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Case Discussion: Mallet finger deformity by Busi da-Silva (5MB)

Mr. Y is 36 years old and works as a joiner. He hit his left little finger with a hammer four days ago. On examination he is now seen to have developed a mallet deformity of his left little  finger. There are blood blisters seen in the soft tissue distal pulp and he is unable to extend this finger. X-ray of his finger revealed no fractures. He was given a size 5 mallet splint for his finger with advice and is to be reviewed in 2 weeks.

Clinical Introduction

Mallet finger injuries are usually seen in clinical practice and were first described in the late 1800s.They often result from direct trauma to the tip of the extended finger, but they also result from minor forces including household tasks such as bed making. It was first called mallet finger in the context of a common sports injury but this term is a misnomer as such a finger does not look like a mallet neither are such injuries sports-related. Another term, drop finger has been proposed as being more accurate but this has not caught on. The fingers which are most commonly injured are the long finger and the ring finger and they occur more often in men than in women.

Mallet finger deformity affects the distal interphalangeal (DIP) joint and arises as a result of a closed injury on the extensor mechanism near its insertion into the distal phalanx. Therefore, as an extensor tendon injury, the mallet finger is a characteristic flexion deformity of the DIP joint which occurs as a result of disrupted continuity of the extensor tendon over the DIP joint.

Normally, the terminal portion of the extensor mechanism that crosses the DIP joint in the midline dorsally is responsible for active extension of the distal joint, but a flexion force on the tip of the extended finger will jolt the DIP joint into flexion. This may result in a stretching or tearing of the tendon substance or an avulsion of the tendon where it inserts on the dorsal lip of the distal phalanx base. In either instance, active extension power of the DIP joint is lost, and the joint rests in an abnormally flexed position.

 

Fig 1. Photogragh showing a mallet finger

After a forced flexion injury at the DIP joint, a patient may notice inability to actively extend the distal joint, even with a full passive extension. The dorsum of the joint may be slightly tender and swollen, but often the injury is painless or nearly painless. Hence, some patients may think that the joint is only sprained until they notice loss of active extension days later. This injury may give rise to any of the following three outcomes:

Damaged tendon with no fractures.
Ruptured tendon with a small fracture caused by the force of the injury.
Ruptured tendon with a large fracture.

Normal anatomy of the hand

A thorough understanding of the normal anatomy of the extensor mechanism of the hand is needed to fully appreciate the consequences of a mallet finger injury. The extensor mechanism of the hand is more intricate and complex when compared to the flexor system especially when considering its anatomy and function. It is a linkage system created by the radial nerve innervated extrinsic system and the ulnar and median nerve innervated intrinsic system[1].

Fig 2. Diagramatic illustration1 of extensor tendons entering the hand via extensor retinaculum. The extrinsic extensor tendons include the following: Extensor carpi radialis longus (ECRL), Extensor carpi radialis brevis (ECRB), Extensor carpi ulnaris (ECU), Extensor digitorum communis (EDC), Extensor digiti minimi (EDM), Extensor indicis proprius (EIP), Abductor polliis longus (APL), Extensor pollicis brevis (EPB) and Extensor pollicis longus (EPL).

The extrinsic extensor tendons enter the hand through six fibrous tunnels that are made by the extensor retinaculum at the wrist, which prevents bowstringing of the tendons. A small synovial sheath is present around each individual tendon at the wrist but not in the hand or the fingers. At the wrist, the extensor tendons are rounded with sufficient bulk to hold a suture, while over the hand, they are thin and flat with longitudinal fibers that do not hold suture well. These extrinsic extensor tendons have four insertions- the metacarpophalangeal joint palmar plate through the sagittal bands, a tenuous insertion on the proximal phalanx, and stout insertions on the middle and distal phalangnes.

 

 

Fig 3. Diagrammatic illustration1 of the extensor mechanism in the finger showing the central slip and lateral bands.

 

At the MCP joint, the extensor tendons are held in place by the intrinsic tendons and the sagittal band arises from the palmar plate and the deep intermetacarpal ligament. The extrinsic extensor tendons extend the MCP joint primarily and the interphalangeal joint secondarily. The intrinsic tendons are made up of four dorsal interossei (abductors), three palmar interossei (adductors), and four lumbrical muscles1.

