Raestock (Deutsche Militärärztl. Zeitschrift, 1887, p. 331) has, by
means of experiments upon the cadaver, shown that this accident occurs
in forced pronation while the radius is resting upon the ulna at the
point where the former crosses the latter, the ulna acting as a fulcrum.
The head of the radius is pressed against its capsule and tears the
latter. More rarely, the accident may occur in forced supination, by
pressing the bone against the posterior edge of the ulna, the head of
the radius being luxated through a rent made by a rupture of the
external lateral ligament between the outer and inner sides; upon
pronating the hand, this outward dislocation is converted into a forward
one. The annular ligament is either torn or else the coronoid process of
the ulna is broken. In either case the interposition of the annular
ligament in the fold of the joint becomes an obstacle to reduction. In
the experiments as detailed, great force was necessary in the production
of the luxation.
Should active and passive movements, manipulation, etc., fail to remove
the obstacles to reduction, the author advises a resort to secondary
resection of the displaced head of the radius; this, with proper
precautions, is certainly a most wise and rational procedure.