Buckle fractures of the proximal ulna only occur in young children and are usually stable and undisplaced.
This is because the thick periosteum acts as a tension band in hyperflexion of the elbow.
Undisplaced fractures may be associated with radial head subluxation/ dislocation (Monteggia lesion) especially when distal to the coronoid.
Note: To rule out a Monteggia lesion or equivalent fracture, check for the stability/fracture of the radial head/neck.
21u-M/2 Ulna, incomplete metaphyseal fracture
An incomplete fracture of the proximal ulna is also referred to as metaphyseal greenstick fracture.
It is sometimes associated with a radial head subluxation, especially if the fracture line is distal to the coronoid.
Due to the elasticity of immature bone, the angulation that is present at examination often underestimates the angulation at the time of injury, which may have resulted in dislocation of the radial head.
Note: If there is no angulation of the fracture and the radial head is not dislocated a Monteggia lesion must still be ruled out. Check for the stability/fracture of the radial head/neck.