Mid-Axial Approach to the Digit

The mid-axial approach to the digit provides safe access to the phalanx, flexor tendon sheath and PIP joint collateral ligaments while protecting the digital neurovascular bundle. The incision is placed on the non-contact border of the finger, joining the dorsal-most points of the flexion creases. The digital artery and nerve remain volar to the incision and are identified and protected early. Dissection proceeds either dorsal to Cleland ligament or volar to Grayson ligament to reach the target structures. This approach is ideal for phalangeal fracture fixation, PIP joint surgery, collateral ligament repair and excision of tumours or mucous cysts on the side of the digit. It avoids the contact surface of the finger and therefore minimises the risk of painful scar contracture during pinch and grasp.

Primary Indications:

• Phalangeal shaft or neck fractures requiring open reduction and internal fixation
• PIP joint fracture-dislocations needing collateral ligament repair or volar plate arthroplasty
• Collateral ligament injuries of the PIP or DIP joint requiring direct repair or reconstruction
• Excision of mucous cysts, giant cell tumours of tendon sheath or other lateral masses
• Flexor tendon sheath exploration or pulley release when volar access is contraindicated
• Osteomyelitis or septic arthritis drainage of the phalanx or PIP joint

Why This Approach is Chosen:

The mid-axial incision provides direct access to the lateral aspect of the phalanx and the flexor sheath while keeping the scar on the non-contact border. It avoids the volar pulp and therefore prevents painful scar contracture that would impair pinch and grasp. The digital neurovascular bundle is protected by remaining dorsal to it throughout the dissection. This approach is particularly useful when the pathology is lateral or when a volar Bruner incision would place the scar on the working surface of the finger.

Contraindications:

• Pathology requiring dorsal access (use dorsal approach for extensor mechanism or dorsal lip fractures)
• Volar pulp or fingertip pathology (use volar zigzag or straight volar incision)
• Previous scarring or infection on the planned mid-axial line
• Need for circumferential access (consider two mid-axial incisions or Bruner)

Alternative Approaches:

• Dorsal approach: For extensor tendon repair, dorsal lip fractures, or central slip injuries
• Bruner volar zigzag: For flexor tendon repair, volar plate exposure, or pulley reconstruction
• Volar straight incision: For limited volar access when mid-axial exposure is insufficient
• Lateral approach with nail fold elevation: For distal phalanx or nail bed pathology

Bony Anatomy:

The phalanges of the fingers are tubular bones with a proximal base, shaft and distal head. The PIP joint is a hinge joint with collateral ligaments that are tight in flexion and lax in extension. The mid-axial line runs along the lateral aspect of each phalanx, connecting the dorsal-most points of the flexion creases. The flexor digitorum profundus and superficialis tendons lie volar to the phalanx within the flexor sheath.

Ligamentous Anatomy:

Cleland ligaments are thick fibrous bands that run from the phalangeal periosteum dorsal to the neurovascular bundle to the dorsal skin. They form a barrier that can be dissected to reach the bone or extensor apparatus. Grayson ligaments run from the flexor sheath volar to the neurovascular bundle to the volar skin. They form the volar boundary of the safe plane around the bundle.

Neurovascular Anatomy:

Each digit has two digital arteries and two digital nerves running along its sides, just volar to the mid-axial line. The arteries lie dorsal to the nerves. The bundle is enveloped by a thin layer of fat and fascia. The nerve supplies sensation to the hemidigit and the artery supplies the pulp and skin. Injury to either structure causes permanent deficit.

Flexor Sheath Anatomy:

The flexor sheath is a fibro-osseous tunnel extending from the metacarpal head to the distal phalanx. The A2 and A4 pulleys are critical for flexor tendon function and must be preserved or reconstructed if divided. The sheath is reached by dissecting either dorsal to Cleland ligament or volar to Grayson ligament, keeping the neurovascular bundle protected.

Deep Internervous Plane:

There is no true internervous plane in the mid-axial approach. All skin, subcutaneous tissue, fascia and periosteum of the digit are supplied by branches of the digital nerves. Safety is achieved by remaining dorsal to the neurovascular bundle and using the natural fascial planes created by Cleland and Grayson ligaments rather than dividing innervated muscle or fascia.

