Abstract
Extensor tendon injury occurs to the muscle-tendon extensor mechanism of the hand. Extensor tendons are prone to laceration, abrasion, crush, burns, and bites. Injury presents as the inability to fully extend the involved digit. Examination should evaluate active and passive range of motion at each digital joint, amount of extensor lag from neutral, and digital neurovascular status. Treatment protocols vary by extensor mechanism zone of injury, mechanism of injury, and time elapsed since injury. Rehabilitation focuses on splinting injured digit. Splinting can be with static extension splints or early motion splint protocols that aim to reduce adhesion and stiffness in the postoperative setting. Closed injuries tend to be more common in zones I and II and are more commonly managed with static splinting. Laceration injuries tend to be more common in zones III through VIII, and more commonly warrant surgical repair with postoperative splinting. Extensor tendon injury can result in permanent loss of finger extension if adhesion or joint contracture forms, and painful degenerative joint disease if normal motion is not restored.
Keywords
Boutonnière deformity, extensor tendon finger injury, mallet finger
| Synonyms | |
| |
| ICD-10 Codes | |
| S66.2 | Injury of extensor muscle, fascia, and tendon of thumb at wrist/hand level |
| S66.21 | Strain injury of extensor muscle, fascia, and tendon of thumb at wrist/hand level |
| S66.22 | Laceration of extensor muscle, fascia, and tendon of thumb at wrist/hand level |
| S66.3 | Injury of extensor muscle, fascia, and tendon of other and unspecified finger at wrist/hand level |
| S66.31 | Strain of extensor muscle, fascia, and tendon of other and unspecified finger at wrist/hand level |
| S66.32 | Laceration of extensor muscle, fascia, and tendon of other and unspecified finger at wrist/hand level |
| M20.0 | Acquired deformities of finger(s) |
| M20.01 | Mallet finger |
| M20.011 | Mallet finger of right finger(s) |
| M20.012 | Mallet finger of left finger(s) |
| M20.02 | Boutonnière deformity |
| M20.021 | Boutonnière deformity of right finger(s) |
| M20.022 | Boutonnière deformity of left finger(s) |
| M66.24 | Spontaneous rupture of extensor tendons, hand |
| M66.241 | Spontaneous rupture of extensor tendons, right hand |
| M66.242 | Spontaneous rupture of extensor tendons, left hand |
Definition
Extensor tendon injuries occur to the extensor mechanism of the digits, a complex muscle-tendon system formed by the finger and thumb extensors with secondary supports from intrinsic hand musculature and the retinacular system of ligaments throughout the wrist, hand, and digits. These injuries are more common than flexor tendon injuries because of their superficial position and relative lack of soft tissue between them and underlying bone. As a result, extensor tendons are prone to laceration, abrasion, crushing, burns, and bite wounds. Demographic data vary per specific injury and are not well documented. 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, or poor pain control. There are eight zones to the extensor mechanism where injury can result in differing pathomechanics ( Fig. 30.1 ).
Symptoms
Patients typically lose the ability to fully extend the involved finger ( Fig. 30.2 ). Lack of motion may be confined to a single joint or the entire digit based on the site of extensor mechanism injury. Pain in surrounding regions often accompanies loss of motion due to abnormal tissue stresses. Diminished sensation may be present if there is concomitant injury to the dorsal branches of the radial or ulnar nerves.
Physical Examination
Ask if any baseline motion deficits in the digits or hand existed prior to the presenting complaint. Note the resting hand position as well as asymmetry upon active extension from a resting position. Complete extensor tendon disruption creates a resting flexed posture of the unsupported finger; however, this may become more apparent upon attempted activation out of the naturally flexion-biased resting hand position. Evaluate active and passive range of motion at each finger joint, noting presence and amount of extensor lag from neutral. Neurological examination should assess for injuries to the adjacent dorsal branches of the radial and ulnar nerves. Evaluate light touch and pin prick sensation throughout, with focus on the dorsal aspects of the digits.
Functional Limitations
Functional limitations 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. There may also be difficulty reaching into confined areas, such as pockets, due to the resting flexed digit position with limited ability to extend.
