Muscle:Hand and Finger Flexors

Hand and Finger Flexors is a group page covering the volar forearm muscles that flex the wrist and fingers: the flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), flexor digitorum profundus (FDP), and flexor pollicis longus (FPL). The pronator teres is included here as T&S treats it in the same chapter, sharing a common activation profile and nerve entrapment risk. All arise predominantly from the medial epicondyle and are treated as a functional group for examination, stretch, and spray.

These muscles are a major source of volar wrist pain, finger pain projecting to the fingertips, and medial elbow pain. They are consistently co-involved and are the volar counterpart to the extensor mass group. Critically, their pain pattern — pain to and beyond the fingertip — distinguishes them from the extensor digitorum, which stops short of the fingertip. They also carry important nerve entrapment risk for both the ulnar and median nerves.

Anatomy

Flexor Carpi Radialis

• Proximal: Medial epicondyle via common flexor tendon; intermuscular septa
• Distal: Base of second metacarpal (primary); slip to third metacarpal
• Location: Subcutaneous, nearly centred on the volar forearm between the pronator teres (radial side) and palmaris longus (ulnar side); belly extends to mid-forearm
• Innervation: Median nerve; C6 and C7
• Architecture: Structured for speed; three separately innervated compartments with a diagonal endplate zone. Fiber/muscle length ratio 0.31.

Flexor Carpi Ulnaris

• Proximal: Two heads — humeral head via common flexor tendon; ulnar head to medial margin of olecranon and proximal dorsal border of ulna via an aponeurosis shared with ECU and FDP
• Distal: Pisiform bone
• Location: Superficially along the volar side of the sharp edge of the ulna
• Innervation: Ulnar nerve; C8 and T1
• Architecture: Designed for force (pennate, fiber/muscle ratio 0.19; nearly longitudinal endplate zone). The ulnar nerve passes beneath the humeroulnar arcade formed by the two heads of the FCU — the cubital tunnel — and then courses through the FCU muscle for 18–70 mm before entering the triangular space between the FCU (superficial), FDS (lateral), and FDP (deep).

Flexor Digitorum Superficialis

• Proximal: Three heads — humeral head (medial epicondyle), ulnar head (medial coronoid process), radial head (oblique line of radius). The median nerve passes beneath the fibrous arch between the ulnar and radial heads.
• Distal: Each tendon divides at the first phalanx to pass around the FDP tendon, inserting into the sides of the middle phalanx of each finger
• Location: Covers most of the volar forearm beneath the palmaris longus and flexores carpi. Belly locations vary by digit: 2nd and 5th digit bellies are relatively distal; 3rd and 4th are more proximal.
• Innervation: Median nerve; C7 and C8
• Primary action: Selectively flexes the middle phalanges; also flexes the proximal phalanx and assists wrist flexion

Flexor Digitorum Profundus

• Proximal: Proximal three-quarters of the volar, medial and dorsal surfaces of the ulna; medial coronoid; ulnar half of the interosseous membrane
• Distal: Base of the terminal phalanx of each finger
• Innervation: Split — ulnar half by ulnar nerve; radial half by median nerve (anterior interosseous branch); C8 and T1
• Primary action: Flexes the terminal phalanx primarily; also flexes all other phalanges and the hand; used for gross closure of the fist simultaneously at all joints

Flexor Pollicis Longus

• Proximal: Radius and adjacent interosseous membrane; variable slip to humerus
• Distal: Base of the distal phalanx of the thumb
• Location: Runs throughout the forearm on the radial side beneath the FDS
• Innervation: Median nerve (anterior interosseous branch); C8 and T1
• Primary action: Flexes the terminal phalanx of the thumb; then proximal phalanx with metacarpal adduction; assists wrist flexion and abduction

Pronator Teres

• Proximal: Two heads — humeral head (proximal to medial epicondyle); ulnar head (medial coronoid). The median nerve enters the forearm between these two heads.
• Distal: Lateral surface of the radius at its midpoint
• Innervation: Median nerve; C6 and C7
• Primary action: Pronation of the forearm (assists pronator quadratus); assists elbow flexion only against resistance
• Architecture: Pennate (10°), short fiber ratio (0.28) — designed for force. Endplate zone nearly longitudinal.

