Muscle:Brachialis
Brachialis is the "workhorse" of the elbow flexors — a deep, single-joint muscle that attaches to the ulna rather than the radius, performing only one motion (elbow flexion) regardless of forearm rotation. Its trigger points (TrPs) produce a clinically distinctive referral pattern: pain concentrated at the base of the thumb and the dorsal web of the thumb, with spillover to the antecubital space and occasional upward referral to the anterior deltoid region. This thumb-base referral from a muscle located in the arm is frequently not recognised as myofascial in origin, and is routinely confused with C5–C6 radiculopathy, De Quervain's tenosynovitis, carpometacarpal arthritis, carpal tunnel syndrome (when pain is perceived over the thenar eminence), or a problem in the thumb itself.
The brachialis is also the site of a clinically important entrapment: taut bands from a TrP in its lateral border can compress the sensory branch of the radial nerve as it exits the musculospiral groove, producing dysesthesia, tingling, and numbness on the dorsum of the thumb and its web space — overlapping with and compounding the TrP's own referred pain pattern.
Anatomy
Proximal attachment: Distal half of the anterior shaft of the humerus and to the medial and lateral intermuscular septa. This proximal attachment reaches as far up as the distal attachment of the deltoid muscle.
Distal attachment: Coronoid process on the proximal end of the ulna.
The brachialis lies beneath the biceps brachii, which covers most of it. The biceps brachii attaches distally to the radius while the brachialis attaches to the ulna — this difference in distal attachment is the key anatomical point that determines their functions. The median and radial nerves lie, respectively, along the medial and lateral borders of the brachialis (as for the biceps brachii above them); this relationship is critical during injection.
Innervation: Musculocutaneous nerve via the lateral cord; C5 and C6 spinal roots.
Primary actions:
- Elbow flexion — the only action; the ulnar attachment means the brachialis is equally active regardless of forearm rotation
- When the humerus is fixed: moves the forearm toward the humerus
- When the ulna is fixed: moves the humerus toward the forearm (pull-up, chinning exercises)
- Eccentric contractions to control (decelerate) the lowering of heavy objects
Unlike the biceps, the brachialis shows no inhibition with forearm pronation and therefore does not benefit from the load-shifting strategy of lifting in pronation (which unloads the biceps but not the brachialis). Its EMG activity is relatively constant during driving, with only occasional short bursts of more intense activity.
Referred Pain Pattern
Essential (solid) referral zone:
- Dorsum of the carpometacarpal joint at the base of the thumb
- Dorsal web space of the thumb
Spillover (stippled) referral zone:
- Antecubital space
- Anterior deltoid region (from the most proximal brachialis TrPs)
Important anatomical note on TrP locations vs. the pain drawing: The most distal tender area shown in the pain pattern figure (a few centimetres above the antecubital space) most likely represents enthesopathy secondary to the midfibre TrPs rather than a primary midmuscle TrP. The true central TrPs are found more proximally in the muscle belly.
Activation and Perpetuating Factors
Brachialis TrPs are activated and perpetuated primarily by sustained or repetitive forearm flexion under load:
- Holding a power tool at elbow height for prolonged periods
- Carrying groceries with the elbow flexed
- Meticulous ironing
- Fingering a violin or guitar with the forearm supinated (when the forearm is supinated the biceps is already shortened and contributes little to flexion, placing the full load on the brachialis)
- Heavy lifting with the elbow flexed against load
In "tennis elbow": Brachialis involvement tends to develop together with biceps brachii involvement after initial TrP activation in the supinator (see Muscle:Supinator). The supinator is typically the primary TrP in this pattern; brachialis and biceps become secondarily involved.
Clinical Examination
Symptoms
Referred pain is felt at the base of the thumb at rest and often also with active use of the thumb. Diffuse soreness of the thumb is characteristic of its referred tenderness.
