Muscle:Supinator
Supinator is a flat, deep muscle of the proximal forearm that spirals around the lateral surface of the radius. It is the muscle most frequently contributing to the pain of "tennis elbow" — in clinical experience, nearly every patient with lateral epicondylar pain and tenderness has an active supinator TrP. Its referred pain pattern overlaps closely with that of the Muscle:Brachioradialis and extensor carpi radialis longus, making it the primary differential target whenever lateral epicondylar pain is the chief complaint. The supinator is typically the first muscle in the forearm extensor sequence to develop TrPs, and its treatment is a prerequisite to resolving the full lateral epicondylar complex.
Anatomy
- Proximal attachment: Primarily to the dorsal surface of the ulna at the elbow; also to the lateral epicondyle of the humerus, the lateral and ventral ligaments of the radioulnar joint, and the anterior capsule of the humeroulnar joint
- Distal attachment: Volar surface of the radius in a Y-shaped configuration, just distal to the biceps brachii tendon; the bare bone between the arms of the Y separates the proximal portion into superficial and deep layers
- Layers: The proximal muscle is divided into superficial and deep layers. The division does not extend into the distal half, where the muscle is undivided.
- Innervation: Deep (posterior interosseous) branch of the radial nerve, posterior cord; primarily C6, partly C5, sometimes C7. The motor branch to the supinator comes off the posterior interosseous nerve before it enters the muscle.
- Primary action: Supination of the forearm at the radioulnar joint. Supinator activity predominates over biceps activity during unresisted supination and holds the forearm in supination. The biceps assists only when the elbow is at least slightly flexed and resistance is encountered — the biceps contributes very little to supination with the elbow straight. Forceful supination therefore requires slight elbow flexion.
- Secondary action: Assists elbow flexion (epicondylar fibres and those attaching to the anterior joint capsule)
Windlass mechanism: When the forearm pronates, the supinator muscle and the biceps tendon wrap around the radius like a windlass into the space between the radius and ulna. This mechanism means full pronation places the supinator under maximal mechanical load.
Arcade of Frohse: The deep radial (posterior interosseous) nerve enters between the superficial and deep layers beneath a fibrous archway of variable thickness formed by the superficial layer — the arcade of Frohse. The arch is tendinous and thickened in approximately 30% of normal adult arms, and in the great majority of surgically treated supinator syndrome cases. This is the primary site for deep radial nerve entrapment in the forearm (see Entrapment).
Referred Pain Pattern
Essential pattern:
- Lateral epicondyle and surrounding lateral aspect of the elbow — the predominant and essential referral site
- Dorsal aspect of the web of the thumb — common spillover
If TrP irritability is sufficiently intense, spillover extends to the dorsal forearm.
Diagnostic pointer: The combination of epicondylar tenderness and pain at the base of the thumb (web or dorsal) strongly suggests an active supinator TrP. Thumb range of motion is usually not restricted and often not painful, distinguishing this from thumb-intrinsic pathology.
Activation and Perpetuating Factors
TrPs are activated by:
- Tennis — mis-hitting the ball off-centre with the elbow fully extended during a backhand stroke; during full elbow extension the biceps cannot assist the supinator, leaving it to resist the added twist alone
- Briefcase elbow — flipping a briefcase onto a desk with the carrying hand, ending with the forearm pronated and the elbow straight; also carrying a heavy briefcase with the elbow straight where each step bumps the briefcase, requiring repeated stabilisation
- Turning stiff doorknobs; wringing clothes during laundry; meticulous ironing
- Unscrewing a tight jar lid using only wrist movement (no shoulder rotation)
- Walking a large dog pulling on a leash; handshaking in long receiving lines
- Erasing chalk lines on a blackboard; washing walls by hand; raking leaves
Any excessively forceful, repetitive, or sustained supination of the forearm — especially with the elbow straight — may activate TrPs. Forceful elbow flexion with the forearm pronated (the position that most loads the supinator while inhibiting biceps assistance) is a particularly effective activator.
Clinical Examination
History and Functional Assessment
The hallmark history is lateral elbow pain both at rest and with activity, particularly after carrying loads with the elbow extended. Ask specifically about briefcase carrying technique — carrying with the elbow straight and forearm pronated is the prototypical supinator load. TrPs in the supinator do not cause the grip-failure pattern characteristic of the wrist extensor group; grip becomes painful only secondarily when the extensor muscles develop satellite TrPs.
Active Range of Motion
Test supinator stretch length by simultaneously pronating the forearm and extending the elbow (the stretch position). This test does not always reveal restriction when the supinator alone is involved, but restriction here is specific to the supinator.
Strength Testing
To test supinator strength with minimum biceps assistance: patient supine, elbow extended along the side of the body, hand and forearm in neutral position; resist the patient's supination effort. Increased TrP tension is revealed by painful limitation of full supination against resistance.
Trigger Point Examination
TrP location — central (most common): Just lateral and slightly distal to the biceps tendon attachment, over the ventral aspect of the radius in the distal antecubital space.