Referred Pain Patterns

Flexor Carpi Radialis

Pain and tenderness centred on the radial aspect of the volar wrist crease, with spillover into the adjacent radial forearm and palm.

Flexor Carpi Ulnaris

Pain and tenderness on the ulnar side of the volar wrist with similar spillover into the ulnar forearm and hypothenar region.

Flexor Digitorum Superficialis and Profundus

No distinction is made between the FDS and FDP referral patterns. TrPs in fibres serving a given digit refer pain:

• Throughout the full length of the corresponding finger on the volar surface
• Pain is often explosive and described as "shooting right out the end of the finger, like lightning" — pain goes to and beyond the fingertip
• Middle finger fibres: pain through the middle finger
• Ring and little finger fibres: pain through those digits
• Index finger fibres: comparable to the middle finger pattern

This "beyond the fingertip" quality is the key differentiator from the extensor digitorum, which stops short of the last phalanx.

When asked if pain is on the top or underside of the finger, patients with flexor TrPs typically rub the volar surface and reply "I don't know" — movement confirms the volar distribution.

Important: Kellgren demonstrated that FDP injection produced MCP joint pain indistinguishable from direct intra-articular injection — finger joint pain attributed to arthritis may originate from FDP TrPs.

Flexor Pollicis Longus

Pain throughout the volar aspect of the thumb to its tip (and beyond).

Pronator Teres

Pain deep in the volar radial region of the wrist and radial forearm. May mimic carpal tunnel syndrome.

Activation and Perpetuating Factors

TrPs in these muscles are activated by abuse of gross gripping movements, not by fine pincer movements (which activate intrinsic hand muscles instead):

• Prolonged tight gripping: ski poles held hard for extended periods; tightly gripping a steering wheel (especially with hand at the top, wrist flexed)
• Tight gripping of small-handled tools: carpenter's, carpenter's work, gardening
• Driving with fingers tightly wrapped around the wheel, especially sustained
• Placing hair curlers or a hair clasp at the back of the head (requires sustained finger flexion)
• Using scissors for cutting heavy cloth or tin shears
• Flexor pollicis longus ("weeder's thumb"): forceful rocking, twisting, then pulling motions straining the thumb muscles
• Pronator teres: fracture at the wrist or elbow; sustained pronation tasks

Satellite TrP relationships:

• Satellite TrPs may develop in the FCR from key TrPs in the pectoralis minor
• Satellite TrPs may develop in the FCU from key TrPs in the pectoralis minor, latissimus dorsi, or serratus posterior superior
• Finger flexor TrPs may develop as satellites to TrPs in neck and shoulder muscles that refer pain into the volar forearm (particularly scalenes and pectoralis minor when also causing nerve entrapment)
• FPL TrPs tend to develop independently of the other forearm flexor TrPs

Important warning: The passive stretch position used to treat the finger extensors (full finger and wrist flexion) can cause sudden shortening activation of latent TrPs in the flexors. Always include flexor stretch and spray routinely when treating the extensors.

Clinical Examination

History and Functional Assessment

Key features distinguishing flexor TrPs:

• Difficulty using scissors (patients with extensor/tennis elbow TrPs report no problem with scissors)
• Difficulty placing hair curlers or clasps
• Pain shooting to the fingertip or beyond
• Pronator teres TrPs specifically: inability to supinate the cupped hand to receive coins — the combined motion of full supination, slight extension, and palm cupping becomes prohibitively painful; patients compensate by rotating from the shoulder

Finger-Extension Test (Global Screen)

Screens both hands simultaneously:

1. Place fingertips of both hands together (Fig. 38.3A)
2. Push palms tightly against each other, bringing forearms into as straight a horizontal line as possible (Fig. 38.3B)

Positive: Feeling of tightness in the muscle(s) and pain in the specific finger/wrist pain reference zones. The final position requires palms flat together with both forearms in a horizontal line — anything less is a positive finding.

