Mallet Finger

Updated 3/2017-- photos and all links removed as many are no longer active and it was easier than checking each one.

The name, mallet finger, is a bit of a misnomer as the finger does not look like a mallet. It is commonly defined as a sports-related injury, but often is not. It is sometimes called a "baseball finger". It may also be called a "drop finger" which is a more accurate description. The long and ring finger are most commonly injuried, and it occurs more often in men than in women. A mallet finger occurs when the extensor tendon is damaged. 

Mallet finger deformity affects the distal interphalangeal (DIP) joint. It occurs as a result of a closed injury of the extensor tendon (ET) near its insertion into the distal phalanx (bone), resulting in a disruption of the tendon's continuity over the DIP joint.. There is then no intact extensor tendon to balance the forces on the DIP by the flexor tendons. The joint is flexed (bent) downward toward the palm by the inherent tension of the flexor tendons. Without an intact extensor tendon, there can be no active extension of the DIP.

This often results from direct trauma to the tip of the extended finger (as from a baseball striking the finger), but also from minor forces including household tasks such as bed making. It may also happen when tucking a sheet under a patient (as it did to a friend of mine). The forces damage the thin extensor tendon by either stretching or tearing of the tendon or by an avulsion of the tendon where it inserts on the dorsal lip of the distal phalanx base. The force of the blow may even pull away a piece of bone along with the tendon. In either instance, active extension power of the DIP joint is lost, and the joint rests in an abnormally flexed position. The finger will not be able to actively straighten itself.

After the injury at the DIP joint, a patient may notice an inability to actively extend the distal joint, even with a full extension. The dorsum of the joint may be slightly tender and swollen, but often the injury is painless or nearly painless. Some patients may think that the joint is only sprained until they notice loss of active extension days later. If untreated for a prolonged time, hyperextension of the PIP joint may develop giving rise to a swan neck deformity because of proximal retraction of the central band.

There are four types of mallet finger injuries:

Type I: Closed with or without avulsion fracture.
Type II: Laceration at or proximal to the DIP joint with loss of tendon continuity
Type III: Deep abrasion with loss of skin, subcutaneous cover and tendon substance
Type IV: (A) Trans-epiphyseal plate fracture in children; (B) Hyperextension injury with fracture of the articular surface of 20-50%; and (C) Hyperextension injury with fracture of the articular surface usually > 50% and with early or late palmar subluxation of the distal phalanx

Treatment:

Type I -- Continuous splinting of the DIP joint in extension is the recommended treatment for six weeks, followed by two weeks of night splinting. It is important to explain to the patient that the splinting is at all times (24 hr a day). This includes using the thumb to apply extension force to the distal phalanx of the injured finger when showering. Although splinting appears to be a simple and non invasive treatment, it has complications such as dorsal skin irritation or necrosis over the DIP joint that results from excessive pressure of the splint at that site and probably is potentiated by a hyperextension posture of the joint.

Type II --These require surgery. The injury may be repaired with a simple figure-of-eight suture through the tendon alone or a roll type suture incorporating the tendon and the skin in the same suture. The DIP joint is splinted in extension for 6 weeks, followed by 2 weeks of night splinting.

Type III --Because of the loss of tendon substance, these injuries require immediate soft tissue coverage and primary grafting or late reconstruction using a free tendon graft.

Type IV-A --These are best treated with closed reduction followed by splinting for 3-4 weeks.

Type IV-B --These have no palmar subluxation and yields good results with 6 weeks splinting and 2 weeks night splinting.

Type IV-C --These have palmar subluxation of the distal phalanx and are usually best managed surgically with open reduction and internal fixation using Kirschner wire and possibly a pull-out wire or suture. This should also be protected with a splint for 6 weeks, after which the wire is removed and motion started. A proximally displaced bone fragment not in continuity with the distal phalanx may also require open reduction and internal fixation.

References

Mallet Finger Deformity by Busi da-Silva (nice pictures and discussion of normal extensor tendon anatomy)
Mallet Deformity: (Baseball finger)--Wheeless' Textbook of Orthopaedics
Complication and Prognosis of Treatment of Mallet Finger--Wheeless' Textbook
Mallet Finger (Baseball finger)--American Academy of Orthopaedic Surgeons
Mallet Finger by Roy A Meals, Md--eMedicine article