A 16 year old right hand dominant schoolboy presented to the emergency department with a painful, swollen right ring finger. Three days earlier he had injured his finger playing rugby and he thought the injury occurred while he was tackling an opponent. Although he was able to finish the game he has had discomfort and reduced movement in the finger since. Ecchymosis and tenderness were noted over the distal phalanx on the palmar aspect of his hand, as well as some swelling and tenderness at the base of the ring finger (fig 1⇓). The finger had no neurovascular deficit and examination of the rest of the right hand was normal. No fracture was seen on a plain radiograph of the ring finger. Fig 1 The patient’s right hand in a relaxed posture showing loss of normal cascade of the ring finger 1. What key aspect of the clinical examination would confirm the diagnosis? 2. What is the name of this injury (the name provides a clue to its mechanism)? 3. Which finger is most commonly affected? 4. How are these injuries classified? 5. How are these injuries managed? ### 1. What key aspect of the clinical examination would confirm the diagnosis? #### Short answer Inability to actively flex the distal interphalangeal joint (DIPJ) is pathognomonic of rupture of the flexor digitorum profundus (FDP) tendon. To test the FDP tendon function, isolate the DIPJ by holding the proximal interphalangeal joint (PIPJ) in extension, thereby preventing the action of the flexor digitorum superficialis (FDS). #### Discussion FDP tendon avulsion is diagnosed on physical examination—patients have a lack of isolated DIPJ flexion. To test for this, the DIPJ is isolated by holding the PIPJ in extension (fig 2⇓). The finger will probably be painful and swollen. Ecchymosis may be present on the volar side of the finger. The affected finger is often in an extended position relative to the other fingers, with loss of …