Extensor and Flexor Tendon Injuries in the Hand, Wrist, and Foot

Extensor Tendons

Extensor tendons are quite superficial, covered only by skin and a thin layer of fascia, and are thus highly susceptible to injury by commonly experienced trauma. Such injuries may result from lacerations, bites, or burns, but they may also be caused by closed injury or with even seemingly superficial lacerations. Whereas some extensor tendon injuries must be managed by a hand surgeon, others may be treated in the emergency department (ED). The emergency provider must understand the anatomy, principles of treatment, repair technique, and postrepair care of these injuries to ensure the best possible patient outcome. The authors suggest that all flexor tendon lacerations be referred to a hand surgeon.

Functional Anatomy

There are 12 extrinsic extensor muscles of the wrist and digits, all of which are innervated by the radial nerve. The muscles that give rise to these tendons originate in the forearm and elbow ( Fig. 48.1 ). The extrinsic extensor tendons reach the hand and digits by passing through a fibro-osseous tendon sheath (retinaculum) located at the dorsal surface of the wrist. This synovium-lined sheath provides smooth gliding of the tendons and prevents bowstringing when the wrist is extended. The dorsal retinaculum contains six compartments or subdivisions ( Fig. 48.2 ). These compartments are numbered from the radial to the ulnar side of the wrist.

Figure 48.1, Extensor muscles and tendons of the right wrist and hand. A, Posterior (dorsal) view. B, Cross-section of the most distal portion of the forearm. C, Radial nerve in the forearm: posterior view.

Figure 48.2, A, The extensor mechanism at the wrist and dorsum of the right hand. The six extensor compartments at the wrist contain ( 1 ) the abductor pollicis longus (APL) and extensor pollicis brevis (EPB), ( 2 ) the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB), ( 3 ) the extensor pollicis longus (EPL), ( 4 ) the extensor digitorum communis (EDC) II to V and the extensor indicis proprius (EIP), ( 5 ) the extensor digiti quinti (EDQ), and ( 6 ) the extensor carpi ulnaris (ECU). An important anatomic detail is the presence of a synovial sheath around each tendon unit within each fibro-osseous canal. Note that the EDQ is also called the extensor digiti minimi by some authors. B, Note that the juncturae tendinum allow some weak extension of the finger when the proximal extensor is completely lacerated.

The first compartment contains two tendons, the abductor pollicis longus (APL) and the extensor pollicis brevis (EPB). The APL tendon is the most radial of the extensor tendons and inserts on the base of the thumb metacarpal. It can be palpated just distal to the radial tubercle. The APL tendon causes thumb abduction and extension and some radial wrist deviation. The EPB travels with the APL through the first compartment but inserts at the base of the proximal phalanx of the thumb. The EPB tendon can be palpated over the dorsum of the first metacarpal when the thumb is extended against resistance. Both tendons can be tested by having the patient spread the fingers apart against resistance.

The second compartment also contains two tendons: the extensor carpi radialis brevis (ECRB) and the extensor carpi radialis longus (ECRL). These two tendons arise from the lateral epicondyle of the elbow. The ECRL inserts on the base of the index finger metacarpal, and the ECRB inserts on the base of the long (middle) finger metacarpal. Both tendons are powerful wrist extensors, and the ECRL also allows some radial wrist deviation. Wrist extension plays an especially important role in the mechanics of the hand because hand-grip strength is maximal only when the wrist is extended.

The third compartment contains only one extensor tendon, the extensor pollicis longus (EPL). This tendon crosses over the ECRB and ECRL and travels along the dorsum of the thumb to insert on the distal phalanx. The EPL forms the top of the anatomic “snuffbox,” and the bottom is formed by the EPB. The EPL can be visualized when the thumb is extended, and its strength can be tested by having the patient hyperextend at the interphalangeal (IP) joint against resistance. The intrinsic extensor of the thumb can provide some degree of extension at the IP joint. Therefore, if an EPL injury is suspected, it is important to compare extension at the IP joint with that of the unaffected thumb.