Examination technique:
- Flex the elbow slightly (15–30°) to slacken the brachioradialis
- Push the brachioradialis laterally to expose the underlying supinator
- Fully supinate the forearm — otherwise the TrPs may be hidden by the ulna rotating over them
- In the supinated position, the TrP lies directly over the radius immediately beneath the skin, between the biceps tendon and the brachioradialis
- Both landmarks are identified by asking the patient to flex the forearm against resistance
- Snapping palpation of very active TrPs may occasionally produce a confirmatory supination twitch response despite the muscle being in a shortened position
Second TrP — attachment (deep): Tenderness to deep palpation through the extensor mass, 4–5 cm distal to the lateral epicondyle and 1–2 cm distal to the head of the radius, pressing downward against the ulna on the lateral side of the forearm. This TrP is sometimes associated with deep radial nerve entrapment. It is reached by probing through the extensor carpi ulnaris longus fibres.
LTR elicitation is often difficult to see or feel from surface palpation in this muscle; it is more reliably identified through the needle during injection.
For TrP diagnostic criteria, see Concept:Trigger_Point.
Epicondyle Tapping Test
Tapping the lateral epicondyle elicits exquisite tenderness of enthesopathy caused by taut-band tension of the central TrPs. Following full TrP inactivation, all tenderness to tapping should be gone. If residual tenderness persists, examine the anconeus and triceps for remaining TrPs.
Joint Play Assessment
Assess the radioulnar (proximal and distal) and radiohumeral joints — these are most critical for normal supinator function. Also check the humeroulnar joint. Restricted joint play must be identified and corrected; TrP treatment alone will not provide lasting relief.
Entrapment
The deep radial (posterior interosseous) nerve may be entrapped as it enters the supinator through the arcade of Frohse. Three clinically distinct scenarios exist:
| Presentation | Likely cause | Key feature |
|---|---|---|
| Painless motor weakness of radial nerve-innervated muscles (extensors of fingers, wrist, thumb) | Usually tumour compressing the nerve | Pain-free; surgical excision relieves motor symptoms |
| Tennis elbow pain without motor weakness or signs of entrapment | Myofascial TrPs without nerve compromise | TrP injection relieves both pain and epicondylar tenderness |
| Tennis elbow pain plus evidence of radial nerve entrapment (motor weakness of posterior interosseous nerve distribution) | Both TrPs and structural arcade thickening | Both components must be treated; TrP inactivation often relieves entrapment without surgery when TrP tension is the cause of arcade tightening |
Mechanism: The deep supinator attachment TrP, when active, shortens the fibres attached to the arcade of Frohse, creating tension on the arch and compressing the nerve as it passes beneath. Inactivation of the supinator TrP on the ulnar side of the nerve typically resolves the entrapment. When the arcade is structurally thickened (30% of normal arms; much higher in surgical patients), the threshold for entrapment is lower.
Historical note on surgical series: Most surgical patients with radial nerve entrapment in published series had been previously treated for lateral epicondylitis — which is commonly caused by myofascial TrPs. The surgical response (division of the arcade of Frohse, splitting the superficial supinator) relieves nerve entrapment but does not inactivate supinator TrPs, explaining incomplete pain relief observed after surgery alone.
Differential Diagnosis
| Condition | Must be present | Must be absent | Merely possible |
|---|---|---|---|
| Supinator TrPs | Taut band with spot tenderness over ventral radius just lateral to biceps tendon; referred pain to lateral epicondyle and/or thumb web; combination of epicondylar tenderness and base-of-thumb pain is strongly suggestive | Motor weakness of wrist/finger extensors; neurological deficit inconsistent with TrP referral | Lateral epicondylar pain; thumb-web pain; dorsal forearm aching |
| Lateral epicondylitis | Localised tenderness at lateral epicondyle and common extensor origin; pain with resisted wrist extension at enthesis | Supinator TrP whose compression reproduces and eliminates the epicondylar pain | Grip weakness; elbow pain with activity |
| Posterior interosseous nerve entrapment (radial tunnel) | Maximum tenderness 3–4 cm distal to lateral epicondyle over radial tunnel; pain with resisted supination; pain with resisted middle finger extension | Pure TrP pattern without motor weakness (unless entrapment is also present) | Lateral epicondylar aching; forearm pain |
| C5–6 radiculopathy | Dermatomal sensory change (thumb/index finger/radial forearm); diminished brachioradialis reflex; positive Spurling's test | Supinator TrP whose compression reproduces pain | Lateral elbow and radial forearm pain |
| De Quervain's tenosynovitis | Positive Finkelstein test; tenderness localised to first extensor compartment at radial styloid | Supinator TrP reproducing thumb-web pain by compression | Thumb-web and dorsal thumb pain |
| Elbow arthritis | Radiological joint changes; restricted ROM at elbow; pain reproduced by passive end-range joint loading | Lateral elbow pain; epicondylar tenderness | |
| Distal radioulnar joint dysfunction | DRUJ joint line tenderness; reduced rotation range; piano-key sign | Lateral elbow pain; rotation pain |
Treatment
Spray and Stretch
- Patient's elbow rests on a padded armrest or over the operator's knee — this permits full elbow extension
- Full forearm pronation takes up all slack in the supinator (windlass position)
- Elbow is supported to prevent medial rotation at the shoulder during the stretch
- After several initial spray sweeps, apply gentle pressure following muscle tension release
- Vapocoolant swept upward and outward diagonally over the forearm, following the muscle fibres from the TrP area to the lateral epicondyle (up-sweep pattern)
- Then down-sweeps over the dorsum of the forearm and web of the thumb
Associated muscles nearly always co-involved must also be treated in the same session: Muscle:Brachioradialis, extensor carpi radialis, Muscle:Extensor_Digitorum, biceps, and brachialis.
