Anatomy

The brachial plexus is formed by the ventral primary rami of C5-T1. It provides innervation to the muscles and skin of the upper extremity. Less often, C4 will contribute a branch to C5 (pre-fixed) and T2 will contribute a branch to T1 (post-fixed).¹ The roots of the plexus emerge between the anterior and middle scalene muscles and descend over the first rib, posterior to the clavicle. In the lower part of the posterior cervical triangle, after traversing between the anterior and middle scalene muscles, the C5 and C6 roots unite to form the upper trunk. Before this union, C5 gives off the dorsal scapular nerve to the rhomboids and a branch to the phrenic nerve. The C5 root, along with the C6 and C7 roots, gives off contributions to the long thoracic nerve to the serratus anterior muscle. The C7 root continues on as the middle trunk, and the C8 and T1 roots unite to form the lower trunk. The upper trunk gives off the suprascapular nerve to the supraspinatus and infraspinatus muscles as well as the nerve to the subclavius muscle.

The trunks divide into anterior and posterior divisions. The anterior divisions of the upper and middle trunks form the lateral cord. The anterior division of the lower trunk continues as the medial cord. The posterior divisions of all three trunks unite as the posterior cord. The divisions form at the level of the clavicle, and the cords continue into the infraclavicular space.

The cords form just distal to the clavicle, below the tendinous insertion of the pectoralis minor muscle. They are named according to their spatial relationship to the axillary artery. Each cord ends in two terminal branches. The lateral cord gives off the lateral pectoral nerve and then terminates as the musculocutaneous nerve and the lateral contribution to the median nerve. The medial cord gives off the medial pectoral, medial brachial cutaneous, and medial antebrachial cutaneous nerves and then terminates as the ulnar nerve and the medial contribution to the median nerve. The posterior cord gives off the thoracodorsal and subscapular nerves and then terminates as the axillary and radial nerves.

Although many variations have been reported, true anomalies of this basic anatomy are rare.²

Positioning

For an anterior approach to the brachial plexus, the patient is placed in the supine position with a bolster under the ipsilateral shoulder (Fig. 28-1). The head is placed in a slight amount of extension and is turned 45 degrees to the contralateral side. The arm is abducted on an arm board. Both lower extremities below the knee are sterilely prepared and draped to allow sural nerve harvesting for grafts. If other sources in the upper extremity, such as medial brachial and antebrachial cutaneous nerves, are to be used for grafting, the entire arm should be prepared. The surgeon should have the ability to work from superior to the clavicle and inferior to it. The arm board should be mobile enough to allow the surgeon to abduct or adduct the arm at the shoulder as necessary.

FIGURE 28-1 A patient positioned for a full brachial plexus exploration. The incisions for a supraclavicular and infraclavicular exposure are marked.

In selected cases, a posterior approach to the plexus is indicated. Indications for this approach include a need for very proximal exposure to the neural foramina and the exiting nerve roots. It is also indicated in patients in whom the anterior neck and chest wall have extensive scarring either from radiation therapy, as in breast cancer treatment, or from a previous plexus operation. This approach will clearly expose the roots, trunks, and divisions but exposure for the cords and nerves is inadequate. As there is a greater potential for damage to the cupula pleurae of the lungs and a subsequent pneumothorax, the surgeon should have equipment for a chest tube on standby.

For the posterior approach, the patient is placed in the prone position (Fig. 28-2). Abdominal bolsters are placed to allow the abdomen to hang freely. An additional bolster should be placed under the patient at the level of the clavicle and upper sternum so that the anterior chest wall is lifted slightly off the operating table. The head is turned to the contralateral side. The contralateral arm is protected and tucked next to the patient’s body. The ipsilateral arm is abducted approximately 30 degrees and bent at the elbow. The elbow is then placed on a padded Mayo stand to the patient’s side. The operating table is slightly tilted in a reverse Trendelenburg position. The surgeon works from above the patient’s head as well as from below the patient’s shoulders and side.

FIGURE 28-2 A patient positioned for a posterior subscapular approach to the brachial plexus. This patient had previous radiation treatments to the anterior neck, making a traditional approach to the plexus not feasible.

For further details of this position and approach, the reader is directed to the paper published by Kline and associates³ or the text by Maniker.⁴

Surgical Exposure

Exposure of the brachial plexus anteriorly may be divided into the supraclavicular and infraclavicular approaches (Fig. 28-3). They can be combined for the full exposure of the plexus or tailored to expose the desired area of the plexus. The supraclavicular portion of the approach exposes the roots, trunks, and proximal portion of the divisions. The infraclavicular portion of the approach exposes the distal portion of the divisions, the cords, and the branches of the brachial plexus.