Individual flexor screen: Fully supinate the forearm with fingers (including distal phalanges) and hand fully extended — this screens all hand and finger flexors simultaneously. For the FPL specifically: extend the wrist and thumb.

Individual Digit Testing

Test each digit by passive extension:

1. Extend the wrist and just the middle phalanx
2. Then add extension of the distal phalanx

Painful limitation at either step identifies involvement of that digit's flexor.

Pronator Teres Test

Ask the patient to supinate the cupped hand as if receiving coins. Pain or inability with this combined motion (full supination + slight extension + palm cupping) is characteristic of active pronator teres TrPs.

Trigger Point Examination

FCR and FCU: Sufficiently superficial for TrPs to be identifiable by spot tenderness of a nodule in a taut band and elicitation of the patient's familiar pain. Locate in midfibre portions. To elicit LTRs, supinate the forearm and let the hand hang limply extended.

FDS, FDP, FPL: These deep flexors are so deeply placed that the examiner often cannot distinguish palpable changes. The diagnostic criterion becomes deep tenderness that reproduces the patient's pain complaint on firm pressure. Deep finger flexor TrPs are usually located approximately 3 cm distal to the medial epicondyle.

For TrP diagnostic criteria see Concept:Trigger_Point.

Joint Play Assessment

Assess the wrist articulations (radiocarpal, intercarpal) and the MCP and IP joints. If restricted, joint play must be restored alongside TrP treatment.

Entrapment

Flexor forearm TrPs can contribute to entrapment of both the ulnar and median nerves. This is clinically important because symptoms may be attributed entirely to structural entrapment when TrP taut bands are the primary or a contributing cause.

Table 38.1 (T&S): Forearm muscles whose TrPs may cause nerve entrapment

Nerve	Muscles
Ulnar nerve	Flexor carpi ulnaris; Flexor digitorum superficialis; Flexor digitorum profundus
Median nerve	Pronator teres; Flexor digitorum superficialis

Ulnar Nerve (Cubital Tunnel)

The ulnar nerve passes behind the medial epicondyle and enters the forearm beneath the humeroulnar arcade formed by the two heads of the FCU (3–20 mm distal to the medial epicondyle). It then courses through the FCU for up to 70 mm before occupying the triangular space bounded by the FCU, FDS, and FDP.

Mechanism: FCU TrP taut bands can compress the ulnar nerve by: (1) pulling the humeroulnar arcade tight against the nerve; (2) direct compression where the nerve penetrates the muscle. FDP TrPs sometimes also seem to contribute, though the precise mechanism is unclear.

Symptoms: Dysaesthesia, burning pain, numbness in the 4th and 5th digits; clumsiness and grip weakness with motor involvement. Confirmed by delayed nerve conduction velocity across and beyond the condylar groove.

Temporary ulnar nerve block during injection of deep finger flexor TrPs is not uncommon — warn the patient in advance.

Median Nerve (Pronator Teres Syndrome)

The median nerve passes between the humeral and ulnar heads of the pronator teres beneath a fibrous arch, and then beneath the aponeurotic arch of the FDS bridging between its radial and humeroulnar heads.

Mechanism: Pronator teres TrP taut bands increase tension on the aponeurotic arch against the nerve and may directly compress the nerve where it penetrates the humeral head. FDS TrPs increase tension on the FDS arch similarly.

Symptoms: Paraesthesiae and hyperaesthesia of the 3rd and 4th digits (sometimes additional digits). This is the pronator teres syndrome.

CTS mimicry: TrPs in the pronator teres, FCR, and/or brachialis are a common TrP-origin cause of symptoms attributed to carpal tunnel syndrome. Even more proximal TrPs in the SCM, infraspinatus, and subscapularis have produced symptoms leading to a CTS diagnosis. Median nerve conduction study and TrP examination together establish the composite diagnosis.

