Rupture of collateral slips of extensor expansion 'Mallet finger' describes the characteristic drooping of the finger observed with injury to the extensor digitorum at its inseion at the base of the distal phalanx (the collateral slips). o A mallet finger may result from direct trauma to the finger tip or more commonly, by forcibly bending the finger in extension, for example, when catching a ball - hence, the synonym, 'baseball finger." o In older patients, the associated trauma may be minor for example, catching the tip of the finger whilst changing the sheets on the bed. o The extensor mechanism is disrupted. The finger is held flexed at the distal interphalangeal joint. There is no active movement but passive movement is unimpaired. In time, the proximal phalanx may become hyperextended. o An x-ray should be obtained to look for any associated chip fracture. o Most injuries are treated conservatively. A mallet finger splint is applied to hold the distal interphalangeal extended whilst permitting movement at the proximal interphalangeal joint. o If conservative treatment fails then pa of the tendon is excised over the terminal phalanx and the joint held extended with aKirschner wire. o Extensor expansion (dorsal expansion, dorsal hood) refers to the flattened tendons (aponeurosis) of extensor muscles that run into the back of the hand. o At the distal end of the metacarpal, the extensor tendon will expand to form a hood, which covers the back and sides of the head of the metacarpal and the proximal phalanx. o The expansion soon divides into three bands: * Two lateral bands pass on either side of the proximal phalanx and stretch all the way to the distal phalanx. The lumbricals of the hand, the palmar & dorsal interossei of the hand, also inse on these bands. * A single median band passes down the middle of the finger along the back of the proximal phalanx, ending at the base of the middle phalanx