Outward displacement of both bones. (Lejars.)
The ulna alone may be dislocated backward, in which case the orbicular ligament must be lacerated and the upper ends of the adjoining bones forcibly separated. The olecranon will present back of its proper position, while the head of the radius will rotate where it belongs.
Fig. 352
Dislocation forward and outward of head of radius. (Lejars.)
Anterior dislocation of both bones is exceedingly rare unless complicated by fractures of the olecranon. When thus injured the forearm is lengthened and fixed. The posterior surface of the humerus here has only a skin covering, the condyles are bulging, the olecranon fossa empty, and the upper ends of the forearm bones felt in front of the elbow.
The head of the radius alone may be displaced in any direction save toward the ulna. The forward dislocation is the most common, which may be produced by a fall upon the overextended and pronated hand. The orbicular ligament here is lacerated or the head of the radius is slipped out of it. In the latter case it may be difficult to replace it. When dislocated backward the capsule is torn posteriorly as well as the orbicular ligament ([Fig. 353]).
Fig. 353