 

 

 

 

Fig 4. The finger anatomy illustrating extensor mechanism with central slip, lateral band, PIP and DIP joints.

 

The extrinsic extensor tendons contribute the central slip to the extensor mechanism in the finger. The intrinsic system contributes the lateral bands that pass palmar to the axis of the MCP joint. The lateral bands join the extrinsic extensor mechanism proximal to the midportion of the proximal phalanx. They continue to the distal finger dorsal to the axis of the proximal and distal interphalangeal joints. The intrinsic muscles flex the MCP joint and extend the PIP and DIP joints. Over the distal portion of the proximal phalanx, the central slip trifurcates as the central slip and lateral bands share fibers. The central slip inserts on the base of the middle phalanx, while the lateral band component continues to insert on the base of the distal phalanx.

 

Due to a less protected anatomical location, extensor tendon injuries are more frequently encountered than flexor tendon injuries such that there is a misconception that they are relatively simple to treat. Hence sometimes it is quite possible for doctors to underestimate the extent of the injury. The management of these injuries require the same skills as when caring for flexor tendon injuries. It is important to consider the relationship between the location of the injury and its outcome. Since the structural and functional systems are different from finger tip to forearm, it is understandable that the type of injury, deformity and even the surgical outcome will be varied. It is this that led to the categorization of tendon injuries into anatomical zones. The most widely accepted is the Verdan’s zone system with eight defined zones – four odd numbered zones overlying each of the joints and four even numbered zones overlying the intervening tendon segments and increasing in number distal to proximal.

 

Mallet finger: Clinical presentation

 

Fig 5.Diagrammatic illustration of a mallet finger injury showing tendon rupture and a fracture.

A mallet finger may be open but it is more often closed. The mechanism of a closed injury is usually a sudden, forceful flexion of the DIP joint in an extended digit. It results in rupture of the extensor tendon or avulsion of the tendon often with a bony fragment from its insertion in the distal phalanx. 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.

 

Mallet injury: Management

 

Before discussing the treatment options for mallet finger injuries, it is advisable to review the investigative steps that help direct treatment plans.

 

 

 

Fig 6. An x-ray illustrating mallet finger injury at the DIP joint

Imaging studies such as plain radiographs will help reveal fractures. A postero-anterior and lateral x-rays centred at the DIPJ of the affected finger are required. These x-rays are used to differentiate between a bony injury and a tendinous mallet injury and reveal any associated metaphyseal, shaft, or tuft fractures of the distal phalanx. Perhaps most importantly, lateral radiographs reveal the presence of volar subluxation of the distal phalanx. These x-ray views also reveal rare condylar fractures of the middle phalanx. X-rays of the whole hand do not suffice, as parallax of the x-ray beams creates an oblique view of the DIPJ which is difficult to interpret[2].

Mallet finger represents a spectrum of injuries and although it is common, its management is still a topic for debate[3]. Over the years a number of treatments have been tried ranging from reassurance with no treatment to conservative splint treatment to various surgical procedures. For many cases, splinting alone seems to be sufficient.

 

For type I injuries, 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 continuous e.g. 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 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.

 

 

Fig 7. A photograph showing the use of a splint in treating closed mallet injury

 

Alternatively or in rare circumstances, Kirschner wire fixation of the DIP joint in extension, with the wire cut off beneath the skin to allow the patient to continue working will achieve the same results. The Kirschner wire should be left in place for six weeks followed by two weeks of night splinting. Type II injuries 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 injuries with loss of tendon substance require immediate soft tissue coverage and primary grafting or late reconstruction using a free tendon graft. Type IV-A is best treated with closed reduction followed by splinting for 3-4 weeks. Type IV-B with no palmar subluxation yields good results with 6 weeks splinting and 2 weeks night splinting. Type IV-C with palmar subluxation of the distal phalanx is usually best managed operatively with open reduction and internal fixation using Kirschner wire and possibly a pull-out wire or suture1. This should also be protected with a splint for 6 weeks, after which the wire is removed and motion started. A proximally displaced fragment not in continuity with the distal phalanx may also require open reduction and internal fixation.

