Hand Extensor Tendon Lacerations

Etiology

Extensor tendon lacerations are very common injuries among young manual workers.[4] Laceration with a sharp object is the most common mechanism, followed by saw injuries, with slightly different anatomical distribution. A saw is likely to cause injury distal to the metacarpophalangeal joint (MCPJ) and be associated with fractures, while sharp object lacerations tend to be proximal to that.[5] Accidental injuries in younger children are seen sometimes involving flexor and extensor injuries. At the same time, much more rarely, they can happen in neonates as a result of iatrogenic injury during delivery – particularly during C-section.[2]

Epidemiology

Patients affected are mostly men in their thirties, and as they are in the working-age group, these injuries have a great economic impact on society.[5][6] They have been reported to cost the United Kingdom economy over £100 million each year, relating to the cost of direct care. They are much higher when you take the loss of wages and poor productivity-related economic losses.[7] The dominant hand is more likely to be injured, and the thumb tends to be most commonly damaged, followed by the index and middle fingers, but extensor tendon lacerations can occur at any site.[5] In the UK, they represent up to 30% of all emergency department visits and are the most common reason to attend.[7] In the United States, they are equally common and are estimated to comprise more than 25% of all soft tissue injuries.[6]

History and Physical

Accurate assessment and management are essential as they directly impact the livelihood and work of affected individuals.[7] A detailed history is crucial and must include the mechanism of injury, position of the hand and fingers at the time, age, occupation, and handedness. Knowing whether a human bite was involved is vital, as any contamination would need formal irrigation and debridement.[1] A systemic and in-depth examination of both hands is crucial, comparing like for like.[1] Unless the injury is part of a larger trauma, and the patient needs to be treated according to the ATLS protocol, hand examination should start with an inspection. Any open wound to the back of the hand should raise suspicion of extensor tendon injury. Neurovascular status should always be tested and documented before any local anesthetic is given.[5] Once that is done, open injuries should be explored with care under local anesthetic and with appropriate magnification.[7] Additional injuries must be sought.[2] Any suspicion of deep injury warrants a referral to the hand surgery team.[7] The radial nerve innervates all extrinsic extensor tendons of the hand. The clinician should look out for radial nerve injury and assess median and ulnar nerves.[1] Extrinsic tendons can be divided into superficial and deep groups as shown below:[5]

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)

The above can be grossly tested even when the patient cannot cooperate by checking for normal tenodesis and digital cascade.[2]

At the wrist level, they are divided into 6 compartments numbered from radial to ulnar side.[5] Fibroosseous sheaths separate them, and the extensor retinaculum acts as a roof over them to prevent bowstringing. The tendons are round within the compartments, but they flatten the more distally they run.[6] Loss of normal digital cascade with extension lag of any single digit should prompt assessment of all 6 components of the extensor compartment:[5] See Table. Extensor Tendon Compartments of the Hand.

• 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

In addition to the above divisions, extensor tendons have been classified into a zone system by Kleinert and Verdan. They have described 8 zones relating to underlying bones and joints. Doyle later added 9 zones in the musculotendinous junction in the forearm, which is about 4 cm proximal to the wrist (see Illustration. Extensor Tendon Mechanism in the Finger).[2][6] All can be seen in the illustration, which shows the odd number of zones broadly over the joints. Each zone differs in anatomy and properties of the extensor mechanism; therefore, all need to be assessed, and any laceration treatment depends largely on its location.[2] Extension in each finger needs to be tested on a joint by a joint basis in isolation, looking at the active range of movement and movement against resistance. 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 1 tendon per digit (EDM and EIP can be tested by extending the relevant finger with the hand flat on a surface). It is worth noting that the full extension of small joints is occasionally possible, even after lacerating those tendons.[1]

Junctura tendinae prevent independent extension of digits, and they allow for an ongoing 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 gets more complex past MCPJ (zone V).[6] The extensor tendon divides into 3 parts over the proximal phalanx (zone IV) to form central slip and lateral bands (zone III). Elson test can be used to test central slip in zone III – it involves flexion of the proximal interphalangeal joint (PIPJ) to 90 degrees and attempting to extend the distal interphalangeal joint (DIPJ) in that position. Normally, DIPJ remains lax unless the central slip is damaged as lateral bands have increased pull.[5] Distally lateral bands join and insert into the base of the distal phalanx, just proximal to the nail germinal matrix.[6] (Zone I). There are several stabilizing extensor mechanisms, including triangular ligament over the middle phalanx (zone II), oblique retinacular ligament running from proximal phalanx to distal phalanx, and transverse retinacular ligament anchoring lateral bands to the volar plates.[5] All of these can potentially be affected in the event of injury.

