Rupture of the central slip of the extensor hood of the finger. A test for early diagnosis

ABSTRACT: Closed rupture of the middle slip of the extensor hood of a finger is easily missed until the late appearance of a buttonhole deformity. Early diagnosis gives the best chance of satisfactory treatment, but Boyes' test becomes positive only at a late stage. A new test is described in which, from a 90 degrees flexed position over the edge of a table, the patient tries to extend the proximal interphalangeal joint of the involved finger against resistance. The absence of extension force at the proximal joint and fixed extension at the distal joint are immediate signs of complete rupture of the central slip. The theoretical basis and the method of performing the test are discussed. END OF ABSTRACT

Closed rupture of the central slip of the extensor tendon hood of the finger can easily be missed at an initial examination, even when it is suspected. Later, a classic buttonhole deformity will develop, but by then correction is difficult. Early diagnosis is essential for successful treatment. Boyes (1970) described a test for the integrity of the central slip. If the proximal interphalangeal joint is held passively extended, it is then possible for the normal individual to flex the terminal interphalangeal joint in isolation. However, if the central slip has been ruptured, there is increasing difficulty in performing this action. Unfortunately this test only becomes positive when the proximal part of the ruptured central slip has retracted and become adherent to the surrounding tissues. The test which is described below becomes positive immediately after complete rupture of the central slip.

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