Distal Radius External Fixation (Spanning and Non-Spanning)

Surgical Indications

Absolute Indications

• Severely comminuted intra-articular distal radius fractures (AO C2-C3) where anatomic reduction and stable internal fixation cannot be achieved
• Open or contaminated distal radius fractures requiring damage-control surgery with delayed definitive fixation
• Polytrauma patients who are physiologically unstable for prolonged ORIF (damage-control orthopaedics)
• Distal radius fractures with associated severe soft-tissue injury precluding immediate open surgery

Relative Indications

• Adjunct to limited internal fixation (K-wires or volar plating) when additional stability is required
• Patients with poor bone quality or medical comorbidities where prolonged surgery is undesirable
• Selected extra-articular fractures with significant shortening or dorsal comminution in young active patients

Contraindications

Absolute:

• Distal fragment too small or osteoporotic to accept two half-pins (non-spanning)
• Active infection at planned pin sites
• Patient non-compliance with pin-site care or follow-up

Relative:

• Simple extra-articular fractures amenable to closed reduction and casting
• Volar shear fractures (AO B3) better treated with volar buttress plating
• Patient preference for definitive internal fixation when conditions allow

Evidence for External Fixation

Ligamentotaxis and Frame Design

• External fixation restores radial length, inclination and palmar tilt through ligamentotaxis in the majority of cases when over-distraction is avoided
• Spanning frames are the workhorse for highly comminuted or open injuries; non-spanning frames preserve more wrist motion but require adequate distal bone stock
• Combination with percutaneous K-wires or limited open bone grafting improves articular surface reduction and reduces late collapse

Complications and Outcomes

• Pin-site infection rates range from 5-15% in published series; most resolve with oral antibiotics and local care, but deep infection requiring frame removal occurs in 1-3%
• Radial sensory neuritis occurs in 3-8% and is largely preventable with careful pin placement and blunt dissection
• Finger stiffness and CRPS are more common with prolonged over-distraction; early motion and avoidance of excessive traction are critical
• Loss of reduction after frame removal is reported in 10-20% of highly comminuted fractures treated with external fixation alone; supplemental K-wires or bone graft reduce this risk

Key Evidence

Relevant Anatomy for External Fixation

Osseous Anatomy

• The distal radius has a triangular cross-section with a relatively thin dorsal cortex and thicker volar buttress
• The radial styloid provides the attachment for the brachioradialis and the radial collateral ligament complex
• The dorsal surface has four extensor compartments; the EPL tendon lies in the third compartment directly over the distal radius
• The volar surface is covered by the pronator quadratus and the flexor tendons; the radial artery lies between the brachioradialis and FCR

Ligamentous Anatomy — Ligamentotaxis Mechanism

• The volar capsule and the radioscaphocapitate, long radiolunate and short radiolunate ligaments remain attached to the distal fragment in most fracture patterns
• Traction applied through an intact volar capsule reduces the articular surface and restores length, palmar tilt and radial inclination indirectly
• The dorsal capsule is thinner and contributes less to ligamentotaxis; excessive dorsal comminution may require supplemental dorsal bone grafting or K-wires

Neurovascular Structures at Pin Sites

• Superficial radial nerve: divides 4-6 cm proximal to the radial styloid into multiple sensory branches that cross the radial styloid subcutaneously; these are at highest risk during proximal radial pin placement
• Radial artery: lies immediately volar to the radial styloid and must be identified and protected during volar distal pin placement
• Extensor tendons: EPL, ECRB and ECRL overlie the dorsal distal radius and radial shaft; must be retracted or avoided during dorsal pin insertion
• First dorsal compartment: contains APL and EPB tendons; pins placed too distally on the radial styloid risk tendon injury or entrapment

Safe Zones for Pin Placement

• Radial shaft safe zone: 8-10 cm proximal to the radial styloid, between the radial artery (volar) and the superficial radial nerve branches (dorsal-radial); a 2-3 cm incision with blunt dissection is required
• Second metacarpal safe zone: the base and proximal shaft of the index and middle metacarpals; crossed pin configuration (one pin in each metacarpal, angled 30-45 degrees) provides rotational stability
• Distal radius fragment (non-spanning): volar or dorsal surface of the distal fragment with at least 1 cm of intact cortex; avoid the articular surface and the EPL groove

Positioning and Preparation

Patient position: Supine on a radiolucent table with the arm abducted 90 degrees on a hand table. The C-arm enters from the opposite side of the table. A tourniquet is applied to the upper arm but is not routinely inflated unless open reduction is planned.

Anaesthesia: Regional (axillary or supraclavicular block) or general anaesthesia. WALANT is not suitable for external fixation because of the discomfort of pin insertion and frame manipulation.

Equipment: 3.5 mm or 4.0 mm self-drilling half-pins, external fixator clamps and carbon-fibre rods (or radiolucent frame), C-arm, 2.0 mm and 2.5 mm drill bits, pin cutters, and a small fragment set for supplemental K-wires if needed.

Consent: Discuss pin-site infection (5-15%), radial sensory neuritis (3-8%), finger stiffness, CRPS, loss of reduction, need for frame adjustment or removal, and the possibility of later conversion to internal fixation.

