Figure 1. Anteroposterior radiographic view of left small finger.
Figure 2. Lateral view of the same finger shows a bony mallet finger.
A 25-year-old man presents with pain to his left small finger and deformity after a fall 2 days ago. He is unable to extend the distal part of his small finger. On physical examination, he has a flexed distal interphalangeal (DIP) joint to the 5th digit. Radiographs of the left small finger (Figures 1 and 2) show a bony mallet finger.
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A mallet finger is caused by loss of extension at the DIP joint caused by an extensor tendon disruption or bony avulsion off the dorsal aspect of the distal phalanx.1 Loss of extension at the DIP causes the flexor digitorum profundus tendon to pull the DIP joint into a flexion deformity. Bony avulsion fractures are stable if no subluxation of the distal phalanx occurs, less than 50% of the joint surface is involved, and less than 2mm to 3 mm of displacement is found.1,2
Treatment of acute mallet injuries (<4 weeks) involves keeping the DIP joint in an extension splint for 6 to 8 weeks. Dorsal or volar-based splints can both be used as studies have shown no greater extension lag deformity with using one or the other.2 It is common for the DIP joint to have some permanent flexion of less than 10° to 20° after treatment, however greater than 25° is considered a poor outcome.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1. Alla SR, Deal ND, Dempsey IJ. Current concepts: mallet finger. Hand. 2014;9(2):138-144. doi:10.1007/s11552-014-9609-y
2. Pike J, Mulpuri K, Metzger M, Ng G, Wells N, Goetz T. Blinded, prospective, randomized clinical trial comparing volar, dorsal, and custom thermoplastic splinting in treatment of acute mallet finger. J Hand Surg Am. 2010;35(4):580-588. doi:10.1016/j.jhsa.2010.01.005