Muscle:Coracobrachialis
Coracobrachialis is a small, deep muscle of the anterior shoulder that requires more clinical skill to identify and manage than most other muscles. Its TrPs are almost never the presenting complaint — they are discovered as a residual problem after TrPs in the surrounding muscles (anterior deltoid, biceps brachii short head, triceps brachii long head) have been successfully treated, and the patient returns reporting that deep anterior shoulder pain persists despite apparent resolution of the muscles previously addressed. The characteristic clinical scenario: all previously treated muscles are now clear of tenderness and local twitch responses, yet severe pain and deep tenderness remain in the region of the anterior deltoid — and careful palpation reveals that the tenderness lies deeper than the deltoid.
The referred pain pattern is clinically distinctive: anterior shoulder pain at the proximal humerus, combined with an interrupted column of pain running down the posterior arm and dorsal forearm to the back of the hand — skipping the elbow and wrist — and potentially extending to the tip of the middle finger. This interrupted, skip-pattern referral is not produced by most other shoulder muscles and is a useful differentiating feature.
Anatomy
Proximal attachment: Apex of the coracoid process of the scapula — in common with the tendon of the short head of the biceps brachii, and from the intermuscular septum between the two muscles.
Distal attachment: Medial surface of the humerus, just proximal to its midpoint, between the attachments of the triceps brachii and brachialis muscles.
The coracobrachialis lies deep to the pectoralis major and anterior deltoid muscles, and medial to the short head of the biceps brachii. It crosses superficial to the attachments of the subscapularis, latissimus dorsi, and teres major muscles.
The musculocutaneous nerve penetrates the midportion of the coracobrachialis as it passes en route to the biceps brachii and brachialis. This penetration may divide the coracobrachialis into superficial and deep portions. The brachial neurovascular bundle passes deep to the pectoralis minor tendon at the coracoid process and continues down the arm alongside the coracobrachialis — lying dorsal and medial to the muscle, between the coracobrachialis and the lateral head of the triceps attachment to the humerus. The pulsating brachial artery is palpable in this bundle and must be identified and avoided during examination and injection.
Anatomical variants include total absence of the muscle and extension of the distal attachment to the medial epicondyle.
Innervation: Branch of the musculocutaneous nerve containing fibres from C6 and C7; this branch separates from the nerve trunk before it penetrates the muscle.
Primary actions:
- Flexion of the arm at the glenohumeral joint
- Adduction of the arm
- Assists return of the arm to neutral from both lateral and medial rotation
- When contracted with the arm abducted, draws the humerus toward the glenoid cavity (stabilisation)
Referred Pain Pattern
Essential referral zone:
- Anterior aspect of the proximal humerus (anterior deltoid region)
- Posterior arm, concentrating over the triceps brachii
- Dorsum of the forearm
- Dorsum of the hand — potentially extending to the tip of the middle finger
Characteristic feature — skip pattern: Pain in this column skips the elbow and wrist — jumping from the posterior arm to the dorsal forearm and then to the dorsal hand, with relative sparing of the joint zones. This interrupted pattern is clinically distinctive. In milder involvement, the referral may extend only as far as the elbow.
With increasing TrP activity, the extent of referral increases, pain intensity rises, pain is more likely to persist at rest, TrP tenderness increases, taut bands become more tense, and local twitch responses become more vigorous.
Activation and Perpetuating Factors
Coracobrachialis TrPs develop secondarily to active TrPs in related muscles of its functional unit. They are not typically activated in isolation. The muscle appears to become involved as part of a broader shoulder complex dysfunction rather than as a primary myofascial problem.
Associated muscles most likely to carry the key TrPs driving coracobrachialis involvement: anterior deltoid, biceps brachii (short head), supraspinatus, triceps brachii (long head).
Activities that strain the functional unit and can contribute to coracobrachialis TrP activation include lifting heavy objects with the arms outstretched forward (loading the muscle during flexion), and repetitive or sustained arm flexion against resistance.
Clinical Examination
Symptom Presentation
The primary complaint is upper limb pain in the front of the shoulder and posteriorly down the arm. The patient experiences pain when reaching behind the body across the low back — as in the Back-rub Test — because of the strong medial rotation with arm extension required, which stretches and then loads the coracobrachialis.
With coracobrachialis TrPs, the arm can be raised to ear level but not behind the ear. Pain is provoked by contraction of the muscle in the shortened position: reaching up in full flexion, then moving the arm behind the ear and toward the midline causes a painful contraction.
With only coracobrachialis involvement, reaching the arm up in some abduction with the elbow bent — as when touching the top of the head — is not painful (this does not maximally load or shorten the coracobrachialis).