Spanning External Fixation — Step-by-Step

Step 1: Closed Reduction and Traction

Apply longitudinal traction to the hand with the wrist in slight flexion and ulnar deviation. Use the C-arm to confirm restoration of radial length (ulnar variance less than 2 mm), palmar tilt (greater than 5 degrees), and radial inclination (greater than 15 degrees). Avoid over-distraction — the carpus should not be distracted more than 3-5 mm and the fingers should remain supple.

Step 2: Proximal Radial Shaft Pin Placement

Make a 2-3 cm longitudinal incision over the radial shaft 8-10 cm proximal to the radial styloid, between the brachioradialis and ECRL. Bluntly dissect to bone, protecting the superficial radial nerve branches and the radial artery. Pre-drill with a 2.0 mm or 2.5 mm bit, then insert two 3.5 mm or 4.0 mm half-pins at a 30-45 degree angle to each other, engaging both cortices. Confirm position with fluoroscopy.

Step 3: Distal Metacarpal Pin Placement (Spanning Frame)

Make two small incisions over the base of the index and middle metacarpals. Bluntly dissect to bone. Pre-drill and insert one 2.5-3.0 mm half-pin into the index metacarpal base and one into the middle metacarpal base, angled 30-45 degrees to each other in a crossed configuration. Engage both cortices of each metacarpal. Confirm position fluoroscopically.

Step 4: Frame Assembly and Final Reduction

Connect the proximal and distal pin clusters with carbon-fibre rods and clamps. Apply gentle traction to fine-tune length, palmar tilt and radial inclination. Lock the frame once radiographic parameters are satisfactory. Verify that the fingers can be passively flexed to 90 degrees at the MCP joints without resistance.

Step 5: Supplemental Fixation (When Indicated)

For AO C2-C3 fractures, add percutaneous K-wires (two or three 1.6 mm K-wires from radial styloid and dorsal-ulnar corner) or limited open bone grafting through a small dorsal incision to support the articular surface and reduce late collapse.

Non-Spanning External Fixation — Key Differences

Distal Pin Placement

The distal pins are placed directly into the distal radius fragment (volar or dorsal surface) rather than the metacarpals. Requires at least 1 cm of intact volar cortex. Two 3.5-4.0 mm half-pins are inserted at divergent angles under direct vision or fluoroscopic guidance. The frame is shorter and does not bridge the wrist.

Indications and Limits

Only suitable for fractures with simple articular patterns and adequate distal bone stock. Provides earlier wrist motion and potentially better final range of motion. Contraindicated in osteoporotic bone, highly comminuted distal fragments, or when the distal fragment is too small to accept two half-pins.

Frame Removal

Non-spanning frames are typically removed at 4-6 weeks once radiographic union is confirmed. The shorter duration and preserved wrist motion reduce stiffness risk.

Post-operative Protocol

Immediate Post-operative (Day 0-7)

• Elevate the arm above heart level for 48-72 hours to reduce swelling
• Begin active finger flexion and extension exercises from day 1 (10 repetitions hourly while awake)
• Pin-site care: chlorhexidine or isopropyl alcohol cleaning twice daily after the first 48 hours; no occlusive dressings
• Analgesia: paracetamol, NSAIDs, and short course of opioids if required
• First follow-up at 48-72 hours for wound and pin-site check, radiograph to confirm frame position

Early Rehabilitation (Week 1-4)

• Continue pin-site care and active finger exercises
• Begin gentle active wrist and forearm exercises if non-spanning frame; spanning frames remain immobilised
• Formal hand therapy referral at 2 weeks for oedema control, scar massage, and progressive strengthening
• Weight-bearing restrictions: no lifting greater than 2 kg with the fixator arm
• Weekly pin-site inspection; any erythema treated with oral antibiotics promptly

Late Rehabilitation (Week 4-12)

• Spanning frame removal at 6-8 weeks once radiographic callus is visible and fracture is stable
• Non-spanning frame removal at 4-6 weeks
• After frame removal: progressive active and passive wrist mobilisation, grip strengthening, scar desensitisation
• Return to light work at 8-10 weeks; heavy manual work at 12-16 weeks
• Final outcome assessment at 3-6 months with radiographs and functional scores (DASH, PRWE)

Frame Care Instructions for Patients

• Keep pin sites clean and dry; report any increasing redness, drainage or fever immediately
• Do not attempt to adjust or loosen the frame
• Protect the frame from impact; use a loose stockinette or sleeve when outdoors
• Continue prescribed finger and (if non-spanning) wrist exercises daily

Special Considerations

Open Fractures and Polytrauma

External fixation is the damage-control method of choice. Perform thorough debridement, apply spanning frame for length and stability, and delay definitive fixation until soft tissues recover (typically 7-14 days). Antibiotic prophylaxis and tetanus status are mandatory.

Osteoporotic Bone

Use smaller pins (2.5-3.0 mm), pre-drill and tap, and consider cement augmentation around pins if purchase is poor. Non-spanning constructs are often contraindicated; spanning frames with supplemental K-wires are preferred.

Conversion to Internal Fixation

When soft tissues allow (usually 10-21 days), convert to volar locking plate fixation. Remove the external fixator in the same procedure or staged 1-2 weeks before plate application to reduce infection risk.