Review Question - QID 217529

The annular ligament is the anatomic structure most likely responsible for blocking radiocapitellar reduction in Monteggia fractures.

Monteggia fractures are defined by a proximal ulna fracture in addition to radial head dislocation. They were initially classified by Bado (Illustration A). The majority of pediatric Monteggia fractures are classified as a Bado type 1. Most pediatric Monteggia fractures are amenable to closed reduction and long arm casting under sedation. Typically, when adequate ulnar length is achieved during the reduction, the radial head will reduce. However, there are instances where closed reduction is not successful and open reduction must be performed. In the vast majority of these cases, the annular ligament represents the primary block to reduction as it can become entrapped between the capitellum and the radial head.

Bae et al. reviewed strategies for successfully managing Monteggia fractures. They discuss that both ulnar length/alignment as well as the radiocapitellar relationship must be restored in order to maintain reduction. Early recognition remains paramount, because chronic reconstruction +/- ulnar osteotomy can be challenging.

Ring et al. discussed operative management of Monteggia fractures in 36 children. They noted that all the patients who were managed within 24 hours had good or excellent results, while 2/8 of the group who were treated at least a week after injury had poor results. They also emphasize that prompt recognition of these injuries and appropriate reduction are important to achieving a good outcome.

Ramski et al. performed a multicenter study evaluating treatment strategies in pediatric Monteggia fractures based on fracture pattern. They noted that in complete ulnar fractures treated nonoperatively, there was a 33% rate of failure, compared to no failures in 52 patients with complete ulnar fractures treated operatively. From these results, they concluded that the severity of the fracture pattern does affect the stability of the reduction and those with complete ulnar fractures may benefit from operative intervention.

Abe et al. published a review on irreducible Monteggia fractures in pediatric patients. They noted 17 cases in which the radiocapitellar joint was unable to be reduced, of which 15 were attributed to annular ligament interposition, 1 was attributed to the biceps tendon and the other the posterior interosseous nerve (PIN). They concluded that if ulnar length was appropriate and the radiocapitellar joint was still unable to be reduced, the annular ligament was the most common block to reduction.

Figures A & B are AP and lateral radiographs demonstrating a long oblique proximal ulna fracture with associated anterior radial head dislocation, indicative of a Bado type I Monteggia fracture. Illustration A is the Bado classification.

Incorrect Answers:
Answers 2-5: While there are case reports of biceps tendon, PIN and joint capsule interposition preventing radiocapitellar reduction, the most common block to reduction by far is the annular ligament.