Superficial Dissection:

The skin and subcutaneous fat are incised directly down to the level of the dorsal margin of the neurovascular bundle. No muscle is divided. The digital nerve and artery are identified within the subcutaneous fat just volar to the incision line and are gently retracted volarly.

Structures at Risk in Each Layer:

Position: Supine with Hand on Hand Table

Pre-positioning Checklist:

• Confirm tourniquet is available and functional
• Loupe magnification (2.5x or greater) confirmed
• Hand table attached and radiolucent if fluoroscopy needed
• Arm board positioned for comfortable access
• Lead hand or lead weights available for positioning

Positioning Details:

• Patient supine with affected arm on hand table
• Tourniquet applied to upper arm, inflated to 250 mmHg (or 100 mmHg above systolic)
• Hand exsanguinated with Esmarch bandage before tourniquet inflation
• Fingers positioned with lead hand or rolled towels for stability
• Operating microscope or loupes available throughout

Alternative Positioning:

• Lateral decubitus with arm on padded bolster if combined procedures required
• Prone positioning rarely needed for isolated digit surgery

Key Bony Landmarks:

• Proximal interphalangeal joint line - palpable as a transverse depression
• Distal interphalangeal joint line - smaller transverse depression
• Metacarpophalangeal joint - palpable at the base of the proximal phalanx
• Flexion creases - mark the level of the PIP and DIP joints

Key Soft Tissue Landmarks:

• Digital neurovascular bundle - palpable as a longitudinal ridge just volar to the planned incision when the finger is flexed
• Flexor tendon sheath - felt as a firm longitudinal structure volar to the phalanx
• Cleland ligaments - palpable as transverse bands when the skin is moved over the phalanx

Incision Planning:

• Select the non-contact border (ulnar for index and middle, radial for ring and little)
• Mark the dorsal-most point of each flexion crease (the apex)
• Join these points with a straight line along the mid-axial border
• Extend proximally into the web space or distally to the nail fold only if required
• Incision length typically 3-5 cm for a single phalanx or PIP joint exposure

Wound Closure:

Skin closure is performed with interrupted non-absorbable sutures. The digital neurovascular bundle is confirmed to lie in its anatomic position without kinking or tension. No attempt is made to close the flexor sheath or periosteum. If a collateral ligament was divided for joint access, it is repaired with braided suture anchored to bone or soft tissue. A bulky compressive dressing with a dorsal plaster slab maintains the finger in slight flexion at the PIP joint.

Aftercare Protocol:

• Strict elevation for 48 hours to minimise oedema
• Active range of motion exercises commence at 48-72 hours unless specific contraindications exist
• Protective splinting for 3-6 weeks depending on the underlying procedure
• Suture removal at 10-14 days
• Oedema control with compression garments once wounds are healed
• Scar massage begins at 3 weeks to prevent contracture

Rehabilitation Milestones:

• Week 0-2: Protection, oedema control, gentle active motion within safe range
• Week 2-6: Progressive active and passive motion, scar management
• Week 6+: Strengthening, functional rehabilitation, return to work or sport

Approach-Specific Complications:

• Digital neurovascular injury (less than 1 percent permanent deficit with careful technique)
• Scar contracture on the contact surface if the wrong border is chosen
• Flexor tendon adhesion if the sheath is violated unnecessarily
• PIP joint stiffness from prolonged immobilisation or scarring
• Nail deformity if the approach is extended too far distally
• Web space contracture if proximal extension damages the transverse ligament

Prevention Strategies:

• Always confirm the non-contact border before marking the incision
• Identify and protect the neurovascular bundle before any deep dissection
• Preserve the A2 and A4 pulleys whenever possible
• Begin early motion within the limits of stability
• Avoid overzealous retraction on the neurovascular bundle

Management of Complications:

• Suspected nerve injury: immediate exploration if recognised intra-operatively, otherwise observe with serial sensory testing
• Flexor tendon adhesion: early tenolysis if motion plateaus
• PIP stiffness: dynamic splinting and intensive hand therapy
• Scar contracture: scar revision with Z-plasty if functionally limiting