Back-rub Test (Fig. 29.3 in Travell & Simons)
The Back-rub Test is the key examination manoeuvre. The patient reaches behind the back in the low lumbar region (extreme medial rotation with arm extension).
Before treatment of the coracobrachialis, the knuckles usually can reach only to the midline of the back because of aching pain in the muscle with full medial rotation in extension. Following successful TrP inactivation, the wrist can reach across the full width of the back.
The test puts the coracobrachialis in a painful stretched and loaded position. Pain on this test in the absence of tenderness in the anterior deltoid and biceps brachii (previously treated) should direct attention to the deeper coracobrachialis.
Strength Testing
Flexion of the humerus may be slightly weak. To isolate the coracobrachialis from biceps brachii assistance:
- Patient elevates the arm to approximately 45° of flexion with lateral rotation
- Elbow is flexed and forearm fully supinated (minimises biceps activation)
- Operator applies downward and slightly outward pressure at the distal humerus (direction of extension and slight abduction)
- Inability to adequately resist = weakness of the coracobrachialis
- Maximal resistance effort is likely to elicit pain if active TrPs are present
Stretch and Loading Provocation
Stretch (provokes pain): Passively extending the arm at the shoulder — particularly when an abduction component is added — stretches the coracobrachialis and reproduces pain.
Loading (provokes pain): Resisting active flexion of the arm at the shoulder.
Relevant TrP identification
When upper limb range of motion testing reveals a soft tissue restriction, ask the patient during the test where they feel tightness or pain, and have them point to the area. Palpation there may reveal a taut band with a TrP — a relevant TrP that may be latent (producing no spontaneous pain) but causing functional restriction. A relevant TrP in the coracobrachialis may be found by passively moving the humerus into simultaneous extension and abduction, particularly when lateral rotation is introduced.
The location of the perceived tightness helps distinguish coracobrachialis tension from biceps brachii tension.
Assess glenohumeral, acromioclavicular, and sternoclavicular joint play — restore any restriction before attributing motion loss to the muscle alone.
Trigger Point Examination
Coracobrachialis TrPs are identified by direct palpation against the humerus by sliding the finger into the axilla deep to the deltoid and pectoralis major.
Two areas of tenderness may be found:
- Central midmuscle TrPs — located approximately at the midpoint of the muscle belly, more distally than the coracoid process. These are the true myofascial TrPs.
- Attachment trigger area (enthesopathy) — in the region of the proximal musculotendinous junction (and occasionally distally). This most likely represents enthesopathy secondary to sustained tension from the taut bands of the midmuscle TrP, rather than a primary TrP itself.
Palpation technique:
- Patient supine, arm placed in lateral rotation at the shoulder
- Slide the examining finger into the axilla deep to the deltoid and pectoralis major
- The finger encounters the adjacent bellies of the short head of the biceps brachii (more anterior) and, more posteriorly, the coracobrachialis — at a level where about half the biceps fibres have become attached to their common tendon
- The axillary neurovascular bundle lies posterior and medial to the coracobrachialis and must be displaced posteriorly before exploring the coracobrachialis for taut bands
- Strum the muscle against the humerus to identify firm taut bands
- The pulsating brachial artery in the neurovascular bundle confirms its location; do not compress this structure
Expected responses: Local twitch responses are generally palpable rather than visible in this deep muscle, and they confirm TrP location. When palpating a taut band, avoid the neurovascular bundle.
