The SCM: Anatomy, MSR Procedures, and Rehabilitation
The sternocleidomastoid (SCM) is a paired, superficial muscle of the anterolateral neck. Its sternal and clavicular heads arise from the manubrium and medial clavicle and ascend to the mastoid process and lateral superior nuchal line. This oblique course makes the SCM a palpable landmark for distinguishing the anterior and posterior cervical triangles.
For the practitioner, the anatomy beneath and around the SCM matters as much as the muscle itself. The carotid sheath lies deep and medial to it, the deep cervical lymph nodes follow the internal jugular vein, and cutaneous branches of the cervical plexus emerge near the midpoint of its posterior border. These relationships help us orient palpation, select an appropriate MSR contact, and recognize findings that warrant further assessment.
Article Index
Anatomy and Biomechanics
The sternocleidomastoid (SCM) has two distinct inferior heads. They are easiest to distinguish near the sternoclavicular joint and converge as they ascend toward the skull.
Attachments and Innervation
Sternal head. The narrower head arises from the anterior surface of the manubrium.
Clavicular head. The broader head arises from the superior surface of the medial third of the clavicle.
Superior attachment. The two heads converge toward the lateral surface of the mastoid process and the lateral half of the superior nuchal line.
Innervation. The spinal accessory nerve (CN XI) provides the principal motor supply. Cervical branches from C2 and C3 carry sensory fibres, including proprioceptive input.
Biomechanical Role
Unilateral contraction. The SCM assists ipsilateral lateral flexion and contralateral rotation. The left SCM helps turn the face to the right and can contribute to side-bending to the left.
Bilateral contraction. The SCM can contribute to flexion in the lower cervical spine while producing extension at the upper cervical and craniovertebral levels. The relative contribution depends on the starting position and how the other cervical muscles control the movement. This helps explain how the head can move forward while the chin lifts.
Accessory inspiration. With the head and neck stabilized, the SCM can help elevate the manubrium and clavicle when inspiratory demand increases.
Relationships That Matter for Palpation
The external jugular vein crosses superficially over the SCM, while the internal jugular vein runs deep to it within the carotid sheath. Cutaneous branches of the cervical plexus emerge near the midpoint of its posterior border. Identifying the muscle belly and its borders helps orient contact in a region where the tissues superficial, deep, and adjacent to the muscle differ.
Functional Kinetic Chains
During a right head turn, the left SCM and right splenius capitis can work together. The side of the movement therefore tells you which muscles can contribute, even when the patient feels symptoms on only one side.
Direct Myofascial Connections
Investing cervical fascia. The investing layer of the deep cervical fascia encloses the SCM anteriorly and the trapezius posteriorly. Both muscles sit within the same fascial layer, which forms the roof of the posterior cervical triangle between them. This relationship helps orient the practitioner to tissue depth in the lateral neck.
Synergists
Contralateral splenius capitis. The SCM turns the head away from its own side, while the opposite splenius capitis turns the head toward its own side. Both can contribute to the same head turn.
Ipsilateral scalenes. The scalenes and SCM can assist side-bending toward the same side. When the neck is stabilized and inspiratory demand rises, they can also assist inspiration. The scalenes act on the upper ribs, while the SCM acts on the manubrium and clavicle.
Stabilizers
Deep cervical flexors. The longus capitis and longus colli contribute to control during low-load craniocervical flexion. During a gentle chin nod, observe whether the patient can maintain the small nod or shifts into a larger neck-flexion effort. Interpret visible SCM activity in the context of the task and the rest of the examination.
Antagonists
Ipsilateral splenius capitis. On the same side, the SCM and splenius capitis pull in opposite directions during axial rotation, yet both can assist lateral flexion toward that side. The direction of the test determines which relationship you are examining.
Assessment and Clinical Reasoning
When a patient feels pulling along the left side of the neck during a right head turn, the left SCM deserves examination. The right splenius capitis also contributes to that turn. Compare the response to movement, resistance, and local palpation to decide whether the SCM warrants treatment.
Compare Motion, Force, and Local Symptoms
Active motion. Compare rotation and lateral flexion to both sides. Record the direction, range, and location of familiar symptoms. Where indicated, compare passive motion to see whether the symptoms change when the patient no longer produces the movement.
Resisted rotation. To bias the left SCM, ask the patient to turn to the right against graded resistance. Use light palpation over the superficial muscle belly to confirm the contraction and compare sides. Distinguish familiar pain with preserved force from an unexplained reduction in force. Resisted rotation recruits several muscles, so interpret it alongside the rest of the examination.
Low-load control. If the concern is cervical motor control, observe a small supine chin nod with the head supported. Note whether the patient can sustain the nod or shifts into a larger effort with prominent SCM activity. That describes how the patient performs the task. Visible SCM activity alone cannot establish deep cervical flexor weakness.
Recognize When the Findings Change the Plan
If SCM contraction is visibly reduced or rotation is unexpectedly weak, compare the trapezius on the same side with a resisted shrug and observation of shoulder position. New weakness or atrophy, particularly after a neck procedure, warrants a focused CN XI examination and timely referral if nerve injury is suspected. If the presentation raises concern for cervical vascular pathology, defer manual care and arrange appropriate medical assessment.
