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

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Chapter 48

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 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 clinician must understand the anatomy, principles of treatment, repair technique, and postrepair care of these injuries to ensure the best possible patient outcome.

Functional Anatomy

There are 12 extrinsic extensors 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 fibroosseous 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.1 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.

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 first 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 second metacarpal, and the ECRB inserts on the base of the third 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 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 clinician 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 bands. The sagittal bands are circumferential structures at the level of the metacarpal head that serve 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), which inserts into 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.

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 fifth 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. 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 to 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).2

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 also 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 clinician 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. Some investigators have advocated for the use of ultrasound in the diagnosis of suspected extensor (and flexor) tendon lacerations in the hand.3 This is a potentially attractive tool since it is easy to use and noninvasive and provides point-of-care analysis, but the use of sonography for detection of hand and digit tendon injuries cannot yet be advocated for routine use by emergency physicians. Because an extensor tendon is a mobile structure, it is imperative that if it is exposed, it be visualized in its entirety through a full range of motion. 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).

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, 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 intrinsic 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, refer the patient for follow-up in 1 to 3 days for a repeated 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 7 to 10 days will still ensure an outcome similar to that of an immediate repair, but this varies depending on the injury. 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 (including antistaphylococcal) 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 lack of immunocompetency, 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, nonabsorbable, synthetic braided sutures are preferred.4 Polyester sutures, such as Ethibond or Mersilene, are recommended. Nylon sutures are acceptable but are less ideal because colored nylon may be visible under the skin. Chromic and plain gut should be avoided because they will 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 sutures, 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 sutures such as polyglactin (Vicryl). 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 sutures tied outside the skin. Tighten the sutures until the digit is in full extension.5

Before repairing a tendon injury, it is imperative that the clinician 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 in anesthetics 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.6 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. 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 inadvertent unraveling of the cuff. Use of a hemostat to clamp the blood pressure cuff tubes helps avoid a slow leak in the cuff with resultant 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 sedation to help the patient tolerate a longer tourniquet time.

Atraumatic technique is essential for minimizing adhesions and scar tissue formation. Tendons should be handled delicately, with crushing force or excessive punctures with forceps and needles avoided. Forceps should be used only on the exposed, cut end of the tendon whenever possible.7

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,8 which divides the hand and wrist into eight anatomically based zones (Fig. 48-10). It is quite useful for emergency clinicians 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 clinicians 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 dorsal plaster or fiberglass 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).

image

Figure 48-10 Dorsum of the left hand. The injury classification system recommended by Verdan8 includes eight anatomically based zones. (Adapted from Blair WF, Steyers CM. Extensor tendon injuries. Orthop Clin North Am. 1992;23:142.)

Zone 7 and 8 Injuries1

Zones 7 and 8 consist of the area over the wrist and the dorsal aspect of the forearm, respectively. Extensor tendon lacerations in these regions can be quite complex and are therefore not repaired in the ED. Because of the close proximity of extensor tendons in the distal part of the forearm, lacerations such as stab wounds may appear innocuous but often result in multiple tendon lacerations. At the wrist level, the extensor tendons are covered by a retinaculum that is lined with synovium. Although this tissue allows smooth gliding of tendons during normal activity, the presence of synovium increases the risk for adhesions after tendon repair. In addition, lacerated tendons in the wrist and distal part of the forearm may retract away from the site of initial injury. This may make tendon retrieval and repair quite difficult and necessitate incision of the retinaculum and exploration of one or more compartments.

As a result of the potential complexity of these injuries, all tendon lacerations in zones 7 and 8 require formal surgical exploration and repair. ED management of these patients includes local wound care with primary repair of the skin and placement of a volar splint in 35 degrees of extension at the wrist and 10 to 15 degrees of flexion at the MCP joints. Promptly refer these patients to a hand surgeon so that repair may be undertaken within 1 week of injury.

Zone 6 Injuries1,4,9

Zone 6 consists of the area over the dorsum of the hand. Extensor tendon injuries in this region are frequently caused by lacerations from broken glass or another sharp object. Common pitfalls in ED management of these injuries are usually related to failure to recognize that the tendon has been injured. It is important to remember that these tendons are superficially located, partial tendon lacerations may occur, and weak extension of a digit is possible with a complete tendon laceration because of transfer of extensor function through the juncturae tendinum. Lacerations of the EIP or EDM tendons are evidenced by an inability to independently extend the index or little finger, respectively. In most cases, missing zone 6 injuries can be avoided if a careful physical examination is performed, including thorough wound exploration under sterile conditions using a tourniquet, adequate local anesthesia, and good lighting.

