Oblique Incisions | NV Bundle Protection | Flexor Sheath Exposure
Surgical Imaging
The Bruner incision uses angled limbs that cross each flexion crease at 45-60 degrees. The apex of each zigzag must lie precisely at the mid-axial line of the digit. This geometry prevents longitudinal scar contracture across the crease that would limit flexion. Incisions placed too volarly create a straight scar across the crease and cause PIP or DIP flexion contracture.
Each digit has paired radial and ulnar digital neurovascular bundles lying along the sides of the flexor sheath. These must be identified and protected before any deep dissection. The bundles lie just dorsal to the mid-axial line. Injury causes numbness, cold intolerance, or vascular compromise of the fingertip. Use gentle retraction and loupe magnification.
The A2 and A4 pulleys are critical and must be preserved or reconstructed to prevent flexor tendon bowstringing. A2 overlies the proximal phalanx and A4 the middle phalanx. A1, A3 and A5 may be divided for exposure or released in trigger finger or stiffness. Loss of both A2 and A4 produces clinically significant bowstringing and reduced active flexion.
Skin flaps must be raised full thickness down to the flexor sheath, preserving the subdermal vascular plexus. Thin flaps or undermining in the wrong plane devascularise the skin edges and cause wound breakdown or necrosis. The plexus lies immediately deep to dermis - stay on the correct plane using sharp dissection under loupes.
The mid-axial approach places a straight incision along the mid-axial line and elevates a single flap. It avoids crossing creases but provides poorer volar exposure, risks displacing the NV bundle dorsally, and is less versatile for extensive tendon or sheath work. Bruner remains the workhorse for zone 2 flexor tendon repair.
Meticulous skin closure with everting mattress sutures or simple interrupted sutures prevents inversion and subsequent contracture. Avoid tension. Early motion protocols after tendon repair reduce adhesion formation. Scar contracture across a crease is a common cause of re-operation and poor functional outcome.
At a Glance
The Bruner volar zigzag approach provides safe, extensile exposure of the flexor tendon sheath and digital neurovascular structures from the distal palm to the fingertip. The classic angled incisions cross each flexion crease obliquely at 45-60 degrees with apices precisely at the mid-axial points on each side of the digit. This geometry distributes scar tension away from the flexion crease and minimises the risk of scar contracture that would limit digital flexion. Full-thickness skin flaps are elevated preserving the subdermal plexus, exposing the flexor sheath from A1 to A5 pulleys. The paired digital neurovascular bundles lie on the radial and ulnar aspects of the sheath and must be identified and protected throughout. The approach is the standard for zone 2 flexor tendon repair, pulley reconstruction, selected digital fractures, and drainage of flexor sheath infections. A2 and A4 pulleys are preserved whenever possible because their loss produces bowstringing and loss of active flexion. No true internervous plane exists; dissection occurs between the paired neurovascular bundles.
ZIGZAGBRUNER ZIGZAG - Incision Principles
Hook:ZIGZAG geometry with mid-axial apices is the key to contracture prevention!
NV-PULLEYNV BUNDLES AND PULLEYS - Protection Priorities
Hook:Protect the paired NV bundles and the even-numbered pulleys every time!
DANGERDANGER STRUCTURES BY LAYER
Hook:Layer-by-layer danger awareness prevents the common complications!
Indications and Approach Selection
Primary Indications:
- Zone 2 flexor tendon repair (most common)
- Flexor tendon grafting or staged reconstruction
- A2 or A4 pulley reconstruction
- Digital phalangeal fracture fixation (volar approach)
- Flexor sheath infection drainage (pyogenic flexor tenosynovitis)
- Trigger finger release with extensive sheath exposure
- Volar plate repair or reconstruction
Why This Approach is Chosen: The Bruner zigzag provides extensile, safe exposure of the entire flexor apparatus while minimising scar contracture risk across flexion creases. The oblique crossing allows wide flap elevation and access to both neurovascular bundles. It is preferred over the mid-axial approach when extensive volar work or bilateral NV protection is required.
Contraindications:
- Active infection with skin involvement over planned incision
- Severe digital swelling precluding safe closure
- Previous volar scars that would compromise flap vascularity
- Isolated dorsal pathology better approached dorsally
Alternative Approaches:
- Mid-axial approach: simpler for limited exposure but poorer volar access and higher NV displacement risk
- Volar transverse incisions: limited exposure, higher contracture risk
- Combined approaches: for complex multi-structure injuries
Anatomy
Bony Anatomy: The finger consists of proximal, middle and distal phalanges. Flexion creases overlie the PIP and DIP joints. The mid-axial line runs along the lateral aspect of each phalanx, equidistant from volar and dorsal surfaces. The digital NV bundles travel along this line but slightly volar to it.
Flexor Tendon and Pulley System:
- FDS inserts on middle phalanx
- FDP inserts on distal phalanx
- Five annular pulleys (A1-A5) and three cruciate pulleys (C1-C3)
- A2 and A4 are biomechanically critical - prevent bowstringing over proximal and middle phalanges
- A1 overlies MCP joint (released in trigger finger)
- A3 at PIP joint, A5 at DIP joint (less critical)
Neurovascular Anatomy: Each digit has radial and ulnar digital arteries and nerves. The nerve lies dorsal to the artery. The bundles are located just volar to the mid-axial line and must be mobilised with the skin flap or protected in situ. The common digital arteries in the palm bifurcate at the web spaces.