Two symptom types may coexist in the thumb:
- Deep aching — from the TrP referred pain pattern
- Dysesthesia, tingling, and numbness on the dorsum of the thumb and its web — from entrapment of the sensory branch of the radial nerve
Both may be relieved by inactivating the brachialis TrPs.
Pain referred over the anterior deltoid region from brachialis TrPs alone does not lead to impairment of shoulder motion — an important distinguishing feature from primary shoulder muscle TrPs.
Key Clinical Finding
Active movement of the thumb usually hurts; active movement of the elbow does not. This dissociation — thumb pain without elbow restriction as the clinical complaint — is characteristic of brachialis TrPs and is the finding that directs clinical attention from the thumb to the arm.
Passive Elbow Extension Test
Pain referred from brachialis TrPs is increased by passively extending the elbow fully. However, limitation of elbow extension range of motion is not a patient complaint and the restriction is only a few degrees — often detectable only by comparison with the other arm or by improvement after treatment.
Distinguishing brachialis from biceps weakness
Test elbow flexion strength in supination and then repeat in pronation with the elbow extended. Pronating the forearm has no effect on brachialis strength (ulnar attachment) but weakens the biceps if it is in a lengthened position. A disproportionate weakness specifically in the supinated position, with preserved strength in pronation, points to biceps brachii involvement; equivalent weakness in both positions points to brachialis.
Radial nerve compression screen
Compress the region where the radial nerve exits the musculospiral groove and pierces the lateral intermuscular septum. The landmark is approximately mid-arm, just below the dimple that marks the apex (distal end) of the triangular deltoid bulge. Tingling in the thumb on compression at this point indicates radial nerve compromise at this level — which may be produced by a taut band from a lateral brachialis TrP (see Entrapment section below).
Trigger Point Examination
The brachialis is a deep muscle; the overlying biceps brachii must be displaced to reach it.
Technique (Fig. 31.3 in Travell & Simons):
- Flex the elbow between 30° and 45°; supinate the forearm to slacken and relax the biceps brachii
- Push the bulk of the biceps medially to uncover the underlying brachialis
- Palpate the brachialis against the humerus for taut bands and TrPs
TrPs are located in the distal half of the arm:
- Some TrPs may be found just deep to the lateral edge of the undisplaced biceps
- Others lie toward the middle of the brachialis, sometimes fully under the biceps
- The most proximal TrPs (which refer pain upward to the deltoid region) are covered by the biceps brachii and require the most displacement to access
The lateral border TrP responsible for radial nerve entrapment feels like an almond in the lateral border of the muscle, just proximal to the nerve exit point.
Assess the elbow joint for normal joint play; restore any restriction before attributing motion loss to the muscle.
Entrapment
The sensory (cutaneous) branch of the radial nerve can be compressed by a TrP — typically in the lateral border of the brachialis — that generates a taut band extending to the level where the radial nerve exits the musculospiral groove and pierces the lateral intermuscular septum.
Entrapment symptoms:
- Numbness, hypoesthesia or hyperesthesia, and dysesthesia on the dorsum of the thumb and its adjacent web space
- Quality is neurogenic (sensory changes) rather than the deep aching of pure referred TrP pain — though both may coexist
These symptoms are relieved by injection of the responsible brachialis TrP. Resolution of the taut band and relief of entrapment signs strongly confirms that muscle tautness from the TrP caused the nerve compression. Confirmatory sensory nerve conduction velocities before and after treatment are recommended to document the entrapment and its resolution.
This entrapment must be distinguished from C5–C6 radiculopathy and from de Quervain's tenosynovitis by the specific location of the responsible TrP and its response to treatment.
