Muscle:Adductor Pollicis and Opponens Pollicis

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Adductor Pollicis and Opponens Pollicis are two intrinsic thumb muscles of the thenar group that together account for the clinical syndrome known as "weeder's thumb" — painful thumb disability from sustained or forceful pincer grip activity. Their referred pain patterns, activation factors, and treatment approaches are closely related, and active trigger points (TrPs) in one are nearly always accompanied by TrPs in the other. Both muscles are frequently confused with carpal tunnel syndrome, DeQuervain's tenosynovitis, and carpometacarpal osteoarthritis.

A distinct mechanical phenomenon — trigger thumb — is also addressed in this chapter. It represents tendon ensnarement of the flexor pollicis longus rather than a TrP, but the TrP tender point responsible for it lies in the same anatomical field and is treated alongside these muscles.

Anatomy

Adductor Pollicis

The adductor pollicis has two heads spanning the web space between the thumb and index finger, lying beneath (dorsal to) the flexor pollicis longus tendon:

  • Oblique head — attaches medially to the bases of the 2nd and 3rd metacarpals and the capitate bone
  • Transverse head — attaches medially to the distal two-thirds of the palmar surface of the 3rd metacarpal bone

Both heads attach laterally to the ulnar side of the base of the proximal phalanx of the thumb, in common with the flexor pollicis brevis and abductor pollicis brevis.

Innervation: Deep palmar branch of the ulnar nerve (medial cord, lower trunk; C8, T1).

Opponens Pollicis

The opponens pollicis runs from a ridge on the trapezium bone of the wrist and the flexor retinaculum medially, to the whole length of the radial side of the first metacarpal bone laterally and distally. It lies partly under the abductor pollicis brevis and between the superficial and deep heads of the flexor pollicis brevis, making palpatory distinction difficult.

Innervation: Branch of the median nerve (lateral cord, upper and middle trunks; C6, C7).

Referred Pain Patterns

Adductor Pollicis

TrPs refer aching pain along the outside (radial side) of the thumb and hand at the base of the thumb, distal to the wrist crease. Spillover encompasses the palmar surface of the first MCP joint and may extend to most of the thumb, the thenar eminence, and the dorsal web space.

Opponens Pollicis

TrPs refer pain to the palmar surface of most of the thumb and to a discrete spot on the radial side of the palmar aspect of the wrist — the patient typically places a fingertip directly on the wrist spot to localise the pain.

Both muscles project pain into the base-of-thumb and radial hand zone. Neither produces autonomic features.

Activation and Perpetuating Factors

Occupational / activity patterns
  • Repeated forceful pincer grip — weeding (grasping and twisting well-rooted weeds), sewing, needlepoint
  • Writing longhand with a ball-point pen held perpendicular to paper (requires firm pressure)
  • Fine paintbrush use requiring sustained thumb tension
  • Opening jar tops
  • Any activity requiring repeated strong pincer grip between thumb and fingers
Post-traumatic perpetuation
  • Fractures of metacarpal or thumb bones may leave residual TrPs; patients attribute continued pain to the old injury and do not realise bone healing should eliminate pain

Clinical Examination

Functional Screen

Before examining the thumb intrinsics, check for active TrPs in the following proximal muscles, all of which can refer tenderness to the web space of the thumb. These must be treated first if active; the referred thumb tenderness may resolve without any local treatment:

In "weeder's thumb," TrPs in the first dorsal interosseous typically respond to treatment immediately, leaving the more complex thumb muscles still symptomatic. Treat first dorsal interosseous first.

Range of Motion and Strength

Test Positive finding Clinical significance
Thumb adduction strength — hold a piece of paper tightly between thumb and 2nd metacarpal bone Paper cannot be held / grip is weak on affected side Adductor pollicis TrP involvement
Thumb abduction and extension Painful, and often restricted Characteristic finding with adductor pollicis TrPs
Opposition — bring thumb pad to pad of little finger Reduced, weak, or painful Opponens pollicis TrP involvement
Flexion and adduction of thumb Weaker on affected side Either muscle; account for handedness

Trigger Thumb Examination

The "trigger thumb" phenomenon is a mechanical locking — the patient cannot extend the thumb without external assistance after flexing it. It must be distinguished from pain alone.

