Mallet Fractures

Andrew D. Sobel

INTRODUCTION

Mallet fractures, or “bony mallets,” are common injuries to the fingers. The differentiation from tendinous mallet finger injuries is important to understand so that excellent patient outcomes can result from prompt and effective diagnosis and treatment.

Pathoanatomy
- Fracture around the base of the distal phalanx that results in a disruption of the extensor mechanism (Figure 7.1A).
- Inability to extend at the distal interphalangeal (DIP) joint leads to an extension lag (Figure 7.1B).
- The lack of force through the terminal slip of the extensor tendon results in overpull through the central slip of the extensor tendon.
- Chronic pull on the central slip can eventually overpower the flexion forces balancing the proximal interphalangeal (PIP) joint in neutral position, leading to hyperextension at the PIP and a resultant swan-neck deformity.¹
Mechanism of injury²
- Begins with axial/compressive force against the distal phalanx
- The type of mallet fracture depends on the ensuing direction of force.
  - Forced flexion³
    - Smaller osseous fragment, typically an avulsion at the dorsal aspect of insertion of the terminal slip
  - Forced hyperextension⁴
    - Typically results in a larger, intra-articular fragment
Epidemiology
- Mallet fracture is less common than tendinous mallet injury in most series.⁵,⁶
  - True incidence rates of mallet fracture have not been well defined.
  - Tendinous mallet finger has an incidence of 9.9/100 000 persons per year.⁷
- Limited information exists, though the age of patients follows a normal distribution.⁵
- The mechanism of injury is different for different ages of patients.
  - Younger individuals
    - High energy
    - Often sports related (eg, jamming finger on a ball)
  - Older individuals
    - Lower energy
    - Typically occurs from trauma during daily activities or falls
- There may be a suggestion of familial trends with tendinous mallet finger, though this has not been seen with mallet fractures.⁸
- The finger most affected is the middle finger,⁵ and injury to the thumb is uncommon.⁹
- The dominant hand is usually affected.⁹

FIGURE 7.1 a, Lateral radiograph of a mallet fracture. From Yoon JO, Baek H, Kim JK. The outcomes of extension block pinning and nonsurgical management for mallet fracture. J Hand Surg Am. 2017;42:387.e1-387.e7. B, Clinical appearance of a mallet fracture. Note the extensor lag. From Kalainov DM, hoepfner pe, hartigan BJ, Carroll C, Genuario J. Nonsurgical treatment of closed mallet finger fractures. J Hand Surg Am. 2005;30:580-586.

EVALUATION

History
- Mechanism
- Hand dominance
- Timing of injury. Don’t confuse an acute mallet injury with a chronic one!
- Current functional limitations
- Occupation
- Prior injury or surgery to the affected finger
- If there is a swan-neck deformity, determine that the inciting cause is a mallet injury, not another cause¹⁰ (Table 7.1).
Physical examination
- Look for an extension lag at the DIP (Figure 7.1B).
- Typically, the flexion deformity is passively correctable.
- Often, there is tenderness over the proximal dorsal distal phalanx.
- Check the tenodesis effect, especially in children who may not comply with the examination as readily as adults do, to evaluate extension at the DIP.
- Ensure that there is no subungual hematoma, disruption of the nail plate, or open fracture.
- Evaluate the PIP and metacarpophalangeal (MCP) joints for evidence of a chronic or alternate problem causing more of a swan-neck deformity.
Imaging
- Anteroposterior and lateral radiographs should be obtained (Figure 7.1A). A perfect lateral radiograph is very important to determine the true articular involvement, displacement, and subluxation of the fracture (Figure 7.2).⁵,¹¹,¹²
- Rule out previous or chronic injury, DIP joint arthritis.
Classification
- Doyle (Figure 7.3)¹³
  - Type I—closed tendon injury
  - Type II—open tendon injury
  - Type III—open tendon injury with tissue loss
  - Type IV—mallet fracture
    - Subtype A—transepiphyseal fracture in children
    - Subtype B—fragment size 20% to 50% of the articular surface
    - Subtype C—fragment size >50% of the articular surface
- Tubiana (Figure 7.4)¹⁴
  - Type I—tendon rupture (no fracture)
  - Type II—bony avulsion
  - Type III—greater than one-third articular surface with subluxation
  - Type IV—physeal fracture
- Wehbé and Schneider (Figure 7.5)⁵
  - Type I—fracture with no volar subluxation of the distal phalanx
  - Type II—fracture with volar subluxation of the distal phalanx
  - Type III—physeal fracture with or without extension into the epiphysis
  - Fracture subtypes
    - A—less than one-third of the articular surface
    - B—one-third to two-thirds of the articular surface
    - C—greater than two-thirds of the articular surface

TABLE 7.1 List of Various Etiologies and Pathophysiologies of Swan-Neck Deformity

Extrinsic	Intrinsic	Articular
Disruption of terminal slip (mallet)	MCP joint volar subluxation	Volar plate attenuation
Flexion contracture of the MCP or wrist	Lateral band translocation/intrinsic tightness	FDS rupture
Note that flexion of the DIP can be the initial or final step in the development of the swan-neck. Abbreviations: DIP, distal interphalangeal; FDS, flexor digitorum superficialis; MCP, metacarpophalangeal.