Extensor Tendon Lacerations

The history of tendon reconstruction can be traced back to the times of Hippocrates and Galen. Interestingly, Galen (131-201 AD), in his Ars Parva, stated that tendons were composed of both ligaments and nerves. He warned, therefore, that placing sutures in tendons would lead to pain, twitching, and eventual convulsions. This erroneous concept was not refuted until 1682, when Meekren observed that tendons are insensitive and described the successful repair of incompletely severed tendons. Modern tendon repair surgery was promoted by Kirchmayr, who, in 1917, published a method of "locking" suture in tendon repair, variants of which are still in use today. ^[9]

Anatomical and functional understanding of the extensor system was advanced significantly by Albinus, who first illustrated the basic structure in extensor tendon anatomy in 1734. Further progress of extensor tendon dynamics and balance forces concepts were made by Fowler in 1942. Landsmeer also contributed to the understanding of the extensor system's dynamic interplay with the oblique retinacular ligament in 1949. ^[2] See Relevant Anatomy for a detailed discussion of anatomy.

Extensor tendon laceration can result from various injuries. The most common mechanisms are sharp object direct laceration, crush injury, avulsions, burns, animal or human bites, and deep abrasions. A study by Naito et al found that 88% of patients with a distal radius fracture with a dorsal roof fragment had an extensor pollicis longus (EPL) tendon injury, with 36% of the study’s patients having a laceration. ^[10]

Extensor lacerations are accompanied by various degrees of skin injury, ranging from minimal (as in puncture wounds) to large avulsions, which can cause significant loss of domain of both elements.

Because of the superficial location of the extensor tendons in the wrist and hand, the laceration often easily directly observed on physical examination with manipulation of the overlying skin. The underlying joint is passively flexed and extended for full visualization of the injury area.

The most common condition wherein the tendon laceration is present outside the area of the skin laceration is the fight bite. In this situation, the metacarpophalangeal joint is flexed and makes contact with an opponent's teeth (see image below). The resultant extensor tendon laceration is located proximal to skin laceration when the hand is in resting position with the MP joints extended, which is the normal position of the hand, especially when being medically examined. In the acute setting, most extensor tendon lacerations exhibit some loss of extensor function, whether it is a decrease in active extension range of motion, decrease in extension strength, or complete loss of extension of affected joints.

In the most straightforward case, the patient presents with one or more digits that stay more flexed than the others when the patient attempts to extend all fingers. This indicates a complete laceration of the extensor tendon on the affected digits. However, if all the extensors in the hand are completely lacerated, then the fingers stay flexed at rest or at attempt to straighten. Also, the position of the fingers does not change regardless of the position of the wrist; this indicates loss of the normal tenodesis effect.

In less straightforward cases, a tendon laceration can be present on examination, but the degree of laceration or surrounding anatomy can hide an extension deficit. Up to 80% of the extensor tendon may be lacerated without loss of function, but the chance of delayed rupture is increased when the laceration includes more than 40% of the tendon. Therefore, the dorsal hand and wrist wound must be explored well when any suspicion of tendon injury exists.

At the wrist, 3 dedicated wrist extensors (extensor carpi radialis longus [ECRL], extensor carpi radialis brevis [ECRB], extensor carpi ulnaris [ECU]) and the finger extensors aid in wrist extension. Therefore, a single wrist extensor laceration can be missed on an initial function examination; thus, careful direct examination must be performed. Finger extension tendon laceration also can be masked. The index and small fingers have 2 extensor tendons apiece, and masking could be present if only one is lacerated. Also, extensor tendon laceration of the dorsal palm occurring proximal to juncturae tendinae may also mask extensor dysfunction. Juncturae tendinae are intertendinous fascia connections that attach diagonally between the tendons of the extensor digitorum communis (EDC).

The purpose of the juncturae is to coordinate the extensor motion of the digits. The interconnection of the juncturae allows continue extension of the affected digit if an extensor tendon laceration occurs proximal to the junctura. Understanding this anatomical subtlety avoids missing the diagnosis of an extensor tendon laceration.

Debris is often present in these wounds, and particles need to be completely cleared for adequate healing, for prevention of infection, and to attain an unobstructed view of injured area. For open dirty wounds of the hand and wrist, after the full sensory examination is complete, local blockage of the extensor area should be performed. This allows adequate cleansing of the wounds without pain or muscle dysfunction, since the extensor muscle bellies and innervations lie much more proximal. After a thorough wound debridement, the direct extensor tendon examination and muscle function testing should be performed.

As with most normal structures, significant disruption should be repaired when possible. Most lacerations of the extensor system should be repaired. However, certain lesser degree lacerations can do well without repair. A laceration of the extensor over the proximal phalanx involving 40% of tendon, in which the patient can extend the finger against resistance, do well with or without repair. ^[11] Small partial extensor lacerations can sometimes demonstrate triggering but do not exhibit the delayed rupture exhibited by lacerations of >40% of the extensor tendon. The general principles and timing of management for extensor tendon injuries are similar to those for flexor tendon injuries. In combined repairs, flexor tendon rehabilitation must take priority.