To locate the responsible TrP / tender point:

  1. Patient supinates the forearm and fully extends the MCP joint of the thumb
  2. Patient alternately flexes and extends the distal phalanx while the examiner identifies the flexor pollicis longus tendon
  3. Place a finger against the bulge of the MCP joint, pressing on the space between flexor pollicis brevis and adductor pollicis where the tendon enters the fascial sheath
  4. The TrP tenderness is located several millimetres lateral (radial) to the tendon, just proximal to the bony bulge of the MCP joint

Note: Locking of the interphalangeal joint of the thumb may alternatively be caused by a sesamoid bone of that joint (not a TrP).

Heberden's Nodes

Heberden's nodes on the ulnar side of the interphalangeal joint of the thumb are closely associated with TrPs in the adductor pollicis. When a node is present there, an associated TrP is nearly always found in the adductor pollicis. This relationship parallels the Heberden's node / palmar interosseous association at the fingers (see Chapter 40).

Symptoms

Active TrPs in either muscle produce:

  • Thumb pain during activity; severe TrPs produce pain at rest
  • Subjective clumsiness of the thumb — patients report difficulty with fine manipulation
  • Illegible handwriting — "can hardly hold a pen"
  • Difficulty with buttons, sewing, drafting, painting — any task requiring the prehensile pincer grip

Differential Diagnosis

Condition Must-have features Features absent with pure TrP Key distinguishing test
Carpal tunnel syndrome Median nerve distribution paraesthesia (thumb, index, middle, radial ring finger); nocturnal pain; positive Phalen's / Tinel's Sensory loss in median distribution; thenar atrophy (late) Nerve conduction study; Phalen's test (60 s wrist flexion)
DeQuervain's stenosing tenosynovitis Pain over radial styloid; tenderness of 1st extensor compartment tendons (APL, EPB) Taut band; referred pain distant from the tendon; TrP nodule Finkelstein's test — positive in DeQuervain's, negative with isolated TrP
Carpometacarpal osteoarthritis Basal joint tenderness; crepitus on grind test; radiographic joint space narrowing Referred pain pattern extending to thenar eminence and wrist CMC grind test; X-ray
First MCP joint disease Localised joint swelling, crepitus, true joint-line tenderness Pain reproduced by distant TrP palpation; taut band palpable Distinguish by inactivating TrP and re-assessing joint tenderness
Trigger thumb (mechanical) Locking — thumb cannot extend without assistance after flexion; tender spot radial to FPL tendon Referred pain pattern; pain in thenar eminence and wrist Locking is present only in trigger thumb; absence of locking with thumb pain = TrP only

Note: An accessory flexor pollicis longus muscle, when present, can cause anterior interosseous nerve compression neuropathy — a rare mimic of thumb weakness. Articular dysfunction, particularly volar subluxation of a metacarpal on a carpal bone at the first CMC joint, may coexist with TrPs and must be identified and corrected separately.

No nerve entrapments are attributed to active TrPs in these muscles.

Trigger Point Examination

Adductor Pollicis

With the patient seated and the hand pronated and relaxed, examine the web space of the thumb by pincer palpation through the dorsal approach. The first dorsal interosseous muscle, which lies superficial to the transversely oriented adductor fibres, is pushed aside. Identify the nodule with exquisite spot tenderness in a taut band; reproduce referred pain the patient recognises; elicit a local twitch response in skilled hands.

Opponens Pollicis

Identify active TrPs by flat palpation across the direction of the muscle fibres over the thenar eminence. When the TrP is deeply located, a local twitch response is more difficult to elicit than when the TrP lies in the superficial abductor or flexor pollicis brevis fibres above it.

Treatment

Spray and Stretch

See Apropos Assessment and Apropos Treatment for general principles.

