Review Question - QID 218113

This patient presents with a boney mallet injury without distal interphalangeal joint (DIPJ) subluxation, which should be initially treated with DIPJ extension splinting for a minimum of 6 weeks. If left untreated, these patients can develop a progressive swan neck deformity, as shown in Figure D.

Mallet finger injuries occur secondary to disruption of the terminal extensor insertion along the dorsal aspect of the distal phalanx. They can result from a hyperflexion moment (i.e avulsing the terminal extensor tendon insertion) or from an axial load on an extended finger (i.e. boney injury from the abutment of the distal phalanx on the head of the middle phalanx). In the setting of stable “boney mallet” injuries (as shown in Figure A), full-time splint immobilization is recommended for a duration of 6-8 weeks. Even in a delayed presentation (>1 month from injury), a trial of full-time splinting can lead to acceptable outcomes and negate the need for surgical intervention. Ultimately, patient compliance is the key to successful nonoperative management with full-time DIPJ extension splinting immobilization. If left untreated, the lateral bands which make up the terminal insertion of the extensor tendon will migrate proximally. This increases the ultimate force placed on the middle phalanx through the central slip. The resultant lack of extension on the distal interphalangeal joint and hyperextension of the proximal interphalangeal joint make up the characteristic swan neck deformity (Figure D).

Lamaris and Matthew performed a systematic review regarding the differing treatments for mallet finger injuries. They found that most cases are reported to be reliably treated with prolonged extension splinting of the distal interphalangeal joint. They also report that surgery is most often indicated in boney mallet cases involving more than 1/3 of the articular surface or in patients who develop progressive volar subluxation of the distal phalanx. Despite the need for surgery, these cases had a reportedly high rate of complications. The authors concluded that further comparison studies are needed to determine the best treatment for complex, operative boney mallet injuries.

Lin and Samora performed a similar systematic review on the management of mallet finger injuries. They reported the average extensor lag was 5.7 degrees after surgical treatment and 7.6 degrees after nonoperative management with comparable complication rates (14.5% versus 12.8%, respectively). The authors concluded that both surgical and nonsurgical treatments lead to good outcomes, and each patient should receive individualized treatment as needed.

Figure A displays the lateral radiographic imaging of this patient’s finger with a boney mallet injury. The avulsed bone fragment is relatively small (~25% of the articular surface) and the joint is well reduced even without being placed in full extension. Figure B displays a boutonniere deformity. Figure C displays an intrinsic plus finger deformity. Figure D displays a swan neck deformity. Figure E displays a Dupuytren’s contracture deformity. Figure F displays a rotational deformity with digit scissoring from a mal-rotated proximal phalanx fracture.

Incorrect Answers:
Answer 1: The boutonniere deformity may develop after a central slip injury, not a mallet finger injury. It is caused by a central slip injury followed by progressive attenuation of the triangular ligament and volar subluxation of the lateral bands.
Answer 2: A lumbrical plus finger deformity may develop after an injury to the flexor digitorum profundus (FDP) tendon distal to its origin on the lumbricals. When the patient attempts to fire their disrupted FDP (i.e. make a closed fist), it results in contraction of the FDP origin, or more simply, isolated lumbrical contraction.
Answer 4: Dupuytren’s disease is a fibroproliferative disorder that affects the palmar fascia of the hand. The characteristic pathologic bands can be appreciated on physical examination and may result in finger contractures. It is unrelated to extensor tendon trauma.
Answer 5: Digit crossover or “scissoring” may result from metacarpal or proximal/middle phalanx fractures that have rotational displacement. In the acute setting, digit scissoring is an indication to perform closed reduction or open reduction with fixation. In the chronic setting, these deformities require corrective osteotomy.