Orthopaedic Hand Trauma CH32 (1)

CHAPTER 32 Mallet Finger

Steven R. Niedermeier and Hisham M. Awan

INTRODUCTION

■ ■ Mallet finger is an injury to the terminal extensor mechanism at the level of the distal interphalangeal (DIP) joint. This can be caused by either tendon rupture in zone 1 or an avulsion fracture of the distal phalanx with a fragment of bone that remains attached to the tendon. ■ ■ There are two proposed mechanisms of injury. ● ● Traumatic impaction blow ( Figure 32.1 )— the initial step involves an axial force to finger held in extension followed by either one of two steps: ◆ ◆ Extreme passive DIP joint hyper flexion , which results most commonly in a tendinous mallet finger. ◆ ◆ Extreme passive DIP joint hyper extension , which results most commonly in a bony mallet finger. ● ● Dorsal laceration— less common; sharp or crushing laceration to the dorsal DIP joint ■ ■ Mallet fingers comprise approximately 9% of all tendinous/ligamentous lesions with an incidence estimated at 5.6% of all tendinous lesions in the hand. The literature does not show any gender difference; however, high-energy injuries are seen in younger, male patients and low-energy mechanisms are seen in the elderly. ■ ■ The ulnar three fingers are the most commonly affected digits, and tendinous injuries are more common than bony avulsion injuries. ■ ■ With the loss of the terminal extensor tendon insertion, the central slip receives all of the tension; the volar plate and transverse retinac- ular ligament attenuate; the lateral bands sublux dorsally; and the proximal interphalangeal (PIP) joint may be forced into extension in chronic injures. The inability to extend the DIP joint and the PIP joint extension is referred to as a swan neck deformity of the finger ( Figure 32.2 ).

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