Scalene Tubercle

tuberculum musculi scaleni anterioris

The scalene tubercle is a small bump on the inner edge of the upper surface of the first rib, where the anterior scalene muscle inserts. It separates two shallow grooves on the rib: the subclavian vein crosses in front of it and the subclavian artery and lowest trunk of the brachial plexus cross behind it. This makes it a central landmark of the thoracic outlet.

Anatomical Data

Structure & Landmarks

Articulations	No joint; part of the first rib
Landmarks	Insertion of the anterior scalene Groove for the subclavian vein in front Groove for the subclavian artery and lower brachial plexus behind Inner (medial) border of the first rib
Ossification	Part of the first rib, which ossifies in cartilage from a primary centre in the shaft, with secondary centres for the head and tubercle appearing at puberty.

Clinical Relevance

Clinical Notes

The scalene tubercle sits at the heart of thoracic outlet anatomy. A tight or enlarged anterior scalene, or an extra cervical rib or fibrous band nearby, can compress the brachial plexus or subclavian artery behind it, while compression of the subclavian vein in front can cause effort thrombosis. In surgery for thoracic outlet syndrome the anterior scalene is divided at this tubercle and the first rib may be removed.

Pathology

Common Injuries & Conditions

Thoracic Outlet Syndrome

Compression of the brachial plexus or subclavian vessels as they cross the first rib on either side of the scalene tubercle, causing arm pain, tingling, weakness or circulation changes.

Effort Thrombosis (Paget-Schroetter Syndrome)

Clotting of the subclavian vein where it crosses the first rib in front of the scalene tubercle, typically after repetitive overhead activity.

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