Associated fractures are common with extensor injuries in the digits. In closed injury over the dorsum of the proximal interphalangeal (PIP) joint, suspect extensor tendon injury. Because of the superficial nature of the extensor tendons and the lack of significant delicate and critical adjacent structures (as opposed to the presence of the neurovascular bundle in a flexor tendon injury) these repairs can be performed immediately in the emergency department, urgent care, or office setting, given the proper lighting and instruments. ^{[1, 12]} (For a detailed description of extensor tendon repair in an emergency department or office setting, see Medscape Reference article Extensor Tendon Repair.) If the repair is likely to be complicated by injury to additional structures, an operating room is the best setting for the repair. ^[12]

When deciding when and where to perform an extensor repair, one of the first questions to address is infection risk due to contamination of the wound. An extensor tendon laceration wound that is not infected or severely contaminated can be repaired immediately. Extensor tendon laceration wounds with significant debris contamination or high risk of future infection (eg, fight bites) must be taken to the operating room for a thorough debridement and washout before repair. The nature of this type of contamination requires optimal lighting, instruments, and surgical support uniquely found in the operating suite. At the completion of the debridement, the clinical decision must be made whether to directly repair the extensor tendon or delay the repair for a course of antibiotics and observation to avoid wound infection.

A study by Al-Qattan indicated that partial extensor tendon lacerations greater than half the width of the tendon can be conservatively treated by immediate nonresistive active mobilization (4 wks), followed by resistive exercises, without the employment of splints or sutures. Specifically, this applied to lacerations in zones II, IV, and VI-VIII of the fingers and II, IV, and V of the thumb. The study included 39 patients, all of whom achieved full range of motion without extension lags by 8- to 9-month follow-up. ^[13]

As with all disorders of the hand, diagnosis and correct therapy application hinges on a thorough understanding of the relevant anatomy. ^{[14, 15]} The upper extremity contains 12 extensor tendons. These tendons comprise an extensor system that dorsally maneuvers the wrist, thumb, and all fingers. Extensor tendons also participate in the radial and ulnar deviation of the wrist and contribute to the supination and pronation of the wrist and thumb. The primary origin site is the lateral epicondyle of the humerus and proximal forearm.

As the extensor tendons travel from proximal to distal, they form an arrangement that can be described as a deep group and a superficial group. The superficial group consists of extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB), the extensor digitorum communis (EDC), the extensor digiti minimi (EDM [otherwise known as extensor digiti quinti]), and the extensor carpi ulnaris (ECU). The deep group comprises the abductor pollicis longus (APL), the extensor pollicis longus (EPL), the extensor pollicis brevis (EPB), and the extensor indicis proprius (EIP). Also coursing along with the tendons in the deep compartment is the deep branch of the radial nerve, which is otherwise referred to as the posterior interosseous nerve (PIN). It provides innervation to all the aforementioned extensor tendons. See the table below for a complete extensor tendon list.

Table. Extensor Tendons of the Hand (Open Table in a new window)

 

As the extensor tendons cross the wrist, they course under the extensor retinaculum. The extensor retinaculum prevents the tendons from dorsal displacement caused by natural tendency to develop a straight line from tendon origin to insertion, known as bowstringing, and is divided into the tendons in 6 extensor compartments by vertical septae. See the image below.

The first extensor compartment contains the EPB and the APL. The second compartment contains the radial wrist extensors, the ECRL and ECRB. The third compartment is occupied by the EPL. The EPL is notable for the diagonal course that it takes after it deviates around the dorsal radius bony protrusion called the Lister tubercle. The EIP and the 4 EDC tendons make up the fourth compartment. The fifth compartment holds the EDM tendon, and the sixth compartment holds the ECU.

The tendons travel distally past the extensor retinaculum to their insertion sites. The ERCL inserts on the dorsal base of the index metacarpal. The ECRB inserts on the dorsal base of the long finger metacarpal, as it is the most central extensor tendon. This fact is important to note when tendons are selected for tendon transfer. The ERCB should not be used for a transfer donor tendon, if possible, because the resultant wrist extension will deviate to the radial or ulnar side because of the laterality of the remaining tendons.

All the extensor tendons to the hand are extrinsic, that is, no tendons that extend the digits originate in the hand. As the digital extensors travel over the hand, dorsum extensor juncturae tendinae are formed to cause interconnections between tendons. These interconnections are important to understand when evaluating extensor injuries. Juncturae tendinae can cause a misdiagnosis of an extensor tendon laceration because they can aid continual extension of a digit whose tendon was cut proximal to the juncturae. See the image below.

Several unique aspects of the extensor tendon system are important to note. Unlike the flexor tendons, extensor tendons do not have flexor sheaths except for at the wrist, as tendons pass below the extensor retinaculum. The EDM tendon is usually split into 2 separate slips as it crosses over the wrist and travels to the metacarpophalangeal (MP) joint. The fifth dorsal compartment, in which the EDM travels, is located just dorsal to the distal radioulnar joint. ^[16] The EDC tendon to the small finger is estimated to be absent in 54% of the population. ^[17]

Extensor apparatus of the fingers

The extensor apparatus of the fingers is called an apparatus or system because of the complex interplay between the multiple extensor tendons, the intrinsic muscle system, and the many interconnecting ligaments between the tendons and the volar plates. The extensor apparatus of the digits begins just proximal to the MP joints. See the image below.

