Executive Editor: James Hunter General Editor: Fergal Monsell

Authors: Andrew Howard, Peter Schmittenbecher, Theddy Slongo

Pediatric forearm shaft 22u-D/6

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Glossary

1 General considerations top

Overcorrection of the ulna enlarge

In Monteggia lesions, reduction and stable fixation of the ulna are required to assist with stable reduction of the radial head. The most important factor is restoration of the length of the ulna.

The radial head usually reduces spontaneously once the ulna is out to length.

If after assessment of the fixation, the radial head is not absolutely centered on the center of the capitellum in AP and lateral views, consider an overcorrection of the ulna (see illustration).


Proximal ulnar osteotomy with overcorrection enlarge

In injuries that result in bowing of the ulna, a proximal ulnar osteotomy with overcorrection may be required.

An external fixator is a versatile device in this situation and allows multidirectional correction.

2 Principles of modular external fixation top

Modular external fixator enlarge

Modular external fixator

The versatility of a modular external fixator is an advantage in the management of children’s fractures and can accommodate age specific variations in fracture biology and anatomy.

An external fixator may be used for definitive management of forearm fractures in children due to the short healing time.

Practical considerations are illustrated in detail in the Basic technique for application of modular external fixator in children.

Specific considerations for the forearm shaft are given below. The procedure illustrates the application of an external fixator in a plastic deformity with osteotomy. The treatment of complete fractures follows identical principles.


Other types of external fixator enlarge

Other types of external fixator

Alterative configurations are available and include monolateral or ring systems.

Disadvantages of these systems in children include:

  • Fixed distance of pin insertion defined by the clamp
  • Excessively stiff construct

Pin size in forearm fractures

External fixation is suitable for all ages, but the pin diameter must be appropriate to the size of the bone.

Pins with a thread diameter of 2.5-4.0 mm are suitable for forearm fractures and should be about 1/3 of the bone diameter.


Sequence of pin insertion

Determined by:

  • Fracture morphology
  • Personal preference

3 Osteotomy and overcorrection in bowing and greenstick injuries top

Modular external fixator enlarge

In a bowing injury the osteotomy should be at the level of the proximal ulna even if the apex is in the midshaft. Greenstick fractures should be overcorrected at the level of the fracture.

The osteotomy should involve approximately 2/3 of the ulnar diameter.

The landmark for osteotomy is the distal end of the radial tuberosity.

This preserves the attachment of the interosseous membrane to the radius, and the reduction force can be transmitted to the radial head.

4 Frame construction on the ulna top

Proximal pin insertion enlarge

Proximal pin insertion

Insert the proximal ulnar pins through the subcutaneous cortex of the posterior border of the ulna between the extensor and flexor muscle masses.


Proximal pin insertion enlarge

Make an 8-10 mm skin incision over the site of pin insertion.

Use an artery clip for blunt dissection down to the bone, protecting important anatomical structures.


Proximal pin insertion enlarge

The posterior border of the ulna is subcutaneous and offers the best access.

Insert the pin in the near cortex and through the center of the bone into the far cortex.

Take care not to advance the tip of the pin beyond the far cortex to avoid damage to neurovascular structures.

Pins should not be placed closer than 1 cm to the physis.


Distal pin insertion enlarge

Distal pin insertion

Safe access to the subcutaneous dorsomedial cortex is improved with the elbow flexed and the forearm in mid-supination.


Distal pin insertion enlarge

Make an 8-10 mm skin incision over the site of pin insertion.

Use an artery clip for blunt dissection down to the bone, protecting important anatomical structures.


Distal pin insertion enlarge

Insert the distal ulnar pins from dorsomedially between the extensor carpi ulnaris and flexor carpi ulnaris.

As the distal ulna in children has a small diameter, oblique pin placement improves bony contact.

Pins should not be placed within 1 cm of the physis.


Completion of osteotomy enlarge

Completion of osteotomy

Complete the osteotomy before applying the rods to the pins. Use a retractor to protect the soft tissues on the far cortex.


Reduction of ulnar fracture and radial head enlarge

Reduction of ulnar fracture and radial head

Manually reduce the ulnar fracture using the unlinked pin blocks as handles. Some overcorrection may be helpful if the radial head does not reduce spontaneously. Loose application of the connecting rod facilitates final tightening.

5 Assessing the radial head position top

Reduction of radial head enlarge

Reduction of radial head

Closed stable reduction of the radial head is usually possible once the ulna has been aligned.

Rotational movements of the forearm may be necessary to complete the reduction of the radial head.

After fixation of the ulna, use an image intensifier to carefully evaluate the position of the radial head relative to the capitellum.

This must be confirmed through a full range of flexion, extension, pronation and supination.


Revision of ulnar reduction and fixation enlarge

Revision of ulnar reduction and fixation

At this stage the ulnar reduction can be revised if required, often to an overcorrected position which usually results in a stable and anatomic reduction of the radial head.


If there is residual subluxation or instability in any position after optimization of the ulnar correction, there may be interposed tissue (usually annular ligament) in the radiocapitellar joint and an open reduction of this joint should be performed.

6 Open reduction of radial head top

Approach to radial head enlarge

Approach to radial head

Perform a lateral approach and manually reduce the radial head.


Removal of blocks to reduction enlarge

Removal of blocks to reduction

The annular ligament is the most common intraarticular block to reduction. In rare cases the ligament can be gently repositioned around the radial head.

More often the ligament must be incised or excised to allow reduction of the radial head.


Reassessment of radial head position

Reassess the position and stability of the radial head by direct visual inspection and image intensification.

7 Assessment of forearm rotation top

Assessment of forearm rotation enlarge

Once the fracture is reduced and stabilized, the position may be checked with an image intensifier.

The rotation of the forearm is also assessed clinically. Pronation and supination may be limited by the injury and fixator configuration.

If there is important radiological malalignment or functional restriction, the external fixator may be adjusted.

v1.0 2018-11-28