Differential Diagnosis
Cardinal differentiating features of brachialis TrP pain
| Feature | Present / Absent / Variable |
|---|---|
| Pain at the base of the thumb / dorsal thumb web at rest and with thumb use | Must be present — the essential referral zone; directs attention from the thumb to the arm |
| Active thumb movement hurts; active elbow movement does not | Must be present — the key clinical dissociation for brachialis |
| Passive elbow extension increases thumb/antecubital pain | Must be present — confirms brachialis as the source |
| Shoulder motion unimpaired | Must be present — anterior deltoid referral from brachialis does not restrict shoulder motion |
| No motor deficit, no reflex change | Must be present — absence of neurological deficit distinguishes from radiculopathy |
| Dysesthesia/tingling/numbness on dorsum of thumb | Variable — indicates radial nerve entrapment component; may coexist with referred aching |
| TrP in the lateral brachialis border (almond-shaped, just proximal to radial nerve exit) | Present in entrapment cases — the specific lesion |
Comparison with the most important differential diagnoses
| Condition | Key differentiating features |
|---|---|
| C5/C6 radiculopathy | Dermatomal sensory deficit in C5 (lateral arm, deltoid patch) and/or C6 (lateral forearm, thumb, index finger) distribution; biceps reflex depression or absence; motor weakness in C5/C6 myotome (shoulder abduction, elbow flexion, wrist extension); neuroimaging confirms. Brachialis TrPs produce no reflex change, no objective sensory deficit, and pain-inhibited rather than true myotomal weakness. |
| Carpal tunnel syndrome | Median nerve distribution: sensory changes on the palmar surface of the thumb, index, middle, and radial half of ring finger; nocturnal hand pain; Tinel's sign at the wrist; Phalen's test. Brachialis referral is to the dorsum of the thumb (not palmar), does not include the fingers, and is not associated with nocturnal wrist/hand symptoms. |
| De Quervain's tenosynovitis | Tenderness and swelling specifically over the radial styloid and the first dorsal compartment tendons; positive Finkelstein's test (thumb in palm, ulnar deviation of wrist reproduces pain). Brachialis referral produces pain at the CMC joint base and dorsal web without localised tendon tenderness or a positive Finkelstein's test. |
| Carpometacarpal (first CMC) arthritis | Grinding, pain, and restricted range of motion on axial compression and rotation of the thumb CMC joint (grind test); radiographic changes; no brachialis TrP on examination. Both conditions can coexist. |
| Bicipital tendinitis / biceps brachii TrPs | Biceps TrPs refer to the anterior shoulder (not the thumb); antecubital space involvement in biceps TrPs is mild spillover. Brachialis TrPs are found beneath the biceps; distinguish by pushing the biceps aside to palpate the deeper brachialis separately. In tennis elbow and violin playing, both muscles are commonly involved together and should be examined simultaneously. |
| Supraspinatus tendinitis | Tenderness at the supraspinatus insertion on the greater tuberosity; painful arc on abduction; no thumb pain. Brachialis TrPs may refer to the anterior deltoid region but do not produce supraspinatus insertion tenderness or a painful abduction arc. |
| Adductor pollicis / supinator / brachioradialis TrPs | All three muscles can refer pain to the base of the thumb or radial forearm. The brachialis is likely to be co-involved when these muscles also harbour TrPs (particularly supinator in tennis elbow). Examine all when thumb-base pain is the complaint. |
Treatment
Trigger Point Release
Spray and stretch (Fig. 31.4 in Travell & Simons):
- Rest the distal end of the patient's humerus on a firm support (operator's knee or a pillowed armrest)
- The elbow gradually extends as the muscle releases
- Apply vapocoolant spray over the brachialis downward, in the direction of the chief referred pain zone, and continuing to the tip of the thumb
- Also spray upward to cover the brachialis again and the anterior deltoid region if pain is felt there
- Augment with postisometric relaxation: patient gently flexes against resistance during slow inhalation, then actively attempts to extend during slow exhalation; cycles of spray and stretch and postisometric relaxation alternate
Following release: warm moist heat to rewarm the skin and further relax the muscle; then full elbow flexion and extension three times to restore normal coordination.
