Muscle:Subclavius
Subclavius is a small muscle lying beneath the clavicle over the first rib whose trigger points (TrPs) can contribute to symptoms of a vascular thoracic outlet syndrome and produce a referred pain pattern extending down the radial side of the arm and forearm to the thumb and index finger — a pattern easily mistaken for that of the overlying pectoralis major or the scalene muscles.
Anatomy
The subclavius muscle lies beneath the clavicle over the first rib. It attaches medially by a short thick tendon to the junction of the first rib with its cartilage and laterally in a groove on the under side of the middle third of the clavicle.
Innervation: The subclavius is innervated by the nerve to the subclavius from spinal nerves C5 and C6.
Primary actions: The subclavius assists protraction of the shoulder indirectly by approximating the clavicle and the first rib. When the humerus is fixed or stabilised, the pectoralis major can function to move the sternal and clavicular attachments toward the humerus. The subclavius assists in supporting the body weight for crutch-walking and parallel-bar work.
Functional unit: The subclavius assists the lower fibres of the pectoralis major in depression of the shoulder girdle. For protraction of the shoulder, the serratus anterior, pectoralis minor, and subclavius muscles assist those parts of the pectoralis major below its clavicular section.
Referred Pain Patterns
TrPs in the subclavius refer pain into the upper extremity on the same side. The pain travels across the front of the shoulder and down the front of the arm along the radial side of the forearm, skipping the elbow and wrist to reappear on the radial half of the hand. The dorsal and volar aspects of the thumb, the index finger, and the middle finger may also hurt.
This pattern is distinct from the ulnar distribution characteristic of brachial plexus lower trunk entrapment by the scalene muscles, and from the breast and precordial patterns of the pectoralis major sternal and costal sections.
Activation and Perpetuating Factors
Subclavius TrPs are activated and perpetuated in association with TrPs in the overlying pectoralis major, particularly the clavicular section. Shortening of the subclavius due to TrPs draws the clavicle down toward the subclavian artery and vein as they pass over the first rib, creating a perpetuating cycle if the underlying mechanical compression is not addressed.
Round-shouldered posture is the primary postural perpetuating factor, shared with the pectoralis major. Any activity that perpetuates pectoralis major TrPs will also tend to perpetuate subclavius TrPs.
Clinical Examination
Subclavius shortening by TrPs can contribute to symptoms of a vascular thoracic outlet syndrome. In some patients this pressure can at least contribute to, if not cause, entrapment and the symptoms of a vascular thoracic outlet syndrome.
Because the subclavius must be palpated through the clavicular division of the pectoralis major, localisation of its TrPs is best achieved with the pectoralis major placed on slack. To do this, the relaxed patient's arm is placed in adduction and medial rotation.
Trigger Point Examination
The examiner can palpate subclavius central TrPs at the lateral portion of the medial third of the clavicle by rolling the thumb underneath the clavicle, deep into the recess and across the tense fibres. Palpation of the nodule or taut band is not reliable through the pectoral muscle (although a different angle may help).
One should distinguish the attachment TrP (ATrP) tenderness just lateral to and below the costoclavicular joint from the central TrP tenderness found closer to midclavicle.
Entrapment
Shortening of the subclavius muscle due to TrPs will draw the clavicle down toward the subclavian artery and vein as they pass over the first rib. In some patients this pressure can at least contribute to, if not cause, entrapment and the symptoms of a vascular thoracic outlet syndrome. This is a predominantly vascular entrapment mechanism — distinct from the neurological lower trunk entrapment produced by the scalene muscles.
Differential Diagnosis
| Condition | Distinguishing features |
|---|---|
| Pectoralis major TrPs (clavicular section) | Overlying muscle with a different but overlapping referred pain pattern; the two commonly coexist and should be examined together; subclavius TrPs are distinguished by their deeper location beneath the clavicle and the specific radial forearm and thumb referral |
| Scalene TrPs | Scalene entrapment produces ulnar distribution symptoms and hand oedema; subclavius entrapment is predominantly vascular (radial pulse loss) rather than neurological; Scalene-relief Test is positive for scalene but not for subclavius |
| Vascular thoracic outlet syndrome | Subclavius shortening is a primary contributing myofascial mechanism to vascular TOS; inactivation of subclavius TrPs should be the first-line intervention before surgical approaches |
| C5–C6 radiculopathy | Radicular pain in the C5–C6 distribution (radial forearm, thumb, index finger) may mimic subclavius referral; scalene TrPs are more commonly responsible for this pattern |
Treatment
Trigger Point Release
Residual TrPs in the subclavius, after release of the overlying pectoralis major TrPs, can usually be inactivated by trigger point pressure release or by injection with 0.5% procaine solution, followed by brief stretch and spray and then moist heat.
For spray and stretch of the clavicular section of the pectoralis major (which simultaneously addresses the subclavius), the arm is laterally rotated and horizontally extended (abducted) slightly below 90° at the shoulder to fully take up the slack in the clavicular fibres. Vapocoolant spray is swept laterally from the clavicle across the muscle and then over the shoulder and upper limb to cover the referred pain pattern.
The tense pectoral fibres and the sternocleidomastoid TrPs must both be released for full relief, as myofascial TrP tightness of the clavicular portion of the pectoralis major can exert forward and downward traction on the clavicle, increasing tension on the clavicular head of the sternocleidomastoid muscle, which in turn may involve autonomic phenomena.
Trigger Point Injection
If, after injection of TrPs in the clavicular section of the pectoralis major, tenderness to deep subclavicular pressure persists — and particularly if this pressure elicits pain in the referral pattern of the subclavius muscle — that muscle should be explored with a needle for TrPs. The needle is directed toward the point of maximum tenderness beneath the clavicle, usually in the middle of the muscle toward the junction of its medial and middle thirds. Strong referred pain responses are likely to be produced by needle penetration of these TrPs.
Corrective Actions
Correction of round-shouldered posture is essential. The In-doorway Stretch Exercise addresses the clavicular section of the pectoralis major and secondarily the subclavius. See Muscle:Pectoralis Major for the full postural correction and stretch programme, which applies equally to the subclavius.
Satellite Trigger Points
- Muscle:Pectoralis Major — the subclavius is almost invariably involved alongside pectoralis major clavicular section TrPs; treat together
- Muscle:Sternocleidomastoid — clavicular head; tightness of the clavicular pectoralis major puts tension on the clavicular head of the SCM, which may then develop TrPs
- Muscle:Scalene — functional unit overlap for shoulder depression and respiratory accessory function
Related Pages
- Muscle:Pectoralis Major — primary co-active muscle; clavicular section TrPs almost always coexist
- Muscle:Scalene — vascular TOS differential; different entrapment mechanism
- Muscle:Sternocleidomastoid — downstream effect of clavicular tightness
- Muscle:Pectoralis Minor — co-active in anterior chest and shoulder depression
References
- Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1: The Upper Half of Body. 2nd ed. Baltimore: Williams & Wilkins; 1999. Chapter 42 (Pectoralis Major and the Subclavius).