Volar exposure of the trapeziometacarpal (basal thumb) joint
- The internervous plane is between the thenar muscles (recurrent motor branch of the median nerve) and adductor pollicis (deep branch of the ulnar nerve).
- Incise exactly along the glabrous–non-glabrous skin junction of the thenar eminence — this plane protects the superficial radial nerve branches lying just deep to the non-glabrous skin.
- The superficial radial nerve branches (2–4, only 2–3 mm deep) are the structure most often injured — identify, loop and protect them; never use self-retaining retractors on the nerve.
- Elevate the thenar origins subperiosteally off the trapezium and metacarpal base; stay extracapsular until you deliberately open the joint to protect the FCR in its trapezial groove.
- The radial artery crosses dorsally between the first and second metacarpal bases — identify and protect it before deep work.
When & Why
What it exposes. The Wagner volar approach gives direct access to the trapeziometacarpal (first CMC) joint, the trapezium and the base of the thumb metacarpal, with good control of the radial artery. It is the workhorse exposure for trapeziectomy with or without LRTI/suspension, CMC arthrodesis, and implant arthroplasty of the basal thumb. Why volar (and not dorsal). The volar approach keeps you away from the first dorsal compartment tendons (abductor pollicis longus and extensor pollicis brevis) that a dorsal approach risks, and it works a genuine internervous plane. A dorsal approach is reserved for specific indications such as Bennett-fracture fixation and dorsal ligament repair. Position & landmarks. Supine, arm on a hand table, upper-arm tourniquet (about 250 mmHg), thumb held in abduction and opposition to relax the thenar muscles, loupe magnification mandatory. Palpate and mark the trapezium (in the snuffbox and volarly at the thenar eminence), the first metacarpal base, the scaphoid tubercle (proximal limit), and the glabrous–non-glabrous junction along the thenar eminence — the line of the incision.
The Exposure
Work down through the layers along the thenar crease, protecting the superficial radial nerve and radial artery, then develop the thenar–adductor internervous plane to the capsule.
Exposure sequence
- A curved incision exactly at the glabrous–non-glabrous junction, from about 1 cm proximal to the scaphoid tubercle (along the radial border of FCR) curving distally to the midshaft of the first metacarpal (5–7 cm).
- This skin line naturally lies superficial to the SRN branches and allows proximal/distal extension.
- Under loupe magnification, identify all crossing superficial radial nerve branches (usually 2–4, only 2–3 mm deep) and tag each with a vessel loop.
- Use bipolar haemostasis; do not apply self-retaining retractors to the nerve, and release retractors periodically.
- Incise the thenar fascia along the skin line, exposing the abductor pollicis brevis.
- Extend proximally along the radial border of FCR and identify the radial artery as it crosses volar-to-dorsal between the first and second metacarpal bases; loop it (and ligate only if exposure demands, preserving the princeps pollicis where possible).
- Elevate the thenar origins (abductor pollicis brevis, opponens pollicis) subperiosteally off the volar trapezium and metacarpal base with a periosteal elevator, working distal to proximal, retracting the muscle flap radially.
- This is the internervous plane between the thenar muscles (median) and adductor pollicis (ulnar); the adductor on the ulnar side is left undisturbed.
- With the joint capsule now exposed, make a longitudinal or T-shaped capsulotomy and tag the edges with stay sutures for later repair.
- Protect the FCR tendon in its groove on the volar trapezium — stay extracapsular until this point.
- Distract the thumb metacarpal to display the whole trapeziometacarpal surface and the trapezial articulations (with the scaphoid, trapezoid and second metacarpal) — ready for trapeziectomy, arthrodesis or implant work.
The commonest and most disabling problem with this exposure is injury to the superficial radial nerve branches, which cross the field only 2–3 mm deep and produce a painful neuroma in up to 10 percent of cases. Incise precisely at the glabrous junction, identify and loop every branch under loupes, never clamp self-retaining retractors onto the nerve, and release retraction regularly.
All dissection stays extracapsular until the deliberate capsulotomy — this keeps the FCR tendon (in its trapezial groove) and the joint stabilisers protected, and gives clean tagged capsular flaps to repair at closure.
Dangers & Extensions
Structures at risk, by layer
- Structure at risk
- Superficial radial nerve branches (2–4, 2–3 mm deep)
- Protection
- Incise at the glabrous junction; loupe identification; vessel loops; no self-retainers on the nerve
- Structure at risk
- Radial artery (between MC1 and MC2 bases) and princeps pollicis
- Protection
- Identify and loop; ligate only if essential, preserving princeps pollicis
- Structure at risk
- FCR tendon in its trapezial groove
- Protection
- Stay extracapsular until capsulotomy; retract and protect during bone removal
- Structure at risk
- Recurrent motor branch of the median nerve to thenar muscles
- Protection
- Stay subperiosteal during thenar elevation; avoid aggressive deep retraction
Extensile options. Extend proximally along the radial border of FCR (2–3 cm) to reach the scaphotrapezial joint or control the radial artery; extend distally along the radial border of the first metacarpal for the metacarpal shaft and for LRTI bone-tunnel creation (this distal extension risks the princeps pollicis). Closure. Reattach the thenar origins to the trapezial remnant or periosteum, repair the capsule over the tagged flaps with absorbable suture, close the fascia loosely, and close skin. Apply a thumb spica with the thumb in palmar abduction.
Procedures Through This Approach
- First CMC arthroplasty (trapeziectomy ± LRTI) — the principal operation done through this exposure.
- Trapeziometacarpal arthrodesis and implant arthroplasty of the basal thumb.
- Trapezial fracture fixation and excision of the scaphotrapezial joint in pantrapezial disease (via the proximal extension).
Viva & Exam Focus
WAGNERWAGNER — the volar CMC exposure
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“What is the internervous plane of the Wagner approach, and what crosses the field superficially?”
“A patient develops a painful, tender scar with thumb numbness after this approach. What has happened and how do you prevent it?”
Incision
- Curved, along the glabrous–non-glabrous junction of the thenar eminence
- Scaphoid tubercle proximally to first-metacarpal midshaft distally
Internervous plane
- Thenar muscles (median) versus adductor pollicis (ulnar)
- Develop by subperiosteal thenar elevation
Dangers
- Superficial radial nerve branches (2–3 mm deep)
- Radial artery between MC1 and MC2
- FCR tendon in its trapezial groove
Uses
- Trapeziectomy ± LRTI/suspension
- CMC arthrodesis and implant arthroplasty
References
Surgical exposures in orthopaedics — the anatomic approach (hand and wrist)
Standard reference describing the volar approach to the trapeziometacarpal joint, its internervous plane and the structures at risk.
Trapeziectomy alone vs interposition vs LRTI — randomised trial
Defines the principal procedure performed through this exposure and shows trapeziectomy alone is equivalent to LRTI.
Superficial radial nerve injury in thumb base surgery
Describes the frequency and prevention of superficial radial nerve injury — the key complication of the volar thumb-base approach.