Evaluation

After the initial assessment is performed, further evaluation should take place. Radiographs must be taken to assess if there are any associated fractures. Glass and some other foreign bodies may also be discovered that way.[1] Anteroposterior, true lateral, and oblique views of the affected area and the neighboring joints should be taken.[7] Complex injuries, such as those associated with significant tissue compromise (be that bone or soft tissue), may require reconstruction well beyond simple tendon repair, which is outside this review's scope. A thorough assessment must be conducted and documented, and basic reconstructive principles may be used to approach defects of any complexity[8]:

1. Restore reliable vascular supply
2. Stabilize the wound bed (debridement)
3. Reestablish skeletal stability

Once the above is fulfilled, the tendons may be assessed for reconstruction, and any potential requirement for graft coverage or fascial flaps may be considered.[8]

Treatment / Management

There is no clear gold standard for treating extensor tendon lacerations.[8] The important thing to note is that the term ‘laceration’ can be used quite widely and can hide more complex injuries associated with the laceration itself.[7] Tetanus prophylaxis should be considered, and antibiotics are commonly used.[5] Repair should occur soon after the laceration and certainly within 2 weeks from the injury (ideally within a week).[1] Modern repair techniques and current protocols for rehabilitation may improve outcomes.[5] 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 is to restore the hand function.[8] Preserving or restoring appropriate tendon length is crucial to the outcome of repair, as even seemingly minor changes in tension can harm finger movement.[6] Despite easy surgical access and the results being generally better than in flexor tendon injuries, it remains a challenge to maintain the correct length and normal function in extensors.[3] Miller’s 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](B2)

Surgery is indicated if[6]:

• more than 25% of the tendon has been cut
• the patient is unable to extend the digit
• there is associated contamination requiring a formal washout and debridement
• the joint is unstable
• conservative approach trial has failed
• the patient can comply with the postoperative protocol.

The procedure can be performed under a local anesthetic or a nerve block, with the patient supine and the arm at their side on an arm table. A pneumatic tourniquet is very useful to control bleeding intraoperatively. Because of varying morphology depending on the zone of injury, treatment is best planned by anatomic classification.[6] Proximal zones (VI to IX) can take a 3-0 suture, but the size needs to be reduced the more distal the injury (see Illustration. Extensor Tendon Zones in the Hand).[6] The more distal repairs are less complicated in repair technique but are still more difficult to operate on because of their smaller size and lack of collagen bundle linkage. This means that the suture material has little grip strength. Equally, they are very flat distally to MCPJ, which means they cannot take a core suture and have a large surface area between the defect and surrounding tissues, making them more prone to adhesions.[1][6]

Contaminated wounds may need to be washed out and left to repair later when the wound bed is clean. If the cut is clear and both ends are seen, they can be repaired in an emergency. Alternatively, the skin may be temporarily loosely closed over the lacerated tendons if a surgical repair is required in theatre. Extensor tendon injuries should be managed in extension splinting to avoid exacerbating the injury and tendon end separation.[5] 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, 2-stage reconstruction, tendon transfer, or graft, but these may result in subpar outcomes. Often, that is due to stiffness and reduced range of motion (ROM). This is seen in adult and pediatric populations, although it is much more pronounced in the former.[2] If immobilization in children is difficult due to small digit size, a K wire fixation may be considered. Alternatively, an aluminum splint can be incorporated into the cast.[2](B2)

Zone 1

Zone 1 lacerations are lacerations at or distal to DIPJ and can be called open mallet fingers.[1] They can be treated using dermatotenodesis – full-thickness single-layer closure of both the skin and the underlying tendon.[2] If there is no underlying bony injury, these can be treated in the emergency department as long as the wound and joint can be thoroughly irrigated.[5] The patient must continue to move PIPJ to avoid stiffness, and they must be warned that they may never regain a full DIPJ flexion and may have some extensor lag, even with a well-done repair.[6](B2)

Zone 2

Zone 2 injuries are overlaying 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 no associated lag and the DIPJ can be extended against resistance. Occasionally, these are associated with significant soft tissue loss and need more complex reconstruction.[5]. Just like in zone 1, the results can be poor in zone 2 – less normal movement is present there, and shortening can impact the ROM in the interphalangeal joints (IPJ).[3](B2)

Zone 3

A zone 3 laceration is over the PIPJ and results in a boutonniere deformity. It disrupts the central slip. Absent or weak PIPJ extension is a positive finding. It can be either reconstructed directly, or a tendon flap can be raised from the proximal part of it.[1] These injuries are often associated with traumatic arthrotomy of the PIPJ or bony injury and should, therefore, be thoroughly explored and managed accordingly.[5] 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.[6](B2)

Zone 4 

The injuries are over the proximal phalanx and usually involve the broad extensor mechanism.[1] Because of this broadness, they are often partial injuries.[5] Partial lacerations have been shown to have good results with splinting only (for 3 to 4 weeks); however, complete lacerations require an operation.[1] The methods used include modified Kessler, modified Bunnel, and modified Becker. Similar to zone 2 injuries, these can be associated with soft tissue injuries and defects, necessitating a more complex approach.[5](B2)