FIGURE 28-3 The full plexus exposed. This cadaveric exposure has had the clavicle removed for visualization, although it is not usually done in the living. The asterisks indicate the cut ends of the clavicle.

Positioning

The patient is placed in the supine position with the arm abducted on an arm board. The shoulder is abducted and externally rotated. The forearm is placed slightly flexed and in supination. The surgeon works from between the abducted arm and the patient’s body.

Surgical Exposure

The sulcus between the biceps brachii and the triceps is located, palpated, and traced proximally to the anterior axillary fold. The skin is then incised, and the interval between the biceps brachii and triceps is developed and the brachial fascia incised. The median nerve lies lateral to the brachial artery. As there are no branches of the nerve in the arm, it is easily mobilized and traced both proximally and distally.

Surgical Exposure

The incision begins 2 to 3 cm above the medial epicondyle over the medial intermuscular septum. Moving inferiorly, it crosses the elbow flexion crease obliquely and just medial to the biceps brachii tendon (Fig. 28-4). The incision continues distally over the bicipital aponeurosis in a gentle curve toward the midline of the forearm. The incision then moves distally down the forearm, following the interval between the flexor digitorum superficialis and brachioradialis. The incision is opened proximally, and the median nerve is located in the interval between the biceps brachii and the medial intermuscular septum. The nerve is traced into the forearm, and the lacertus fibrosus crosses its path obliquely. The nerve next passes deep to the pronator teres muscle. As the nerve is traced, it dives between the two heads of this muscle. The nerve then moves deep to the arch of the flexor digitorum superficialis, and this arch is divided. The median nerve may then be traced to the wrist, where it lies between the flexor carpi radialis and the flexor digitorum superficialis.

FIGURE 28-4 The incision for exposure of the anterior interosseous nerve.

The anatomy and surgical exposure of the median nerve in the wrist are covered in other chapters.

Positioning

If the radial nerve needs to be exposed only from the triangular interval, where it emerges into the posterior compartment of the arm, to the spiral groove, the patient may be placed in the lateral decubitus, the prone, or the supine position. I find that the lateral decubitus position offers the most comfortable positioning for this exposure. If the nerve must be exposed on both sides of the spiral groove, the posterior and anterior surfaces of the arm must be available for exposure. Once again, the patient may be positioned in the lateral decubitus, prone, or supine position. In the lateral position, the surgeon must be able to move freely from the posterior aspect of the arm to the anterior aspect. In the supine position, the arm must be able to swing freely over the patient’s body so that the posterior aspect of the arm is easily exposed.

Surgical Exposure

The incision is made on the posterolateral aspect of the arm. An incision in a line connecting the acromion and olecranon, both of which are easily palpated, exposes the sulcus between the long and lateral heads of the triceps (Fig. 28-5). The fascia is incised along the lateral border of the long head of the triceps. The interval between the long and lateral heads is divided bluntly. Retraction of the superficial muscle exposes the radial nerve and profunda brachii artery. The radial nerve may then be traced distally as it passes from the posterior compartment into the anterior compartment of the arm.

FIGURE 28-5 A patient in the lateral decubitus position for exposure of the radial nerve. Note that in this position, the surgeon may move from the posterior aspect of the patient to the anterior aspect of the patient to reach the radial nerve distal to the spiral groove.

Positioning

The patient is placed in the supine position with the arm on an arm board. The shoulder is abducted and externally rotated. The hand is fully supinated. The operator is most comfortable superior to the arm, just lateral to the neck and head of the patient.

Surgical Exposure

The incision begins 3 to 4 cm proximal to the elbow flexion crease in the interval between the biceps brachii and brachioradialis muscles. It crosses the elbow flexion crease obliquely and then curves down onto the forearm lateral to the biceps brachii tendon. The incision should reach the midline of the forearm 4 to 5 cm distal to the elbow flexion crease and then continue distally in the forearm just radial to the midline. The nerve may be identified in the interval between the biceps and brachioradialis just proximal to the elbow flexion crease. The nerve is then traced down into the plane between the brachioradialis and extensor carpi radialis longus muscles. The posterior interosseous nerve should be traced distally as it passes under a vascular leash of vessels, inferior to the arcade of Frohse and into the supinator muscle.⁵

Positioning

The patient is placed in the supine position with the arm on an arm board. The shoulder is abducted and externally rotated. The hand and forearm are fully supinated, and the elbow is gently flexed. The surgeon works from a position between the abducted arm and the patient’s body. A seated position is often the most comfortable for operating.

