Monteggia fracture is due to:

Ref: Apley's System of Orthopaedics and Fractures, 9th edition, page 770 & 773Explanation:Monteggia fractureThe injury described by Monteggia in the early nineteenth century (without the benefit of x- rays!) was a fracture of the shaft of the proximal third of ulna associated with dislocation of the proximal radioulnar joint. The radio-capitellar joint is dislocated as well.More recently, the definition has been extended to embrace almost any fracture of the ulna associated with dislocation of the radio- capitellar joint, including transolecranon fractures in which the proximal radioulnar joint remains intact.If the ulnar shaft fracture is angulated with the apex anterior (the most common type) then the radial head is displaced anteriorly, if the fracture apex is posterior, the radial dislocation is posterior, and if the fracture apex is lateral then the radial head w ill be laterally displaced.In children, the ulnar injury may be an incomplete fracture (greenstick or plastic deformation of the shaft ).Fractures of the distal third of radius with dislocation of the ulnar head from the distal radioulnar joint was described by Galeazzi in 1934 and named after him. It is commoner than Monteggia fracture dislocation.