Symptoms due to TrP entrapment are relieved by inactivating the contributing TrPs.

Trigger Finger

Trigger finger (also "locking finger" or "trick finger") is a painless but very annoying dysfunction in which the digit locks in the flexed position and must be extended by external force.

Mechanism: A nodule in the flexor tendon is caught by the constriction of the annular band anchoring the tendon sheath, apparently near the distal palmar synovial sheath for digits 2, 3, and 4. The nodule may result from a lumbrical muscle TrP.

Diagnosis: Tender point deep in the fascial sheath just proximal to the corresponding metacarpal head.

Conservative release technique: The locking mechanism is less effective when the tendon is loaded. With the finger locked:

1. Have the patient flex the digit slightly more
2. Apply active resistance to place the tendon under tension
3. Have the patient gradually extend the finger while maintaining the tension

This loading technique is more effective than passively pulling the finger back to normal position (which aggravates the mechanism). Firm pressure on the tender spot may also restore function.

Injection: The needle is aligned with the midline of the finger and inserted into the centre of the tender point, deep in the restricting fibrous ring, in the midline just proximal to the metacarpal head. Inject 1–1.5 ml of 0.5% procaine. No LTR is observed — this TrP is purely fascial, not within muscular tissue. Relief may be prompt but full function may take several days to return. Combined steroid/analgesic injection has a 60% success rate vs 16% for analgesic alone, suggesting an inflammatory component.

Avoid recurring heavy pressure on the tender spot (e.g. from a cane handle or tool grip against the metacarpal head).

Differential Diagnosis

Condition	Must be present	Must be absent	Merely possible
Flexor forearm TrPs	Taut band with spot tenderness in midfibre flexor belly; referred pain to volar wrist or finger reproduced by compression; Finger-Extension Test positive; pain to or beyond fingertip	Neurological deficit inconsistent with TrP referral; structural joint changes	Volar wrist pain; finger pain; medial epicondylar tenderness; grip weakness
Medial epicondylitis	Localised tenderness at medial epicondyle and common flexor origin; pain with resisted wrist flexion at the enthesis	Flexor belly TrP whose compression reproduces medial epicondylar pain	Volar forearm aching; grip weakness
Ulnar neuropathy (cubital tunnel)	Delayed nerve conduction velocity across the cubital tunnel; sensory/motor deficit in ulnar nerve distribution (4th/5th digits, intrinsic hand muscles)	FCU TrP compression alone reproducing all symptoms	Ring/little finger dysaesthesia; grip weakness; cubital tunnel tenderness
Carpal tunnel syndrome	Positive Phalen's test; nocturnal median nerve distribution paraesthesiae; Tinel's sign at carpal tunnel; electrophysiological median nerve compression	Pronator teres or FCR TrP whose compression reproduces and relieves the volar wrist/hand symptoms	Volar wrist and hand pain; finger numbness; grip weakness
Pronator teres syndrome	Paraesthesiae in median distribution below the elbow; Tenderness at the pronator teres belly (not the carpal tunnel); pronation resisted at the elbow reproduces symptoms	Positive Phalen's test; Tinel's sign at wrist	Volar forearm and wrist pain; median digit numbness
C8/T1 radiculopathy	Dermatomal sensory change in C8 distribution (ring/little finger, ulnar forearm); reflex changes	TrP in humeral head FDS or FDP reproducing symptoms by compression	Finger pain; grip weakness; medial elbow pain
Finger joint arthritis	Joint swelling; radiographic changes; morning stiffness > 1 hour	FDP TrP whose compression reproduces the joint pain (Kellgren showed FDP TrP injection produces MCP pain indistinguishable from intra-articular injection)	MCP joint pain; PIP tenderness; grip stiffness
Osteoarthritis of the wrist	Radiographic joint changes; wrist ROM restriction with end-range pain	Flexor belly TrP reproducing wrist pain by compression	Volar wrist pain; wrist stiffness

Treatment

Spray and Stretch

For FCR, FCU, FDS, FDP:

1. Patient supine, elbow resting on a padded surface, forearm supinated
2. Hand hangs over the edge — hand and fingers are passively extended simultaneously, while the hand is pressed into full supination
3. All three positions must be established together (supination + wrist extension + finger extension) — partial positioning does not achieve full stretch
4. Vapocoolant applied in parallel sweeps from the medial epicondyle to the fingertips over the muscles and their referred pain zones
5. Three slow cycles of full active ROM; moist heat promptly to the volar forearm

For the FPL: hand and thumb extended similarly; spray sweeps travel from medial epicondyle down over the radial forearm and thumb.

