Hand Extensor Tendon Lacerations

Etiology

Extensor tendon lacerations are injuries that are particularly common among younger manual workers.[4] Laceration with a nonmotorized sharp object is the most frequent mechanism, followed by saw injuries, with slightly different anatomical distributions.[5] Saws more commonly cause injury distal to the metacarpophalangeal joint and are associated with concomitant fractures, while sharp object lacerations tend to be more proximal.[6] Accidental injuries in younger children are occasionally observed involving flexor and extensor ruptures. Much more rarely, they can occur in neonates as a result of iatrogenic injury during delivery, particularly in the setting of a cesarean section.[2][7] Additionally, attritional extensor tendon ruptures can occur in the absence of acute trauma. These ruptures may result from malunion of a remote fracture, such as a thumb extensor tendon rupture following a distal radius fracture, or progressive tendinopathies from the degradation effects of inflammatory conditions such as Vaughan-Jackson syndrome.[8][9][10]

Epidemiology

Patients who sustain extensor tendon lacerations are predominantly men in their third decade of life; these patients are in the working-age cohort, therefore these injuries have a notable economic impact on society.[6][11] In the United Kingdom, such injuries have been reported to cost the economy over £100 million each year due to the cost of direct care.[12] This figure is much higher when accounting for lost wages and poor productivity-related economic losses. Similarly, in the United States, upper extremity extensor tendon lacerations are estimated to cost $307 to $531 million annually, depending upon the influence of worker absenteeism.[13]  

The dominant hand is more likely to be injured, and while the middle finger tends to be most commonly affected (followed by the thumb and index finger), extensor tendon lacerations can occur at any site.[6][14] In Europe, they represent up to 30% of all emergency department visits.[12] In the United States, these lacerations comprise approximately 17% of all orthopedic soft tissue injuries, with an annual incidence of 17.9 per 100,000 patients.[11][13]

History and Physical

Accurate assessment and management of tendon lacerations are essential as these injuries directly impact the livelihood and work of affected individuals.[12] Obtaining a detailed history is necessary; this history should include the mechanism of injury, position of the hand and fingers at the time, patient age, occupation, and hand dominance. Knowing whether a human bite or animal bite was involved is vital, as any contamination would likely need formal irrigation and debridement due to the increased risk of infection.[1][15] Additionally, a review of the patient's medical history should include an evaluation for conditions and medications that can further predispose to infection, such as diabetes and the use of immunosuppressants or steroids, as well as the time of the last tetanus booster. 

A systemic and in-depth examination of both hands is crucial.[1] Unless the injury is part of a larger trauma, and the patient needs to be treated according to the advanced trauma life support protocol, hand examination should start with an inspection. Any open wound to the dorsum of the hand should raise suspicion of extensor tendon injury. Neurovascular status should be tested and documented before any local anesthetic is administered.[6] Once that is performed, open injuries may be explored with care under local anesthetic and with appropriate magnification, as needed.[12] An evaluation for additional injuries must be conducted.[2] Suspicion of trauma to vital structures or deep injury warrants a referral to a hand surgeon.[12] The radial nerve innervates the extrinsic extensor tendons of the hand. The clinician should, therefore, specifically assess for radial nerve injury and note median and ulnar nerve function.[1] 

Extrinsic tendons can be divided into superficial and deep groups, as described below:

Superficial Extrinsic Extensors

• Extensor carpi radialis longus (ECRL)
• Extensor carpi radialis brevis (ECRB)
• Extensor digitorum communis (EDC)
• Extensor digiti minimi (EDM)
• Extensor carpi ulnaris (ECU)

Deep Extrinsic Extensors

• Abductor pollicis longus (APL)
• Extensor pollicis longus (EPL)
• Extensor indicis proprius (EIP) [6]

These extensors can be grossly tested even when patients cannot adequately cooperate by checking for normal tenodesis and digital cascade.[2] At the wrist level, the extensor tendons are divided into 6 compartments numbered from radial to ulnar side.[6] Fibroosseous sheaths separate each compartment, and the extensor retinaculum serves as a roof to prevent bowstringing. The tendons are morphologically round within the compartments but flatten more distally.[11] Loss of normal digital cascade with an extensor lag of any individual digit should prompt assessment of all 6 extensor compartments, as described below:

• Compartment 1 - APL and extensor pollicis brevis (EPB)
• Compartment 2 - ECRL and ECRB
• Compartment 3 - EPL
• Compartment 4 - EDC and EIP
• Compartment 5 - EDM
• Compartment 6 - ECU [6]

