Vessels of the Leg



Vessels of the Leg





Surgical Anatomy of the Leg

The popliteal artery branches in the proximal leg to ultimately form the anterior tibial, posterior tibial, and peroneal trunks. The older term “trifurcation” is a misnomer because the common tibioperoneal trunk is interposed between the origin of the anterior tibial artery and the bifurcation of the other two vessels some 2 to 3 cm more distally (Fig. 18-1). The popliteal artery terminates in a true trifurcation approximately 3% of the time.1,2 To understand the relationships of these arteries, it is necessary to review the muscle groups and fascial girdle of the leg. Then the nerves and vessels can be conceptually laid in place.






Fig. 18-1 The division of the leg vessels distal to the popliteal artery normally occurs in two stages. The anterior tibial artery arises first, leaving a common tibioperoneal trunk that bifurcates into the posterior tibial and peroneal arteries.



Fascia of the Leg

A dense fascial layer, continuous with the fascia lata of the thigh, encircles the leg. This crural fascia is adherent to underlying structures around the knee joint and ankle joint. Thickened bands of this fascia form retinacula at the ankle that restrain the extensor (dorsiflexor), flexor (plantar flexor), and peroneal (evertor) tendons (Fig. 18-2).






Fig. 18-2 A, B: Thickened bands of the dense crural fascia form restraining retinacula at the ankle over the extensor, flexor, and peroneal tendons. The two principal neurovascular bundles lie beneath the extensor and flexor retinacula.





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Strong septa join the crural fascia to the fibula and partition the leg into anterior, posterior, and lateral compartments (Fig. 18-3). The tough interosseous membrane completes the division of the anterior from the posterior space. In addition, a secondary septum arches from the tibia to the fibula posteriorly, creating a deep and superficial posterior compartment.






Fig. 18-3 Strong septa between the crural fascia and the bones of the leg separate the leg into discrete compartments.


Interestingly, the three primary arterial trunks of the leg occupy only two of the four spaces (Fig. 18-4). The anterior tibial artery lies in the compartment of the same name. Both the posterior tibial and peroneal arteries lie in the deep posterior compartment and send penetrating branches to the overlying superficial posterior compartment and to the adjacent lateral compartment.






Fig. 18-4 The major arteries of the leg lie in the anterior and deep posterior compartments and supply adjacent compartments through perforating branches.


The nerve distribution differs slightly from the arterial pattern in that a discrete trunk enters each major compartment. The tibial nerve supplies the posterior compartment flexor muscles. The peroneal nerve divides into a superficial branch to the peroneal muscles (peroneus longus and brevis) and a deep branch to the anterior compartment muscles (Fig. 18-5).

The unyielding nature of the crural fascia and its tight adherence at the knee and ankle make the closed compartmental spaces susceptible to buildup of pressure after leg injury. Intramuscular tissue pressure is normally zero. Trauma such as fracture, severe compression, or prolonged ischemia can result in compartmental edema that increases tissue pressure. As the pressure exceeds lymphatic and then venous closing pressure, any egress of fluid from the leg is blocked, and the pressure escalates more quickly. Such compartment syndromes can result in irreversible neuromuscular damage if not relieved by prompt fasciotomy. Four-compartment fasciotomies are usually performed through separate medial and lateral leg incisions (Fig. 18-6). Alternatively, all compartments can be simultaneously decompressed through a single lateral incision combined with a fibulectomy (Fig. 18-7).






Fig. 18-5 A major nerve trunk runs in each major compartment of the leg.







Fig. 18-6 Four-compartment fasciotomy can be performed through separate medial and lateral leg incisions.







Fig. 18-7 A septum of each compartment attaches to the fibula, allowing universal compartment decompression by fibulectomy.



Musculoskeletal Relationships

The muscle groups of the leg are composed of the large posterior gastrocnemius/soleus complex and three groups of long muscles: the plantar flexors, dorsiflexors, and evertors of the foot. The gastrocnemius muscle group (including the small plantaris muscle) attaches to the calcaneus through the large Achilles tendon (Fig. 18-8).






