Volar Palmar (Flexor) Approach to the Carpal Canal and Mid-Palm

The volar palmar approach to the carpal canal and mid-palm is the workhorse incision for open carpal tunnel release, flexor tendon exploration in zones 3-4, drainage of mid-palmar abscesses and excision of mid-palmar masses. The incision is placed along the radial border of the ring finger axis, kept strictly ulnar to the thenar crease to protect the palmar cutaneous branch of the median nerve. The transverse carpal ligament is divided under direct vision from proximal to distal while protecting the median nerve and flexor tendons. The superficial palmar arch is the critical distal structure and must be identified before extending into the mid-palm. Proximal extension across the wrist crease provides access to the distal forearm for flexor tendon ruptures or Volkmann contracture release. Distal extension along the flexor sheath axis allows zone 2 tendon repair or digital infection drainage.

Primary Indications:

• Open carpal tunnel release for idiopathic or secondary carpal tunnel syndrome
• Flexor tendon exploration and repair in zones 3 and 4 (mid-palm)
• Drainage of mid-palmar space infections and deep palmar abscesses
• Excision of mid-palmar masses (ganglia, lipomas, giant cell tumours of tendon sheath)
• Release of Dupuytren contracture involving the mid-palm
• Revision carpal tunnel surgery with nerve reconstruction or tenosynovectomy
• Combined procedures requiring access to both carpal tunnel and mid-palm

Why This Approach is Chosen:

The volar palmar approach provides direct access to the carpal tunnel contents, the transverse carpal ligament, the median nerve throughout its course in the hand, and the mid-palmar space. It allows complete division of the flexor retinaculum under direct vision, inspection of the median nerve for hourglass constriction or tenosynovitis, and safe extension into the mid-palm while protecting the superficial palmar arch. No other single incision gives equivalent access to both the carpal canal and the mid-palmar flexor apparatus.

Contraindications:

• Active infection in the planned incision site (consider two-stage drainage then release)
• Severe thenar wasting with fixed contracture (may need alternative or combined approach)
• Known transligamentous recurrent motor branch with high risk of injury (consider endoscopic if expertise available)
• Patient inability to tolerate local or regional anaesthesia when general anaesthesia contraindicated

Alternative Approaches:

• Endoscopic carpal tunnel release: faster recovery but limited visualisation of nerve and no mid-palm access
• Limited open carpal tunnel release (mini-incision): smaller scar but limited exposure for complex pathology
• Extended carpal tunnel approach with forearm extension: for proximal median nerve pathology or Volkmann contracture
• Combined volar and dorsal approaches: for complex trauma involving both flexor and extensor surfaces

Bony Anatomy:

The carpal tunnel is formed by the carpal bones (scaphoid, trapezium, trapezoid, capitate, hamate) forming the floor and walls, with the transverse carpal ligament (flexor retinaculum) as the roof. The hook of the hamate and the pisiform form the ulnar attachments of the TCL. The scaphoid tubercle and trapezium ridge form the radial attachments. The carpal tunnel contains the median nerve and nine flexor tendons (FDS x4, FDP x4, FPL).

Soft Tissue Layers:

The skin and subcutaneous fat overlie the palmar aponeurosis. The palmar cutaneous branch of the median nerve travels superficial to the TCL between palmaris longus and flexor carpi radialis. The recurrent motor branch of the median nerve emerges at the distal edge of the TCL, usually extraligamentous but may be subligamentous or transligamentous.

Neurovascular Anatomy:

Flexor Tendon Zones in the Palm:

• Zone 3: Mid-palm from distal edge of TCL to proximal edge of A1 pulley (flexor tendon repair, lumbrical origin)
• Zone 4: Carpal tunnel (within TCL)
• Zone 5: Distal forearm (proximal extension of approach)

Deep Internervous Plane:

There is no classical internervous plane in the volar palmar approach because the thenar muscles receive dual innervation from both median (recurrent motor branch) and ulnar nerves (deep branch). The dissection passes between the thenar eminence (median-innervated) and the hypothenar eminence (ulnar-innervated) but the interval is not strictly internervous.

Superficial Dissection:

The approach is through the palmar aponeurosis and subcutaneous fat. The palmar cutaneous branch of the median nerve is identified and protected superficial to the TCL. The flexor carpi radialis and palmaris longus tendons are landmarks for the radial and ulnar boundaries respectively.

Structures at Risk in Each Layer:

Position: Supine with Arm on Hand Table

Pre-positioning Checklist:

• Confirm tourniquet available and functioning (usually 250 mmHg for adults)
• Arm board positioned at 90 degrees abduction
• Radiolucent or standard hand table confirmed
• Lead hand or lead weights available for positioning
• Loupe magnification (2.5x or 3.5x) and headlight prepared
• Microscope available if nerve reconstruction or complex tendon work anticipated

Positioning Details:

• Patient supine with arm abducted 90 degrees on hand table
• Tourniquet applied high on upper arm (or forearm tourniquet for distal procedures)
• Hand positioned with palm up, fingers extended or slightly flexed
• Lead hand or lead weights used to maintain position
• Surgeon seated at the end of the hand table, assistant opposite
• C-arm positioned for intraoperative fluoroscopy if needed for associated fractures

Alternative Positioning:

• WALANT (wide-awake local anaesthesia no tourniquet): patient awake, can test flexor tendon function intraoperatively
• Regional anaesthesia (brachial plexus block): good muscle relaxation, patient awake or sedated
• General anaesthesia: for complex combined procedures or patient preference

Key Bony Landmarks:

