The shaft of the _metacarpal of the thumb_ is frequently broken by a blow with the closed fist. The fracture is usually transverse, and situated near the proximal end of the shaft; frequently it is comminuted, and in some instances there is a longitudinal split.
_Treatment._--When the fracture is transverse, and especially when it implicates the middle or ring fingers, the most convenient method is to make the patient grasp a firm pad, such as a roller bandage covered with a layer of wool, and to fix the closed fist by a figure-of-eight bandage. In this way the adjoining metacarpals are utilised as side splints. Active and passive movements must be carried out from the first, and the bandage may be dispensed with at the end of a week or ten days.
In oblique fractures with a tendency to overriding of the fragments, especially in the case of the index and little fingers, it is sometimes necessary to apply extension to the distal segment of the digit, by means of adhesive plaster, to which elastic tubing is attached and fixed to the end of a bow splint, reaching well beyond the finger-tips (Fig. 52). This should be worn for a week or ten days.
[Illustration: FIG. 52.--Extension apparatus for Oblique Fracture of Metacarpals.]
#Bennett's Fracture of the Base of the First Metacarpal Bone.#--Bennett of Dublin described an injury of the thumb which, although comparatively common, is often mistaken for a sub-luxation backward of the carpo-metacarpal joint, or a simple "stave of the thumb." It consists in an "oblique fracture through the base of the bone, detaching the greater part of the articular facet with that piece of the bone supporting it which projects into the palm" (Fig. 53). We have frequently observed the fracture extend for a considerable distance along the palmar aspect of the shaft.
[Illustration: FIG. 53.--Radiogram of Bennett's Fracture of Base of Metacarpal of Right Thumb.]
It usually results from severe force applied directly to the point of the thumb, driving the metacarpal against the greater multangular bone (trapezium), and chipping off the palmar part of the articular surface, but it may result from a blow with the closed fist. The rest of the metacarpal slips backward, forming a prominence on the dorsal aspect of the joint. The pain and swelling in the region of the fracture often prevent crepitus being elicited, and as the deformity is not at once evident, the nature of the injury is liable to be overlooked. The fracture is recognised by the use of the X-rays. Unless properly treated this injury may result in prolonged impairment of function, full abduction and fine movements requiring close apposition of the thumb being specially interfered with.