‘Mallet finger’ is a common traumatic lesion resulting in flexion deformity of distal interphalangeal joint. The basic pathology of this condition is
A. Avulsion fracture of middle phalanxB. Rupture of collateral slips of extensor expansion
C. Rupture of central slip of extensor expansion
D. Dislocation of distal interphalangeal joint
Answer. B.
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
insertion 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 part of the tendon is excised over the terminal phalanx and the joint held
extended with a Kirschner 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 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 insert 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