 

Fig 8. Diagrammatic illustration1 showing how palmar subluxation of a distal phalanx can be managed operatively with open reduction and internal fixation using a K-wire which is passed antegrade through the bulk of the distal phalanx. Reduction is completed and K-wire is passed retrograde through the fragment and into the middle phalanx.

Indications for surgery include large fragment that are rotated, or fractures associated with subluxation of the distal phalanx that cannot be corrected by closed reduction or both. Open reduction technically is demanding because of the small size of the fragment and the difficulty in observing the articular surface of the distal phalanx. Some complications have been reported [3] to occur with surgical treatment of a mallet finger including early avascular necrosis of the fragment, nail growth deformities, soft tissue scar formation, infection, implant failure and subsequent joint stiffness.

However, it appears that in 1988, Ishiguro et al [4]described a new method for closed reduction of mallet fractures. They described an extension block Kirschner wire technique which minimises complications of surgical treatment, but it caused a few degrees extensor lag and tightening of the terminal tendon. Tetik et al [3] have modified this technique which now allows complete anatomic reduction of the fracture fragment.

 

A new surgical technique for treating mallet finger has been described by Kaleli et al[5]. A mini external fixator is used to maintain the joint in extension with a simple and efficient method. This does not require follow-up for splint and dressing adjustment. This technique holds the DIP joint extended while allowing motion at the PIP and MCP joints. No transarticular wire is used, so DIP joint damage or infection should not occur, while good joint mobility and congruency should be achieved.

 

 

 

Fig 9. Photograph of the external fixator system used to immobilize the DIP joint.

 

 

 

Fig 10. Photograph showing external fixator in position.

 

 

Conservative and surgical treatment of mallet finger

 

Conservative splint treatment has been recommended for the treatment of acute mallet finger but there is still a controversy regarding issues such as type of splint, duration of splinting or how to immobilise the PIP joint. The aim of conservative treatment is to hold the DIP joint in extension while the extensor mechanism heals. Holding the PIP joint in flexion and the DIP joint in extension in order to relax the extensor mechanism may allow better approximation of the detached extensor tendon.

Some have argued for an expanded role of surgery in the treatment of acute mallet finger. A small number of acute complex injuries as well as cases of failed conservative treatment, despite a full 6 months period of observation, should be treated surgically5.

It is now recognised that untreated mallet finger have a considerable likelihood for some degree of functional impairment, often with pain and stiffness. Hence sorting through treatment alternatives is important so as to offer optimal treatment plan for patients with this problem. From most literatures[6], the following can be concluded:

(1)   Conservative treatment by external splintage is the treatment of choice and is effective for most cases of closed mallet finger injuries including those with associated mallet fractures involving up to one third of the articular surface.

(2)   Careful attention to detail and appropriate patient education are required to maximize the outcomes of conservative treatment of mallet finger injuries.

(3)   Various surgical techniques are available and are indicated for a limited number of complex mallet finger injuries as well as for chronic or recurrent mallet finger.

 

  Reference:

1.      Rockwell, W.B., Butler, P.N., and Byrne, B.A. Extensor Tendon: Anatomy, Injury and Reconstruction. Plastic and Reconstructive surgery 106: 1592-1603, 2000

2.      Roy A Meals, MD. Mallet finger article. eMedicine World Medical Library, January 2002

3.      Tetik, C. and Gudemez, E. Modification of the Extension Block Kirschner wire technique for mallet fractures. 1: 284-290, 2002

4.      Pegoli L., Toh S., Arai K., Fukuda A., Nishikawa S. and Vallejo I.G. The Ishiguro Extension block technique for the treatment of mallet finger fracture: indications and clinical results. J. Hand Surg [Br]. 28: 15-17; 2003

5.      Kaleli T., Osturk C., Ersozlu S. External fixation for surgical treatment of a mallet finger. J. Hand Surg [Br] 28: 228-230; 2003

6. Geyman J.P., Fink K. and Sullivan S.D. Conservative versus Surgical treatment of mallet finger: a pooled quantitative literature evaluation. J. Am Board Fam Pract. 11: 382-390; 1998

 

 

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Last updated: February 19, 2004.