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.
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.
Often sports related (eg, jamming finger on a ball)
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 dominant hand is usually affected.9
Timing of injury. Don’t confuse an acute mallet injury with a chronic one!
Current functional limitations
Prior injury or surgery to the affected finger
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.
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.
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
Type I—tendon rupture (no fracture)
Type II—bony avulsion
Type III—greater than one-third articular surface with subluxation
Type IV—physeal fracture
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
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