Muscles of the leg – Musculi cruris
9.3
Muscles
The muscles of the leg are organised into three groups: the anterior, lateral and posterior groups. The anterior group is innervated by the deep fibular nerve, the lateral group is innervated by the superficial fibular nerve, and the posterior group is innervated by the tibial nerve. 1 Anterior group
• • •
1.1 Tibialis anterior (musculus tibialis anterior) 1.2 Extensor digitorum longus (musculus extensor digitorum longus) 1.3 Extensor hallucis longus (musculus extensor hallucis longus)
2 Lateral group
• 2.1 Fibularis longus (musculus fibularis longus) • 2.2 Fibularis brevis
1.2
2.1 1.1
(musculus fibularis brevis)
1.2 2.2
3 Posterior group Superficial layer
• 3.1 Triceps surae (musculus triceps surae) • 3.2 Plantaris
1.3 1.3
(musculus plantaris) Deep layer 3.3 Popliteus (musculus popliteus) 3.4 Tibialis posterior (musculus tibialis posterior) 3.5 Flexor digitorum longus (musculus flexor digitorum longus) 3.6 Flexor hallucis longus (musculus flexor hallucis longus)
• • • •
Anterior view of the right and left legs
3.3 3.4
3.1
3.1 2.1
The tibialis anterior prevents plantar flexion of the foot at the beginning of the stance phase of gait. In addition, it helps prevent the toes from coming into contact with the ground during the swing phase of gait. The dorsal aponeurosis (aponeurosis dorsalis) is a fibrous structure on the back of the toes which attaches to the middle and distal phalanges. The extensor digitorum longus and brevis, lumbricals and interossei are attached to the phalanges by means of the dorsal aponeurosis.
Clinical notes
3.2
1.1
The fibularis tertius is part of the extensor digitorum longus, which inserts on the tuberosity of the fifth metatarsal bone by a slim and often doubled tendon. The muscle is present in 92 % of cases and is innervated by the deep fibular nerve. It helps the extensor digitorum longus in extension of the toes and pronation of the foot.
3.5
Trigger points in the tibialis anterior cause pain on the ventromedial surface of the ankle and on the dorsal and medial surfaces of the big toe. The trigger points are usually situated in the proximal third of the muscle and they are very painful. They can be caused by driving for long periods of time with highpositioned pedals. The extensor digitorum longus is called the “mallet toe muscle”. The muscle is more effective during walking as a dorsal flexor of the foot when the metatarsophalangeal joints are fully extended. If the muscle is used for dorsal flexion of the foot instead of the tibialis anterior, a deformity called mallet toe may develop (see page 56). A hypertonic extensor digitorum longus can compress the deep fibular nerve against the fibula.
1.2 3.6 2.2
Weakening of the fibular muscles predisposes to ankle instability syndrome and sprained ankles. A trigger point in the fibular muscles causes pain in the area of the lateral malleolus. A hypertonic fibularis longus can compress the common fibular nerve against the fibula.
Lateral view of the right leg
156
Posterior view of the right and left legs
The fibularis brevis often develops trigger points following ankle sprains or immobilisation in plaster.