Fig. 18-8 The powerful gastrocnemius and soleus muscles occupy the superficial posterior compartment of the leg.


The other three groups of muscles cross the ankle joint closely applied to bony structures. Their tendons lie beneath thickenings of the deep fascia of the leg that prevent bowstringing of the long tendons at the ankle. The plantar flexors (Fig. 18-9) consist of the tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles. Their tendons pass behind the medial malleolus under the flexor retinaculum (lacinate ligament) (Fig. 18-10).






Fig. 18-9 Muscles of the deep posterior compartment are shown.







Fig. 18-10 Tendons of the plantar flexor muscles pass behind the medial malleolus under the flexor retinaculum.


The dorsiflexors (Fig. 18-11) consist of the tibialis anterior, extensor digitorum longus, and extensor hallucis longus muscles. Their tendons are held by the superior extensor retinaculum above the ankle and the inferior extensor retinaculum below the ankle (Fig. 18-12). The tendons of the foot evertors, the peroneus longus and brevis muscles, pass behind the lateral malleolus and are held by the superior and inferior peroneal retinacula (Fig. 18-13). Deep attachments of the retinacula to the bones of the ankle and foot form sheathlike compartments for the tendons.






Fig. 18-11 Muscles of the dorsiflexor group are shown.







Fig. 18-12 Tendons of the dorsiflexors are held at the ankle and foot by the superior and inferior extensor retinacula.







Fig. 18-13 Tendons of the foot evertors pass behind the lateral malleolus.



Anterior Compartment

The anterior, or extensor, compartment is enclosed by the crural fascia attaching to the lateral subcutaneous margin of the tibia and the anterior septum from the fibula to the crural fascia. It contains two parallel muscle masses (Fig. 18-14). The large tibialis anterior muscle lies adjacent to the tibia, arising from that bone and the adjacent interosseous membrane. Lateral to the tibialis anterior is a column of muscles originating sequentially from the fibula and adjacent interosseous membrane. From proximal to distal, these are the extensor digitorum longus, extensor hallucis longus, and peroneus tertius muscles. The anterior tibial vessels and deep peroneal nerve lie between these muscular columns and are directly accessible from an anterior approach. The arched origin of the anterior tibial vessels, passing through the proximal hiatus in the interosseous membrane, can be made more accessible by removing the head of the fibula. The distal anterior tibial artery continues beneath the Y-shaped inferior extensor retinaculum to reach the dorsum of the foot as the dorsalis pedis artery lateral to the tendon of extensor hallucis longus muscle.






Fig. 18-14 The anterior tibial artery and deep peroneal nerve lie between the tibialis anterior and extensor digitorum longus muscles in the proximal leg and between the tibialis anterior and extensor hallucis longus muscles in the distal leg. All cross sections are shown from a caudal view.



Posterior Compartment

The superficial posterior compartment contains the bulky superficial gastrocnemius/soleus complex that fuses to form a common termination in the calcaneal tendon (Fig. 18-15). The hoodlike origin of the soleus muscle blocks direct access to the underlying posterior tibial and peroneal arteries. From the apex at the fibular head, the shorter lateral fibular origin descends in a straight line down the fibula. The tibial head is in two parts. The proximal diagonal portion originates from the soleal line of the tibia and is interrupted by the hiatus for the popliteal vessels and tibial nerve. On reaching the medial subcutaneous border of the tibia, the tibial origin descends vertically to the midpoint of the tibia. The diagonal muscle fiber disposition of the lateral and medial origins should be used to advantage when stripping the muscle off the bone.

Between the superficial and deep posterior muscle groups, there is a fascial layer that is less dense than the crural fascia and septa. Within and beneath this layer lie the posterior tibial and peroneal vessels. Although the arteries are usually single trunks, the tendency of accompanying veins to be multiple is pronounced in the leg. Exposure of the arteries requires careful dissection of the surrounding veins.






Fig. 18-15 A thin fascial septum covers the muscles and neurovascular structures of the deep posterior compartment.


