Image Interpretation: The proximal portion of the distal phalanx at the distal interphalangeal joint was avulsed off the base of the distal phalanx. The fragment was displaced 0.8 cm proximally with an intact extensor digitorum tendon attaching to the avulsed fragment. No hyperemia or soft tissue swelling was noted. No obvious disruption of the extensor tendon fibers. A 0.8 cm avulsion fracture at the 4th distal interphalangeal joint (Bony Mallet)

Teaching Pearl: Ultrasound is a highly accurate diagnostic tool for the evaluation of small, superficial structures in the finger. Studies show it to be more sensitive in showing bony fragments when compared to MRI. Additional evaluation to dynamically assess the function of the extensor tendon is made possible by ultrasound. In the case of a mallet finger, point-of-care ultrasound can be critical in earlier diagnosis with high accuracy and intervention. Two variations of this pathology include bony vs nonbony injury. Bony mallet finger includes extensor tendon injury with avulsion at the base of the distal phalanx. Whereas a non-bony injury may show extensor tendon injury with normal bony anatomy. Conservative treatment includes 6-8 weeks of splinting of the DIP in constant extension. Nocturnal splinting and appropriate rehab may be utilized following this period. Surgical indications include volar subluxation of the distal phalanx and relative indications include greater than 50% of articular surface involved, greater than 2mm articular gap, and open injuries. Wang T, Qi H, Teng J, Wang Z, Zhao B. The Role of High Frequency Ultrasonography in Diagnosis of Acute Closed Mallet Finger Injury. Sci Rep. 2017;7(1):11049. Published 2017 Sep 8. doi:10.1038/s41598-017-10959-x Lin JS, Samora JB. Surgical and Nonsurgical Management of Mallet Finger: A Systematic Review. J Hand Surg Am. 2018;43(2):146-163.e2. doi:10.1016/j.jhsa.2017.10.004