Carry one finding into reassessment. If light palpation of the SCM reproduces the familiar symptoms and the motion and loading findings agree, that combination can support a trial of local MSR care. Repeat the same head turn or resisted effort under comparable conditions and document what changes.
MSR Procedures and Precautions
Use the examination to decide whether the sternocleidomastoid warrants treatment. If a resisted head turn and light palpation of the SCM reproduce the patient’s familiar symptoms, record the movement and symptom response before starting so you can repeat the test afterward.
Supine SCM Procedure
Setup. The patient lies supine with the head beyond the end of the table. In the demonstration, I guide the head down and back into the working position. Use a range the patient can comfortably tolerate.
Superior contact. Locate the SCM near its mastoid attachment. I use my third and fourth digits to engage the superficial muscle and apply gentle superior traction.
Progress along the muscle. Work inferiorly along the belly toward the lower attachments. Use a light pincer contact where you can clearly identify and gently grasp the muscle. Move slowly and check the patient’s comfort as you change contacts.
Opposing traction. Near the lower portion, apply inferior traction with one hand and superior traction with the other. These are opposing contacts along the muscle. In the demonstration, I then work back up the belly and finish with an inferior traction contact.
Precautions
Explain the procedure and obtain consent before positioning the head. Keep the contact superficial and directed at the muscle belly. Avoid deep pressure toward the carotid sheath or direct pressure over a palpable arterial pulse. If the history or examination raises concern for cervical vascular pathology or another serious condition, defer the procedure and arrange appropriate medical assessment.
SCM Release: Neck Pain, Headaches, Whiplash
In this video, I change the contact from the mastoid region to the lower SCM and introduce opposing traction. At the end, I repalpate the muscle to compare how it feels. In practice, pair that observation with the original movement or loading test. Repeat the same head turn or resisted effort and record any change in symptoms, range, or force.
Exercise and Reassessment
Use the examination to decide what the patient needs to regain. A restricted head turn calls for a different exercise than a head turn that becomes difficult after several repetitions. Difficulty sustaining a small chin nod gives you a separate finding to address.
PNF Neck Stretches
Use this video when the examination identifies a cervical mobility limitation in flexion, lateral flexion, or extension. Choose the direction that matches the finding. If rotation is the main restriction, practise slow, active head turns through the available range and reassess the direction that was limited.
Supported Chin Nod
If the patient struggled to sustain a small nod during the examination, practise it with the head supported. Keep the effort low enough to maintain the nod without lifting the head. Progress the hold or add repetitions once the patient can reproduce the same movement consistently. The purpose is to develop low-load cervical control.
Neck Strengthening Exercises That Work
Use this routine when the examination identifies reduced cervical strength or endurance. If the patient has sufficient rotation but symptoms emerge after repeated head turns, gradually build tolerance to that task. If resisted rotation reveals a force deficit appropriate for exercise, consider graded isometric rotation. Progress repetitions, hold time, or resistance according to the finding and how symptoms settle afterward.
Reassess What Matters
Repeat the original test under comparable conditions. For a restricted head turn, compare range and familiar symptoms. For a sustained nod, compare how long the patient maintains the same movement. For repeated rotation, compare how many turns they tolerate before symptoms begin. At follow-up, check whether the change carries over to the activity that brought them in.
Conclusion
A right head turn recruits the left SCM and the right splenius capitis. That relationship gives us a useful starting point, but it takes movement, resisted testing, and local palpation to decide whether the SCM warrants treatment. Unexpected weakness changes the plan and may warrant a closer look at the spinal accessory nerve.
When the findings support an MSR procedure, let the anatomy guide the contact and the examination guide the exercise. Repeat the finding that led you to treat, then check whether the change carries over. A head turn that feels easier on the table is an immediate response. Being able to check a blind spot comfortably or turn repeatedly at work tells us what that change means to the patient.
References
Blomgren, J., Strandell, E., Jull, G., Vikman, I., & Röijezon, U. (2018). Effects of deep cervical flexor training on impaired physiological functions associated with chronic neck pain: A systematic review. BMC Musculoskeletal Disorders, 19, Article 415.
Bordoni, B., Jozsa, F., & Varacallo, M. A. (2026). Anatomy, head and neck: Sternocleidomastoid muscle. In StatPearls. StatPearls Publishing.
de Haan, J. B., & Hernández, N. (2025). Anatomy. In D. Patel, S. J. Kim, H. V. Bhatt, & A. M. Patel (Eds.), BASIC Essentials. Cambridge University Press.
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Garner, D. H., Kortz, M. W., & Baker, S. (2023). Anatomy, head and neck: Carotid sheath. In StatPearls. StatPearls Publishing.
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Jull, G. A., O’Leary, S. P., & Falla, D. L. (2008). Clinical assessment of the deep cervical flexor muscles: The craniocervical flexion test. Journal of Manipulative and Physiological Therapeutics, 31(7), 525–533.
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DR. BRIAN ABELSON, DC. - The Author
Dr. Brian Abelson is a chiropractor, author, and educator with more than 30 years of clinical experience in musculoskeletal care, rehabilitation, and sports performance. His educational work focuses on musculoskeletal conditions, human movement, sports biomechanics, and evidence-informed approaches to treatment and rehabilitation.
He is the developer of Motion Specific Release (MSR) and Clinical Director of Kinetic Health in Calgary, Alberta, Canada.
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