The deep layer of posterior muscles consists of the central tibialis posterior muscle, running the length of the interosseous membrane and into the foot, flanked by the shorter flexor digitorum longus muscle medially and the short flexor hallucis longus muscle laterally. Both the proximal posterior tibial and peroneal arteries descend on the tibialis posterior muscle. The distal third of the peroneal artery runs within and behind the belly of the flexor hallucis longus muscle. It terminates in a variable branch perforating through the distal interosseous membrane and in calcaneal branches. The posterior tibial neurovascular bundle reaches the ankle posterior to the tendons of tibialis posterior and flexor digitorum longus muscles beneath the flexor retinaculum.






Fig. 18-16 The peroneal muscles of the lateral compartment must be mobilized for access to the fibula and deep posterior leg arteries.


Lateral Compartment

The peroneus longus and brevis muscles originate from the lateral border of the proximal and distal fibula, respectively (Fig. 18-16). Their tendons pass under the superior peroneal retinaculum posterior to the lateral malleolus. The importance of this muscle group in vascular surgery lies in the fact that it must be mobilized from the fibula to resect that bone for lateral access to the posterior compartment vessels and when simultaneous decompression of all compartments through a single incision is necessary.

Henry3 emphasized fine points for liberating the fibula without damaging adjacent nerves and vessels. Proximal exposure is obtained by gently
elevating the common peroneal nerve posterior to the biceps femoris tendon. The overlying origin of the peroneus longus is divided to expose the branches (Fig. 18-17). The length of the muscle origins are then elevated laterally to medially, creating a long trapdoor with an intact superficial peroneal nerve (Fig. 18-18). The bias of the muscle fibers dictates stripping upward toward the knee, whereas the dominant bias of the interosseous membrane mandates stripping in the opposite direction. Confining dissection to the periosteal plane in the distal leg prevents damage to the nearby peroneal vessels.






Fig. 18-17 The path of the peroneal nerve and its branches is dissected free of overlying muscles to protect the nerve during mobilization of the fibula.







Fig. 18-18 A long flap of peroneal muscles is created by shaving the muscles off the fibula distally to proximally. The interosseous membrane strips best in the opposite direction.



Cross-Sectional Anatomy

The muscle groups are compartmentalized by septa connecting the deep fascia to the tibia and fibula and by the interosseous membrane between the two bones. At the level of the calf (Fig. 18-19), the dorsiflexors lie in the anterior compartment of the leg along with the anterior tibial artery and deep branch of the peroneal nerve. The neurovascular bundle lies on the interosseous membrane. The peroneal compartment is bounded by septa connected to the fibula, and contains the superficial peroneal nerve lying close to the bone at this level. The posterior compartment is bounded externally by the deep fascia running from the lateral peroneal septum to the tibia medially. The superficial compartment containing the gastrocnemius and soleus muscles is separated from the deep posterior compartment containing the plantar flexors by the deep septum spanning from the tibia to the fibula. The posterior tibial and peroneal vessels and the tibial nerve lie between the deep muscles and deep septum at the level of the calf. The long saphenous vein and saphenous nerve lie in the anteromedial subcutaneous tissue. The small saphenous vein lies subcutaneously in the posterior midline, soon to be joined by the sural nerve, seen here deep to the fascia between the gastrocnemius bellies.






Fig. 18-19 In the midcalf, the neurovascular structures are grouped in the central portion of the leg.


In the lower leg (Fig. 18-20), the unified gastrocnemius/soleus tendon is enclosed by the deep fascia posteriorly and the deep intermuscular septum anteriorly. The narrowed span of the deep fascia over the Achilles tendon puts the medial fusion point posterior to the tibia, allowing direct access to the deep compartment directly over the plantar flexors and posterior tibial neurovascular bundle. The tibialis posterior and flexor digitorum longus muscles are mostly tendinous in the relatively larger deep posterior compartment, whereas the flexor hallucis longus muscle remains fleshy and muscular right down to the ankle. The peroneal artery, which is beginning to diminish above the distal tibiofibular syndesmosis, lies on the interosseous membrane covered by the mass of the flexor hallucis longus muscle. The peroneal tendons lie posterior to the fibula on the lateral side of the Achilles tendon. The deep peroneal nerve remains in the anterior compartment with the anterior tibial artery, whereas branches of the superficial peroneal nerve have penetrated the deep fascia of the lateral compartment to lie in the subcutaneous plane. The anterior tibial artery is moving anteriorly over the flare of the tibia.






