Opponens Pollicis Anatomy

Origin

• The tubercle (crest) of the trapezium.
• The adjacent flexor retinaculum (transverse carpal ligament) on its palmar surface.
• Some fibres arise from the trapezial ridge in continuity with the origin of abductor pollicis brevis.

Insertion

• The entire length of the radial border and adjacent palmar surface of the shaft of the first metacarpal, from just distal to the base to the neck.
• This is the defining feature. Abductor pollicis brevis and flexor pollicis brevis both insert into the base of the proximal phalanx (via the radial sesamoid and the extensor hood); opponens pollicis alone inserts into the metacarpal shaft, which is precisely why it rotates the ray rather than moving the joint distal to it.

Architecture

• The fibres run distally, laterally and dorsally, curving around the metacarpal in a spiral — the anatomical signature of a rotator.
• Fibre length is short (of the order of 2-3 cm) with a modest cross-sectional area; it is a positioning muscle, not a strength muscle. This matters when selecting a donor: an opponensplasty needs excursion and vector, not raw power.

Recurrent (Thenar) Motor Branch of the Median Nerve — C8, T1

• Arises from the radial (lateral) or radial-palmar aspect of the median nerve, classically at or just distal to the distal edge of the transverse carpal ligament, roughly 1-2 cm distal to the distal wrist crease.
• It then turns sharply radially and proximally — hence "recurrent" — running over the palmar surface of flexor pollicis brevis before entering the thenar muscles from their deep surface.
• Order of supply: abductor pollicis brevis, then opponens pollicis (entering its deep surface near the junction of the proximal and middle thirds), then the superficial head of flexor pollicis brevis.

The Lanz classification of median nerve variation

Lanz (1977) reviewed 246 operatively explored carpal tunnels and, combining his findings with published reports, classified median nerve variation into four groups:

• Group I — variation in the course of the thenar motor branch. Lanz cited Poisel's dissection of 100 cadaver hands for the frequencies:
  • Extraligamentous (Ia, 46%): arises distal to the transverse carpal ligament and recurs around its distal edge. The commonest and safest pattern.
  • Subligamentous (Ib, 31%): arises within the carpal tunnel and passes distally beneath the ligament before turning radially.
  • Transligamentous (Ic, 23%): arises within the tunnel and pierces the transverse carpal ligament. This is the variant divided by a blind or endoscopic release and by an open release carried too radially.
• Group II — accessory branches at the distal portion of the carpal tunnel (18 of Lanz's 29 observed variations).
• Group III — high division of the median nerve in the forearm (7 cases), sometimes with a persistent median artery between the two limbs.
• Group IV — accessory branches proximal to the carpal canal (4 cases).

Lanz's own conclusion is the operative rule that still applies: approach the median nerve from the ulnar side when opening the carpal tunnel.

The other communications

• Martin-Gruber anastomosis: a median-to-ulnar motor communication in the forearm (usually from the anterior interosseous nerve), present in roughly 15-20% of limbs. It can preserve intrinsic function after a proximal ulnar lesion and confounds nerve conduction studies.
• Riche-Cannieu anastomosis: an ulnar-to-median communication in the palm, between the deep ulnar branch and the recurrent motor branch. It can preserve thenar function after complete median division — the all-ulnar hand — and is the classic explanation for a patient with a divided median nerve who can still oppose.

Arterial

• Superficial palmar branch of the radial artery — arises just proximal to the wrist, passes through or superficial to the thenar muscles and joins the superficial palmar arch. It is the dominant supply to opponens pollicis.
• Branches from the princeps pollicis artery and the first dorsal metacarpal artery supply the distal muscle.
• Twigs from the superficial palmar arch contribute.

Pedicle position and flap relevance

• The superficial palmar branch of the radial artery enters the thenar muscle mass from its radial and proximal aspect, at the proximal border of the thenar eminence approximately 1 cm distal to the level of the radial styloid.
• This vessel is the pedicle of the superficial palmar branch of the radial artery flap used for small palmar and digital defects, and it is the vessel divided by an over-extended volar approach to the scaphoid or a thenar-crease incision carried too proximally.
• The thenar flap for fingertip reconstruction raises skin from the thenar eminence over opponens pollicis and abductor pollicis brevis, relying on the subdermal plexus fed by these vessels.

Venous

• Small venae comitantes drain into the superficial palmar venous network and thence to the cephalic vein system over the anatomical snuffbox.

Superficial (palmar) to the muscle

• Abductor pollicis brevis covers it almost completely; the opponens is exposed only at the distal radial margin of the thenar eminence when abductor pollicis brevis is retracted.
• The recurrent motor branch lies on the palmar surface of the muscle mass before diving into it.
• The palmar cutaneous branch of the median nerve runs subcutaneously over the thenar eminence. Arising 5-7 cm proximal to the wrist crease and travelling between palmaris longus and flexor carpi radialis, it supplies the skin of the thenar eminence and central palm. It is not deep to the retinaculum and is injured by an incision placed too radially or crossing the wrist crease.

Deep (dorsal) to the muscle

• The first metacarpal shaft.
• The flexor pollicis longus tendon, ulnar and deep, running between the two heads of flexor pollicis brevis to the thumb IP joint.
• Proximally, the trapeziometacarpal joint capsule and the flexor carpi radialis tendon in its groove on the trapezium — a relation that matters in trapeziectomy and in FCR-based ligament reconstruction.

