Mallet finger: a simulation and analysis of hyperflexion versus hyperextension injuries.
The goal of this study was to simulate the mechanisms of hyperflexion and hyperextension injuries of the distal interphalangeal (DIP) joint of the hand and to analyze the resulting extensor tendon injury patterns. The hypotheses were raised that hyperflexion trauma leads to a plastic deformation of the extensor tendon aponeurosis, with or without a small bony avulsion fragment but without joint surface involvement, and that hyperextension injuries can create a shear fracture of the dorsal lip of the distal phalanx, without injury to the extensor tendon aponeurosis. Loading was applied with a swinging pendulum impacting the distal phalanx in 103 human specimens in either an extended or flexion position. After loading, injury patterns were analyzed radiologically and histologically. There was evidence that hyperflexion trauma leads to a plastic deformation or rupture of the extensor tendon. Bony tendon avulsion was evident in 12.2 % of cases. With hyperextension, the extensor tendon remained intact in all cases, but there were large fracture fragments involving the articular surface in 4.1 % of cases. The results of the study show that force on the flexed joint leads to overstretching of the extensor tendon, and to an associated dorsal bony avulsion with intact joint line. Force applied to the joint in extension can lead to a bony dorsal edge fracture with articular involvement and with it, a palmar DIP joint capsule rupture. The results illuminate a direct correlation between the mechanism of injury and the pattern of injury in the clinical picture of mallet finger.
Clinic for Orthopaedics and Trauma Surgery, University of Cologne, Joseph-Stelzmann Strasse 9, 50924, Cologne, Germany.
Andrea
A
Kreuder
Department of Trauma Surgery, Orthopaedics, Hand- and Reconstructive Surgery, Teaching Hospital, St. Vinzenz Hospital Cologne, University of Cologne, Merheimer Strasse 221-223, 50733, Cologne, Germany.
Dietmar
D
Pennig
Clinic for Orthopaedics and Trauma Surgery, University of Cologne, Joseph-Stelzmann Strasse 9, 50924, Cologne, Germany.
Christoph Kolja
CK
Boese
Clinic for Orthopaedics and Trauma Surgery, University of Cologne, Joseph-Stelzmann Strasse 9, 50924, Cologne, Germany.
Peer
P
Eysel
Clinic for Orthopaedics and Trauma Surgery, University of Cologne, Joseph-Stelzmann Strasse 9, 50924, Cologne, Germany.
Johannes
J
Oppermann
Clinic for Orthopaedics and Trauma Surgery, University of Cologne, Joseph-Stelzmann Strasse 9, 50924, Cologne, Germany. jens.dargel@uk-koeln.de.
Jens
J
Dargel
D003198:Computer Simulation; D006230:Hand Injuries / Q000209:etiology*; D006801:Humans
Extensor tendon; Finger; Histology; Pathomechanics; Tendon avulsion fracture