Radiography
Posteroanterior (PA) and lateral radiographs centered at the distal interphalangeal (DIP) joint of the affected finger are required. These radiographs are used to differentiate between a bony mallet injury (see the first image below) and a tendinous one. They also reveal any associated metaphyseal, shaft, or tuft fractures of the distal phalanx. Perhaps most important, lateral radiographs reveal the presence of volar subluxation of the distal phalanx (see the second image below). In addition, these radiographic views reveal rare condylar fractures of the middle phalanx.

Radiographs of the whole hand do not suffice in the evaluation of mallet finger, because parallax of the x-ray beams creates an uninterpretable oblique view of the DIP joint. No imaging studies other than radiography are indicated in mallet finger.
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Despite active extension effort, the distal interphalangeal joint of the index finger rests in flexion, characteristic of a mallet finger.
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Typical mallet finger deformity.
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This radiograph depicts a large, dorsal-lip avulsion fracture from the distal phalanx, a bony mallet injury.
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Mallet fracture with volar subluxation of the distal phalanx.
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Stable mallet fracture that involves 40% of the joint surface.
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Dorsal aluminum foam splint for the treatment of a mallet finger.
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Stack splints are widely used for the treatment of mallet finger.
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Molded plastic stack splint for the treatment of mallet finger.
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A skin-tight plaster cast can effectively hold the distal interphalangeal joint extended and the proximal interphalangeal joint (PIP) flexed when a mallet deformity is accompanied by a hyperextensible PIP. Not immobilizing the PIP in partial flexion risks the development of a swan-neck deformity.
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Pressure-sore formation can result from a splint that is applied too tightly, especially if the joint is maintained in a hyperextended position rather than a position of neutral extension.
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This photo demonstrates a thermoplastic blank for a custom-molded mallet finger splint and an oblique view of the molded splint in place.
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Dorsal view of the custom-molded thermoplastic splint in place.
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Volar view of the thermoplastic splint in place.
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Application of the thermoplastic splint.