Skin and Subdermal Plexus: The volar skin of the digit is thick with dense fibrous septa. The subdermal vascular plexus lies immediately deep to the dermis and must be preserved by raising full-thickness flaps. Undermining in the wrong plane causes edge necrosis.
Internervous Plane
Deep Internervous Plane: There is no true internervous plane in the Bruner approach. Dissection proceeds between the paired radial and ulnar digital neurovascular bundles, which define the safe corridor to the flexor sheath. The bundles themselves carry the neurovascular supply and are the structures that must be protected rather than crossed.
Superficial Dissection: Skin and subcutaneous tissue are divided along the marked zigzag. Full-thickness flaps are elevated radially and ulnarly down to the flexor sheath, preserving the subdermal plexus on the deep surface of the dermis. The digital NV bundles are identified at the radial and ulnar margins of the exposure and protected with vessel loops or gentle retraction.
Structures at Risk in Each Layer:
- Structure
- Subdermal plexus
- Protection Strategy
- Raise full-thickness flaps only, avoid undermining dermis
- Structure
- Digital arteries (volar to nerves)
- Protection Strategy
- Identify early, gentle retraction, loupe magnification
- Structure
- Digital nerves (dorsal to arteries)
- Protection Strategy
- Protect with vessel loops, avoid excessive stretch
- Structure
- Flexor tendons
- Protection Strategy
- Preserve A2 and A4, repair or reconstruct if divided
- Structure
- Volar plate at PIP/DIP
- Protection Strategy
- Limit dissection to necessary exposure only
The Bruner approach is defined by staying between the paired digital neurovascular bundles rather than between muscles innervated by different nerves. The critical technical step is early identification and protection of both bundles before any deep work on the flexor sheath. This principle distinguishes it from true internervous approaches in larger limbs.
Positioning and Patient Setup
Position: Supine with Hand on Hand Table
Pre-positioning Checklist:
- Arm board or hand table attached to operating table
- Tourniquet applied to upper arm (usually 250 mmHg)
- Loupe magnification (2.5x or 3.5x) available
- Bipolar diathermy and fine instruments ready
- Finger trap or lead hand for positioning if needed
Positioning Details:
- Patient supine, affected arm on hand table
- Shoulder abducted 90 degrees, elbow extended or slightly flexed
- Tourniquet inflated after exsanguination
- Hand positioned with palm up, digits extended or in slight flexion
- Assistant or lead hand maintains position during dissection
Tourniquet time should be kept under 120 minutes when possible. Loupe magnification is mandatory for safe identification of digital NV bundles. Poor lighting or inadequate magnification increases risk of iatrogenic nerve or vessel injury.
Alternative Positioning:
- Arm board with wrist extension for combined wrist and digit exposure
- Lead hand or finger traps for complex multi-digit procedures
Surface Anatomy and Landmarks
Key Bony Landmarks:
- Flexion creases at MCP, PIP and DIP joints
- Mid-axial line on radial and ulnar aspect of each phalanx
- Distal palmar crease and proximal digital crease
Key Soft Tissue Landmarks:
- Digital NV bundles palpable or visible under loupes along mid-axial line
- Flexor tendon sheath palpable as firm cord in palm and digit
- Web spaces define bifurcation of common digital vessels
Incision Planning:
- Mark mid-axial points on both sides of each phalanx first
- Draw zigzag limbs crossing each flexion crease at 45-60 degrees
- Apex of each angle exactly at the marked mid-axial point
- Extend proximally into palm with Y-shaped limb if zone 2-3 continuity needed
- Length of each limb approximately 1.5-2 cm depending on digit size
Surgical Technique
Patient Position and Setup
- Supine on operating table with hand on radiolucent or standard hand table
- Upper arm tourniquet at 250 mmHg after Esmarch exsanguination
- Loupe magnification (2.5x minimum) essential throughout
- Hand positioned palm up with digits in comfortable extension
- Assistant maintains position or use lead hand/finger traps
Surface Marking
- Identify and mark the mid-axial line on radial and ulnar sides of each phalanx
- Mark the flexion creases at PIP and DIP joints
- Plan zigzag limbs crossing each crease at 45-60 degrees obliquely
- Ensure each apex sits precisely at the mid-axial mark
- Extend proximally into palm with gentle curve or Y if required
Equipment
- Fine Adson or skin hooks for flap retraction
- Bipolar diathermy for haemostasis
- Vessel loops for NV bundle protection
- Fine tenotomy scissors and scalpel (15 blade)
Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 28-year-old carpenter sustains a zone 2 flexor tendon laceration to the index finger. Describe your surgical approach and key technical points for repair.”
“During zone 2 flexor tendon repair you find that the A2 pulley is severely damaged and cannot be repaired primarily. What are your options and how do you decide?”
“You are planning exposure for a zone 2 flexor tendon repair. What are the advantages of the Bruner approach over the mid-axial approach?”