Mallet finger (baseball finger)

Introduction

Mallet finger is a flexion deformity of the finger at the distal interphalangeal (DIP) joint due to an injury of the extensor mechanism at the base of the distal phalanx, with or without a concomitant avulsion fracture at the tendon insertion.

Anatomy

The extensor tendon attaches to the epiphysis of the distal phalanx, and the flexor digitorum profundus (FDP) tendon attaches to the meta-diaphyseal portion of the distal phalanx.

Figure 1. Normal anatomy of the finger

Pathogenesis

Mallet finger is typically caused when a ball or other heavy object strikes the fingertip. The DIP joint is forcibly flexed while the extensor mechanism is contracting. This eccentric force causes an avulsion of the tendon with or without a piece of bone. The FDP acts unopposed and causes flexion of the joint.

Figure 2. Mallet finger

Natural History¹

• Incidence: 9.9/100,000 per year
• Most common in middle age
• Male:Female ratio = 60:40
• Long, ring, and small digits of the dominant hand are most frequently injured

Clinical Presentation

The patient usually presents with a history of an acute injury to the finger. The DIP joint is held in flexion and the patient is unable to fully extend the joint. The finger may also be bruised and swollen. Laxity of the volar plate at the PIP joint puts the patient at risk for developing a swan neck deformity. The extensor force becomes concentrated on the PIP joint through the central slip and causes hyperextension of the PIP joint.

   
Figures 3a-b. Swan neck deformity that developed after a mallet finger

Imaging and Diagnostic Studies

AP and true lateral (and possibly oblique) radiographs of the injured digit should be ordered to assess for an avulsion fracture (Figures 4a-c). On the true lateral, the joint should be evaluated for subluxation.

           
Figures 4a-c. AP, lateral, and oblique radiographs of a mallet fracture

Classification

• Acute: Within 4 weeks of injury
• Chronic: Greater than 4 weeks after injury³

Doyle’s Classification of Mallet Finger Injuries⁴

Treatment

Medical Therapy

• NSAIDs can be given for pain and swelling

Non-Operative Treatment

• The DIP joint should be splinted in extension for 6-8 weeks to re-approximate the extensor tendon and the distal phalanx.
• It is imperative for the finger to remain fully extended at all times. Maintaining extension can be difficult when the patient is changing the splint. Resting the finger in extension on a flat table can aid this process. Patient education in this matter is important.
• When applying the splint, ensure that the patient has full motion at the PIP joint.
• Two splints are commonly utilized: the dorsal aluminum splint (Figures 5 and 6) and the perforated thermoplastic splint (Figure 7). With the dorsal aluminum splint, the proximal piece of tape should be distal to the PIP joint to allow flexion, and the splint should extend just proximal to the PIP joint to prevent hyperextension

Figure 5

Figure 6

Figure 7

• After approximately 6 weeks, the splint can be removed and the efficacy of treatment may be assessed by asking the patient to place his/her hand palmar side down on the examining table and hyperextending the injured digit. A DIP joint does not droop is a good indication that treatment is working.
• It is common for the mallet finger to heal with a bump over the DIP joint and a slight extensor lag. This is somewhat correlated to the degree of patient compliance.
• Skin breakdown can occur if the skin becomes macerated or if the skin breaks down under the splint. The skin over the dorsum of the DIP joint is at risk if the DIP joint is immobilzed in significant hyperextension. The hyperextension causes blanching of the skin and decreased skin blood flow. If this is combined with pressure from the splint and skin maceration from the splint getting wet or from sweat, then skin irritation or breakdown can occur.⁵

Operative Treatment

Relative Indications

• Injuries failing conservative management
• Absence of full passive extension of the joint
• Fracture to greater than 30% of the articular surface. Large articular fragments can be treated non-operatively if there is no subluxation, however. Husain et al found that subluxation occurred consistently if more than 52% of the dorsal rim was damaged.²
• Avulsed fragments that fail reduction
• Volar subluxation of the distal phalanx²
  • The presence of joint subluxation is more important than the size of the fracture fragment when determining whether operative treatment is necessary.

A Kirschner (K) wire can be driven distal to proximal through the DIP joint to act as an internal splint (Figure 8). The pin should be removed after 8 weeks. Pinning is advantageous for patients with poor compliance with the external splint.

Figure 8. K-wire acts as an internal splint

Outcome

Mallet finger may result in permanent deformity of the DIP joint; however this deformity is rarely functionally significant.

Complications^{3, 5, 6}

• Residual DIP extensor lag
• Swan neck finger deformity
• Dorsal DIP joint prominence

Pearls and Pitfalls

• A trial of external splinting can be done prior to surgery.
• Splinting may still be successful even if treatment is delayed up to 3 months.
• Potential for healing remains when there is swelling and tenderness over the DIP joint

References

1. Clayton R, Court-Brown CM. The epidemiology of musculoskeletal tendinous and ligamentous injuries. Injury. 2008;39(12):1338-44.
2. Husain SN, Dietz JF, Kalainov DM, Lautenschlager EP. A biomechanical study of distal interphalangeal joint subluxation after mallet fracture injury. J Hand Surg. 2008; 33: 26-30.
3. Bendre AA, Hartigan BJ, Kalainov DM. Mallet Finger. J Am Acad Orthop Surg. 2005; 13(5) 336-344.
4. Doyle JR. Extensor tendons-acute injuries, in Green DP, Hotchkiss RN, Pderson WC (eds): Green’s Operative Hand Surgery, ed 4. New york, NY: Churchill Livingstone, 1999, pp 1962-1987.
5. Stern PJ, Kastrup JJ. Complications and Prognosis of Treatment of Mallet Finger. J Hand Surg. 1988; 13 (3) 329-334.
6. Kalainov DM, Hoepfner PE, Hartigan BJ, Carroll C, Genuario J. Nonsurgical Treatment of Closed Mallet Finger Fractures. J Hand Surg. 2005; 30(3) 580-586.