With the forearm supinated and resting on a supporting surface that permits full thumb extension:

  • Adductor pollicis: Abduct the thumb to the onset of resistance to lengthen the adductor; apply vapocoolant in parallel sweeps across the palm toward and over the radial surface of the thumb
  • Opponens pollicis: Extend then adduct the thumb (hyperadduction stretch); add a proximal spray pattern across the radial side of the wrist to cover the opponens referral zone

Follow with three slow full cycles of active range of motion and application of moist heat.

Important: Trigger thumb is not released by spray and stretch alone. Trigger point pressure on the tender spot at the point of restriction is sometimes effective; TrP injection is more reliably effective.

Trigger Point Pressure Release

An alternative to spray and stretch using contract-relax:

  1. Apply trigger point pressure on the TrP combined with intermittent cold application
  2. Have the patient contract the muscle during the pressure application, then fully relax while the clinician takes up the slack
  3. Alternate pressure with voluntary contraction and cold application
  4. Tenderness may take several hours to begin subsiding; repeat every one to two days for several cycles before the TrP is fully inactivated

Trigger Point Injection

See Trigger Point Injection for general injection technique and post-injection care.

Adductor pollicis

Palpate for TrPs with the hand pronated (Section on TrP Examination above). When located, press against the TrP from the palmar side to fix it and provide guidance. Direct the needle from dorsal to palmar; it should pass to the radial side of, or possibly penetrate, the first dorsal interosseous muscle. Following injection: passive stretch with vapocoolant sweeps, three cycles of full active range of motion, moist heat.

Opponens pollicis

Locate the TrP by flat palpation. Inject via palmar approach. Passively stretch with vapocoolant application, move through full range, rewarm the skin.

Trigger thumb injection

Locate the tender spot radial to the flexor pollicis longus tendon at the head of the first metacarpal (Section on TrP Examination above). With the thumb fully extended, probe widely down to the head of the first metacarpal bone, lateral and deep to the tendon. The tendon itself usually need not be injected to eliminate the locking mechanism.

Note on natural history: Of 30 patients presenting with trigger thumb, 25 resolved spontaneously without treatment over an average of 6.8 months (range 2–15 months).

Active TrPs in the adductor and opponens pollicis are almost always accompanied by TrPs in the first dorsal interosseous muscle, which is typically secondarily affected due to its synergistic function. The first dorsal interosseous typically responds to treatment first; the thumb muscles are the primary problem.

The flexor pollicis brevis and abductor pollicis brevis are also likely to become involved. The pain patterns and treatment approach for the opponens pollicis are similar to those of the abductor and flexor pollicis brevis, which lie partly over the opponens and are difficult to distinguish by palpation.

Corrective Actions

Activity modification
  • Avoid persistent, vigorous weeding — limit time, alternate hands, loosen soil with a spading fork before pulling
  • Replace ball-point pens held perpendicular to paper with soft felt-tip pens (far less pressure required)
  • Limit continuous needlepoint sessions
  • Artisans using tools requiring sustained fine grip: pause every 10–15 minutes for a stretch exercise
Home Exercises
  • Adductor Pollicis-stretch: Place hands in a basin of warm water; press the thumb and index finger of both hands against each other to achieve full passive abduction and extension of the thumbs
  • Opponens Pollicis-stretch: Fully extend the thumb, then passively adduct (hyperadduct) it using the fingers of the opposite hand as the external force. A slightly less extended position stretches the opponens fibres specifically. Most effective done under a warm shower or in warm water.
  • Artisan's Finger-stretch Exercise (Fig. 35.8 in T&S): Recommended as the break exercise during gardening or fine grip activity
  • Finger-flutter Exercise (Fig. 35.9 in T&S): Drop hands at sides with elbows straight and shake the fingers in a limp fluttery motion to relax the muscles and increase circulation

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 39 (pp. 774–785).
  • Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1. 2nd ed. Chapter 33 (pp. 685–689).
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