The scalenus minimus is a small and inconstant muscle present in approximately 36 percent of people, arising from C7 and inserting on the first rib and the cervical pleural dome (Sibson fascia). Its most clinically significant function is tensioning the Sibson fascia over the lung apex during inspiration to prevent the pleural dome from inverting. When absent, the function is performed by scalenus minimus-like fibres from the anterior scalene.
| Origin | Anterior tubercle of the transverse process of C7 |
|---|---|
| Insertion | Inner aspect of the first rib and the pleural dome (Sibson fascia) |
| Nerve Supply | Ventral ramus of C7 or C8 |
| Blood Supply | Ascending cervical artery |
| Actions | Tenses the pleural dome (Sibson fascia) to prevent it collapsing during forced inspiration; Elevates the first rib during deep inspiration |
|---|
The cervical pleural dome extends above the clavicle and is vulnerable to pneumothorax from needle trauma at the root of the neck — central line insertion, brachial plexus blocks, and deep cervical injections. The scalenus minimus tension of the Sibson fascia helps prevent inadvertent pneumothorax by maintaining structural support over the lung apex.
The scalenus minimus is of surgical importance in thoracic outlet decompression where its fibres, when present, may contribute to brachial plexus compression alongside the anterior scalene. Its variable presence means surgeons must assess for it during scalenectomy procedures. Sibson fascia itself is the landmark for identifying the apex of the pleural cavity during neck surgery.
Not individually palpable due to its small size and deep position behind the anterior scalene.
Inconstant scalenus minimus contributing to thoracic outlet compression when hypertrophied, requiring surgical resection during scalenectomy for thoracic outlet syndrome.
