Ulna non-union leading to Monteggia fracture deformity. Two cases of slowly developing radial head luxation.

The author presents two cases in which pseudoarthrosis of the ulnar diaphysis resulted in dislocation of the head of the radius. The pathogenesis of this secondary dislocation is discussed. The cause of anterior Monteggia fractures is not yet clear. Various explanations have been put forward: direct action of a force (Speed and Boyd, 1940), forced pronation (Evans, 1949) and hyperextension with strong contraction of the biceps (Wright, 1963). This work presents two cases of Monteggia fracture characterized by a "slow" fracture mechanism. The biomechanical aspects are discussed.