In addition to the above divisions, extensor tendons have been classified into a zone system by Kleinert and Verdan.[16] They described 8 zones relating to the underlying bones and joints. Doyle later added 9 zones in the musculotendinous junction in the forearm, which is approximately 4 cm proximal to the wrist (see Image. Extensor Tendon Zones in the Hand).[2][11] All can be seen in the image, which shows the odd number zones broadly over the joints. Each zone differs in anatomy and properties of the extensor mechanism. Therefore, all zones should be assessed, as laceration treatment depends largely on its location.[2] 

Extension in each digit should be tested at each joint in isolation, carefully observing for active range of motion and movement against resistance (see Image. Extensor Tendon Mechanism in the Finger). Some special considerations must be taken depending on the zone affected by the injury as per their specialized anatomy and in cases with more than one tendon per digit (eg, EDM and EIP can be tested by extending the relevant finger with the hand flat on a surface). Of note, full extension of small joints is occasionally possible even after lacerating the corresponding tendon(s).[1]

Junctura tendinae prevent independent extension of digits, and they allow for the continued extension of the metacarpophalangeal joint (MCPJ) even if 1 of the tendons is lacerated. Saggital bands are crucial for MCPJ extension without direct tendon attachment to the proximal phalanx. The extensor mechanism becomes more complex distal to the MCPJ (zone 5).[11] The extensor tendon divides into three parts over the proximal phalanx (zone 4) to form the central slip and lateral bands (zone 3). The Elson test can be used to test the central slip in zone 3 by flexing the proximal interphalangeal joint (PIPJ) to 90 degrees and attempting to extend the distal interphalangeal joint (DIPJ) in that position.

Normally, the DIPJ remains lax unless the central slip is damaged, as lateral bands have increased pull.[6] Distally, lateral bands join and insert into the base of the distal phalanx as the terminal tendon, just proximal to the nail germinal matrix (zone 1).[11] There are several stabilizing extensor mechanisms, including the triangular ligament over the middle phalanx (zone 2), oblique retinacular ligament running from the proximal phalanx to the distal phalanx, and the transverse retinacular ligament anchoring the lateral bands to the volar plate.[6] All of these can potentially be affected in the event of an extensor injury.

Evaluation

After the initial assessment is performed, further evaluation with imaging should be conducted. Radiographs are taken to assess if there are any associated fractures or dislocations. Metal, glass, and certain other foreign bodies may also be visualized.[1] Anteroposterior, true lateral, and oblique views of the affected area and the adjacent joints should be taken.[12] More advanced modalities, such as magnetic resonance imaging or ultrasonography, can be utilized to evaluate the integrity of the extensor tendons when clinical examination is equivocal. Complex injuries, such as those associated with significant bony or soft tissue compromise, may require reconstruction well beyond simple tendon repair, which is outside the scope of this discussion. A thorough assessment must be conducted and documented, and basic repair and reconstructive principles may be used to approach defects of any complexity.[17] These principles are:

• Restore reliable vascular supply
• Stabilize the wound bed (debridement)
• Reestablish skeletal stability (in the setting of a fracture)

Once the above principles are met, the tendons may be assessed for repair, and any potential requirement for graft coverage or fascial flaps may be considered.[17]

Treatment / Management

There is no clear gold standard for treating extensor tendon lacerations.[17] An important consideration is that the term "laceration" can be used widely and may mask more complex injuries associated with the laceration itself.[12] Tetanus prophylaxis should be considered, and antibiotics are commonly administered.[6] Repair should occur soon after the laceration, ideally within 1 week and certainly within 2 weeks from the injury.[1](B2)

Modern repair techniques and current protocols for rehabilitation may improve outcomes.[6] Tendon injury repair may include primary repair, secondary repair, immediate reconstruction with a tendon graft, staged tendon reconstruction, and tendon transfer. The greater the number of tissues involved in the injury, the more challenging it becomes to restore hand function.[17] Preserving or restoring appropriate tendon length is crucial to the outcome of repair, as even seemingly minor changes in tension can compromise finger movement.[11] Despite ready surgical access and outcomes that are generally better than those in flexor tendon injuries, maintaining appropriate length and tension and restoring normal function remains a challenge with extensor tendons.[3] (B2)

The Miller criteria are used to evaluate extensor tendon injuries, and they have shown that laceration severity, the zone of injury, surgical technique used for repair, accompanying trauma to surrounding tissues, hand therapy, and patient compliance are all important to the outcome.[3] Surgery is typically indicated if the following criteria are present:

• More than 50% of the tendon has been lacerated
• The patient is unable to actively extend the digit
• There is associated contamination requiring formal irrigation and debridement
• The adjacent joint is unstable
• Conservative approaches have failed
• The patient can comply with the postoperative protocol [11][18]
(A1)

