Muscles of the Dorsum of the Foot
Anatomy and supply
The muscles of the dorsum of the foot are a group of two muscles which together represent the dorsal foot musculature. They lie within a flat fascia on the dorsum of the foot (fascia dorsalis pedis). Hereby their muscle bellies form the surface of the lateral dorsum of the foot. The deep peroneal nerve (L5-S1) is responsible for the innervation. The two muscles are:
- Extensor digitorum brevis muscle: originates at the calcaneus and divides into three muscle bellies whose tendons insert at the dorsal aponeurosis and the middle phalanges of the second to fourth toes.
- Extensor hallucis brevis muscle: also originates at the calcaneus and inserts at the dorsal aponeurosis and proximal phalanx of the big toe.
The dorsal fascia of the foot is the continuation of the deep fascia of the lower leg (crural fascia). Apart from the muscles of the dorsum of the foot, it incloses the tendons of the anterior muscles of the lower leg, the dorsalis pedis vessels (continuation of the anterior tibial artery) and branches of the deep peroneal nerve. In contrast the dorsal venous network (rete venosum dorsale pedis) lies above the fascia and is easily visible due to the relatively thin and low-fat skin.
The contraction of the extensor digitorum brevis muscle results in the dorsal extension of the second to fourth toe. The extensor hallucis brevis muscle causes a dorsal extension of the metatarsophalangeal joint of the big toe (MTP I). Interestingly the dorsal foot muscles have no insertion at the little toe. This means that the little toe can only be extended by the extensor digitorum longus muscle only. The dorsal aponeurosis of the toes supports the effect of the dorsal foot muscles by redirecting the force line of their tendons to the longitudinal axis.
The subcutis of the dorsum of the foot is quite flexible and elastic. It quickly tends to accumulate fluids and swell (edema). The edema of the dorsum of the foot is a common symptom in numerous clinical conditions, e.g. right heart failure, venous and lymphatic obstructions, inflammation and allergic reactions. In chronic venous insufficiency (CVI) the edema occurs particularly after lack of exercise or standing too long.