As the extensor tendons travel over the MP, a dorsal sling of transverse fibers is present. The sling attaches to the extensor tendon dorsally and passes palmarward on each side of the MP joint to attach to the volar plate and the transverse metacarpal ligament. This dorsal sling is called the sagittal band. These transverse fibers are layered in a crisscross pattern that changes its arrangement as the finger flexes and extends. ^[16]

MP joint extension is accomplished by the contraction of the finger extensor tendons and its attachment to the proximal phalanx via sagittal band fibers. The sagittal band acts both as a static tether to prevent radial or ulnar displacement of the extensor tendon and as a dynamic tether that allows proximal and distal gliding of the extensors tendons during flexion and extension. Complete laceration of the sagittal bands on either side can cause instability in the extensor tendon position as it travels across the MP joint. Laceration to the radial side of the sagittal band causes far more instability than injury ulnar side. ^[18] Complete laceration of one side of the sagittal band causes a subluxation of the extensor tendon to the opposite side of the laceration when the MP joint is flexed. When the MP joint is extended and tension is removed from the EDC, the tendon snaps back into the central position.

The extensor apparatus becomes a complex interplay of intrinsic muscle contribution as it travels from the MP joint distally. Three intrinsic sets of muscles (volar interossei, dorsal interossei, and lumbricals) contribute dynamic function to the extensor system through the lateral slips. See the image below.

The tendons of the interossei muscles split in two; the superficial slip inserts on the proximal phalanx (causing MP flexion), and the deep tendon becomes part of the lateral slip. Interossei muscles contribute to the lateral slip on both sides of the finger while the lumbrical tendons only join the lateral slip on the radial side.

In discussion the extensor mechanism, some confusion often arises in the terminology of lateral slips and lateral bands. The lateral slip is the tendon by which the intrinsic muscle contributes (as just previously discussed) to the extensor mechanism. The lateral band is the extrinsic contribution (EDC tendon) to the extensor mechanism. The lateral slip and lateral band join together distal to the central slip insertion to make up a conjoined lateral band. The lateral slip gives tendon attachments to the central slip and terminal tendon to help extend the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. Likewise, the EDC tendon provides the major portion of the central slip. It splits into 2 tendinous branches on either side of the central slip, which join with the lateral slip to make the conjoined lateral band. Finally, both sides merge to form the terminal tendon, which inserts on the dorsal aspect of the distal phalanx and extends the DIP.

Between, around, and over this extensor system array are ligaments and fascial constructs (also called the reticular system), which aid the function and interplay of the extensor tendons. See the image below.

The principal components of the retinacular system are the transverse and oblique ligaments (eg, Landsmeer ligament). The transverse fibers originate from the flexor sheath and proximal phalanx on the volar aspect, pass through a window in the Cleland ligament, and insert into the lateral bands and triangular ligament dorsal to the axis of proximal interphalangeal joint rotation. The deeper and more tendinous oblique retinacular ligament arises from the volar proximal interphalangeal joint capsule and proximal two thirds of the middle phalanx and inserts distally into the conjoined tendon (conjoined lateral band).

Distal to the proximal interphalangeal joint, the lateral bands first are separated by a triangular ligament and then fuse to form a conjoined tendon, which inserts into the base of the distal phalanx. The extensor hood is free to slide proximally with MP extension and distally with MP flexion. With the hood in the distal position, the interossei contribute to MP flexion through their vertical fibers, with little effect on the interphalangeal joints. With the hood in the proximal position and the MP joints fixed in extension, the interossei, through the oblique fibers of the lateral bands, are able to extend the interphalangeal joints.

Conversely, the lumbrical muscles are effective IP extensors irrespective of the degree of MP flexion. Similar to the interossei, they provide flexion of the MP joint via their vertical fibers. The lateral bands normally lie dorsal to the axis of motion of the extended PIP joint and shift volarward with PIP flexion. The triangular ligament prevents the lateral bands from shifting volar to the axis of motion to become flexors of the PIP joint. The primary function of the EDC is MP function, but with full MP extension or MP extension blocked, the EDC can extend the IP joints. The EPL traverses the third dorsal compartment of the wrist. It adducts and supinates the first ray and extends the MP and IP joints.

The extensor pollicis brevis and abductor pollicis longus are important stabilizers of the first metacarpal base. The extensor pollicis brevis extends the carpometacarpal and MP joints, inserting into the base of the proximal phalanx. It occasionally inserts into the distal phalanx, as well. The anatomy of the thumb MP joint resembles the PIP joint anatomy of the digits. The adductor and abductor pollicis longus tendons contribute to a dorsal expansion, which has transverse fibers acting like the retinacular system to stabilize the tendons of extensor pollicis brevis and extensor pollicis longus. The intrinsics are able to extend (but not hyperextend) the IP joint through fibrous interconnections in the dorsal expansion.