The fourth and fifth compartments contain the six tendons that extend the index through the little fingers. Each finger has its own extensor digitorum communis (EDC) tendon. The index and little fingers have an additional independent extensor tendon, the extensor indicis proprius (EIP) for the index finger and the extensor digiti minimi (EDM) for the little finger. The fourth compartment contains the EIP and EDC tendons, and the fifth compartment contains only the EDM tendon. These six tendons can be seen over the dorsum of the hand, where they are poorly protected and prone to injury. In this region the tendinous, ligamentous, and fascial connections between these tendons are known as the juncturae tendinum. Because of these redundant interconnections, a patient may be able to extend a digit, albeit weakly, even when there is a complete laceration of its EDC tendon. To avoid missing a tendon injury on the dorsum of the hand, it is important that the examiner test for tendon strength and not just for active extension.

The course of the extensor tendons along the fingers is more complex, but a basic understanding of this anatomy is essential for the emergency provider to evaluate and treat extensor tendon injuries ( Fig. 48.3 ). The EIP tendon joins the EDC tendon at the level of the metacarpophalangeal (MCP) joint in the index finger; the EDM tendon parallels the course of the EDC tendon. The four EDC tendons eventually insert at the base of the proximal, middle, and distal phalanges. The most proximal insertion of the EDC tendon is at the level of the base of the proximal phalanx. The tendon actually inserts in two ways. First, there is a loose dorsal insertion just distal to the MCP joint. In addition, the EDC tendon inserts into the volar plate via the sagittal band. The sagittal band is a circumferential ligament at the level of the metacarpal head that serves to keep the EDC tendon centered over the metacarpal head, as well as to provide a stable connection with the volar plate located on the palmar side of the hand. After its primary insertion at the level of the MCP joint, the EDC tendon then extends dorsally along the digit. The EDC trifurcates over the proximal phalanx ( Fig. 48.4 ). Its major central slip inserts on the base of the middle phalanx ( Fig. 48.5 ). The lateral branches of the EDC tendon join with the lateral bands from the interossei and lumbricals to form the conjoined lateral bands. The two conjoined lateral bands then fuse together over the middle phalanx to form the terminal extensor mechanism (TEM) that inserts on the base of the distal phalanx ( Fig. 48.6 ). The triangular ligament is a connection between the two conjoined lateral bands that assists in keeping these structures on the dorsal aspect of the digit.

Figure 48.3, Flexor and extensor tendons in the fingers. A, Posterior (dorsal) view. B, Finger in extension: lateral view. C, Finger in flexion: lateral view. Note the directions of force when the extensor tendon is activated (arrows).

Figure 48.4, Zone of convergence of the digital extensor mechanism, which begins at approximately the midportion of the proximal phalanx and ends at the level of the insertion of the central slip into the dorsal base of the middle phalanx. Proximal to the zone of convergence, the extrinsic and intrinsic components of the extensor mechanism are separate: the central slip is extrinsic, whereas the lateral slips are intrinsic. Within the zone of convergence there is complete reciprocal crossover of fibers from the central slip and lateral slips. The products of the completed convergence are the central slip insertion and the conjoined lateral bands, both of which have dual muscular activity.

Figure 48.5, The extensor mechanism on the dorsum of a finger. Arrows point to the radial and ulnar lateral band portions of the extensor mechanism, and the probe is lifting the entire structure up off the phalanx.

Figure 48.6, The terminal extensor mechanism.

The sixth dorsal compartment of the wrist contains only one tendon, the extensor carpi ulnaris (ECU). This tendon originates at the lateral epicondyle of the elbow and inserts at the base of the small finger metacarpal. The ECU functions as a wrist extensor and ulnar deviator. It can be palpated just distal to the tip of the ulna, and its strength can be tested by forced ulnar deviation of the wrist.

