Lateral and Back of Leg Anatomy PDF

# Lateral and Medial Sides of the Leg ## Chapter 29 ### Specific Learning Objectives After studying this chapter, the student should be able to: - Enumerate the muscles of the lateral compartment of the leg and describe: - origin - insertion - nerve supply - actions - Enumerate:...

# Lateral and Medial Sides of the Leg ## Chapter 29 ### Specific Learning Objectives After studying this chapter, the student should be able to: - Enumerate the muscles of the lateral compartment of the leg and describe: - origin - insertion - nerve supply - actions - Enumerate: - tendons attached on the upper medial surface of the tibia - muscles acting as 'guy ropes' to stabilize the pelvis on the femur/thigh - Give the anatomical basis of: - Anserine bursitis - Talipes varus and valgus deformities of foot - Sensory loss on the dorsum of foot, except in the first web space. ## Lateral Side of the Leg The lateral side of the leg deals with the lateral compartment, or peroneal compartment, of the leg and its contents. The small lateral compartment of the leg contains the primary extensors of the foot, specifically the peroneus longus and peroneus brevis muscles. It is important to note that no artery courses within this compartment, therefore perforating branches of the anterior tibial and peroneal arteries supply the compartment by piercing intermuscular septa. The most common nerve injury in the lower limb is the common peroneal nerve, which winds around the upper lateral aspect of the fibular neck. ### Lateral Compartment of the Leg **Boundaries (Fig. 29.1)** - **Anterior:** Anterior intermuscular septum. - **Posterior:** Posterior intermuscular septum. - **Medial:** Lateral surface of the fibula. - **Lateral:** Deep fascia of the leg. **Contents** - **Muscles** - peroneus longus - peroneus brevis - **Nerve:** Superficial peroneal nerve. - **Artery:** The lateral compartment does not have its own artery. It is supplied by the peroneal/fibular artery and anterior tibial artery. - **Veins:** Small unnamed veins mostly drain into the short saphenous vein. ## Peroneal Retinacula (Fig. 29.2) The peroneal retinacula (Latin retinaculum = retainer) are two thick bands of deep fascia on the lateral side of the ankle which keep the long tendons of the peroneus longus and peroneus brevis in position and also act as a pulley for them. ### Superior Peroneal Retinaculum It is situated just behind the lateral malleolus. **Attachments** - **Anteriorly:** It is attached to the back of the lateral malleolus. - **Posteriorly:** It is attached to the lateral surface of the calcaneum. **Relations** The tendons of both peroneus longus and peroneus brevis lie deep to this retinaculum in a single compartment. The tendon of peroneus longus lies superficial to the tendon of peroneus brevis; both these tendons are enclosed in a common synovial sheath. ### Inferior Peroneal Retinaculum The inferior peroneal retinaculum is a thickened fibrous band of deep fascia situated anteroinferior to the lateral malleolus. **Attachments** - **Superiorly:** It is attached to the anterior part of the superior surface of calcaneum, close to the stem of inferior extensor retinaculum. - **Inferiorly:** It is attached to the lateral surface of calcaneum. - **In between:** It attached to the peroneal trochlea, thus forming two loops, one for the tendon of peroneus brevis and other for the tendon of the peroneus longus (Fig. 29.2). **Relations** The tendon of peroneus brevis passes through the superior loop and that of peroneus longus passes through the inferior loop of the inferior retinaculum. Each tendon is enclosed in a separate synovial sheath, which are the prolongations of the common synovial sheath above, underneath the superior peroneal retinaculum. ### Clinical Correlation The synovial sheaths enclosing the tendons of peroneus longus and peroneus brevis are subject to friction and inflammation in athletes who wear tight shoes. ## Peroneal Muscles ### Peroneus Longus (Fig 29.3) The peroneus longus is the longer, larger, and more superficial of the two muscles of the lateral compartment. It is bipennate in the upper part and unipennate in the lower part. **Origin** - Upper two-third of the lateral surface of the shaft of the fibula - Adjacent surface of the head of the fibula - Anterior and posterior intermuscular septa of the leg and deep fascia overlying it **Insertion** - Medial cuneiform - Base of the 1st metatarsal The tendon of peroneus longus contains a sesamoid bone where it winds around the lateral side of the cuboid bone. **Nerve supply** The peroneus longus is supplied by the superficial peroneal nerve. **Actions** - Chief evertor of the foot - Maintains the lateral longitudinal arch - Maintains the transverse arches of the foot. ### Peroneus Brevis (Fig. 29.4) It's a fusiform bipennate muscle and lies deep to the peroneus longus. It is shorter than its partner, the peroneus longus, in the lateral compartment. **Origin** - Lower two-third of the lateral surface of the shaft of the fibula - Anterior and posterior intermuscular septa of the leg. **Insertion** - Lateral side of the base of the 5th metatarsal **Nerve Supply** The peroneus brevis muscle is supplied by the superficial peroneal nerve. **Actions** - Evertor of the foot - Maintains the lateral longitudinal arch ## Superficial Peroneal Nerve (Musculocutaneous Nerve of the Leg) It is the nerve of the lateral compartment of the leg. **Origin** - One of the two terminal branches of the common peroneal nerve at the neck of the fibula (Fig. 29.5) - Arises in the substance of peroneus longus on the lateral side of the neck of fibula. - Its root value is ventral primary rami of L5 and S1. **Course and Relations (Fig. 29.6)** - Begins on the lateral side of the neck of the fibula. - Descends for a short distance between the peroneus longus and peroneus brevis, and then lies in a groove between the peroneus brevis and extensor digitorum longus. - At the junction of the upper two-third and lower one-third of the leg, it pierces the deep fascia, and soon divides into a medial and a lateral terminal branches which reach the dorsum of the foot. **Branches and Distribution** - Muscular branches to peroneus longus and peroneus brevis - Cutaneous branches supply the skin of the lower one-third of the lateral side of the leg and dorsum of the foot, except for the territories supplied by the saphenous, sural, and deep peroneal nerves. The medial terminal branch of the superficial peroneal nerve crosses the ankle and divides into two dorsal digital nerves, one for the medial side of the big toe and the other for the second interdigital cleft. The lateral terminal branch of the superficial peroneal nerve also divides into two dorsal digital nerves for the third and fourth interdigital clefts. ## Arterial Supply of Lateral Compartment of Leg - Peroneal artery, a branch of the posterior tibial artery - Anterior tibial artery. ## Clinical Correlation - Deformity foot due to overactivity of invertor and evertor muscles (Fig. 29.5) - Following injury to the superficial peroneal nerve, paralysis of the peroneal muscles and associated overactivity of the invertor muscles of the foot produces a deformity of the foot called talipes **varus**. - The overactivity of the evertors of the foot (peroneal muscles) following paralysis of the anterior tibial muscles (invertors of the foot) produces a deformity of the foot called talipes **valgus**. ## Clinical Testing of Peroneus Longus And Brevis Both these muscles strongly evert the foot of the patient, against resistance. If normal, the tendons of those muscles can be seen and palpated inferior to the lateral malleolus. The origin, insertion, nerve supply, and actions of the muscles of the lateral compartment of the leg are summarized in Table 29.1.