Definition

Extensor tendon injuries occur to the extensor mechanism of the digits. They include the finger and the thumb extensors and abductors. These injuries are more common than flexor tendon injuries because of their superficial position and relative lack of soft tissue between them and the underlying bone. As a result, the extensor tendons are prone to laceration, abrasion, crushing, burns, and bite wounds [1]. Demographic data defining age, gender, and occupation for the development of extensor tendon injury are not well documented. However, in our clinical experience, extensor tendon injuries commonly occur from lacerations, fist to mouth injuries, and rheumatologic conditions.

Extensor tendon injuries result in the inability to extend the finger because of transection of the tendon itself, extensor lag, joint stiffness, and poor pain control [2,3]. There are eight zones to the extensor mechanism where injury can result in differing pathomechanics [4] (Fig. 30.1).

Symptoms

Patients typically lose the ability to fully extend the involved finger (Fig. 30.2). This lack of motion may be confined to a single joint or the entire digit. Pain in surrounding regions often accompanies the loss of motion because of abnormal tissue stresses. Diminished sensation may be present if there is concomitant injury to the digital nerves.

Physical Examination

Physical examination begins with observation of the resting hand position. If the extensor tendon is completely disrupted, the unsupported finger will assume a flexed posture. Range of motion, both active and passive, is evaluated for each finger joint. Grip strength is commonly measured by use of a hand-held dynamometer. Individual finger extension strength can be recorded by manual muscle testing or finger dynamometry. Sensation should be checked because of the proximity of the extensor mechanism to the digital nerves. The radial and ulnar sides of the digit should be checked to assess light touch, pinprick, and two-point discrimination.

Functional Limitations

The positioning of the hand in preparation for grip or pinch is occasionally more important and limiting than the inability to grasp. Functional limitations therefore are manifested as the inability to produce finger extension in preparation for grip or pinch. As a result, writing and manipulation of small objects can be problematic. Patients may also have difficulty reaching into confined areas, such as pockets, because of a flexed digit with the limited ability to extend.

Diagnostic Studies

Anteroposterior and lateral radiographs of the involved hand and fingers are obtained when there is a possibility of bone or soft tissue injury, such as fracture of a metacarpal from a bite wound, foreign body retention from glass or metal, or air in the soft tissues or joint space secondary to penetration of a foreign object. Ultrasonography is an inexpensive alternative to magnetic resonance imaging for the detection of foreign bodies and identification of traumatic lesions of tendons. However, ultrasonography and magnetic resonance imaging are generally not necessary but can be used to confirm clinical suspicion of chronic and partial extensor tendon injuries.

The treatment protocols for extensor tendon injuries vary by zone, mechanism, and time elapsed since the injury. If the disruption of the extensor mechanism is due to a laceration, crush injury, burn, or bite, surgical referral is warranted. In open injuries, if repair is not immediate, appropriate antibiotics should be initiated, the injured tendon should be promptly irrigated, and primary coverage by skin suturing should be performed to protect the tendon and to decrease the potential for infection. The surgeon who will be performing the definitive repair should be contacted before this, however [5]. Conservative splinting can be attempted for closed zone I and zone II extensor tendon injuries.

Rehabilitation

Conservative treatment and splinting have been recommended for zone I and zone II injuries. Conservative treatment of injuries involving zones III through VIII has limited success in restoring normal range of motion and function. Acute injuries in these zones usually require surgical repair, and chronic injuries often require surgical review.

Zone I (Mallet Deformity)

Disruption of continuity of the extensor tendon over the distal interphalangeal (DIP) joint produces the characteristic flexion deformity of the DIP joint [6]. Injury in this region is the result of a traumatic event, such as sudden forced hyperflexion of an extended DIP joint with tendinous disruption or avulsion fracture at the site of insertion. The digits most commonly involved are the long, ring, and small fingers of the dominant hand [7]. When it is left untreated for a prolonged time, hyperextension of the proximal interphalangeal (PIP) joint (swan-neck deformity) may develop because of proximal retraction of the central band [6].

In a closed injury, the most common method of treatment is 6 weeks of continuous immobilization of the DIP joint in full extension or slight hyperextension (0 to 15 degrees) [8–12]. The DIP joint should not be immobilized in excessive hyperextension because of compromise of the vascular supply to the dorsal skin [7