1 Note on illustrations topenlarge
Throughout this treatment option illustrations of generic fracture patterns are shown, as four different types:
A) Unreduced fracture
B) Reduced fracture
C) Fracture reduced and fixed provisionally
D) Fracture fixed definitively
2 Principles of joint-spanning external fixation topenlarge
Joint-spanning external fixation of the wrist may be used as a temporary or definitive treatment in simple or complex distal forearm fractures.
The external fixator may be used on its own or to supplement K-wire fixation. Specifics of K-wire fixation are given in separate treatment options for each appropriate fracture type.
Details of external fixation are described in the basic technique for application of modular external fixator.
Specific considerations for the wrist are given below.
In joint-spanning external fixation of the wrist, the 4 mm (small) external fixator system is commonly used and may be combined with the 8 mm (medium) system. They are applied as described in the basic technique for the 11 mm (large) system.
There are several other external fixation systems available.
3 Pin insertion (wrist) topenlarge
Complications with pin insertion
The following three potential complications are of concern when inserting threaded pins for external fixation:
- Injury to extensor tendons
- Injury to the superficial branch of the radial nerve
- Metacarpal fracture
The following precautions minimize the risk of these complications:
- Knowledge of the anatomy and specific landmarks for pin insertion
- Larger surgical incisions (1 cm over the second metacarpal, longer incision over the radius), instead of stab incisions
- Blunt dissection to the bone
- Predrilling prior to insertion of the pins
Landmarks for pin insertion into the second metacarpal
The distal pin should be inserted proximal to the transition of the metacarpal head into the shaft.
The more proximal pin is inserted distal to transition of the shaft into the metacarpal base.
The pins should obtain a good hold in both cortices.
Pitfall: Eccentric pin positioning
An eccentric position of a pin may weaken the metacarpal, leading to fracture.
The extensor tendon hood must not be transfixed with the distal metacarpal screw.
To avoid this complication, the index metacarpophalangeal (MCP) joint should be passively flexed 90° so that the extensor hood moves slightly distally, and the tendons are pulled in an ulnar direction.
In the frontal plane, the pins should be inserted at an angle of 30°-40° in relation to the sagittal plane to avoid transfixing the extensor tendon/hood.
Landmarks for pin insertion in the radial shaft
The proximal two pins should be inserted proximal to the muscle bellies of abductor pollicis longus (APL) and extensor pollicis brevis (EPB), and should not penetrate them.
These muscles are usually easy to identify. Proximal to these muscles, the radial shaft can be palpated through the skin between the bellies of the extensor digitorum communis (EDC) and extensor carpi radialis longus/brevis (ECRL/ ECRB) over 3-4 cm. This is the preferred area for proximal pin insertion in the radial shaft.
The pins are inserted perpendicular to the transverse section of the radius.
4 Frame construction / reduction and fixation (wrist) top
AO teaching video: Distal Radius - Small External Fixator: Wrist-spanning Frame
Reduction and fixation
Longitudinal traction is applied on the thumb and index finger or the distal partial frame to reduce the fracture. Additional maneuvers may be necessary depending on the specific fracture pattern. Pressure from the dorsal side of the carpus may be helpful to restore volar tilt of the distal radius joint surface.
In multifragmentary fractures, additional K-wires may be inserted percutaneously, if the external fixator is used as a definitive treatment.
For details of K-wire insertion see the corresponding treatment option for the specific fracture type.