Orthopaedic Surgery - Mallet Finger

Basics

Mallet finger is an extensor mechanism injury at the distal interphalangeal (DIP) joint that causes loss of active extension and a characteristic flexed posture of the fingertip.

The injury results from disruption of the terminal extensor tendon, sometimes with an associated avulsion fracture from the dorsal base of the distal phalanx.

In children, a mallet deformity associated with fracture is often caused by a physeal or transepiphyseal injury of the distal phalanx.

Synonyms

Mallet finger is also called:

Dropped finger or baseball finger.

Classification

A commonly used classification helps guide treatment.

Type I

The most common form.

It results from:

Closed or blunt trauma with disruption of the terminal extensor tendon, with or without a small dorsal avulsion fracture.

Type II

An open injury caused by a:

Laceration at or proximal to the DIP joint with complete loss of tendon continuity.

Type III

A deeper open injury with:

Loss of skin, subcutaneous tissue, and extensor tendon substance.

Type IV

Type IV injuries are bony mallet injuries.

Type IV-A

A transepiphyseal fracture in a child.

Type IV-B

A hyperflexion injury producing a fracture involving approximately 20–50% of the articular surface.

Type IV-C

A larger fracture, usually involving more than 50% of the articular surface, often associated with early or late volar subluxation of the distal phalanx.

Prevention

There is no reliable method of preventing mallet finger.

Early recognition and correct treatment improve the likelihood of restoring good DIP extension.

Epidemiology

Mallet finger can occur at any age.

Men are affected more commonly overall.

Historical studies describe the highest incidence in:

Adolescent and young adult males, approximately 11–40 years of age, and

Middle-aged women, approximately 41–60 years of age.

The injury becomes increasingly common toward the ulnar side of the hand, with the ring and small fingers frequently affected.

Etiology

Mallet finger may occur during:

Sports, work activities, or routine household activities.

Closed injuries are more common than open injuries.

Closed Injury Mechanism

The classic mechanism is:

Sudden forced flexion of an actively extended DIP joint.

This can rupture the terminal extensor tendon or avulse a small fragment from its insertion on the distal phalanx.

Bony Mallet Injury

Forced loading of the distal phalanx may produce a dorsal base fracture involving a substantial portion of the articular surface.

When this occurs, the lesion should be viewed primarily as an intra-articular fracture with secondary mallet deformity.

Open Injury

Open mallet injuries may result from:

Sharp laceration or crush trauma.

These injuries can directly disrupt the terminal extensor tendon and surrounding skin.

Vascular Considerations

The terminal extensor tendon near its insertion has a relatively limited blood supply.

This may contribute to:

Tendon vulnerability and slower healing in this region.

Diagnosis

Signs and Symptoms

The fingertip rests in a flexed posture at the DIP joint.

The patient is unable to actively extend the DIP joint fully.

Passive Motion

Passive extension is usually preserved in an acute uncomplicated injury.

PIP Hyperextension

Some patients demonstrate compensatory hyperextension of the proximal interphalangeal joint, especially when the deformity becomes chronic.

This may eventually contribute to a swan-neck pattern.

Physical Examination

Skin and Nail

Inspect carefully for:

Open wounds, skin loss, nail-bed injury, swelling, and bruising.

Active Motion

Document:

Active DIP extension and flexion.

The degree of active extension lag should be recorded.

Passive Motion

Assess whether the DIP joint can be fully extended passively.

A fixed flexion deformity suggests a more chronic or complicated lesion.

Proximal Joints

Examine the:

PIP and MCP joints

for hyperextension, stiffness, or associated injury.

Imaging

AP and true lateral radiographs of the involved finger are mandatory.

They help determine:

Whether a fracture is present

Size of the dorsal fragment

Articular involvement

Joint congruity

Presence of volar subluxation

These findings directly influence treatment.

Laboratory Tests

No laboratory studies are routinely useful in diagnosing mallet finger.

Pathoanatomy

The terminal extensor mechanism is formed by the conjoined lateral bands.

These bands merge distally and insert onto the dorsal base of the distal phalanx.

Disruption at or near this insertion removes the active extension force across the DIP joint.

The unopposed flexor digitorum profundus then pulls the distal phalanx into flexion.

Differential Diagnosis

Important alternatives include:

Dorsal base fracture of the distal phalanx

Physeal injury of the distal phalanx in a child

Chronic DIP flexion contracture

DIP osteoarthritis

Other extensor tendon injuries

Treatment

General Principles

Most closed mallet injuries are treated nonoperatively.

The main principle is:

Continuous maintenance of the DIP joint in full extension or slight hyperextension while allowing the PIP joint to move freely.

Splinting Duration

Continuous splinting is generally required for at least 6 weeks, and many clinicians prefer approximately 8 weeks.

The DIP joint must remain continuously extended during this period.

Even brief flexion may disrupt early tendon healing and effectively restart the treatment period.

Night Splinting

After the full-time phase, night splinting is often continued for an additional 2–4 weeks.

If an extension lag reappears, prolonged night splinting or another course of full-time splinting may be required.

Recurrent Extension Lag

A mild recurrent lag is common.

If substantial lag develops, another period of continuous splinting, sometimes up to approximately 8 weeks, may be considered.

Delayed Presentation

Even mallet deformities first seen 2–3 months after injury may improve with prolonged splinting if the DIP joint remains passively correctable.