Differential Diagnosis
Cardinal differentiating features of coracobrachialis TrP pain
| Feature | Present / Absent / Variable |
|---|---|
| Pain anterior shoulder + interrupted posterior arm/dorsal forearm/dorsal hand column (skip pattern) | Must be present — the skip pattern (elbow and wrist spared) is clinically distinctive |
| Residual deep anterior shoulder pain after successful treatment of anterior deltoid and biceps brachii | Must be present as the classic discovery scenario; tenderness lies deeper than the deltoid |
| Back-rub Test painful (knuckles reach only to midline) | Must be present with active TrPs — resolves after TrP inactivation |
| Arm can be raised to ear level but not behind the ear | Must be present — pain on contraction in the shortened position; distinguishes from anterior deltoid TrPs (where the motion is painful earlier in range) |
| No spontaneous pain at rest in mild involvement | Variable — present at rest when TrPs are more active |
| Symptoms of isolated musculocutaneous nerve entrapment absent | Must be absent for a pure TrP picture — see Entrapment section |
Comparison with the most important differential diagnoses
| Condition | Key differentiating features |
|---|---|
| Anterior deltoid TrPs | Most important differential — the coracobrachialis lies deep to the anterior deltoid in the same region. With anterior deltoid TrPs: tenderness is in the deltoid belly at or near the midportion; pain is reproduced by thumb-up abduction resistance; Back-rub Test may also be restricted. The distinguishing manoeuvre: if anterior deltoid TrPs are cleared but deep anterior shoulder tenderness persists, the coracobrachialis is implicated. Tenderness deeper than the deltoid is the key finding. |
| Acromioclavicular joint dysfunction | Tenderness slightly inferior to the AC joint could reflect coracobrachialis enthesopathy (proximal attachment). Distinguish with the AC compression test: passively place the arm in full horizontal adduction (compresses the AC joint); additionally apply resistance to horizontal abduction in this position to increase sensitivity. Both manoeuvres will elicit pain if AC joint dysfunction is present, and should not elicit pain if the source is only a coracobrachialis TrP. If pain is severe, radiological exclusion of AC separation may be needed. |
| C7 radiculopathy | Dermatomal sensory deficit (middle finger primarily); triceps reflex depression; motor weakness in C7 myotome (elbow extension, wrist flexion). Coracobrachialis TrP pain can extend to the middle finger but produces no reflex change, no objective sensory deficit, and no myotomal weakness. Note: musculocutaneous nerve entrapment by the coracobrachialis (see below) must also be considered when C7 radiculopathy is suspected. |
| Musculocutaneous nerve entrapment (by coracobrachialis) | Reduced biceps brachii size and strength; absent or diminished biceps tendon reflex; diminished sensation over the lateral forearm (lateral antebrachial cutaneous nerve distribution); electrodiagnostic confirmation (prolonged distal latency and decreased evoked response amplitude in biceps and brachialis). The coracobrachialis function itself is spared (the motor branch to coracobrachialis leaves the nerve before it penetrates the muscle). This entrapment must be distinguished from C5–C6 radiculopathy (which affects the coracobrachialis itself) and from a lateral cord brachial plexus lesion. |
| C5–C6 radiculopathy / lateral cord brachial plexus lesion | These produce weakness of the coracobrachialis itself (unlike musculocutaneous entrapment distal to the coracobrachialis, which spares it). Dermatomal sensory deficit in C5/C6 distribution; biceps reflex depression or absence; neuroimaging or electrodiagnostic confirmation. |
| Carpal tunnel syndrome | Sensory symptoms in the median nerve distribution — thumb, index, middle, and radial half of ring finger on the palmar surface; Tinel's sign at the carpal tunnel; Phalen's test; nocturnal pain. Coracobrachialis referral extends to the dorsum of the hand, not the palmar median distribution. The skip pattern (elbow and wrist spared) further distinguishes it. |
| Subacromial bursitis / supraspinatus tendinitis | Tenderness at the greater tuberosity and supraspinatus insertion; painful arc on abduction (60°–120°); positive Neer's or Hawkins–Kennedy test. TrP examination of the coracobrachialis reveals tenderness deep to these structures. Consider both conditions simultaneously — TrPs should be inactivated first before injecting the bursa. |
Entrapment: musculocutaneous nerve
The musculocutaneous nerve penetrates the coracobrachialis en route to the biceps brachii and brachialis. TrPs in the coracobrachialis (with their associated taut bands) are expected to be capable of compressing the nerve at this passage — and latent TrPs, which cause no clinical pain complaint, can be associated with well-developed taut bands sufficient to produce serious neural dysfunction without any local pain.
Clinically documented causes of musculocutaneous nerve entrapment at this site include: exercise-induced hypertrophy of the coracobrachialis (500 daily press-ups; heavy weight lifting; building a rock wall); vigorous repeated elbow extension (throwing a football, racquetball backhand, arm gesturing); and carrying heavy packages. In reported cases, coracobrachialis TrPs were not examined — the TrP contribution to the entrapment in these cases remains unknown.
Clinical features of musculocutaneous nerve entrapment distal to the coracobrachialis:
- Reduced biceps brachii bulk and strength
- Absent or diminished biceps tendon reflex
- Diminished or absent sensation over the lateral forearm (lateral antebrachial cutaneous nerve)
- Electrodiagnostic confirmation: prolonged distal latency; decreased amplitude of evoked responses in biceps and brachialis
- Coracobrachialis function preserved (nerve branch to this muscle is proximal to the entrapment)
Most cases resolve with cessation of the precipitating activity within a few months. Surgical neurolysis has been required when a structural impingement (e.g., biceps tendon impingement on the nerve with full elbow extension) is demonstrated.
