Boundaries and contents
The dorsum is built in layers, and each layer holds a predictable set of structures.
- Skin and superficial fascia: thin and mobile, so swelling shows early here. The dorsal venous arch lies across the metatarsals and drains into the great saphenous vein medially and the small saphenous vein laterally.
- Deep fascia and extensor retinacula: the superior extensor retinaculum is a band between the tibia and fibula just above the ankle. The inferior extensor retinaculum is Y-shaped: its stem arises from the upper surface of the calcaneus and its two limbs pass to the medial malleolus and the medial side of the sole.
- Tendons: from medial to lateral at the ankle, tibialis anterior, extensor hallucis longus, extensor digitorum longus and fibularis (peroneal) tertius.
- Extensor digitorum brevis and the dorsalis pedis artery with the deep fibular nerve, lying on the tarsal bones.
Muscles and tendons
Four muscles reach the dorsum from the anterior compartment of the leg, and one arises in the foot itself.
| Muscle | Origin | Insertion | Nerve |
|---|---|---|---|
| Tibialis anterior | Lateral tibial condyle and upper lateral tibia, interosseous membrane | Medial cuneiform and base of first metatarsal | Deep fibular (L4, L5) |
| Extensor hallucis longus | Middle of the anterior fibula, interosseous membrane | Base of the distal phalanx of the great toe | Deep fibular (L5) |
| Extensor digitorum longus | Lateral tibial condyle, upper anterior fibula, interosseous membrane | Extensor expansions of the lateral four toes | Deep fibular (L5, S1) |
| Fibularis tertius | Lower anterior fibula, continuous with extensor digitorum longus | Dorsum of the base of the fifth metatarsal | Deep fibular (L5, S1) |
| Extensor digitorum brevis | Upper surface of the calcaneus, inferior extensor retinaculum | Long extensor tendons of toes 2 to 4; the medial slip (extensor hallucis brevis) to the proximal phalanx of the great toe | Deep fibular, lateral branch (S1, S2) |
Tibialis anterior dorsiflexes and inverts the foot and lowers the forefoot smoothly after heel strike. The long extensors extend the toes and help dorsiflex. Extensor digitorum brevis extends the medial four toes at the metatarsophalangeal joints; it sends no tendon to the little toe.
Blood supply and innervation
The dorsalis pedis artery is the continuation of the anterior tibial artery, and it takes the new name as it crosses the front of the ankle midway between the malleoli. It runs forward on the talus, navicular and intermediate cuneiform, lateral to the tendon of extensor hallucis longus, and is crossed by the tendon of extensor hallucis brevis. At the back of the first intermetatarsal space it dives into the sole as the deep plantar artery, passing between the two heads of the first dorsal interosseous to complete the deep plantar arch. On the way it gives the medial and lateral tarsal arteries, the arcuate artery (which supplies the dorsal metatarsal arteries of spaces two to four) and the first dorsal metatarsal artery.
The deep fibular nerve accompanies the artery, lying lateral to it at the ankle. It divides into a lateral branch to extensor digitorum brevis and a medial branch that supplies the skin of the first web space, its only cutaneous territory.
| Skin area | Nerve |
|---|---|
| Most of the dorsum | Superficial fibular nerve |
| First web space | Deep fibular nerve |
| Lateral border and little toe | Sural nerve |
| Medial border, towards the great toe | Saphenous nerve |
Clinical relevance
The dorsum is where the anterior compartment of the leg is tested and where the foot pulse is most often checked.
- Dorsalis pedis pulse: felt against the tarsal bones just lateral to the tendon of extensor hallucis longus. It is absent or impalpable in a minority of healthy people, so check the posterior tibial pulse too before calling a foot ischaemic.
- Foot drop: a common fibular nerve palsy or an L5 root lesion weakens tibialis anterior and the long extensors, giving a high-stepping gait. Extension of the great toe is the standard test of the L5 myotome.
- Anterior tarsal tunnel syndrome: compression of the deep fibular nerve under the inferior extensor retinaculum, often by tight footwear, causes pain and numbness in the first web space.
- Anterior compartment syndrome: pain on passive flexion of the toes, which stretches the long extensors, is an early sign.
- Superficial fibular nerve: its branches cross the anterolateral ankle under the skin and can be cut by an arthroscopy portal or incision.
On the specimen
The station shows the dorsum of the foot with the skin and fascia removed, so the tendons can be traced to their insertions. Use the malleoli to orient: the medial malleolus belongs to the tibia and sits higher and further forward; the lateral malleolus belongs to the fibula and sits lower and further back.
Then read the tendons from medial to lateral. The thickest and most medial is tibialis anterior, running to the inner side of the midfoot. The next is extensor hallucis longus, heading straight for the great toe. Extensor digitorum longus splits into four slips for the lateral toes. The fleshy belly on the lateral dorsum, in front of the lateral malleolus, is extensor digitorum brevis; its thin tendons run deep to, and join the lateral sides of, the long extensor tendons. Do not confuse fibularis tertius with a toe tendon: it ends on the fifth metatarsal.