Ulnar

• Flexor pollicis brevis (superficial head), then adductor pollicis across the thenar septum.

The thenar space

• The thenar space lies deep to the index flexor tendons and radial to the thenar (oblique) septum, which runs to the third metacarpal. The thenar muscles form its radial wall. Thenar space pus therefore presents with a swollen, abducted thumb and a full first web, and is drained through a palmar incision parallel to the thenar crease, sometimes combined with a dorsal first web incision.

Low median nerve palsy (wrist level)

• Deficit: abductor pollicis brevis, opponens pollicis, superficial head of flexor pollicis brevis and the radial two lumbricals; sensory loss over the radial three and a half digits (palmar cutaneous territory spared if the lesion is within the tunnel).
• Posture: the ape hand — thumb adducted and supinated in the plane of the palm.
• Causes: carpal tunnel syndrome, laceration at the wrist, distal radius fracture with acute carpal tunnel syndrome, iatrogenic recurrent branch division.

High median nerve palsy (elbow or proximal forearm)

• Adds loss of flexor pollicis longus, flexor digitorum profundus to index and middle, flexor digitorum superficialis, pronator teres and pronator quadratus.
• Benediction (pointing) hand on attempted fist: index and middle fail to flex. Note carefully that this is the high median posture on active fist, and it must not be confused with the ulnar claw, which is a resting posture of the ring and little fingers in ulnar palsy.
• Opponensplasty in high median palsy must use a donor that is not itself median-innervated: extensor indicis proprius or abductor digiti minimi (Huber). Palmaris longus and ring flexor digitorum superficialis are median-supplied and unavailable.

Carpal tunnel syndrome

• Thenar wasting is a late finding, indicating axonal loss, and predicts incomplete recovery of opposition after release.
• A patient with established wasting should be counselled that release relieves pain and prevents progression but may not restore opposition, and that opponensplasty (commonly a Camitz at the time of release) is a reasonable adjunct.
• Acute carpal tunnel syndrome after a distal radius fracture is a surgical emergency; unremitting pain with progressive median paraesthesia mandates urgent release, not observation.

Thumb hypoplasia

The thenar muscles, including opponens pollicis, are deficient in congenital thumb hypoplasia. The modified Blauth classification drives treatment:

• Type I: minor hypoplasia, all structures present. No treatment.
• Type II: thenar hypoplasia, first web narrowing, ulnar collateral ligament insufficiency, stable trapeziometacarpal joint. Treat with opponensplasty (usually Huber), first web release and UCL reconstruction — reconstruct.
• Type IIIA: as type II plus extrinsic tendon abnormalities and skeletal deficiency, but the trapeziometacarpal joint is stable — still reconstruct.
• Type IIIB: the trapeziometacarpal joint is absent or unstable; the metacarpal base is deficient. Pollicisation of the index finger is the standard treatment.
• Type IV (pouce flottant, floating thumb): attached only by a skin bridge. Pollicisation.
• Type V: complete absence. Pollicisation.

The decision point examiners test: the stability of the trapeziometacarpal joint separates IIIA from IIIB, and therefore reconstruction from pollicisation.

Syndromic screening

Thumb hypoplasia is frequently part of radial longitudinal deficiency, so screen for:

• Fanconi anaemia — chromosomal breakage testing is mandatory before elective surgery; it is life-limiting and changes the entire plan.
• Thrombocytopenia-absent radius (TAR) syndrome — note that in TAR the thumb is characteristically present despite absent radii.
• Holt-Oram syndrome — cardiac septal defects; echocardiography.
• VACTERL association — vertebral, anorectal, cardiac, tracheo-oesophageal, renal and limb anomalies; renal ultrasound and spinal imaging.

Why Huber in the congenital hand

The Huber transfer is preferred because the hypoplastic thenar eminence is not merely weak but absent in bulk. Transferring abductor digiti minimi rotates a muscle belly, not just a tendon, onto the thenar eminence, restoring contour and motion together. It also spares median-innervated donors, which may themselves be abnormal.

Cervical and systemic causes of thenar wasting

• C8-T1 radiculopathy and true neurogenic thoracic outlet syndrome (the Gilliatt-Sumner hand): wasting is worse in abductor pollicis brevis than in the hypothenar and interossei, a pattern that superficially mimics median palsy but is accompanied by medial forearm sensory loss in the medial antebrachial cutaneous nerve territory, which is not median.
• Motor neurone disease: the split hand phenomenon — disproportionate wasting of abductor pollicis brevis and first dorsal interosseous with relative sparing of abductor digiti minimi. Painless bilateral thenar wasting with fasciculation is not a carpal tunnel problem.
• Leprosy remains a major global cause of combined median and ulnar intrinsic palsy and is the setting in which opponensplasty is most frequently performed worldwide.
• Charcot-Marie-Tooth disease and other hereditary neuropathies produce symmetrical intrinsic wasting with pes cavus and areflexia.

The trap

Bilateral, painless, progressive thenar wasting is not carpal tunnel syndrome until proven otherwise. Examine the neck, test medial forearm sensation, and look for fasciculation.

Trapeziometacarpal osteoarthritis

• Advanced disease adducts the metacarpal and shortens the thumb ray. Opposition is lost through joint mechanics rather than muscle failure, so Kapandji scores fall despite an entirely normal median nerve. Distinguish by testing abductor pollicis brevis strength, which is preserved, and by the presence of a positive grind test and radiographic changes.