Trigger point pressure release: Effective when applied with the muscle in either a position of slight lengthening or a position of ease (slightly shortened).
Trigger Point Injection
Technique (Fig. 31.5 in Travell & Simons):
- Flex the arm to approximately 45° and supinate the forearm to slacken the biceps brachii; press it aside medially
- Use a needle at least 3.8 cm (1½ inch) — the brachialis is a surprisingly thick muscle and TrPs frequently lie deep, next to the humerus
- Approach from the lateral side of the arm
- Direct the needle medially and upward, probing widely to explore lateral and middle portions for LTRs
- The needle may lightly contact the humerus — this ensures reaching the full depth of the muscle
- If bony contact bends the needle tip so that it "catches" when pulled through tissue, replace the needle immediately
- Avoid the medial border (median nerve) and lateral border (radial nerve) of the muscle throughout
Inject TrPs with 0.5% procaine or lidocaine. LTRs confirm accurate placement. After injection, spray and stretch to release any overlooked TrPs, then moist heat, then full range of motion three times.
Note on Satellite TrP Relationships
The brachialis is commonly involved together with the biceps brachii, brachioradialis, and supinator in loading patterns that overload elbow flexion. In the tennis elbow pattern, the supinator is typically activated first, with brachialis and biceps developing TrPs subsequently.
Related TrPs that refer to the same thumb-base zone should be examined in all cases of brachialis TrP pain:
- Supinator — also refers to the base of the thumb and radial forearm
- Brachioradialis — also refers to the thumb/radial hand
- Adductor pollicis — refers locally to the thumb CMC region
Patient Education
Lifting and Loading
Avoid stress overload of forearm flexion — lift only light or moderate loads. When lifting with the forearm supinated (which brings the biceps into play), the brachialis load is relatively reduced because the biceps contributes substantially. This principle is the reverse of the brachialis-sparing goal: for the brachialis, moderating total elbow flexion load is the priority; pronated lifting shifts load away from the biceps but not from the brachialis.
Sleep Position
Place a pillow in the angle of the elbow at night (see Fig. 30.8 in Travell & Simons). This prevents sleeping with the arm tightly folded — a position that immobilises the brachialis in a shortened position. Similarly, avoid holding the elbow sharply flexed during prolonged telephone calls; switch hands occasionally or use a headset.
Carrying
A bag or purse strap should not hang on the forearm with the elbow bent. Carry the bag in the fingers with the elbow straight, hang it over the opposite shoulder, or best hang it on a belt.
Musicians
When playing an instrument such as the violin, allow the elbow to hang down straight at every opportunity to relieve sustained brachialis loading.
Self-Release (Fig. 31.6 in Travell & Simons)
The patient supports the humerus just above the elbow and allows gravity to assist postisometric relaxation of the brachialis without arm assistance:
- Perform a series of contract-relax manoeuvres synchronised with respiration
- After several cycles, additional release may be obtained by gently assisting gravity with the other hand
- This process should not be painful — at most a sense of stretch tension
- Perform once or twice daily after soaking the arm in warm water or applying moist heat
Satellite Trigger Points
- Biceps brachii — most common co-involved muscle; share the elbow flexion functional unit; examine together
- Supinator — common co-involvement, particularly in tennis elbow; typically the primary TrP
- Brachioradialis — elbow flexion synergist; common satellite
- Adductor pollicis — referred pain overlaps at the thumb CMC region
Related Pages
- Muscle:Biceps Brachii — most common co-involved muscle; share elbow flexion load; examine together
- Muscle:Supinator — tennis elbow pattern: supinator is the primary TrP; brachialis develops secondarily
- Muscle:Brachioradialis — elbow flexion synergist; common co-involvement; also refers to thumb
- Muscle:Adductor Pollicis — overlapping thumb referral zone; examine when brachialis treatment produces incomplete relief
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 31.Bold text