Sir: The maxim, “when you hear hoofbeats, think of horses rather than zebras,” reminds clinicians to focus on the most common diagnoses consistent with presenting symptoms. Trigger finger is a common cause of pain and impaired digital mobility, with a reported lifetime risk of 2.6 percent.1,2 The diagnosis is made clinically and can be aided by palpation of a firm, tendinous nodule on the volar surface that catches on the pulley system. A more rare cause of impaired finger extension is subluxation of the extensor digitorum communis at the metacarpophalangeal joint. Patients present with inability to fully extend the involved digit, often accompanied by pain and catching.3 On attempted finger extension, the extensor tendon exhibits ulnar deviation over the metacarpal head. In this communication, we describe a patient with concomitant trigger finger and extensor tendon subluxation of the same digit, a combination not previously reported in the literature. The workup and management of this clinical “zebra” is presented. A 78-year-old, right-hand-dominant woman presented with several months of progressive inability to extend the middle finger of her left hand. She was nondiabetic and had no previous history of hand trauma, osteoarthritis, or rheumatoid arthritis. On examination, she was unable to extend the index finger metacarpophalangeal joint beyond 45 degrees and had a palpable lump at the A1 level. A diagnosis of trigger finger was made and the patient underwent an uncomplicated open A1 pulley release a few weeks later, with free excursion of the profundus tendon confirmed. The patient recovered without incident, but at the first postoperative visit 2 weeks later, she continued to complain of limited extension of the left middle finger with a catching sensation. Examination of the dorsum of the hand revealed subluxation of the extensor digitorum communis between the metacarpal heads of the ring and middle fingers. The patient was informed that an error in complete diagnosis had been made and that a repair procedure of the extensor mechanism would be needed. Six weeks later, under intravenous regional anesthesia, the extensor indicis proprius tendon was transferred around the extensor digitorum communis tendon of the middle finger to secure it in its normal position in flexion and extension. This was confirmed with active motion in the operating room. At her most recent visit, 10 weeks postoperatively, range of motion was full with the exception of 10 degrees of lag at the middle finger metacarpophalangeal joint, which was improving (Figs. 1 and 2).Fig. 1.: Postoperative photograph demonstrating extension of the middle finger with 10 degrees of residual lag.Fig. 2.: Postoperative photograph demonstrating full flexion of all digits.Our report illustrates the need for comprehensive physical examination even when confronting a common and predictable constellation of findings. An initially thorough examination of the volar and dorsal aspects of our patient's hand would have revealed the coexistence of two causes for her functional limitation. Although a staged repair would still have been performed in this case, both patient and surgeon would have been spared the anxiety of an unsatisfactory outcome to the first operation. Sometimes, hoofbeats do come from zebras. Sashank K. Reddy, M.D., Ph.D. James W. May, Jr., M.D. Massachusetts General Hospital Harvard Medical School Boston, Mass.