Fig. 18-20 In the distal leg, the anterior and posterior tibial neurovascular structures become more superficial.


Just above the ankle joint (Fig. 18-21), the tendon groups are tightly bound by thickened bands of deep fascia, the inferior extensor retinaculum anteriorly, the flexor retinaculum posteromedially, and the superior peroneal retinaculum posterolaterally. The tendon of the extensor hallucis longus muscle crosses over the anterior tibial neurovascular bundle, and the artery continues onto the dorsum of the foot as the dorsalis pedis artery. The peroneus longus tendon lies posterolateral to the peroneus brevis muscle as they pass behind the medial malleolus. The partially tendinous flexor hallucis longus muscle remains a posterior midline structure right down to the ankle joint. The tibial nerve lies posterior to the posterior tibial artery as the neurovascular bundle enters the foot.






Fig. 18-21 Cross section demonstrates the anatomic relationships at the level of the ankle.



Vessels of the Lower Leg

The tibial nerve joins the popliteal vessels in the midpopliteal space (Fig. 18-22) and sural neurovascular bundles splay out to the heads of the gastrocnemius muscles at the junction. Below the gastrocnemius branches, the small saphenous vein joins the popliteal vein, and the median sural nerve branch runs along the course of the vein, tightly bound to it. The continuation of the tibial nerve passes through the hiatus in the tibial attachment of the soleus muscle, along with the popliteal vessels. At the upper end of the interosseous membrane, the anterior tibial artery passes into the anterior compartment. The tibioperoneal trunk lies on the upper part of the tibialis posterior muscle and divides into the smaller peroneal artery laterally and the posterior tibial artery medially. The anterior tibial artery lies on the interosseous membrane, first between tibialis anterior and extensor digitorum longus muscles and then between the tibialis anterior and extensor hallucis longus muscles that arise lower down. The posterior tibial artery lies on tibialis posterior and flexor digitorum longus muscles, medial to flexor hallucis longus muscle, down the length of the leg. The peroneal artery is progressively covered by, and sometimes within, the belly of the flexor hallucis longus muscle as that muscle expands from its low origin.






Fig. 18-22 The tibial nerve joins the popliteal vessels in the midpopliteal space.







Fig. 18-23 The dorsalis pedis artery and deep peroneal nerve emerge at the ankle between the tendons of the extensor digitorum longus and extensor hallucis longus muscles.

At the ankle, the anterior tibial artery and deep peroneal nerve emerge between extensor digitorum longus and extensor hallucis tendons after passing under the latter medially to laterally (Fig. 18-23).
They run along the lateral border of the extensor hallucis muscle beneath the deep fascia of the foot.

Posteromedially, the posterior tibial artery and tibial nerve lie between the flexor digitorum longus and flexor hallucis longus muscles before passing beneath the flexor retinaculum to enter the foot (Fig. 18-24). Posterolaterally, calcaneal branches of the peroneal artery pass down from beneath the lower muscular border of the flexor hallucis longus muscle.






Fig. 18-24 The posterior tibial artery and tibial nerve lie posterior to the medial malleolus in a groove between the flexor digitorum longus and flexor hallucis longus tendons.


With the flexor hallucis longus muscle partially cut away, the course of the peroneal artery can be seen lying on the interosseous membrane just medial to the fibula (Fig. 18-25).






Fig. 18-25 The peroneal artery lies on the interosseous membrane on the medial side of the fibula.

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May 22, 2016 | Posted by in ANATOMY | Comments Off on Vessels of the Leg
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