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.
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.
The treatment consists in reducing the fracture by extension in the attitude of full abduction and applying an accurately fitting pad over the extremity of the displaced bone, maintained in position by a light angular splint. This splint is first fixed to the extended and abducted thumb, and while extension is made by pushing it downwards the upper end is fixed to the wrist ([Fig. 54] A). The apparatus is worn for three weeks, being carefully readjusted from time to time to maintain the extension and abduction. A moulded poroplastic splint added on the same principle may be employed, and is more comfortable ([Fig. 54] B). Excellent results are obtained after reduction of the displacement, by massage and movement from the first, and the support merely of a figure-of-eight bandage (Pirie Watson).