The procedure can be performed under a local anesthetic or a nerve block, with the patient supine and the arm abducted to their side on an arm table. A pneumatic tourniquet is useful to control bleeding intraoperatively. Due to varying morphology depending on the zone of injury, treatment is best planned by anatomic classification.[11] Proximal zones (6 to 8) may require a 3-0 suture, but the size will need to be reduced the more distal the injury.[11] More distal repairs may be more difficult because of the smaller tendon size and minimal collagen bundle linkage. Consequently, the suture material may have less purchase or grip strength. Additionally, extensor tendons are flat distal to the MCPJ, which may preclude the use of a core suture, and they have a large surface area between the defect and surrounding tissues, making them more prone to adhesions.[1][11]

Contaminated wounds may need to be washed out and left to repair later when the wound bed is clean. If the laceration is clear and both ends are visualized, the injury can be repaired in an emergency department.[19] Alternatively, the skin may be temporarily loosely closed over the lacerated tendons if a surgical repair is required in a formal operating room. Extensor tendon injuries should be managed with extension splinting to avoid exacerbating the injury and worsening the tendon-end separation.[6] Partial injuries can be managed with wound care and splinting, but most complete injuries require a primary repair. If not immediately possible, the patient may be a candidate for delayed treatment, two-stage reconstruction, tendon transfer, or graft, but these may result in suboptimal outcomes. Often, this is due to stiffness and reduced range of motion; while observed in both adult and pediatric populations, it is much more pronounced in the former.[2] If immobilization in children is difficult due to small digit size, K-wire fixation may be considered to stabilize any adjacent joints and prevent excessive motion of the repaired tendon. Alternatively, an aluminum splint can be incorporated into a splint or cast.[2](B2)

Zone 1

Zone 1 lacerations are lacerations at or distal to the DIPJ and are often termed open mallet fingers.[1] Typically, these can be treated with local wound care and extension splinting for 8-12 weeks. Alternatively, they may be managed using dermatotenodesis—full-thickness single-layer closure of both the skin and the underlying terminal tendon.[2] If there is no underlying bony injury, these injuries can be treated in the emergency department as long as the wound and joint can be thoroughly irrigated.[6] The patient must continue to move the PIPJ to avoid stiffness, and they must be warned that they may never regain full DIPJ flexion and may have some residual extensor lag, even with a well-done repair.[11](B2)

Zone 2

Zone 2 injuries overlay the middle phalanx. Injuries of over 50% of the tendon should be repaired.[1] Injuries involving less than 50% of the tendon may be treated with 1 to 2 weeks of splinting, provided there is no associated extensor lag, and the DIPJ can be extended against resistance. Occasionally, these injuries are associated with significant soft tissue loss and need more complex reconstruction.[6]. As with zone 1, the results can be poor in zone 2—impaired movement and shortening can impact the range of motion in the interphalangeal joints (IPJ).[3](B2)

Zone 3

A zone 3 laceration is over the PIPJ and results in a boutonniere deformity as it disrupts the central slip. Absent or weak PIPJ extension is a positive finding. This injury can be either repaired directly, or a tendon flap can be raised from its proximal portion.[1] These injuries are often associated with traumatic arthrotomy of the PIPJ or bony injury and should, therefore, be thoroughly explored and managed accordingly.[6] If a primary repair cannot be achieved, a turndown technique can be used, or the lateral bands can be sutured together to compensate for the lack of central slip.[11](B2)

Zone 4 

These injuries are over the proximal phalanx and usually involve the broad extensor mechanism.[1] Because of this, they are often partial injuries.[6] Partial lacerations have been shown to have satisfactory results just with splinting for 3 to 4 weeks. However, complete lacerations require surgery.[1] The methods used include modified Kessler, modified Bunnel, and modified Becker techniques. Similar to zone 2 injuries, zone 4 injuries can be associated with soft tissue injuries and defects, necessitating a more complex approach.[6](B2)

Zone 5

These injuries occur over the MCPJ and should be assumed to be human bites until proven otherwise. Repair should be attempted, and care must be taken to ensure that the sagittal bands are intact or repaired to maintain a central tendon position. If a bite is confirmed, the wound must be extended, irrigated, and left open, and antibiotic therapy should be initiated after the cultures have been collected.[1] Traumatic arthrotomies are common in this region, and because these injuries often occur while the MCPJ is in a flexed position, the resulting injury can be more proximal than anticipated, making the repair more challenging due to the proximal retraction of the tendon.[6] Postoperatively, splinting is performed with the wrist in approximately 30 to 45 degrees of extension and the MCPJ in 20 to 30 degrees of flexion. The PIPJ and DIPJ are left free to permit an active range of motion.[1](B2)

