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Within the leg there are three predominant muscle groups: extensor,
These are thickenings of the deep fascia of the leg. They serve to stabil-
peroneal and flexor. Each of these groups has an individual blood and
ize the underlying extensor tendons.
nerve supply.
Students are often confused about the description of movements The extensor retinacula (Fig. 49.1)
• The superior extensor retinaculum: is a transverse band attached to
of the foot. Extension of the foot (dorsiflexion) refers to lifting the the anterior borders of the tibia and fibula.
toes and the ball of the foot upwards. Conversely, foot flexion (plan- • The inferior extensor retinaculum: is Y shaped. Medially the two
tarflexion) is the opposing action. limbs attach to the medial malleolus and the plantar aponeurosis and
laterally the single limb is attached to the calcaneus.
The deep fascia of the leg
The deep fascia of the leg is continuous above with the deep fascia of The peroneal compartment of the leg (Figs 49.2 and 49.4)
the thigh. It envelops the leg and fuses with the periosteum of the tibia This compartment consists of two musclesaperoneus longus and
at the anterior and medial borders. Other fascial septa, and the inter- brevis. These muscles are the predominant foot everters. The contents
osseous membrane, divide the leg into four compartments: extensor, of the peroneal compartment include:
peroneal, superficial and deep flexor. • Muscles: peroneus longus and brevis (see Muscle index, p. 166).
Following fractures of the leg, oedema within one or more compart- • Artery: the peroneal artery (p. 95).
ments can lead to obstruction to blood flow with consequent infarction • Nerve: the superficial peroneal nerve (p. 101).
of tissuebthe ‘compartment syndrome’. When this occurs immediate
decompression (fasciotomy) of all four compartments is necessary. Peroneal retinacula (Fig. 49.2)
The superior peroneal retinaculum is a thickening of deep fascia
The superior and inferior tibiofibular joints attached from the lateral malleolus to the calcaneus. The inferior per-
These are, respectively, synovial and fibrous joints between the tibia oneal retinaculum is a similar band of fascia which is continuous with
and fibula at their proximal and distal ends. the inferior extensor retinaculum. The tendons of peroneus longus and
brevis pass in their synovial sheaths beneath.
The interosseous membrane (Fig. 49.4)
The interosseous borders of the tibia and fibula are connected by a The flexor aspect of the leg (Fig. 49.3)
strong sheet of connective tissueathe interosseous membrane. The The flexor muscles of the calf are considered in two groupsasuperficial
fibres of the membrane run obliquely downwards from tibia to fibula. and deep flexor groups. All flexor muscles of the calf receive their
Its function is to bind together the bones of the leg as well as providing nerve and arterial supplies from the tibial nerve and the posterior tibial
a surface for muscle attachment. artery, respectively.
The contents of the flexor compartment of the calf include:
The extensor aspects of the leg and dorsum of the foot • Superficial flexor muscle group: gastrocnemius, soleus and plan-
(Figs 49.1 and 49.4) taris (the last is rudimentary in humans). Note that all of these muscles
The extensor group consists of four muscles in the leg (see below) and are inserted into the middle third of the posterior surface of the cal-
extensor digitorum brevis in the foot. These muscles dorsiflex the foot. caneus via the tendocalcaneus (Achilles tendon). A small bursa (the
The contents of the extensor compartment of the leg are as follows: retrocalcaneal bursa) occupies the space between the upper third of the
• Muscles: tibialis anterior, extensor hallucis longus, extensor digito- posterior surface of the calcaneus and the Achilles tendon. Within
rum longus and peroneus tertius (unimportant in function) (see Muscle soleus, and to a lesser extent gastrocnemius, there is an extensive
index, p. 166). venous plexus. These muscles act as a muscle pump squeezing venous
• Artery: the anterior tibial artery (p. 95) and its venae comitantes blood upwards during their contraction. It is in these veins that deep
form the vascular supply of the extensor compartment. The artery con- venous thromboses readily occur post surgery in the immobile patient.
tinues as the dorsalis pedis artery in the foot. • Deep flexor muscle group: tibialis posterior, flexor digitorum
• Nerves: the deep peroneal nerve (p. 101) supplies all of the muscles longus, flexor hallucis longus (see Muscle index, p. 166).
of the extensor compartment. Injury to this nerve results in the inability • Artery: posterior tibial artery (p. 95).
to dorsiflex the footafootdrop. • Nerve: tibial nerve (p. 101).

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