Zone 5

These are over the MCPJ and must be assumed to be human bites until proven otherwise. They ought to be repaired, and care must be taken to ensure sagittal bands are intact or repaired to ensure central tendon position and a good clinical outcome. If a bite is involved, the wound must be extended, washed out, left open, and the patient should be started on antibiotics after the cultures have been sent off from the theatre.[1] Traumatic arthrotomies are common, and because these injuries often happen while the MCPJ is in a flexed position, the resulting injury can be more proximal than anticipated, making the repair more difficult due to the proximal portion of the tendon retracting.[5] Postoperatively splinting is done with the wrist in 30-45 extension and MCPJ in 20 to 30 flexion. PIPJ and DIPJ are left free.[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 MCPJ in these injuries because of the junctures, even if the laceration involves the whole tendon. This makes diagnosis more difficult if not explored.[5]. Tendons are becoming larger here and may need (and be able to accommodate) a core suture and a peripheral repair.[1] The methods include running-interlocking horizontal mattresses, modified Bunnel, augmented Becker, Halsted, or Silfverskiold.[5] More complex degloving injuries may require grafting or a flap.[1](B2)

Zone 7

These injuries happen underneath the extensor retinaculum, and it is unclear if it is necessary to be released to visualize the damage and repair it. There’s no other way to repair the damage.[1] The repair of tendons here can lead to poorer results because of injury to the extensor compartments or a bowstring effect if the retinaculum is not repaired properly.[3] It may also result in adhesions, particularly if splinted statically.[1] If repaired too tightly, it can also impair tendon glide. What follows from both is a loss of motion. Repair may also impact that, especially if it is too bulky. The retinaculum can be lengthened using step-cut or Z-plasty to prevent that. Early mobilization should also be considered, so repair must be strong enough to cope.[5](B2)

Zone 8

This zone lies in the distal forearm, and lacerations likely involve more than just 1 tendon, muscle bellies, and musculotendinous junction. Repair should start with the thumb and wrist extensor and move from there.[1] The repair is more likely difficult as the tissues are not as strong. The repair can be done using a figure of 8 sutures. Care should be taken to assess the posterior interosseous nerve (PIN) beforehand and protect it intraoperatively. Both wrist and elbow splinting may need to be considered to protect the repair postoperatively.[5](B2)

Thumb

Mallet is less likely here as the tendon is broader, but it should be repaired primarily if it occurs.[1] It is often robust enough to take a dedicated tendon suture, but dermatotenodesis is also an option.[5] EPB may be lacerated with no functional deficit, and the need for its repair is debatable. Still, EPL affects both IPJ and MCPJ in the thumb and requires reconstruction if lacerated.[1] T4 and T5 zones may involve superficial radial nerves, and large branches may need repair (smaller ones may need to be buried to avoid neuromas). Anything more proximal to this may be treated as zone 8 and 9 injuries.[5](B2)

Differential Diagnosis

The term laceration implies the mechanism of injury; however, other things may present with a similar clinical picture of a deficit in the extensor mechanism function:

• Mallet finger: an avulsion of the extensor tendon insertion from the distal phalanx, with or without the involvement of a bony fragment.
• Arthritis: chronic irritation to the 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: results in loss of passive extension as well as active.
• Posterior interosseous nerve syndrome: the patient cannot extend actively, but tenodesis remains normal.

Treatment Planning

Given that there is more than 1 way to manage these types of injuries, care must be taken when planning your treatment, and adjustments have to be made depending on several factors, including anatomical location, concomitant injuries, and patient compliance, for example, in the case of young children.[2]

Prognosis

Because of the population, these injuries often happen, and an early return to work is often the goal of treatment.[4] Generally, better outcomes are seen in proximal zones compared to distal due to more forgiving tendon excursion.[6] A substantial difference was shown in outcomes depending on how soon post-injury the repair was done with patients managed within 5 days, having 97.8% of ROM of the other limb, compared to 89.5% in those managed after 5 days.[9] In contrast to adults, children can heal rapidly and easily regain their full range of motion despite prolonged immobility. Their rehabilitation and recovery stages are much better, achieving excellent results with limited complications.[2]

Complications

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

• Tendon rupture[1]
• Reduction in both active and passive ROM[3]
• Adhesions[1]
• Extension lag (especially in MCPJ)[4]
• Loss of flexion and reduced ability to grip[1]
• Finger deformities[3]
• Swan neck deformity: This is usually due to prolonged flexion of the DIPJ and dorsal subluxation of lateral bands with consequent PIPJ hyperextension.
• Boutonniere deformity is characterized by DIPJ hyperextension and PIPJ flexion. It is usually caused by a central slip injury and volar subluxation of the lateral bands.

The adhesions are the most common of the above and can result in a loss of flexion.[10][3] Loss of flexion is a larger problem than extensor lag, especially in zones 3 and 4, as it has a higher effect on grip.[6] When adhesions happen, additional treatments are required, including intense hand therapy, and sometimes re-operation may be required (tenolysis rates are between 0 and 17%).[4] To compare, repair rupture rates are estimated to be between 0 and 8%.[6] Extensor tendon laceration outcomes can be measured using Miller's criteria, which divide them into excellent (extension lag, 0 flexion loss), good (less than 10 extension lag, less than 20 flexion loss), fair (11 to 45 extension lag, 21 to 45 flexion loss) and poor (greater than 45 extension lag, greater than 45 flexion loss). Notably, all of the above is measured purely on the extent of complications.[10]