Zone 6

This area covers the dorsum of the hand over the metacarpals. There may not necessarily be a loss of extension at the MCPJ in these injuries because of the junctura tendinae even if the laceration involves the entire tendon. This may make diagnosis more difficult if the tendon is not adequately explored.[6] The extensor tendons are larger at this location and may be able to accommodate a necessary core suture and a peripheral repair.[1] The methods to accomplish this are varied and include running-interlocking horizontal mattresses, modified Bunnel, augmented Becker, Halsted, or Silfverskiold.[6] More complex degloving injuries may require grafting or a flap.[1](B2)

Zone 7

These injuries occur at the level of the extensor retinaculum. The tendon repair here can lead to poorer results because of injury to the extensor compartments or a bowstring effect if the retinaculum is improperly repaired.[3] These injuries may also result in adhesions, particularly if splinted statically.[1] If the repair is not properly tensioned, it can impair tendon glide, leading to loss of motion. Additionally, a prominent repair site due to protruding tendon edges or suture ends may further impair glide through the compartment. The retinaculum can be lengthened using a step-cut or Z-plasty to help mitigate this. Early mobilization should also be considered.[6](B2)

Zone 8

This zone lies in the distal forearm, and lacerations in this zone likely involve more than a single tendon, muscle belly, or musculotendinous junction. Repair should begin with the thumb and wrist extensors.[1] The integrity of the repair may be inherently weaker, particularly near the musculotendinous junction. Figure-of-8 suturing can be performed, among other techniques. Care should be taken to assess the posterior interosseous nerve beforehand and protect it intraoperatively. Both wrist and elbow splinting may need to be considered to protect the repair postoperatively.[6](B2)

Thumb

A mallet injury to the thumb is less common as the tendon is broader, but it should be repaired primarily if it occurs.[1] The EPL tendon is typically robust and able to accommodate a dedicated core suture, but dermatotenodesis is an option if this is not possible.[6] The EPB may be lacerated with no functional deficit, and the need for its repair is debatable. However, the EPL affects both the IPJ and MCPJ of the thumb and requires repair or reconstruction if lacerated.[1] T4 and T5 zones may involve superficial radial nerves; large branches may need repair and smaller branches may need to be buried to avoid neuroma formation. Injuries more proximal to this may be treated as zone 8 and 9 injuries.[6](B2)

Differential Diagnosis

The term "laceration" implies the mechanism of injury. However, other conditions may present with a similar clinical picture of a deficit in extensor mechanism function, including:

• Arthritis: Chronic irritation to tendon may damage the extensor mechanism, causing a classical deformity like a boutonniere, swan neck, or a simple tendon rupture near the joint affected
• Trigger finger: May result in loss of passive and/or active extension
• Posterior interosseous nerve syndrome: Patient cannot extend actively, but tenodesis remains normal

Treatment Planning

Given that there is more than one method of managing these types of injuries, care must be taken when planning treatment, and modifications have to be made depending on several factors, including anatomical location, concomitant injuries, and patient compliance.[2]

Prognosis

As these injuries frequently occur in working-age patients, an early return to work is often the goal of treatment.[4] Generally, better outcomes are observed in proximal zone lacerations compared to distal zones due to more forgiving tendon excursion.[11] A substantial outcomes difference has been shown depending on the timing of repair, with patients managed within 5 days achieving 97.8% of the range of motion of the corresponding contralateral digit, compared to 89.5% in those managed after 5 days.[20] In contrast to adults, children can heal rapidly and more easily regain their range of motion despite prolonged immobilization, often achieving excellent results with limited complications.[2]

Complications

The complications that can manifest with hand extensor mechanism lacerations include:

• Postoperative tendon re-rupture [1]
• Reduction in both active and passive range of motion [3]
• Adhesions [1]
• Extensor lag [4]
• Loss of flexion and reduced ability to grip [1]
• Finger deformities [3]
  • Swan neck deformity: Usually due to chronic flexion of the DIPJ and dorsal subluxation of lateral bands with consequent PIPJ hyperextension
  • Boutonniere deformity: Characterized by DIPJ hyperextension and PIPJ flexion and usually caused by a central slip injury and volar subluxation of the lateral bands

Of the above complications, adhesions are the most common following surgery and can result in a loss of flexion.[3][21] Loss of flexion is generally a more substantial problem than an extensor lag, especially in zones 3 and 4, as it has a greater effect on grip.[11] When adhesions occur, additional treatments are required, including intense hand therapy and sometimes reoperation; tenolysis rates are between 0% and 17%.[4] To compare, repair rupture rates are estimated to be between 0% and 8%.[11] 

Extensor tendon laceration outcomes can be measured using the Miller criteria, which divide them into excellent (no extensor lag, 0 degrees of flexion loss), good (less than 10 degrees of extensor lag, less than 20 degrees of flexion loss), fair (11 to 45 degrees of extensor lag, 21 to 45 degrees of flexion loss) and poor (greater than 45 degrees of both extension lag and flexion loss).[21]