Overview
The ankle is the joint which connects the foot to the lower limb. It is a hinged synovial joint with a joint
capsule; the capsule of which thickens medially to form the deltoid ligament
and laterally to form the lateral ligament (which has three parts). The ankle also includes the distal
tibiofibular joint which is a fibrous joint (syndesmosis). There are many ligaments which stabilise the
ankle and subtalar joint.
Gross Anatomy
The ankle
joint is made up of three bones – the distal fibula, the distal tibia and the
dome of the talus. The talus itself does
not have any muscular attachments, these pass from the proximal tibia/fibula,
across the talus to insert distally. The
articular surface of the ankle joint (tibiotalar joint) is made up of hyaline
cartilage, this is relatively thin on the talar dome leading to future issues
with OA in traumatic ankle injuries.
The attachments for the capsule proximally are the distal tibia and
fibula. Distally the capsule attaches to
the talus, navicular and calcaneus.
Thickenings in the capsule give rise to the lateral ligament (laterally)
and the deltoid ligament (medially).
The dorsal or anterior aspect of the ankle joint is covered superficially
to deep by: skin, subcutaneous fat, the long saphenous vein, the saphenous
nerve, the extensor retinaculum (superior and inferior), the extensor tendon
sheaths and the following extensor tendons from medial to lateral: Tibialis
anterior, EHL, EDL, and peroneus tertius.
In between EHL and EDL lies the dorsalis pedis artery (arising from the
anterior tibial artery) and the deep peroneal nerve.
Posterior to the lateral malleolus are found the following structures:
peroneus longus and, underneath it, peroneus brevis (distally p. brevis lies in
front of p. longus). These structures
are held in place by the superior and inferior peroneal retinaculum. The superior retinaculum runs from the
lateral malleolus to the lateral calcaneus.
The inferior retinaculum runs from inferior extensor retinaculum and attaches to the lateral calcaneus
also. Distally the two tendons have
separate sheaths, proximally they share one sheath.
General
development: Limb
buds develop from the end of the 4th week (upper limb 1-2 days
before lower limb), broadly governed by HOX genes. They arise from the venterolateral wall
mesenchymal cells. This is mesoderm
covered by ectoderm. The end of the limb
has an apical ectodermal ridge (AER) which causes mesenchyme to grow. The mesenchyme farther away from this ridge
becomes muscle/cartilage.
At 6 weeks
old the limb bud flattens distally and the AER undergoes apoptosis around week
8 to create the ‘gaps’ between the toes (same applies for fingers). Hyaline cartilage begins to form and
condenses in areas where future joints will exist – this is the beginning of
synovial joints.
In week 7
the limbs rotate. The lower limbs rotate
~90 degrees medially (upper limbs rotate 90 degrees laterally) which explains
why the extensors are ‘anterior’ in the lower limb but ‘posterior’ in the upper
limb.