Radial Head, Dislocation

The dislocated radial head is an easily missed lesion, not infrequently resulting in litigation. The forearm fracture is readily identified and attention is drawn away from the co-existing elbow injury. It is vital that for long bone fractures, the adjacent joints are both imaged and properly reviewed. 

In acute presentations, the dislocated radial head can generally be reduced by closed means. Under general anaesthesia, the elbow is flexed to enable... 

Fig. 18.13a,b. Type I Monteggia fracture with plastic deformation of the ulna, a AP radiograph shows minimal displacement and dislocation could easily he missed, b Lateral radiograph clearly demonstrates the dislocated radial head... 

A line drawn along the centre of the proximal radius should intersect the capitellum (the radiocapitellar line). Failure to do so suggests dislocation of the radial head. This rule is always valid on a true lateral image, in all stages of flexion (Storen 1959). 

The Monteggia lesion is dislocation of the radial head associated with a forearm injury. This should not he confused with the Galeazzi injury which is fracture of the radius and dislocation of the distal radioulnar joint. 

Monteggia injuries occur most frequently between the ages of 5 and 7. Patients will generally complain of forearm and elbow pain. If the ulna is fractured, pain will be maximal in the arm and there may be swelling and deformity. The elbow will also be swollen. In 10%-20% of cases, a neuropraxia of the radial nerve will be present, particularly if the radial head is dislocated laterally or anteriorly. Most of these nerve injuries will recover within 6-9 weeks and intervention is not indicated unless there is no sign of clinical or electromyographic recovery at 6 months. 

A number of equivalent lesions have also been described. Commonest of these is the Type 1 variant Where the radial head is dislocated anteriorly but the ulna has plastic deformation rather than a fracture. Other variants include dislocations with associated radial neck fractures, olecranon fractures and dislocations of the ulnar-humeral joint. In some respects, the pulled elbow , commonly seen in infants, can also be considered a Bado I equivalent. The injury occurs when the elbow has traction applied, usually resulting in hyperextension and pronation. The radial head subluxes through the annular ligament but does not truly dislocate and radiographs are either normal or will show an effusion with elevation of the fat pads. 

When imaging any long bone injury, it is imperative to include both the joint above and the joint below. Whilst Galeazzi lesions are rare in children, Monteggia lesions are not uncommon. It should also be stressed that the joint must be imaged in two planes. The elbow may look normal on the AP view but dislocation of the radial head is readily appreciated on the lateral projection. A straight line drawn up the shaft of the radius should intersect the capitellum in both AP and lateral views, irrespective of the degree of flexion of the joint (Fig. 18.13). 

Monteggia lesions. The articular surface of the radius is normally concave where it articulates with the capitellum. When the radial head has been dislocated for some time, the head becomes convex. This makes relocation of the joint difficult. Similar appearances may also occur in congenital dislocations of the radial head. In this instance, the dislocation is always posterior and thus confused with type II injuries. 

The radial head may also be displaced following dislocation of the elbow, either during dislocation or following subsequent reduction. 

Rarely, the radial head is completely displaced, often lying adjacent to the capitellum. This fracture can occur during the reduction of a dislocated elbow if there is an undisplaced radial neck fracture (Fig. 18.18). The radial head may be reduced by closed manipulation aided by manipulation with percutaneous K-wire. One should be careful to make sure that the reduced radial head is not rotated 180° (Wood 1969). 

Fig. 18.18. a,b AP and lateral radiographs of radial neck fracture displaced by reduction of the dislocated elbow. Radial head lies adjacent to the capitellum. c Intraoperative radiographs showing intramedullary nancy nail and percutaneous wire used to manipulate the femoral head, d Post reduction film... 

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