Posterior Scalene

Origin, Insertion, Action, Innervation

Origin: Posterior tubercles of the transverse processes of C5–C7
Insertion: External surface of the second rib
Action:
Primary: Lateral flexion of the cervical spine (ipsilateral)
Elevation of the second rib (accessory muscle of respiration)
Innervation: Ventral rami of C6–C8

Palpation Guide

Client position: Supine with head in neutral.
Landmark sequence:

Locate the middle scalene. The posterior scalene lies immediately behind it, in the groove between the middle scalene and the anterior border of the upper trapezius.
Place your fingertip posterior to the middle scalene, at approximately C6–C7 level. The posterior scalene is a thin, small muscle that is difficult to isolate from the middle scalene by palpation alone.
Trace inferiorly — it descends to the second rib, not the first rib. This lower insertion distinguishes it from the middle scalene.

Tissue feel: The smallest of the three scalenes. It feels like a thin cord posterior to the more substantial middle scalene. In many clients, it is indistinguishable from the middle scalene by palpation.
Confirmation test: Resisted ipsilateral lateral flexion engages all three scalenes simultaneously. The posterior scalene cannot be reliably isolated by palpation or testing alone — it is assessed as part of the scalene group.
Common errors:
Attempting to isolate the posterior scalene from the middle scalene — in practice, these two muscles are assessed and treated together.
Confusing the posterior scalene with levator scapulae — levator is larger, lies more posteriorly, and attaches to the scapula, not the ribs.
Working too deeply in the posterior triangle where the spinal accessory nerve is superficially vulnerable.

Trigger Point Referral

Common TrP locations: The primary TrP is in the mid-belly at approximately C6 level, behind the middle scalene.
Referral pattern: Refers to the lateral arm (deltoid region) and the dorsal forearm. May also produce a deep aching in the upper lateral chest.
Clinical significance: The posterior scalene's referral to the lateral arm is easily confused with axillary nerve distribution (C5–C6 myotome). In combination with anterior and middle scalene referral, the entire group can mimic cervical radiculopathy from C5 through C8.

Trigger point referral diagram — coming soon

Image coming soon. For visual reference, see [Scalenes at TriggerPoints.net](http://www.triggerpoints.net/muscle/scalene).

Clinical Notes

Common conditions:

Participates in the scalene contribution to conditions/thoracic-outlet-syndrome, though its role is secondary to the anterior and middle scalenes because it does not border the interscalene triangle directly.
Elevation of the second rib may contribute to upper thoracic rib dysfunction and localized intercostal pain.
In chronic chest-breathers, the posterior scalene is hypertonic along with the anterior and middle scalenes.

What you'll typically find:

The posterior scalene is rarely the primary clinical finding — it is almost always treated as part of the scalene group. When the anterior and middle scalenes are hypertonic, the posterior scalene follows.
Students should assess and treat all three scalenes as a functional unit rather than attempting to differentiate individual dysfunctions.

Treatment effects:

Same principles as the other scalenes — short-duration sustained compression, monitoring for arm paresthesia. Because the posterior scalene is behind the brachial plexus (not directly bordering the interscalene triangle), the neurovascular risk is slightly lower than with the anterior scalene.
Responds to the same stretching and respiratory retraining protocols as the rest of the group.

Cautions:

The spinal accessory nerve (CN XI) crosses the posterior triangle superficially — avoid prolonged deep pressure in the space between SCM and the upper trapezius.
While the posterior scalene is not a direct border of the interscalene triangle, aggressive pressure can still compress the brachial plexus indirectly.

Clinical pearl:

The posterior scalene is clinically important not for its own dysfunction but because it anchors the second rib. If the second rib is elevated and fails to descend during exhalation, the posterior scalene may be the holding muscle. Rib mobilization (downward pressure on the second rib during exhalation) combined with posterior scalene release can resolve localized upper thoracic pain.

Assessment

Manual muscle testing:

Cervical lateral flexion: Client supine. Resisted ipsilateral lateral flexion tests all three scalenes as a group. Posterior scalene cannot be isolated.

Stretch test:

Cervical contralateral lateral flexion with slight extension: Same protocol as for the middle scalene. All three scalenes stretch together.

Related special orthopedic tests:

Adson's test — scalene compression of the subclavian artery
Roos test (EAST) — neurogenic thoracic outlet syndrome

Muscle Groups

Scalene group (anatomical):

Cervical lateral flexors (functional):

Accessory respiratory muscles (functional):

Related Muscles

Synergists for cervical lateral flexion:

anatomy/muscles/anterior-scalene — forms the anterior wall of the interscalene triangle
anatomy/muscles/middle-scalene — largest scalene; forms the posterior wall of the interscalene triangle

Antagonists:

Contralateral scalenes — opposing lateral flexion

Clinically related:

anatomy/muscles/levator-scapulae — lies posterior to the posterior scalene; both contribute to cervical lateral flexion

Key Takeaways

Smallest scalene — rarely the primary clinical finding; always assess and treat as part of the scalene group.
Attaches to the second rib, not the first — this distinguishes it from the anterior and middle scalenes.
A holding muscle for second-rib elevation — relevant when upper thoracic rib dysfunction is the complaint.