Diagnostic Studies
Obtain anteroposterior and lateral radiographs of the involved hand and fingers when there is a possibility of bone injury or foreign body in the soft tissues. If clinical suspicion of injury is in question, diagnostic imaging for direct tendon visualization can be performed with ultrasonography or magnetic resonance imaging (MRI). Ultrasonography is an inexpensive alternative to MRI for detection of extensor tendon injuries and has been shown to be more accurate than physical examination or MRI for detection of these injuries. Ultrasonography can be particularly helpful for detection of foreign bodies, diagnosis of partial tendon injuries, and dynamic evaluation of extensor tendon function.
Fracture dislocation
Joint dislocation
Peripheral nerve injury
Osteoarthritis
Rheumatoid arthritis
Trigger finger (stenosing tenosynovitis)
Treatment
Initial
The treatment protocols for extensor tendon injuries vary by zone, mechanism, and time elapsed since injury. If the disruption of the extensor mechanism is due to laceration, crush injury, burn, or bite, surgical referral is warranted. In open injuries, wound care should be performed. If surgical 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 decrease potential for infection. The surgeon who will be performing the definitive repair should be contacted as soon as possible, ideally prior to skin suturing.
In general, closed injuries are treated conservatively with splint immobilization, open injuries with less than 50% tendon involvement are managed with skin closure only and splint immobilization, and open injuries with greater than 50% tendon involvement are managed with primary tendon repair and subsequent postoperative splinting. Closed injuries tend to be more common in zones I and II; thus initial treatment is with splints. Laceration injuries tend to be more common in zones III through VIII, thus initial treatment with surgery is more common.
Rehabilitation
Splinting can be with static extension splints or early motion splint protocols that aim to reduce adhesion and stiffness. There is no current strong evidence to show significant advantage of early mobilization over traditional static immobilization. However, as surgical technique has advanced to create stronger extensor repairs, there has been a shift towards more aggressive postoperative rehabilitation protocols with early motion. Early motion splints can be categorized into “short arc motion splints” that passively immobilize the joint while allowing intermittent splint-assisted passive flexion and active extension, “relative motion splints” (also called controlled active mobilization splints) that allow active joint extension while limiting joint flexion, or “dynamic splints” that create passive joint extension with customizable active joint flexion. Early motion splinting does require close oversight by a skilled therapist to ensure motion occurs in specific protected ranges.
Zone I (Mallet Deformity)
Zone I lesions involve the terminal extensor tendon over the distal interphalangeal (DIP) joint.
Mechanism of injury is a sudden flexion force applied to a DIP joint that is actively extending. The tendon can tear at its insertion, creating a “soft issue” mallet, or there can be associated avulsion fracture of distal phalanx with tendon injury, creating a “bony” mallet. Injury produces a characteristic mallet flexion deformity of the DIP joint. The digits most commonly involved are the long, ring, and small fingers of the dominant hand. When left untreated, the mallet deformity can lead to DIP joint osteoarthritis or a swan neck deformity with hyperextension of the proximal interphalangeal (PIP) joint.
Closed injury is treated conservatively with 6 to 8 weeks of continuous immobilization of the DIP joint in full extension to slight hyperextension (0 to 15 degrees). Splinting in full extension may be best suited for bony mallet injuries, whereas mild hyperextension splinting may be best for soft tissue injury. Excessive DIP hyperextension should be avoided due to risk of compromising the dorsal skin vascular supply. Different types of splint orthoses exist; no specific orthotic has been proven superior. Prefabricated Stack mallet splints have classically been recommended. Custom splints may be warranted, particularly in vulnerable population, as there is less risk of developing skin complications when compared to prefabricated splints for management of mallet finger. After 6 to 8 weeks of continuous splint immobilization, the splint may be transitioned to nighttime use only for an additional 2 to 4 weeks. When the splint is removed, the DIP joint should be able to maintain an extended position.
A graded home exercise program should be initiated after completion of continuous splint immobilization, with progression from active DIP joint range of motion for the first week, to active and passive motion exercises the subsequent week. Exercises should be performed hourly when awake, 10 repetitions per hour, and through a pain-free range ( Table 30.1 ).
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