General Approach to Extensor Tendon Injuries

The key to detecting extensor tendon injuries in the ED is to perform a careful and thorough history and physical examination. These injuries are easy to miss with a cursory examination. Closed injuries may appear innocuous at first but can result in tendon injuries that may lead to severe deformities or dysfunction if undetected ( Figs. 48.7–48.9 ). Closed injuries are also commonly associated with fractures. A hand radiograph is recommended for closed-hand injuries when a fracture is suspected or for open-hand injuries in which a fracture or foreign body is suspected. It is generally accepted that all open injuries that result from glass should be radiographed. Plain radiographs have a sensitivity of approximately 98% for detecting radiopaque foreign bodies (e.g., gravel, glass, metal).

Figure 48.7, Because of their superficial location, it is difficult to avoid at least partial injury to the extensor tendons with even superficial lacerations of the dorsum of the wrist, hand, or fingers. A, This complete extensor tendon laceration is obvious because the index finger cannot be extended. B, This partial tendon laceration was not appreciated on initial examination, which seemingly demonstrated full tendon function. The entire tendon could not be visualized because of an uncooperative patient. The unappreciated partial laceration progressed to a complete rupture by the time of suture removal. Expeditious delayed primary repair resulted in a good outcome.

Figure 48.8, To examine for a tendon injury, use a bloodless field. Note the sterile glove on the patient to maintain a clean field. It is almost impossible to cut the dorsum of the hand or fingers and avoid at least a partial tendon injury. A, The location and depth of this laceration suggest an extensor tendon injury. On examination, the patient had full extension. B, No tendon injury is visualized when the laceration was examined with the fingers in extension. When the laceration was extended and probed with the finger flexed, a 60% laceration of the extensor tendon could be viewed in the depths of the wound. C and D, Note the typical shiny white appearance of the fully exposed tendons (arrows).

Figure 48.9, Given the superficial location of extensor tendons, suspect a tendon injury even with seemingly superficial lacerations of the dorsum of the hand and fingers. Full function is possible with a significant tendon laceration, and delayed total rupture can occur days to weeks later if the injury is not repaired or splinted. Most partial extensor tendon lacerations do well with 3 to 4 weeks of splinting and no surgical repair. When in doubt, clean the laceration, suture the skin, splint, and refer for subsequent examination in a few days.

Injuries to extensor tendons from lacerations are quite common, especially on the dorsum of the hand where they are located superficially. All dorsal wrist, hand, and digit lacerations should be assumed to have an underlying tendon laceration until proved otherwise. Digital extension, albeit weak, can still occur with partial tendon lacerations of up to 90%, so visualization of the tendon and careful strength testing are required to definitively rule out a partial injury. In some cases the specific diagnosis simply cannot be made on the first examination (see later). Complete laceration of an EDC tendon on the dorsum of a hand can still allow digital extension through the juncturae tendinum.

After assessing the strength and neurovascular status of the injured hand it is imperative that the emergency provider visually inspect the wound thoroughly. Inspection should include an assessment of the degree of wound contamination, as well as a search for foreign bodies and occult tendon lacerations. It is often necessary to extend the skin laceration to aid in the visualization of a possible tendon injury. Because an extensor tendon is a mobile structure, it is imperative to visualize it in its entirety through a full range of motion if it is exposed. It is especially important to examine the tendon in the position that it occupied at the time of injury because the tendon injury frequently does not lie directly under the external skin wound (see Fig. 48.8 ).

Some investigators have advocated the use of ultrasound in the diagnosis of suspected extensor (and flexor) tendon lacerations in the hand. This is a potentially attractive tool because it is easy to use, noninvasive, and provides point-of-care analysis. Ultrasound has the added advantage of facilitating dynamic evaluation of tendons through their range of motion. In a study of 34 patients with upper extremity tendon injuries treated by emergency physicians, ultrasound was faster and more accurate than exploration, magnetic resonance imaging (MRI), and specialty consultation. Accuracy of sonography for detection of hand and digit tendon injuries greatly depends on operator experience and is not a routine component of emergency medicine ultrasound practice.