Surgery is reserved for selected persistent symptomatic deformities.

Type I Treatment

Closed tendon injuries and small avulsion fractures are usually managed with:

A dorsal, volar, or circumferential DIP extension splint, such as a Stack-type splint.

Expected Results

When treatment begins early and splinting is performed correctly, most patients achieve a good functional result.

A small residual extensor lag may remain without causing significant disability.

Direct Tendon Repair

Routine direct surgical repair of closed Type I injuries is generally avoided because:

The terminal tendon is extremely thin and relatively poorly vascularized.

Nonoperative splinting usually produces better overall results with fewer complications.

Transarticular Kirschner Wire

A temporary K-wire across the DIP joint may be considered when:

The patient cannot reliably maintain splint immobilization or when other surgical indications are present.

Type II Treatment

Open tendon lacerations require:

Irrigation, tendon and skin repair, and DIP extension immobilization.

A simple repair technique may approximate both skin and tendon.

Postoperative Immobilization

The DIP joint is maintained in extension for a minimum of approximately 6 weeks, followed by cautious motion.

If extension loss develops, splinting should be resumed.

Type III Treatment

Deep open injuries with tissue loss require more complex reconstruction.

Treatment may include:

Soft-tissue coverage, staged tendon reconstruction, free tendon grafting, or DIP arthrodesis in severe chronic cases.

Pediatric Mallet Injury

Mallet deformity associated with a distal phalanx fracture in a child is commonly a physeal injury.

Closed reduction often corrects the deformity.

Pediatric Immobilization

Continuous extension splinting for approximately 3–4 weeks may be sufficient in many stable pediatric fractures, depending on age and fracture characteristics.

Type IV Bony Mallet Injury

Large dorsal fracture fragments require careful assessment of:

Fragment size, joint congruity, and volar subluxation.

Nonoperative Treatment

Many bony mallet injuries can still be treated successfully with splinting if:

The joint remains congruent and there is no persistent volar subluxation.

Surgical Considerations

Historically, surgery was often recommended when the fragment involved more than approximately one-third of the articular surface.

Current decision-making is more strongly influenced by:

Joint instability and volar subluxation rather than fragment size alone.

Range of Motion After Immobilization

After approximately 6–10 weeks of continuous immobilization, guarded DIP flexion can begin.

Night splinting should continue during the transition.

Physical and Occupational Therapy

Formal therapy is not required for every patient.

Occupational or hand therapy can be helpful when:

DIP flexion is slow to return, stiffness develops, or a pin has been used surgically.

Surgery

Surgical treatment is considered for:

Open injuries

Large bony fragments with persistent volar subluxation

Irreducible fracture-dislocations

Patients unable to comply with splint treatment

Chronic symptomatic deformity

Operative Fixation

A bony mallet fracture may be reduced and stabilized with:

A transarticular K-wire, extension-block pinning, screws, or other small-fragment fixation techniques.

The goal is restoration of:

Joint congruity and stable extension.

Chronic Mallet Finger

Options for persistent chronic deformity include:

Tendon plication or reefing

Tenodermodesis

Spiral oblique retinacular ligament reconstruction

DIP arthrodesis

More extensive salvage procedures are rarely required.

Prognosis

Most patients achieve useful function with proper splinting.

Residual extension lag is common but often clinically insignificant.

Poor Prognostic Factors

Factors historically associated with a less favorable result include:

Delayed treatment

Large initial extensor lag

Poor splint compliance

Failure to improve after several weeks of proper immobilization

Short, broad digits

Some older studies also identified age-related associations, though outcome is influenced more directly by injury severity and treatment quality.

Complications of Splinting

Skin complications are common but usually minor and reversible.

These include:

Maceration

Pressure ulceration

Tape allergy

Skin irritation

Pain from the splint

Skin Protection

Dorsal splints may cause pressure injury.

Protective measures include:

Tubular gauze, soft padding, moleskin, and frequent skin inspection.

Hyperextension Injury From Splinting

Excessive DIP hyperextension may compromise skin circulation.

The joint should be splinted only to the degree necessary to maintain extension.

Hyperextension should not be forced to the point of:

Skin blanching or pressure necrosis.

Nail Changes

Temporary or permanent transverse nail grooves may develop.

These may result from:

Initial injury, pressure from the splint, or damage to the germinal matrix.

Surgical Complications

Operative treatment has a higher complication burden than uncomplicated splinting.

Potential problems include:

Infection

Pin migration or failure

Nail deformity

Joint incongruity

DIP deviation

Prominent hardware

Loss of reduction

Stiffness

Need for repeat surgery

Patient Monitoring

Early close follow-up is important to ensure:

Proper splint position, intact skin, and continuous DIP extension.

Early Visits

Patients may benefit from more frequent review during the first week to assess:

Skin tolerance and splint fit.

Ongoing Review

Subsequent follow-up should monitor:

Extension lag, compliance, skin condition, fracture alignment when present, and return of flexion.

Final Phase

After approximately 6–10 weeks, the finger is reassessed.

If active extension is maintained, gradual motion can begin while:

Night splinting continues for several additional weeks.

Key Principle

The most important element of treatment for a typical closed mallet finger is uninterrupted immobilization of the DIP joint in extension while keeping the PIP joint free.

Successful treatment depends more on:

Correct splinting, skin care, and patient compliance

than on aggressive surgical intervention.