Sternocleidomastoid

Clinical Notes

• SCM shares CN XI innervation with the trapezius — they are the only two muscles supplied by this cranial nerve. Because CN XI is a cranial nerve, SCM hypertonicity is influenced by central and emotional pathways, not just postural mechanics.

• One of Janda's "tight" muscles in conditions/upper-crossed-syndrome. SCM shortening pulls the head forward and extends the upper cervical spine, creating the classic "chin poke" posture.
• SCM TrPs produce proprioceptive disturbances — dizziness, spatial disorientation, and balance problems. This is the SCM's unique contribution to conditions/cervicogenic-dizziness.
• Major muscle involved in conditions/whiplash — the rapid flexion-extension mechanism loads the SCM eccentrically, producing significant post-injury spasm and TrP activation.
• SCM TrPs contribute to conditions/tension-headache — the vertex, frontal, and periorbital referral patterns overlap with tension-type headache.
• Relevant to conditions/torticollis — unilateral SCM shortening or spasm produces the classic head-tilt (ipsilateral lateral flexion) with chin rotation to the contralateral side.

• SCM is often bilaterally hypertonic in forward-head posture. The sternal heads are typically more prominent and tighter than the clavicular heads. Pincer palpation frequently reveals multiple TrPs in both divisions, and clients are often surprised by the intensity of tenderness ("I didn't know that was tight").
• In clients with chronic headache, the sternal division TrPs commonly reproduce their headache pattern during palpation — this is a diagnostic finding.

• Pincer compression is the primary technique — grasp the muscle between thumb and fingers and apply sustained compression to each TrP for 30–60 seconds. The client may report referral to the forehead, eye, ear, or vertex during compression.
• The muscle releases relatively quickly with pincer technique compared to many other cervical muscles. Post-treatment, clients often report immediate headache reduction and a sense of the head feeling "lighter."
• Caution with treatment intensity — post-treatment dizziness is possible due to proprioceptive effects. Have the client sit up slowly after supine SCM work.

• The carotid artery, internal jugular vein, and vagus nerve are deep and medial to the SCM in the carotid sheath. Never apply sustained deep pressure medially — always use pincer palpation, lifting the muscle laterally away from the neurovascular bundle.
• The external jugular vein crosses superficially over the SCM — visible in most clients. Avoid compressing it.
• The spinal accessory nerve (CN XI) crosses the posterior triangle after emerging from the posterior border of the SCM — it is vulnerable approximately one-third of the way down from the mastoid process.
• If the client experiences nausea, dizziness, or visual disturbance during SCM treatment, stop and allow recovery. These are proprioceptive effects from TrP referral, not vascular compromise, but treatment should be gentler.

• In upper crossed syndrome, SCM shortens along with upper trapezius, levator scapulae, and suboccipitals. The bilateral contraction pattern of SCM is complex — it flexes the mid-cervical spine while extending the upper cervical spine. This contributes directly to the forward-head posture with chin poke that characterizes upper crossed syndrome.

• SCM TrPs can produce a remarkable autonomic referral: tearing of the ipsilateral eye, conjunctival redness, and rhinorrhea (runny nose). If a client reports that their "cold" or "allergies" always seem to be on one side, palpate the ipsilateral SCM — the symptoms may be TrP-driven autonomic phenomena, not infectious or allergic.