Definitive examination of any wound must occur under the best possible conditions, with a good light source, a bloodless field, adequate local anesthesia, and a cooperative patient. It may be impossible to adequately assess some patients completely during the first ED visit. In this case, final diagnosis must be delayed until the proper circumstances permit the required conditions. Occasionally, patient noncompliance thwarts even the most carefully planned follow-up. Frequently, the patient's pain, swelling, anxiety, or degree of intoxication or altered sensorium limits the clinician's diagnostic ability. Therefore it would not be considered standard to diagnose the presence or the full extent of all extensor tendon injuries immediately. Whenever logistically possible, emergency providers should consult a specialist when an extensor tendon injury is suspected by mechanism, location of the wound, or tendon dysfunction. Under most circumstances, however, there is no value in obtaining an immediate on-site consultation with a hand or orthopedic surgeon because the scenario would similarly limit any clinician's diagnostic acumen.

If the examining clinician suspects but is unable to locate a tendon laceration, or if a patient is uncooperative with the examination and the circumstances prohibit ideal initial care, patients should be referred for follow-up in 1 to 3 days for a repeat examination. Close the skin and apply a splint for interim wound care. A delay of a few days for definitive diagnosis, surgical repair, or both does not result in any significant alteration in the final outcome. Delayed primary repair, without the need for tendon grafting or tendon transfer, is a well-accepted technique. In fact, many hand surgeons are reluctant to immediately repair even a complete extensor tendon laceration in a contused, potentially contaminated wound. The exact time frame under which such delayed repair results in an outcome similar to that of immediate repair is not well defined and depends on the clinical scenario. Usually, repair delayed for up to 10 days will still ensure an outcome similar to that of an immediate repair, but this varies depending on the injury. Providers should clearly document the inability to rule out a tendon injury in the ED and the mandate for follow-up within a specified time frame on the medical record and discharge instructions.

Use of Antibiotics

There are no data to support or refute the use of prophylactic antibiotics as a routine adjunct after tendon injury. In general, prophylactic antibiotics have not been demonstrated to reduce infection rates after soft tissue injury in the setting of proper wound cleaning. Nor have they been proved to reduce infection rates in the absence of gross contamination, retained foreign material, extensive contusion, or a delay in cleaning. Many clinicians opt for antibiotics with gram-positive (e.g., anti-staphylococcal) coverage if the tendon has been injured or sutured, but no universally accepted standard of care exists. An individualized approach is advocated. Prophylaxis is generally used for only 3 to 5 days after injury unless there are extenuating circumstances such as immunocompromise, diabetes, a human bite, an unusual source of contamination, or peripheral vascular disease. If the sterility of a wound is in doubt, do not attempt tendon repair.

Preparation for Repair

Before attempting repair of an open extensor tendon injury in the ED, be prepared and have the proper equipment available. Place the patient supine on a gurney that ideally has an arm board attached. Bright overhead lighting is important for wound exploration so that the presence of tendon injuries and foreign bodies can be adequately assessed. Instruments should include, at a minimum, a needle holder, two skin hooks and retractors, sharp (i.e., iris) and blunt-nosed scissors, several small hemostats, and one pair of small single-toothed (i.e., Adson) forceps.

The choice of suture material depends on the location of the tendon injury. For repair of complete tendon injuries on the dorsum of the hand, non-absorbable, synthetic braided suture is preferred. Polyester suture, such as Ethibond (Ethicon, Somerville, NJ) or Mersilene (Ethicon), is recommended. Nylon suture is acceptable but is less ideal because colored nylon may be visible under the skin. Chromic and plain gut should be avoided because it may dissolve before adequate tendon healing has occurred. Silk is not desirable because of its reactivity. Most extensor tendons on the dorsum of the hand will accommodate 4-0 suture, but 5-0 suture material may be needed for smaller tendons. Small, “plastic repair” tapered needles should be used to avoid tearing the tendon. Partial tendon injuries in the digits are best repaired with fine, synthetic absorbable suture such as polyglactin (Vicryl [Ethicon]). Complex lacerations that involve tissue loss and fraying of the tendon margins (e.g., table-saw injuries) represent a particularly challenging clinical scenario that may make an otherwise straightforward tendon repair very difficult. In these cases, Lalonde and Kozin recommend closing the lacerated skin and tendon together (i.e., dermatotenodesis). Take large, composite bites of skin and tendon together, 5 to 10 mm on either side of the wound, with 3-0 or 4-0 nylon suture tied outside the skin. Tighten the suture until the digit is in full extension.