Surgical Exposure

Exposure of the nerve within the cubital tunnel begins with a skin incision 5 cm proximal to the medial epicondyle that curves gently up and over the epicondyle (Fig. 28-6). The incision then continues down onto the forearm for another 4 to 5 cm. The posterior cutaneous nerve of the forearm may cross the operative field, and it should be identified and protected. Once the skin is retracted, the nerve may be found within the cubital tunnel and traced both proximally and distally as needed. Further details may be found in Chapter 28.

FIGURE 28-6 A patient positioned with an incision drawn for an ulnar nerve exposure. The asterisk marks the palpated olecranon.

Anatomy

The ventral rami of the fourth lumbar to third sacral nerve roots unite to form the sciatic nerve. In the lesser pelvis, the nerve lies anterior to the piriformis muscle. Just caudad to this muscle, the nerve enters the buttock through the sciatic foramen. The nerve then moves laterally in an oblique direction beneath the gluteus maximus muscle toward the midline of the posterior aspect of the leg. The nerve descends in the thigh close to the midline. In the majority of individuals, the nerve divides into tibial and common peroneal branches at the mid to distal third of the thigh.

Once divided, the common peroneal nerve then moves obliquely across the distal thigh to travel on the lateral aspect of the popliteal fossa. Close to its origin, one or more branches of the peroneal nerve leave to contribute to the formation of the sural nerve. The tibial nerve will also contribute to the formation of the sural nerve. Moving distally, the nerve then crosses the lateral head of the gastrocnemius muscle to reach the area just posterior to the fibular head. Once it curves over the posterior rim of the fibular head, it enters a tunnel formed by the two heads of the peroneus longus muscle and the fibular neck. The common peroneal nerve divides into superficial and deep branches. The superficial portion of the nerve takes a relatively straight course to innervate the peroneus longus muscle and continues descending distally to innervate the peroneus brevis muscle.

The deep peroneal nerve, once it is past the neck of the fibula and after it passes beneath the fibrous lateral edge of the peroneus longus, gives off geniculate branches and branches to the tibialis anterior. The nerve descends in the anterior compartment of the leg lateral to the tibialis anterior. In the very distal leg, the nerve divides into medial and lateral terminal branches.

The tibial nerve continues the line of the sciatic nerve after its bifurcation in the mid to distal third of the thigh. In the popliteal fossa, the tibial nerve becomes more superficial, first lying posterior and lateral to the popliteal vessels and then crossing obliquely to their medial side before moving into the leg. It travels distally in the leg between the gastrocnemius and the tibialis posterior muscles. Finally, the nerve curves anteroinferiorly into the sole of the foot behind the medial malleolus, deep to the flexor retinaculum and between the tendons of the flexor hallucis longus and the flexor digitorum longus. The nerve in the so-called tarsal tunnel ends at this level as it divides into medial and lateral plantar nerves. A calcaneal branch is also given off at this level. The sural nerve, a cutaneous branch of the tibial nerve, arises at the mid or lower aspect of the popliteal fossa. It gives off branches to the skin on the lower lateral leg and heel.⁶ The terminal portion of the sural nerve is the lateral dorsal cutaneous nerve that supplies sensation to the lateral foot and small toe.

Positioning

After intubation and induction of general endotracheal anesthesia on a stretcher, the patient is placed on the operating table in the prone position on abdominal bolsters. The arms are brought forward on arm boards. The ipsilateral buttock and leg are draped.

Surgical Exposure

A curvilinear incision in a reverse question mark shape is fashioned. The stem of the question mark will follow the midline of the posterior aspect of the thigh; the curve will follow the inferior margin of the gluteus muscle around the contour of the buttock and up onto the lateral aspect of the buttock (Fig. 28-7). After the skin is incised, the inferior margin of the gluteus maximus muscle is located. At the midline of the leg, just inferior to the edge of the gluteal muscle, a fat pad is found. The sciatic nerve is located within this fat. For more proximal exposure, the gluteus muscle must be divided. A cuff of muscle both medially and laterally must be left for reattachment at the completion of the case. Once the muscle is divided, it is reflected in a unit medially for exposure of the sciatic nerve in the buttock. Exposure of the sciatic nerve more proximal to the sciatic notch will require an abdominal extraperitoneal approach.⁷

FIGURE 28-7 A patient positioned with an incision drawn for a sciatic nerve exposure. The patient is in the prone position on abdominal bolsters. The incision may be extended distally as needed.

