medial and lateral collateral ligaments
This fits with movements, as plantar and dorsiflexion big movements but inversion and eversion more limited
Describe the ligaments of the ankle
Lateral ligament: consists of 3 separate ligaments
- anterior talofibular: flat, weak, from lateral malleolus to neck of talus
- posterior talofibular: thick, quite strong, runs from malleolar fossa to lateral tubercle of talus
- calcaneofibular: round cord from tip of lateral malleolus to lateral surface of calcaneus
Medial ligament: large and strong, also called deltoid ligament, attaches proximally to medial malleolus then fans out into 4 adjacent and continuous parts:
- tibionavicular
- tibiocalcaneal
- anterior tibiotalar
- posterior tibiotalar
Role of the medial ligament of the ankle?
Stabilise the ankle during EVERSION and prevents subluxation of the joint
What are the main movements of the ankle, and how are they performed?
Dorsiflexion: by anterior compartment muscles
Plantarflexion: by posterior compartment muscles. Because the narrow end of the trochlea of talus lies loosely between malleoli during plantar flexion some “wobble” (small amounts of abduction, adduction, inversion and eversion) can occur in this unstable position
Neuromuscular supply of the ankle
Blood: arteries derived from malleolar branches of the fibular and the anterior and posterior tibial arteries
Nerves: from tibial nerve and deep fibular nerve
Role of the lateral ankle ligaments?
Resist inversion
What could an inversion injury cause?
The relatively weak lateral ligament is likely to partially or fully tear, causing “sprained ankle”. Most likely is the anterior talofibular
In severe cases the lateral malleolus may fracture
Pott’s fracture-dislocation
Foot forcibly everted, so pull of the medial ligament often causes an avulsion fracture of the medial malleolus and lateral displacement of talus, causing fracture of the lateral malleolus and/or fracture of the fibula above the inferior tibiofibular joint
Which muscle groups produce the movements of the ankle and foot?
Plantar flexion: inserting posterior to malleoli
Dorsiflexion: inserting anterior to malleoli
Inversion: inserting on medial aspect of foot
Eversion: inserting on lateral aspect of foot
Why is dorsiflexion more limited than plantarflexion?
Talus is wider anteriorly, so when dorsiflex the talus is wedged and thus more stable
What is the tarsal tunnel?
Medial aspect of ankle. Roof: flexor retinaculum Floor: medial surfaces of talus and calcaneus Contents (from anterior to posterior): -tibialis posterior tendon -flexor digitorum longus tendon -neurovascular bundle (posterior tibial artery and vein + tibial nerve) -flexor hallucis longus tendon
Tom, Dick And Very Nervous Harry
Describe the innervation of the sole of the foot
Similar distribution to median and ulnar nerve: serial homologue
LOOK AT DIAGRAM
Medial plantar nerve: medial 3.5 digits
Saphenous nerve: small area on medial side towards heel
Tibial nerve: heel area
Sural nerve: small area on lateral side towards heel
Lateral plantar nerve: lateral 1.5 digits
Describe the 3 major joints of the foot
SUBTALAR JOINT: inferior surface of body of talus articulates with superior surface of calcaneus. Plane synovial joint which performs inversion and eversion
CALCANEOCUBOID JOINT: anterior end of calcaneus with posterior surface of cuboid. Plane synovial joint, helps with inversion and eversion
TALOCALCANEONAVICULAR: clinically is included within the subtalar joint because it only works when with the anatomical subtalar joint. The head of talus articulates with calcaneus navicular
Describe the arches of the foot
Lateral longitudinal arch: act as a unit with the transverse arch, spreading weight in all directions. Flat, rests on ground during standing. Made up of calcaneus, cuboid and lateral 2 metatarsals
Medial longitudinal arch: higher and more important than the LLA. Made up of calcaneus, navicular, 3 cuneiforms and 3 metatarsals. Keystone is the talar head. Fibularis longus tendon supports
Transverse longitudinal arch: cuboid, cuneiforms and bases of metatarsals. Many now doubt its existence and believe MLA is the only one of importance.
Function of the arches of the foot
Distribute weight over the foot acting as shock absorbers and “spring board” (elasticity) for propelling it during walking, running and jumping. Become slightly flattened by body weight during standing and normally resume their curvature when body weight is removed
What is “flat feet” (pes planus)?
Excessive stretching of the spring ligaments and plantar aponeurosis: talar head is displaced inferomedially and MLA is flattened so some lateral deviation is produced
Flat appearance of sole of foot. Can be flat only when weight-bearing (flexible) or all the time (rigid)
Acquired flatfeet “fallen arches” likely to be secondary to dysfunction of tibialis posterior due to trauma, degeneration with age or denervation