Before repairing a tendon injury, it is imperative that the provider use adequate anesthesia so that thorough wound exploration can occur. A field block or regional nerve block can be used on the dorsum of the hand, whereas local anesthesia or a digital nerve block can be used on the fingers. The choice of anesthetic composition has been the subject of long-standing controversy. Traditional teaching admonishes the use of epinephrine-containing anesthetic for fear of digital ischemia; however, many clinicians readily use lidocaine with epinephrine in the hand and fingers without complications. There is ample anecdotal and clinical evidence supporting the safety profile of epinephrine in digital anesthesia. Epinephrine has the benefit of prolonging the anesthetic effect and promoting a bloodless field during wound exploration and repair. It is important that the digits be fully anesthetized or, in the case of more proximal wounds on the hand, that the area around the wound be liberally anesthetized because many lacerations must be extended to afford access to the surgical field. It is a common error to avoid extending a laceration and to attempt examination, cleaning, or repair through a small initial skin laceration.

Following the administration of an anesthetic, place a tourniquet on the involved limb if hemostasis is problematic (see Fig. 48.8 ). It is absolutely essential that adequate control of blood flow be obtained before attempting to repair a tendon laceration. It is very difficult to find the proximal end of a retracted tendon in a bloody field. Before applying a tourniquet, wrap the patient's arm in several layers of cast padding as a comfort measure and elevate the arm for at least 1 minute to allow blood to drain by gravity. Place a blood pressure cuff on the middle to upper part of the arm, wrap several more layers of cast padding around the cuff, and then inflate it to 260 to 280 mm Hg. Once inflated, clamp the tubes tightly with a hemostat. The use of cast padding during inflation helps avoid premature opening of the cuff. Use of a hemostat to clamp the blood pressure cuff tubes helps avoid cuff deflation. A blood pressure cuff tourniquet is generally well tolerated by patients for approximately 15 to 20 minutes. If tendon repair cannot be accomplished in this time it is likely that the injury is too complex for repair in the ED. When necessary, use parenteral analgesia or anxiolysis to help the patient tolerate a longer tourniquet time. For finger examination, placing a rubber ring tourniquet at the base of the finger should give excellent hemostasis.

Atraumatic technique is essential for minimizing adhesions and scar tissue formation. Tendons should be handled delicately, avoiding crushing force or excessive punctures with forceps and needles. Forceps should be used only on the exposed, cut end of the tendon whenever possible.

Patterns of Injury and Management

Treatment of extensor tendon injury ( ) depends primarily on whether the injury is open or closed, as well as the anatomic location of the injury. The most widely accepted classification system is that developed by Verdan, which divides the hand and wrist into eight anatomical zones ( Fig. 48.10 ). It is quite useful for emergency providers to become familiar with this classification because in many instances the zone of injury can help determine whether tendon repair should be attempted in the ED. One must keep in mind that repair of lacerated extensor tendons within 72 hours of injury is still considered primary closure. Therefore although emergency providers may repair many extensor tendon injuries immediately, some injuries are best managed with delayed repair. In these cases, initial care in the ED should consist of sterile skin preparation, copious wound irrigation and inspection for foreign bodies, skin closure, splint application, and referral to a hand specialist for further care in 1 to 5 days. A plaster, metallic, or fiberglass dorsal splint in which a metal foam finger splint is incorporated is an ideal way to totally immobilize a finger ( Fig. 48.11 ) (see Chapter 50 ).