Vein in front of the scalene tubercle, artery and lower trunk behind it
Mnemonic
“Two grooves and a tubercle”, from front to back across the superior surface:
- Subclavian vein, in the anterior groove, in front of scalenus anterior
- Scalene tubercle, for the insertion of scalenus anterior
- Subclavian artery and the lower trunk of the brachial plexus, in the posterior groove, behind scalenus anterior
“Vein in front, artery and nerves behind, with the muscle between them.”
That arrangement defines the thoracic outlet: compression there gives neurogenic thoracic outlet syndrome (much the commonest, affecting the lower trunk, C8 and T1), venous (Paget-Schroetter effort thrombosis) or arterial presentations.
A cervical rib compresses the same lower trunk and subclavian artery, giving wasting of the intrinsic hand muscles and an ulnar sensory pattern.
The first rib is short, broad, flat and the most curved, has a single articular facet on its head, and its fracture indicates severe trauma because it is well protected.
Expansion
Working from front to back across the superior surface of the first rib:
- Subclavian vein (in the anterior groove)
- Anterior scalene muscle, inserting on the scalene tubercle
- Subclavian artery (in the posterior groove)
- Lower trunk of the brachial plexus
The order is the same “vein, then artery, then nerve” sequence seen elsewhere in the body. It explains why a cervical rib or a fibrous band compressing the structures behind anterior scalene produces arterial and neurological symptoms, while venous thoracic outlet obstruction is a separate anterior problem.