Page 249 - Clinical Anatomy

ECA4 7/18/06 6:47 PM Page 234

234 The lower limb

Movements of the ankle
The ankle joint is capable of being flexed and extended (plantar- and
dorsiflexion).
The body of the talus is slightly wider anteriorly and, in full extension,
becomes firmly wedged between the malleoli. Conversely, in flexion, there
is slight laxity at the joint and some degree of side to side tilting is possible:
test this fact on yourself.
The principal muscles acting on the ankle are:
•◊◊dorsiflexors — tibialis anterior assisted by extensor digitorum longus,
extensor hallucis longus and peroneus tertius;
•◊◊plantarflexors—gastrocnemius and soleus assisted by tibialis posterior,
flexor hallucis longus and flexor digitorum longus.

Clinical features

1◊◊The collateral ligaments of the ankle can be sprained or completely torn
by forcible abduction or adduction, the lateral ligament being far the more
frequently affected. If the ligament is completely disrupted the talus can be
tilted in its mortice; this is difficult to demonstrate clinically and is best con-
firmed by taking an anteroposterior radiograph of the ankle while forcibly
inverting the foot.
2◊◊The most usual ankle fracture is that produced by an abduction-external
rotation injury; the patient catches his foot in a rabbit hole, his body and his
tibia internally rotate while the foot is rigidly held. First there is a torsional
spinal fracture of the lateral malleolus, then avulsion of the medial collat-
eral ligament, with or without avulsion of a flake of the medial malleolus
and, finally, as the tibia is carried forwards, the posterior margin of the
lower end of the tibia shears off against the talus. These stages are termed
1st, 2nd and 3rd degree Pott’s fractures. Notice that, with widening of the
joint, there is forward dislocation of the tibia on the talus, producing char-
acteristic prominence of the heel in this injury.

The joints of the foot

Inversion and eversion of the foot take place at the talocalcaneal articula-
tions and at the mid-tarsal joints between the calcaneum and the cuboid and
between the talus and the navicular. Of these, the talocalcaneal joint is the
more important. Test this on yourself— hold your calcaneus between your
finger and thumb; inversion and eversion are prevented.
Loss of these rotatory movements of the foot, e.g. after injury or because
of arthritis, results in quite severe disability because the foot cannot adapt
itself to walking on rough or sloping ground.
Inversion is brought about by tibialis anterior and posterior assisted by
the long extensor and flexor tendons of the hallux; eversion is the duty of
peroneus longus and brevis, (peroneus tertius forms part of the extensor
muscles).