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).
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.
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
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
Safe zones for pin placement
The forearm anatomy is complex due to the presence of three major neurovascular bundles. Pin placement should avoid these structures.
Read more about
Safe zones for pin placement in the ulna
.
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.
This procedure is normally performed with the patient in a
supine position
.
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.
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.
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
Safe access to the subcutaneous dorsomedial cortex is improved with the elbow flexed and the forearm in mid-supination.
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.
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
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
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.
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
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.
Approach to radial head
Perform a lateral approach and manually reduce the radial head.
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.
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.
