This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The head is to be turned strongly to the opposite side and the shoulder depressed. This lowers the clavicle and raises the omohyoid muscle and therefore gives more room to work. The skin is to be drawn down and an incision 7.5 cm. long made on the clavicle. The drawing down of the skin is done to avoid wounding the external jugular vein. This vein is really fastened to the deep fascia, and the skin, platysma, and superficial fascia slide over it. On releasing the skin it slides up above the clavicle. The middle of the incision should be a little to the inside of the middle of the clavicle. The deep fascia is to be incised and the clavicular origin of the sternomastoid and trapezius muscles cut to the same extent as the superficial incision. The length of the adult male clavicle is about 15 cm. (6 in.).
The clavicular origin of the sternomastoid extends out on the clavicle one-third of its length. The trapezius inserts into the outer third. This leaves the middle third or 5 cm. of the clavicle on its upper surface free from muscles. As the incision is 7.5 cm. long this necessitates the division of 2.5 cm. (1 in.) of muscle, and as the middle of the incision is a little to the inner side of the middle of the clavicle this will make it necessary to divide more of the clavicular origin of the sternomastoid than of the trapezius. After the division of the deep fascia, fat and veins are encountered. The scalenus anticus muscle has the subclavian vein in front of it and the artery behind, therefore the vein must be attended to before a search is made for the edge of the scalene muscle. The veins to be encountered are the external jugular vein, which empties into the subclavian in front of or to the outer side of the anterior scalene muscle, and its tributaries, the suprascapular and transverse cervical veins, as well as the anterior jugular and a communicating branch from the opposite side of the neck. The cephalic vein not infrequently sends a communicating branch over the clavicle to empty into the external jugular. The fat is to be picked away with forceps; the veins are to be held out of the way with a blunt hook or ligated and cut. The suprascapular artery may be seen close to or under the clavicle. The transverse cervical artery may perhaps be above the level of the wound. The omohyoid muscle may or may not be seen, as its distance from the clavicle is quite variable. The transverse cervical and suprascapular arteries are not to be cut, as they are needed for the collateral circulation. As was mentioned in speaking of the ligation of the external carotid artery, so also here it is not always easy to distinguish between arteries and veins. The veins being disposed of, the anterior scalene muscle is to be sought at the internal portion of the wound. It runs somewhat like the lower portion of the sternomastoid, the posterior edges of the two muscles coinciding. The phrenic nerve runs down first on the anterior surface and then on the inner surface of the scalenus anticus. The edge of the muscle being recognized, by following it down the finger feels the first rib. The artery lies on the first rib immediately behind the muscle and the vein immediately in front of the muscle. The tubercle on the first rib may not be readily felt because the muscle is inserted into it. The prevertebral fascia coming down the scalenus anticus muscle passes from it to the subclavian artery, forming its sheath; hence, as pointed out by George A. Wright, of Manchester (Annals of Surgery, 1888, p. 362), the edge of the muscle may not readily be distinguished and the brachial plexus is a better guide. This is above the artery and the lower cord of the plexus lies directly alongside of the artery. It is closer to the artery above and to its outer side than the subclavian vein is below and to its inner side. The greatest care should be exercised in passing the aneurism needle around the artery. The vein is not so much in jeopardy as are the pleura and lowest cord of the brachial plexus, hence the needle is passed from above down between the nerve and the artery and brought out between the artery and vein.
Wounding of the pleura may cause collapse of the lung and later a septic pleurisy, while including the nerve will cause severe pain, etc.
Collateral Circulation after Ligation of the Third Portion of the Subclavian Artery. - (1) Internal mammary with superior thoracic and long thoracic. (2) The posterior scapular branch of the suprascapular with the dorsalis branch of the subscapular. (3) Acromial branches of suprascapular with acromial branch of acromial thoracic. (4) A number of small vessels derived from branches of the subclavian above with axillary branches of the main axillary trunk below (Gray).