Approach to mallet finger injury

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Literature searches were performed in PubMed and Google Scholar using the following key words and subject headings: mallet finger, extensor tendon injuries, distal interphalangeal joint injuries, bony mallet fractures, soft tissue mallet injuries, chronic mallet finger, DIP joint splinting, and management of mallet finger. Reference lists of included articles were also searched to identify relevant articles missed by the original search. Recommendations were generated from clinical evidence and expert opinion, and categorized into 3 levels. Level I evidence comes from systematic reviews, meta-analyses, or randomized controlled trials. Level II is derived from other comparative studies, such as nonrandomized cohort studies. Level III is based on expert opinions. Guidelines on the management of mallet finger injuries published by the American Society for Surgery of the Hand¹ and the British Society for Surgery of the Hand² are also referenced.

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Background. A mallet finger injury occurs following an axial load (“jamming the finger”), where the DIP joint is forced into flexion, resulting in the avulsion of the terminal extensor tendon (Figure 1).^3-5 While this may or may not be associated with an underlying avulsion fracture of the distal phalanx, the result is the same: the finger DIP joint rests in flexion, with the patient unable to extend it. In an examination of electronic consultation referrals to plastic surgeons in eastern Ontario, we found that there was a need for education and knowledge translation and found mallet finger injuries to be one of the most common subjects of questions.⁶ As most mallet finger injuries may be successfully managed by primary care physicians (PCPs) with excellent results, here we review the evidence on mallet finger injuries, including the care of these injuries and the importance of patient education.

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Figure 1.

Clinical presentation of a mallet finger injury of the little finger

Recognition and diagnosis. Diagnosis of a mallet finger injury is made by taking a history and by physical examination. The inability of the patient to actively extend the DIP joint is diagnostic. Passive correction of the finger (the examiner moving the joint into extension) is possible, but the patient will be unable to maintain this. If the injury is acute, there may be associated swelling, bruising, and tenderness over the dorsal DIP joint. X-ray scans are usually obtained to determine the presence of an associated distal phalanx fracture and joint alignment (Figure 2).¹ Ultrasound scans can confirm avulsion of the extensor tendon from the distal phalanx, but this is not necessary for diagnosis.

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Figure 2.

Lateral x-ray scans of bony mallet finger injuries affecting the distal phalanx of the right hand: A) Bony mallet injury with an avulsion fracture at the dorsal base of the distal phalanx. B) Bony mallet injury with associated volar subluxation of the distal phalanx at the distal interphalangeal joint, indicating that surgical intervention may be required.

The differential diagnosis for a mallet finger injury is limited but includes other finger trauma, including fingertip or nail injury, bony or joint changes with arthritis, and Kirner deformity (dystelephalangy).^1,7 Kirner deformity is a rare congenital condition characterized by a progressive painless curvature of the distal phalanx, typically the little finger.⁸ Unlike a mallet finger, Kirner deformity lacks the acute traumatic onset and is typically painless. In children, a Seymour fracture (through the physis of the distal phalanx) may be mistaken for a mallet finger injury. This misdiagnosis should be promptly recognized, as Seymour fractures have a risk of osteomyelitis if an open injury is missed (Figure 3).⁹

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Figure 3.

Seymour fracture: A) Clinical photo of a Seymour fracture. B) Clinical photo of a Seymour fracture with a tourniquet applied. C) X-ray scan of a Seymour fracture.

PCPs’ role in management. Mallet finger injuries are generally treated nonsurgically with continuous uninterrupted splinting. A systematic review⁴ found that both surgical and nonsurgical management led to excellent outcomes, while another systematic review of randomized controlled trials¹⁰ found insufficient evidence to determine which method was superior. As such, the American Society for Surgery of the Hand¹ and the British Society for Surgery of the Hand² recommend nonsurgical management with splinting.

A variety of splints can be used with the goal of keeping the DIP joint in extension to enable healing of the tendon (Figure 4). Splint options include plastic splints, aluminum foam splints, and custom thermoplastic splints. A systematic review and retrospective study demonstrated that all were equally effective in treating a mallet finger injury.^11,12 While there is some variability in recommended protocols, most recommend splinting in an uninterrupted fashion for 6 to 8 weeks.^1,2,13-15 Further, a prospective cohort study¹⁶ found written instructions to be helpful in improving treatment adherence and patient outcomes (Appendix, available from CFPlus*). Additional instructions include encouraging range of motion (ROM) of the proximal interphalangeal joint to prevent stiffness, and if the splint is removed for hygiene, care must be taken to prevent the DIP joint from flexing and disrupting healing.^11,15

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Figure 4.

Various splint types used for the conservative treatment of a mallet finger injury: A) Aluminum foam splint. B) Custom thermoplastic splint. C) Plastic splint.

Expected outcomes. In general, patient outcomes following splinting are excellent, with most patients achieving full ROM and full use following treatment. However, up to 12% of patients with acute mallet finger injuries and 25% of those with delayed presentation (more than 4 weeks after injury) may experience a small persistent extensor (mean [standard deviation] 11° [12°]) lag or a small deformity on the dorsum of the finger.^4,17,18 This, however, usually does not result in any functional problems.¹ Infrequently, some patients may also experience nail ridging and mild nail deformities after injury that often resolve with nail growth.^19,20

While delayed presentation and treatment may be associated with higher rates of residual extension lag compared to acute treatment, multiple retrospective comparative studies^18,21,22 have demonstrated that splinting for an average of up to 8 weeks may still yield good outcomes. Failure to treat a mallet finger injury, however, can result in permanent deformity in the affected finger. If left untreated, a chronic mallet finger can lead to tendon imbalances and secondary deformities such as swan-neck deformity, affecting the entire finger.²³ This may result in chronic pain and impaired finger mechanics, limiting hand function.^24,25

Guidelines for referral to a plastic or hand surgeon. Referral should be considered for mallet finger injuries with joint subluxation on x-ray scan. It is uncommon for joint subluxation to occur without a large displaced avulsion fracture (more than one-third of the articular surface). Even with large displaced avulsion fractures, splinting is appropriate if joint congruency can be maintained. Additionally, referral should be considered for open injuries (resulting in direct laceration of the extensor tendon) or patients whose symptoms do not respond to splinting treatment.²