Ie thoracic outlet; bounded by 1st T vertebra, first ribs & their cartilages, and manubrium.
- scalenus anterior is key anatomical landmark
Arises: Anterior tubercles C3-6; slender tendons end-end with longus capitus
Inserts: Inner upper border 1st rib (scalene tubercle)
Innervation: Branches anterior rami C4,5,6
Action: Weak flexor, rotator, stabilises 1st rib, respiration.
Phrenic n: down obliquity of scalenus ant; plastered there by prevertebral fascia (Pl 28 upper, 182)
- leaves medial muscle border low ¨ ant to subclavian a, behind vein
- on subpleural membrane ¨ medial to lung apex ¨ front of vagus ¨ sup mediastinum
Asc cervical a: off inf thyroid or thyrocervical trunk ¨ up fascia medial to phrenic n (28)
Transverse cervical and suprascapular: off thyrocervical trunk ¨ lateral b/n sc. ant and c. sheath.
Vagus: in sheath ¨ descends ant to subclav artery; R gives ¨ recurrent laryngeal br
- this hooks under the artery ¨ upwards
- vagus inclines posteriorly ¨ medial surface of lung apex ¨ sup mediastinum (195)
IJV: surrounded by deep cervical lymph nodes.
Subclavian vein: grooves 1st rib lower than scalenus ant insertion ¨ IJV at its medial border
- thus = brachiocephalic vein (see 195)
- thoracic duct on L and right lymph duct on R enters at confluence of these veins
Infraclavicular, from 2cm below midline of clavicle ¨ aim towards jugular notch
- pierce clavipectoral fascia (174) ¨ enter vein
Medial edge of scalenus anterior forms pyramidal space with longus colli
- prevertebral fascia is attached to bone at opposing margins (no fascial roof)
- base = subclavian artery, apex = carotid tubercle of transverse process C6
- CCA (and IJV laterally) lies deep to SCM in the front of the space
Space contains:
Inferior cervical ganglion, with vertebral artery and vein in front.
Inf thyroid artery runs medially curving up over apex of the space (C6 level)
- sympathetic chain (and usually middle ganglion) in front of artery.
Thoracic duct makes a similar convexity arching over lung apex and subclavian artery.
Relationship of scalenus anterior to subclavian described in three parts:
1st part: medial to scalenus anterior, arches over suprapleural membrane, grooving apex of lung.
3 branches: vertebral artery: from upper convexity of subclavian ¨ foramen of transverse C6.
- accompanying sympathetic nerve runs up behind this artery, with ansa subclavia connecting loop between middle and inferior cervical ganglia in front of subclavian artery.
- Remember R recurrent nerve loops under R subclavian, thoracic duct loops over the L.
Thyrocervical trunk: lateral to vertebral artery, also upper surface subclavian.
- divides immediately ¨ transverse cervical, suprascapular and inferior thyroid
Internal thoracic: from lower surface subclavian ¨ over lung apex (crossed by phrenic n)
Vertebral vein: from foramen in transverse process C6 ¨ in front of vertebral & subclavian arteries
- empties into brachiocephalic
- has companion vein from foramen of transverse process C7; passes behind subclavian; also ¨ brachiocephalic
Subclavian artery and anterior rami of brachial plexus separate scalenus ant from scalenus med.
2nd part: (of subclavian) lies behind scalenus anterior.
1 branch: costocervical trunk: passes back across suprapleural membrane to first rib ¨ divides:
- superior intercostal artery: enters thorax across neck of first rib
- deep cervical artery: ascends back behind transverse process C7
3rd part: and brachial plexus emerge from lateral border to scalenus anterior
- lie behind the prevertebral fascia on floor of posterior triangle.
1 branch: Dorsal scapula: runs laterally through plexus then deep to levator scapulae ¨ the scapular anastomosis. Frequently replaced by deep branch of transverse cervical artery.
Surface marking: along a line from SC jt ¨ middle of clavicle and about 2cm above it.
Expose by detaching clavicular head SCM from clavicle, then detaching scalenus anterior from 1st rib.
- donŐt damage the phrenic nerve
Fibrous bands / cervical ribs can compress the subclavian artery
Elevation of 1st rib by scalenus anterior can aggravate thoracic outlet syndrome
- may need to divide the muscle surgically as part of treating that condition.
Arises: lateral ends of transverse processes atlas and axis and posterior tubercles other cervical vertebrae
Inserts: quadrangular area b/n neck and subclavian groove of first rib.
Small unimportant. Posterior tubercles lower c vertebrae ¨ second rib.
Nerves: segmentally by anterior rami C3-8
Actions: medius= lateral flexor, can elevate for respiration if required.