In the adult, mallet injury commonly occurs as either a soft tissue injury, less often associated with a dorsal avulsion fracture. It arises from the combination of an external flexion force on the distal interphalangeal joint at the same time as attempted extension of this joint, with tissue failure occurring at the extensor tendon insertion (Fig. 17).

• Soft tissue mallet injuries may occur after a relatively trivial event, such as using the fingertips to push folds out of a bedspread, a painless event with no bruising. Soft tissue mallet injuries are best treated with continuous extension splinting for six to eight weeks. Splinting may be helpful even if the initial treatment is delayed as long as three months. If the patient can not tolerate a continuous splinting program, the distal interphalangeal joint may be pinned in slight hyperextension for six weeks.
• Mallet fractures more often result from obvious trauma, such as being struck on the fingertip while trying to catch a ball: "baseball finger". In the majority of adult mallet fractures, the distal phalanx articulation remains congruent and the fracture fragment involves less than one-third of the joint surface. These injuries are best treated with extension splinting for one month. Residual deformity is more likely with delayed treatment, with an associated hyperextension posture of the proximal interphalangeal joint, and in mallet fractures with a large avulsion fragment or with palmar subluxation of the distal phalanx. Recognizing both the technical difficulty and known complications of open treatment, these latter two fractures are probably best treated with a percutaneous indirect reduction using extension block pinning (Darder-Prats) (Fig. 17). The majority of pediatric mallet injuries are fractures involving the growth plate - usually Salter I, less often Salter III.