above the insertion of the deltoid the
upper fragment is usually dragged towards the middle line by the
muscles inserted into the inter-tubercular groove, while the lower is
tilted laterally by the deltoid. When the break is below the deltoid
insertion the displacement of the fragments is reversed. The signs of
fracture--undue mobility, deformity, shortening, and crepitus--are at
once evident, and the patient himself usually recognises that the bone
is broken.

The nerve-trunks in the arm--the median, ulnar, and radial
(musculo-spiral)--are apt to be damaged in these injuries; in
fractures of the lower part of the shaft the radial nerve is specially
liable to be implicated. This may occur at the time of the injury, the
nerve being contused by the force causing the fracture, or pressed
upon by one or other of the fragments, or its fibres may be partly or
completely torn across. When there is evidence of nerve injury, the
practitioner should draw the attention of the patient to it then and
there, and so guard himself against actions for malpraxis should
paralysis of the muscles ensue. Later, the nerve may become involved
in callus, or be damaged by the pressure of ill-fitting splints.
Weakness or paralysis of the extensors of the wrist and hand results,
giving rise to the characteristic "wrist-drop." The actions of the
muscles should always be tested before applying splints, and each time
the apparatus is removed or readjusted, to assure that no undue
pressure is being exerted on the nerves.

Union takes place in from four to six weeks in adults, and in from
three to four weeks in children. Delayed union, or want of union and
the formation of a false joint, is more common in fractures of the
middle of the shaft of the humerus than in any other long bone--a
point to be borne in mind in treatment. Arrest of growth in the bone
from injury to the nutrient artery is also said to have occurred.

_Treatment._--To restore the alignment of the bone, extension is made
on the lower fragment and the ends are manipulated into position. This
may necessitate the use of a general anaesthetic, and care must be
taken that no soft tissue intervenes between the fragments, as is
evidenced radiographically by the persistence of a clear space between
the ends even when they appear to be in apposition.

In _transverse_ fractures the position may be maintained by a simple
ferrule of poroplastic or Gooch-splinting. The elbow is flexed at a
ri