________ LATERAL SIDE OF THE LEG _________

The lateral or peroneal compartment of the leg is bounded anteriorly by the anterior intermuscular septum, posteriorly by the posterior intermuscular sptum, medially by the lateral surface of the fibula, and laterally by the deep fascia (Fig. 8.4).

Contents

Muscles: (1) Peroneus longus and (2) peroneus brevis.

Nerve: Superficial peroneal nerve.

Vessels: The arterial supply is derived from the branches of the peroneal artery which reach the lateral compartment by piercing the flexor hallucis longus and the posterior intermuscular septum. The veins drain into the small saphenous vein.

DISSECTION

Reflect the lateral skin flap of leg further laterally till peroneal muscles are seen. Divide the deep fascia longitudinally over the peroneal muscles. Clean the superior and inferior peroneal retinacula situated just above and below the lateral malleolus. Identify the peroneus longus and peroneus brevis muscles. Trace their tendons through the retinacula towards their insertion. Study the deep fascia and peroneal muscles.

PERONEAL RETINACULA ~

The superior peroneal retinaculum is a thickened band of deep fascia situated just behind the lateral malleolus.

It holds the peroneal tendons in place against the back of the lateral malleolus. It is attached

anteriorly to the posterior margin of the lateral malleolus, and posteriorly to the lateral surface of the calcaneum and to the superficial transverse fascial septum of the leg (Figs 8.4, 8.21).

The inferior peroneal retinaculum is a thickened band of deep fascia situated anteroinferior to the lateral malleolus. Superiorly, it is attached to the anterior part of the superior surface of the calcaneum, where it becomes continuous with the stem of the inferior extensor retinaculum. Inferiorly, it is attached to the lateral surface of the calcaneum. A septum attached to the peroneal tubercle or trochlea divides the space deep to the retinaculum into two parts.

The peroneal retinacula hold the tendons of the peroneus longus and brevis in place. Under the superior retinaculum the two tendons are lodged in a single compartment, and are surrounded by a common synovial sheath. Under the inferior retinaculum each tendon lies in a separate compartment: The tendon of the peroneus brevis in the superior compartment and that of the peroneus longus in the inferior compartment. Here each tendon is enclosed in a separate extension of the synovial sheath (Fig. 8.21).

ments of inversion and eversion help to adapt the fw to uneven ground.

2. Alongwith other invertor muscles present around j the ankle, the peronei help to maintain the stability! of this joint.

3. The peroneus longus helps to maintain lateral longitudinal arch and transverse arches i the foot.

| _____________ PERONEAL MUSCLES _____________ |

These are the peroneus longus and the peroneus brevis.

Their attachments are given in Table 8.2. Their nerve supply and actions are described below.

Nerve Supply

The peroneal muscles are supplied by the superficial peroneal nerve which is described below.

Actions

1. The peroneus longus and brevis are evertors of the foot when the foot is off the ground. The

move-SUPERFICIAL PERONEAL NERVE ||

Surface Marking

It is marked by joining the following two points (Figl 8.9).

(a) First point on the lateral aspect of the neck of J the fibula.

(b) Second point on the anterior border of the

peroneus longus at the junction of the upper two-l thirds and lower one-third of the leg.

At the lower point the nerve pierces the deep fascia and divides into medial and lateral branches.

Table 8.2: The peroneal muscles

Muscle Origin from Insertion

1. Peroneus longus (a) Head of the fibula, and The tendon passes deep to the peroneal retinacula, runs through It lies superficial to sometimes the adjoining part of a tunnel in the cuboid, and is inserted into (a) the lateral side of the the peroneus brevis the lateral condyle of the tibia base of the first metatarsal bone and (b) the adjoining part of the (Fig. 8.22) (b) Upper one-third, and posterior medial cuneiform bone. The tendon changes its direction below

half of the middle one-third of the lateral malleolus and again on the cuboid bone. A sesamoid the lateral surface of the is present in the tendon in the latter situation

shaft of the fibula

2. Peroneus brevis (a) Anterior half of the middle The tendon passes deep to the peroneal retinacula, and is Lies deep to the one-third and the lower one- inserted into the lateral side of the base of the fifth metatarsal peroneus longus third of the lateral surface bone

(Figs 8.23, 8.24) of the shaft of fibula (b) Anterior and posterior

intermuscular septa of the leg

Front, Lateral and Medial Sides of Leg and Dorsum of Foot 107

les

Introduction

This is the main nerve of the lateral compartment of the leg.

Origin

It is a smaller terminal branch of the common peroneal nerve.

I Course and Relations

It begins on the lateral side of the neck of the fibula, under cover of the upper fibres of the peroneus longus.

In the upper one-third of the leg, it descends through the substance of the peroneus longus. In the middle one-third, it first descends for a short distance between the peroneus longus and brevis muscles, reaches the anterior border of the peroneus brevis, and the descends in a groove between the peroneus brevis and the extensor digitorum longus under cover of deep fascia.

At the junction of the upper two-thirds and lower one-third of the leg, it pierces the deep fascia to become superficial. It divides into a medial and a lateral branch which descend into the foot.

DISSECTION

Carefully look for common peroneal nerve in relation to the neck of fibula. Superficial peroneal nerve one of the terminal branches of common peroneal nerve supplies both the peroneus longus and brevis muscles and in lower one-third of leg it becomes cutaneous to supply most of the dorsum of foot.

Branches and Distribution

Muscular branches are given off to the peroneus longus and the peroneus brevis.

Cutaneous branches. Through its terminal . branches, the superficial peroneal nerve supplies

108 Lower Limb

the lower one-third of the lateral side of the leg and the greater part of the dorsum of the foot, except for the territories supplied by the saphenous, sural and deep peroneal nerves (Fig. 8.3).

The medial branch crosses the ankle and divides into two dorsal digital nerves — one for the medial side of the big toe, and the other for the adjoining sides of the second and third toes.

The lateral branch also divides into two dorsal digital nerves for the adjoining sides of the third and fourth, and fourth and fifth toes.

Communicating branches. The medial branch communicates with the saphenous and deep peroneal nerves and the lateral branch with the sural nerve.