• Pisiform - palpable ulnarly at wrist crease, attachment of TCL ulnarly
• Hook of hamate - 1 cm distal and radial to pisiform, deep landmark for TCL ulnar attachment
• Scaphoid tubercle - palpable radially, TCL radial attachment
• Trapezium ridge - palpable in thenar eminence, TCL radial attachment
• Flexor carpi radialis tendon - palpable radial border of wrist
• Palmaris longus tendon - midline, present in 80-85 percent of individuals

Key Soft Tissue Landmarks:

• Thenar crease - radial boundary for safe incision (stay ulnar)
• Distal wrist crease - proximal limit of standard incision
• Kaplan cardinal line - line from hook of hamate to radial border of index finger metacarpophalangeal joint; recurrent motor branch emerges near this line
• Flexor tendon sheaths - palpable in mid-palm when tendons are tensed

Incision Planning:

• Longitudinal incision along radial border of ring finger axis
• Length: 4-6 cm for standard carpal tunnel release, longer for extensile exposure
• Starts at distal wrist crease and extends distally toward mid-palm
• Kept strictly ulnar to thenar crease throughout
• Can be extended proximally across wrist crease in zig-zag fashion for forearm access
• Can be extended distally along flexor sheath axis for mid-palm or digital access

Median Nerve Injury Management:

• If nerve identified as damaged intra-operatively: primary epineurial repair if clean transection, otherwise refer to specialist
• If neurapraxia suspected: observe, document, follow up closely with serial examination
• Post-operative new deficit: urgent EMG/NCS at 3 weeks, consider exploration if no recovery by 3 months
• Painful neuroma of PCBMN: difficult to treat, may require nerve transposition or capping

Proximal Extension (Forearm):

• Indication: Flexor tendon ruptures in zone 5, proximal median nerve pathology, Volkmann contracture release, forearm compartment syndrome
• Technique: Extend incision proximally across wrist crease in zig-zag fashion. Incise antebrachial fascia. Identify median nerve proximal to carpal tunnel. Develop plane between flexor digitorum superficialis and profundus.
• Structures at risk: Median nerve, anterior interosseous nerve, radial artery (if extending radially)
• Closure: Layered closure of fascia, subcutaneous tissue, and skin. Consider drain if extensive dissection.

Distal Extension (Mid-Palm and Digits):

• Indication: Zone 3-4 flexor tendon injuries, mid-palmar abscess drainage, mid-palmar mass excision, Dupuytren contracture release
• Technique: Continue incision distally along flexor tendon axis. Use Brunner zig-zag for digital extension. Identify and protect superficial palmar arch first. Retract lumbricals and flexor tendons to access mid-palmar space.
• Structures at risk: Superficial palmar arch, common digital nerves and vessels, lumbrical muscles
• Closure: Layered closure, consider leaving palmar aponeurosis open to prevent contracture.

Combined Approaches:

For complex trauma or infection involving both flexor and extensor surfaces, combine with dorsal approaches through separate incisions. Staged surgery may be required for severe contamination.

Intra-operative Complications:

Post-operative Complications:

Immediate Post-operative:

• Bulky dressing with plaster splint in neutral wrist position
• Elevation above heart level for 48 hours
• Neurovascular observations (median nerve distribution sensation and motor function)
• Analgesia (paracetamol, NSAIDs, weak opioid if needed)
• Tourniquet time documented

Wound Care:

• First dressing change at 48-72 hours
• Suture removal at 10-14 days
• Early scar massage from 3 weeks
• Silicone gel or sheet for scar management if prone to hypertrophy

Rehabilitation Protocol:

• Week 0-2: Splint immobilisation, gentle finger ROM exercises, elevation
• Week 2-4: Remove splint, active wrist and finger ROM, scar massage, desensitisation
• Week 4-6: Progressive strengthening, return to light activities
• Week 6-12: Full activities, return to work (desk job 2-4 weeks, manual work 6-12 weeks)
• Beyond 12 weeks: Consider work conditioning or hand therapy if persistent stiffness or weakness

Return to Driving:

Usually 2-4 weeks when patient can safely grip steering wheel and react to emergency situations. Document advice given.

DVT Prophylaxis:

Not routinely required for hand surgery unless patient has additional risk factors (previous DVT, malignancy, immobility).

The volar palmar approach to the carpal canal and mid-palm is used worldwide for carpal tunnel release, flexor tendon surgery, and hand infection drainage. Principles are convergent across examination systems (FRCS, FRACS, EBOT, ABOS). Open carpal tunnel release with direct nerve inspection remains the gold standard for complex, revision, or teaching cases, while endoscopic release is accepted for straightforward idiopathic carpal tunnel syndrome in experienced hands.

Side-by-side principles (where guidance converges):

Registry / population evidence:

• Carpal tunnel syndrome prevalence is 3-5 percent in the general population, higher in women and manual workers.
• Open carpal tunnel release has greater than 85 percent long-term success rate; incomplete TCL release is the most common cause of recurrence.
• Endoscopic release shows faster return to work but slightly higher transient nerve injury rate in meta-analyses.

Global practice variation:

In high-resource settings, both open and endoscopic techniques are available with surgeon and patient choice. In resource-limited settings, open release with basic instruments is the standard, and the same incision principles apply. WALANT (wide-awake local anaesthesia no tourniquet) is increasingly used globally to reduce cost and allow intra-operative tendon testing.

Consent (globally applicable):

Discuss palmar cutaneous branch injury (1-3 percent, painful neuroma risk), recurrent motor branch injury (less than 1 percent, thenar weakness), incomplete release requiring revision (5-10 percent), scar tenderness or pillar pain (10-20 percent, usually resolves), infection (1-2 percent), and the possibility of persistent or recurrent symptoms. For extensile procedures, discuss superficial palmar arch injury and digital ischaemia risk.