Postisometric relaxation (Lewit technique) is effective and suitable for home use.

For general principles see Concept:Apropos_Treatment.

Trigger Point Injection

FCR: Patient supine, elbow extended, hand supinated. Locate by flat palpation; inject 0.5% procaine. Stretch passively after injection.

FCU: Patient supine; ask patient to flex the elbow and laterally rotate the arm to expose the FCU. Superficial enough for flat palpation. LTR observed when the needle encounters an active locus.

FDS, FDP: Tender spots located by flat palpation for the superficial FDS. Deep flexor TrPs located approximately 3 cm distal to the medial epicondyle; needle must penetrate to at least 2 cm beyond the FCU surface, reaching the FDS or FDP. Warn the patient: temporary ulnar nerve block is not uncommon — local anaesthesia resolves in 15–20 minutes.

TrP injection is usually not required for these flexors unless TrPs are aggravating ulnar nerve entrapment at the elbow, or responsible for trigger fingers.

Every injected muscle must be extended to full range of motion at once — passively first, then actively through three slow cycles in both directions. Moist heat applied promptly.

For general injection principles see Concept:Trigger_Point_Injection.

Patient Education

• Avoid prolonged tight gripping — relax the grip frequently during sustained activities (skiing, driving)
• When driving: grasp the steering wheel halfway between top and bottom, not at the top where the wrist is flexed; pronate the hand rather than holding it supinated; stretch at intervals
• When rowing or paddling: fully open the fingers on the return stroke, holding the oar between thumb and palm only — this stretches and rests the flexors
• In racquet sports: maintain a neutral or slightly cock-up wrist position; do not let the racquet droop
• Keep the hand and forearm supported on the armrest when seated — do not let the hand dangle (leaves flexors in a shortened position)

Exercise Programme

Four exercises form the daily maintenance programme:

• Finger-extension Exercise (Fig. 38.7): passive self-stretch with the forearm well supported
• Artisan's Finger-stretch Exercise (see Muscle:Extensor_Digitorum corrective actions, Fig. 35.8): stretches and activates both flexors and extensors
• Finger-flutter Exercise (Fig. 35.9): passive relaxed shaking of the hands
• Interosseous-stretch Exercise (see Muscle:Interossei, Fig. 40.6)

Satellite Trigger Points

Key TrP sources driving flexor group as satellites:

• Muscle:Pectoralis_Minor — key TrPs drive satellite TrPs in FCR and FCU
• Muscle:Latissimus_Dorsi — key TrPs can drive satellite TrPs in FCU
• Muscle:Serratus_Posterior_Superior — key TrPs can drive satellite TrPs in FCU
• Scalene muscles — shoulder/neck TrPs referring into the volar forearm, especially when also causing nerve entrapment
• FPL TrPs develop independently — check for independent activation factors

Parallel co-involvement:

• FCR and FCU TrPs tend to develop together
• FDS and FDP TrPs tend to develop together
• FCR may develop TrPs in isolation following elbow fracture

Related Pages

• Muscle:Extensor_Digitorum — functional antagonist group; treat together when extensors are being stretched
• Muscle:Palmaris_Longus — lies between FCR and FCU; commonly co-involved in volar forearm pain
• Muscle:Pectoralis_Minor — key TrP source for FCR/FCU satellite involvement
• Muscle:Interossei — intrinsic hand muscles; co-examine when fine pincer pain is present
• 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 38.