Post-treatment check: The elbow should straighten to a previously unobtainable degree of extension. Tapping the lateral epicondyle should produce no further tenderness. If tenderness persists, check the anconeus and triceps for residual TrPs.
Postisometric relaxation (Lewit technique) responds well and is suitable as a home self-treatment programme.
For general principles see Concept:Apropos_Treatment.
Trigger Point Injection
Patient positioned as for TrP examination (elbow flexed 15–30°, brachioradialis pushed aside, forearm supinated).
A 22–27 gauge, 3.8 cm (1½ inch) needle is directed proximally into the TrP just lateral to the biceps tendon attachment, where maximum nodule tenderness is found. LTR is often difficult to see or feel externally in this muscle except via needle feedback.
With the forearm supinated, the deep radial nerve passes lateral to this TrP area (Fig. 36.2B–C) and is not usually encountered during central TrP injection.
The attachment TrP (ulnar-side, deep location) is injected by directing the needle through the extensor mass toward the point of deep tenderness close to the ulna. When this TrP is injected, temporary local anaesthetic block of the nearby nerve is possible — the patient should be warned.
Probe the tender area thoroughly to reach all sensitised loci. No focal TrP tenderness should remain after injection.
After injection: stretch and spray → active pronation and supination (full range) → hot pack. Can be repeated in a few days if needed.
Note on steroid injection: For central TrP injection, adding steroid provides no advantage and some disadvantage. Steroid may be appropriate for attachment TrP injections to speed resolution of enthesopathy. Corticosteroid injections to the lateral epicondyle region are effective short-term (2–6 weeks) because they treat attachment TrPs but leave central TrPs unaddressed, explaining limited duration of relief.
For general injection principles see Concept:Trigger_Point_Injection.
Patient Education
Tennis
- Keep the wrist slightly extended and the elbow slightly bent during play — this position places the forearm flexors at mechanical advantage and enables the biceps to assist the supinator
- Never allow the head of the racquet to drop (Fig. 36.6 in T&S) — a dropped racquet head with a straight elbow is the highest-risk position
- The two-handed backhand protects the supinator by preventing full elbow extension during the stroke; players using this technique have significantly less tennis elbow
- If grip is weak, reduce racquet handle size so fingers wrap fully around it — a large handle forces the ring/little finger extensors to function at a disadvantage
- Rest the supinator between sessions; do not play on consecutive days until TrPs are inactive
- A snug figure-8 elastic support encompassing muscles above and below the elbow (with an opening for the olecranon) discourages full elbow extension and provides counter-pressure
Carrying loads
- Carry packages with the forearms supinated (palms upward) rather than pronated — this transfers the load from the supinator to the much stronger biceps brachii
- With a briefcase: tuck under the arm with the elbow bent; do not flip onto a desk; place it there in two steps (lift first, then lay flat)
Strengthening
After pain has resolved: progressive isotonic exercise of alternating supination and pronation while holding a weight (Fig. 36.7 in T&S), increasing resistance as strength improves. This is started only after TrP pain has fully subsided.
Satellite Trigger Points
Supinator TrPs are typically the primary key TrPs driving the lateral epicondylar complex. When active, they commonly induce satellite TrPs in:
- Muscle:Brachioradialis — almost universally co-involved; the usual second muscle in the sequence
- Extensor Carpi Radialis Longus and Brevis — third in the typical sequence
- Muscle:Extensor_Digitorum — middle and ring finger fibres; fourth in sequence
Muscles that may become involved as part of the supinator's functional unit but do not refer pain to the lateral epicondyle:
- Brachialis; biceps brachii (distal third); sometimes palmaris longus
When all extensor TrPs have been eliminated, an Muscle:Anconeus TrP may still cause residual lateral epicondylar pain and tapping tenderness.
Related Pages
- Muscle:Brachioradialis — almost always co-involved; examine and treat in the same session
- Muscle:Extensor_Carpi_Radialis — radial wrist extensors; next in the typical spread sequence
- Muscle:Extensor_Digitorum — finger extensors; examine when grip and twisting are painful
- Muscle:Anconeus — examine if lateral epicondylar tenderness persists after all other TrPs are resolved
- Concept:Trigger_Point — diagnostic criteria, taut band, LTR, contraction knot
- Concept:Apropos_Treatment — general treatment principles
- Concept:Trigger_Point_Injection — injection principles and post-injection protocol
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 36.