Treatment
Trigger Point Release
Joint play must be restored in the glenohumeral, acromioclavicular, and sternoclavicular joints if restricted before proceeding.
Spray and stretch: Applied in the same manner as for the anterior deltoid (same stretch position — horizontal abduction with lateral rotation of the arm). For the coracobrachialis, the vapocoolant spray pattern is extended:
- Carry the spray closer to the axilla
- Extend over the back of the arm and forearm
- Cover the dorsum of the hand to the tip of the middle finger (following the full referred pain pattern)
Trigger point pressure release:
- The proximity of the median, ulnar, musculocutaneous, medial antebrachial cutaneous nerves, and the nerve to the coracobrachialis means that forceful compression against the humerus can easily and painfully damage these structures. Pressure must be gentle. Apply light pressure to the TrP to the point of tissue resistance, wait for release, then follow the tissue to take up slack to the next barrier. Do not force.
Manual lengthwise massage of the muscle belly is an alternative stretch approach.
Following any release, the patient performs three cycles of active full range of motion and moist heat is applied.
Trigger Point Injection
The injection is performed with the patient supine, arm by the side in lateral rotation.
Technique:
- Palpate deep in the axilla by reaching beneath the pectoralis major, pressing against the humerus on the dorsal aspect of the combined short head of biceps/coracobrachialis bundle
- The pulsating brachial artery in the neurovascular bundle (dorsal and medial to the coracobrachialis, between it and the triceps attachment) must be clearly identified and avoided before proceeding
- The needle is inserted through the pectoralis major or anterior deltoid, directed toward the tender area localised by the operator's other palpating hand
- For the attachment enthesopathy trigger area: approach through the anterior deltoid at the level of the greater tubercle of the humerus
- For the central midmuscle TrP: approach through the anterior deltoid or pectoralis major, more distally
When the needle encounters an active TrP, the patient usually experiences a confirmatory local twitch response and may feel a vivid flash of referred pain — similar to striking a nerve, and following the referred pain pattern.
Important caution: Steroids and long-acting anaesthetics are not recommended at this location because of the proximity of major neurovascular structures. Use 0.5% procaine — if temporary musculocutaneous nerve anaesthesia occurs (weakness and sensory changes in the forearm), recovery is expected within 15–20 minutes.
The midmuscle TrP is best injected with the fingers of the non-injecting hand palpating the coracobrachialis posterior to the pectoralis major; take care not to penetrate the palpating finger with the needle.
Following injection: spray and stretch, three cycles of active full range of motion, then a moist warm pack.
If attachment enthesopathy is present, it should also be injected to expedite recovery — but the midmuscle TrP must also be inactivated, or the enthesopathy will recur from continued taut band tension.
Note on Satellite TrP Relationships
Coracobrachialis TrPs are satellites, developing secondarily to key TrPs in the functional unit muscles. The treatment implication is clear: address the surrounding shoulder muscles first, and return to examine the coracobrachialis if deep anterior shoulder pain persists after the other muscles are clear.
Patient Education
Activity Modification
- Avoid lifting heavy objects with the arms outstretched in front; keep elbows close to the body when lifting to reduce coracobrachialis load
- Do not overstretch during home exercises — excessive body weight in the stretch position aggravates this muscle; alternate-day programmes may be necessary if post-exercise soreness is a problem
Home Stretching
- Against-door-jamb Exercise (Fig. 30.7 in Travell & Simons) — daily
- In-doorway Stretch Exercise, lower hand position (Fig. 42.9A in Travell & Simons) — daily; restores full resting length of the coracobrachialis
- Apply moist heat to the muscle before or after passive stretch exercises to reduce soreness
Satellite Trigger Points
Key TrP sources that drive coracobrachialis satellite TrPs (treat these first):
- Anterior deltoid — most common associated muscle; clear this before examining coracobrachialis
- Biceps brachii (short head) — shares coracoid process origin; functional unit member
- Supraspinatus — associated in functional unit
- Triceps brachii (long head) — functional unit antagonist; commonly co-active
Functional unit members (may develop TrPs together):
- Pectoralis major — synergist in flexion and adduction
Related Pages
- Pain:Posterior Shoulder Pain — diagnostic algorithm
- Muscle:Deltoid — must be cleared before coracobrachialis is implicated; overlying muscle
- Muscle:Biceps Brachii — shares coracoid origin; functional unit; must be cleared first
- Muscle:Subscapularis — differential: posterior shoulder with wrist band; deep to coracobrachialis
- Muscle:Pectoralis Minor — adjacent at the coracoid process; overlying the neurovascular bundle
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 29.