In exposure of the nerve distally, the posterior femoral cutaneous nerve travels superficially and should not be confused with the sciatic nerve. For more distal exposure, the incision may be extended distally along the posterior midline of the thigh, tracing the nerve beneath the long head of the biceps femoris muscle and on to its division into the common peroneal and tibial nerves (Fig. 28-8).

FIGURE 28-8 The sciatic nerve fully exposed.

Positioning

The patient is placed on the operating table in the prone position on abdominal bolsters. The arms may be either tucked to the side or brought forward on arm boards. The midline of the popliteal fossa and just superior to it should be marked. The biceps femoris tendon can usually be palpated at the lateral aspect of the popliteal fossa and should also be marked. Last, the fibular head should be palpated and marked.

Surgical Exposure

The skin incision is laid out so that the proximal end is just superior to the popliteal fossa. In the medial-lateral direction, it lies midway between the biceps femoris tendon and the midline of the fossa. Care should be taken in making the skin incision, particularly around the fibular head, as the nerve is surprisingly superficial. As the nerve is followed distally beyond the popliteal fossa, a thick fascial covering is encountered that is contiguous with the fibrous lateral edge of the peroneus longus muscle. This edge should be incised, revealing a portion of the muscle. This muscle may also be incised to expose the nerve further. Dissection should continue to fully expose and identify both the superficial and deep branches of the nerve. The deep branch must be traced around the neck of the fibula.

Positioning

The tibial nerve at the level of the popliteal fossa is explored in the prone position. After intubation and induction of general endotracheal anesthesia, usually on a stretcher, the patient is placed on the operating table on abdominal bolsters. The arms may be either tucked to the side or brought forward on arm boards. The midline of the popliteal fossa and just superior to it should be marked.

Surgical Exposure

The patient is in the prone position with the midline marked. The incision begins at the midline and extends distally to run obliquely across the popliteal fossa. It then cuts laterally across the fossa and continues down the leg just medial to the midline. Once the skin and subcutaneous tissue are divided, the tibial nerve may be located in the midline in close approximation to the popliteal artery and vein. Much beyond the popliteal fossa, the nerve is difficult to expose and will require a medial leg incision.

Positioning

The patient is placed in the supine position with a bolster under the contralateral buttock.

Surgical Exposure

The incision runs in a curvilinear fashion in a radius approximately 2 to 3 cm around the posterior aspect of the medial malleolus. The incision should also extend at least 5 cm proximal to the malleolus up into the leg and 5 cm distal to the malleolus out onto the foot, paralleling the medial border of the plantar foot pad. The skin is incised, and after a small amount of dissection, the tendons that course through the tunnel are immediately apparent. Just posterior to these tendons, the nerve, posterior tibial artery, and vein will be located. The artery and vein are often intertwined with the nerve at this level, making the dissection more difficult. As the nerve is traced distally, further sectioning of the flexor retinaculum reveals the nerve dividing into medial and lateral plantar nerves and a calcaneal branch. The proximal belly of the abductor hallucis muscle may overlie the area where the nerve divides. The belly of the muscle must be partially sectioned to visualize this last portion of the nerve.

Positioning and Surgical Exposure

Positioning for exposure of the sural nerve will most often depend on the reason for operation. If sural nerve exposure is required for harvesting a cable graft and the primary nerves to be operated on require the body to be placed in a supine position (e.g., brachial plexus, femoral nerve), the sural nerve may be harvested from a supine position. It is somewhat awkward to perform in this position, particularly as the nerve is traced more proximally, but it can be accomplished. The knee should be bent and the leg tilted medially to facilitate exposure. An incision is laid out two fingerbreadths posterior and two fingerbreadths superior to the lateral malleolus. If sural nerve exposure is required for operations that are performed in the prone position (e.g., harvesting of a cable graft for sciatic nerve), the sural nerve is easily exposed through the same incision as outlined for a supine position. This positioning is much less awkward for the operator, but the exposure and anatomy are identical to those encountered in supine positioning (Fig. 28-9).

FIGURE 28-9 A patient positioned for exposure of the sural nerve. The lateral malleolus is marked.

The nerve and muscle tendon are fairly superficial, and care should be exercised accordingly in making the incision. The skin and subcutaneous tissue are exposed. If the nerve is not immediately visible, it will lie slightly anterior in the fat layer just beneath the subcutaneous tissue. Care should be taken not to disrupt the lesser saphenous vein that travels with the nerve. If it is traced proximally, the nerve may be followed, accompanied by the lesser saphenous vein, until its disappearance beneath the two heads of the gastrocnemius muscle.