WHILE engaged recently in investigating another problem of the upper thorax upon the cadaver,* I came almost by accident on a relatively simple method of ligaturing the first stage of the left subclavian artery. After demonstrating this method upon several occasions in the School of Anatomy of the Royal College of Surgeons in Ireland, I found that another posterior approach had been used by Sherrill in 1910 and published by him in 1911.l Only 21 cases of ligature of the left subclavian in its first stage are on record, and 7 of these were performed since Sherrill's operation, which is the solitary instance of a posterior approach to this forbidding artery.t
The anterior approach to the left subclavian is notoriously difficult ; a formidable array of nerves and vessels screen the artery. Through these but narrow access is gained, even after resection of the inner end of the clavicle, the first rib cartilage, and part of the manubrium. In actual practice, too, the upward bulge of an aneurysm into the neck will not simplify the surgeon's task. The posterior route has the merit of simplicity, and surgery advances through simplification to security. I thus venture to describe in detail the route upon which I chanced.
The transverse process of the second dorsal vertebra, and three inches of the second rib, measured from its head, were removed from the left chest of a hunchbacked cadaver after carefully separating the rib from the parietal pleura. In effecting this separation the pleural dome was slightly depressed, and the first stage of the left subclavian artery appeared in the field. Further separation and depression of the pleura exposed the artery from its point of origin a t the aortic arch to the first rib, and definition of all its branches except the thyro-cervical trunk was easy. These structures were rendered surprisingly superficial by the kyphotic deformity of the back. Examination of normal subjects showed that in them the left subclavian artery and its branches are further from the dorsal surface of the trunk. The first stage of the artery, however, is just as easily tied in spite of the depth a t which it lies, for once the lung and pleura have been depressed, the artery, except for a delicate sheath, lies naked in the thoracic cavity, and is immediately accessible. There is no barrier of vein or nerve ; the vessel is directly under the finger. With a suitable needle it is easy t o pass a ligature round the artery, and a t my request this was done by students who had never previously tied any vessel in the body. Before describing the steps of the operation, certain anatomical points must be dealt with.
ANATOMICAL CONSIDERATIONS.
T h e Muscular Planes.-The part of the second left rib which is removed lies between the scapula and the vertebral spines : it is concealed by muscles which anchor the scapula to the vertebrae. The trapezius is spread over the rhomboids, which cover the upper serratus posterior, Division of these muscles allows the surgeon to widen the space * " Posterior Route for Excision of the Cervico-dorsal Ganglion of the Sympathetic." (Section of Surycry, Royal Academy of Medicine in Ireland, April 28, 1922.) f Sherrill raised a flap of skin and muscle and removed about three inches of the 2nd, 3rd, and 4th ribs. After pushing aside the pleura, the artery was exposed at the level of the 4th dorsal vertebra as it left t h e aorta.