Fracture of both bones may result from a direct blow, from a fall on the hand, or from their being bent over a fixed object. The line of fracture is usually transverse, both bones giving way about the same level. The common situation is near the middle of the shafts. In children, greenstick fracture of both bones is a frequent result of a fall on the hand—this indeed being one of the commonest examples of greenstick fracture met with ([Fig. 41]).
Fig. 41.—Greenstick Fracture of both Bones of the Forearm, in a boy.
The displacement varies widely, depending partly upon the force causing the fracture, partly on the level at which the bones break, and on the muscles which act on the respective fragments. It is common to find an angular displacement of both bones to the radial or to the ulnar side. In other cases the four broken ends impinge upon the interosseous space, and may become united to one another, preventing the movements of pronation and supination. There may be shortening from overriding of fragments.
When the radius is broken above the insertion of the pronator teres, its upper fragment may be supinated by the biceps and supinator muscles, while the lower fragment remains in the usual semi-prone position. If union takes place in this position, the power of complete supination is permanently lost.
The usual symptoms of fracture are present, and there is seldom any difficulty in diagnosis.
The prognosis must be guarded, especially with regard to the preservation of pronation and supination. These movements are interfered with if union takes place in a bad position with angular or rotatory deformity of one or both bones, or if callus is formed in excess and causes locking of the bones. In some cases the callus fuses the two bones across the interosseous space, and pronation and supination are rendered impossible.
Persistent angular deformity of the forearm is also liable to ensue, either from failure to correct the displacement primarily, or from subsequent bending due to ill-applied splints or slings. Want of union, or the formation of a false joint in one or both bones, is sometimes met with, particularly in children, and, like the corresponding fracture of the leg, is liable to prove intractable.
A considerable number of cases of gangrene of the hand after simple fracture of the forearm are on record. This is sometimes attributable to damage inflicted upon the blood vessels by the fractured bones, or to the force that caused the fracture, but is oftener due to a roller bandage applied underneath the splints strangulating the limb, to injudiciously applied pads, or to too tight bandaging over the splints. Volkmann's ischæmic contracture occasionally develops after fractures of the forearm.