A. Avulsion of tendon at the base of the middle phalanx.
B. Avulsion of extensor tendon at the base of the distal phalanx.
C. Fracture of distal phalanx.
D. Fracture of the proximal phalanx.
The condition shown in the picture above represents mallet finger.
The mallet finger deformity is characterized by a loss of full active distal interphalangeal joint extension with full passive ROM evident.
The mallet finger reflects the loss of normal extensor force transmission via the terminal tendon insertion onto the distal phalanx.
The unopposed flexor digitorum profundus pulls the distal joint into flexion.
The usual mechanism of injury involves sudden passive flexion of the actively extended distal interphalangeal joint. Disruption of the terminal tendon may be entirely confined to the tendon or may involve an avulsed fracture fragment from the dorsal lip of the distal phalanx proximal articular surface.