Extensor tendon injuries in zone 6 are generally appropriate for repair in the ED. Because of the juncturae tendinum, extensor tendons in zone 6 are less likely to retract than those in zone 7 or 8; however, the severed tendon may retract when the injury is more proximal. The distal end of a severed tendon is usually easy to find by passively extending the patient’s affected digit to bring the end into view. Retrieval of the proximal portion of a severed tendon is sometimes required and can usually be accomplished in the ED. Before searching for the proximal end of the tendon, the clinician should have a 4-0 nylon suture loaded onto a needle holder. When the proximal end is located, place this suture as a holding suture as far proximal as possible so that the tendon is not lost again. It is often necessary to use a scalpel to extend the wound proximally in a direction parallel to the course of the injured tendon to obtain adequate exposure. One should then begin to search for the tendon by lifting up this overlying skin with forceps and inspecting the proximal portion of the wound. Sometimes, the blood-stained end of a tunnel can be seen; this may contain the proximal end of the tendon. By gently placing a small hemostat or toothed forceps up this tunnel, the tendon stump can often be pulled into view.

Once both ends of the injured tendon have been located, the technique used for repair depends on the size and shape of the tendon. Whereas larger, round tendons can accommodate sutures that pass through the core of the tendon, smaller or flat tendons are difficult to repair with this technique. Most of the tendons in zone 6 can be repaired with either a modified Kessler or a modified Bunnell core suture technique using 3-0 or 4-0 nonabsorbable suture (Fig. 48-12). Both these techniques involve first placing a single suture in half of the cut tendon. Place the suture in the tendon core by inserting the suture needle into the exposed, cut end and then weaving the suture through the lateral tendon margins. Next, place the same suture through the core of the opposite half of the cut tendon. Tie the suture ends in a square knot in between the cut ends of the tendon to bring the two halves together.

Smaller tendons may be repaired with a figure-of-eight or horizontal mattress suture (see Fig. 48-12). Small, tapered needles should be used to avoid tearing the tendon. In a cadaver study comparing these multiple suture techniques, it was found that the modified Bunnell technique provided the strongest extensor tendon repair.10 In addition, this technique produced no gapping between the repaired tendon ends and minimized the postrepair restriction of flexion at the MCP and proximal interphalangeal (PIP) joints. It is important to passively test the degree of flexion at the MCP joint after a zone 6 tendon repair to be certain that the tendon has not been excessively shortened.

To improve the tensile strength of the repair, a number of other suture techniques may be used.4 One option is to increase the number of suture strands that cross the repair site (e.g., four strands rather than two). A cadaver study that compared various four-strand tendon repair techniques concluded that the Massachusetts General Hospital technique was more resistant to gap formation than either the Krackow-Thomas or the four-strand modified Bunnell technique.11 However, this cadaver model could not assess tendon shortening or subsequent range of motion.12 Another way to improve tensile strength is to place a peripheral suture in addition to the core suture. Place a running cross-stitch suture of synthetic, absorbable material (e.g., 5-0 polyglycolic acid, polyglactin, polydioxanone) circumferentially around the repair site or just on the dorsal surface of the tendon across the laceration site. Alternatively, place sutures laterally along both sides of the tendon, starting at about 1 cm on either side of the repair site. The ultimate choice of repair technique will depend largely on the treating clinician’s familiarity with extensor tendon repair, as well as the size of the tendon.

The approach to partial extensor tendon lacerations is not well defined, and no definitive standard of care exists. One evidence-based analysis identified 141 papers in its literature search, but none were relevant to the question of repair of partial extensor tendon injuries.13 The authors concluded that there is no direct evidence to assist in answering this question. Given the lack of literature on the subject, a reasonable approach may be to extrapolate from data on flexor tendon injuries. It has been demonstrated that many partial flexor tendon lacerations do well without repair,14 but hand surgeons still disagree on the need for repair of these injuries. In a survey of hand surgeons, 30% of respondents repaired all partial flexor tendon lacerations and 45% repaired only lacerations with greater than 50% involvement of the cross-sectional area.15 Except at the wrist level, extensor tendons are not covered with synovium and are less likely than flexor tendons to form adhesions after repair. This encourages some authors to recommend repair of most partial extensor tendon lacerations. Although the ideal approach to these injuries is not known, it is reasonable to consider repair of partial extensor tendon lacerations to be optional if less than 50% of the cross-sectional area is involved. However, if not repaired, such injuries must be splinted for 3 to 4 weeks to ensure that a partial laceration is not converted into a complete injury. Skin closure, splinting, and referral for follow-up is a standard approach to unsutured partial extensor tendon lacerations.

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