Authors of section


Matej Kastelec, Pavel Dráč

Executive Editor

Simon Lambert

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Dorsal avulsion injuries of the proximal end segment (mallet finger)


Discontinuities of the extensor insertion are often referred to as “mallet injury” or “baseball finger.” They can be purely tendinous or bony avulsion fractures.

Bony avulsions (partial articular) of the distal phalangeal base are classified by the AO/OTA as 78.2–5.3.1B, where 2–5 indicates which finger is involved.

Large bony avulsions often are associated with palmar joint dislocation.

Mallet injury with bony dorsal avulsion of the extensor insertion and palmar joint dislocation

Further characteristics

The injuries can result in subluxation or total dislocation of the joint.

A large fragment remains minimally displaced because the volar plate attachment, the collateral ligament, and the A4 pulley remain largely intact.

An avulsion injury destroys the synergistic balance of the pull exerted by the flexor and extensor tendons. The continuity of the flexor tendon is lost. This results in an inability to flex the DIP joint.

Mechanism of injury

Flexion injury

The commonest cause of these injuries is forcible flexion of the actively extended DIP joint, as when stubbing a straight finger against resistance.

Forces (flexion injury) leading to a dorsal avulsion injury
Axial compression injury

Occasionally, the injury results from an axial overload of the terminal segment of the finger, causing joint impaction and a dorsal marginal fracture, which is retracted by the pull of the extensor tendon.

Forces (axial compression injury) leading to a dorsal avulsion injury
Fracture subluxation of DIP joint

An obliquely orientated axial compression force sometimes results in a dorsal marginal fracture, involving approximately half the articular surface, and can disrupt the collateral ligaments.

Forces leading to DIP joint subluxation and a dorsal avulsion injury

Presentation of injury

Partial tendon disruption

In incomplete tendon injuries, the resulting extension lag is no greater than 30°. The patient retains a partial ability actively to extend the DIP joint.

Partial disruption of the extensor tendon at the DIP joint
Disruption of the central part of the extensor mechanism

In complete disruption of the central part of the extensor mechanism, the patient is unable to actively extend the DIP joint.

The flexor digitorum profundus exerts a flexion deforming force on the distal phalanx, partly counterbalanced by the intact oblique retinacular ligaments and the collateral ligaments.

Disruption of the central part of the extensor mechanism at the DIP joint
Bony avulsion

A similar clinical picture is presented by bony avulsion of the extensor mechanism at its insertion. The dorsal avulsion fracture is of variable size.

Bony avulsion of the extensor mechanism at its insertion
Swan-neck deformity

In some patients, the elasticity of the ligaments and a lax PIP joint can result in swan-neck deformity because, after disruption of the extensor mechanism at the DIP joint, all extensor forces are concentrated on the PIP joint via the middle extensor slip.

Swan-neck deformity


In this case, the pull of the flexor digitorum profundus results in palmar subluxation of the distal phalanx. The palmar plate is commonly intact, and the collateral ligaments are partially ruptured.

AP and lateral x-ray showing a bony dorsal avulsion of the distal phalanx of a finger
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