The most common cause of flexor tendon injury is laceration.
Flexor tendon lacerations can be subtle. A distal-to-proximal five-zone
(I to V) classification system for flexor tendon injuries has been
developed based on location, treatment considerations, and prognosis.2
Zone I extends from the insertion of the flexor digitorum superficialis
to the profundus tendon. Patients with these injuries lose flexion at
the distal interphalangeal joint. Retrieval of the proximal tendon
is often difficult.
Zone II involves the portion of the digital canal occupied by both
flexor digitorum superficialis and flexor digitorum profundus tendons
(Figure 265-5). The close proximity of these
tendons makes it essential for exact repair with minimal operative
trauma. Lacerations in this zone are common, and partial lacerations
are more common than complete injuries.
Zone III extends from the distal edge of the carpal tunnel to
the proximal edge of the flexor sheath. The lumbrical muscles originate
from the flexor digitorum profundus tendons in this region. Outcomes
are generally favorable.
Zone IV involves the carpal tunnel and related structures. The area
must be explored carefully because so many vital structures traverse this
region. Isolated injuries are the exception.
Zone V involves injuries to tendons proximal to the carpal tunnel.
Injuries here tend to be severe and often involve multiple tendons
as well as the median or ulnar nerve. Examine and test all major
structures. A hand surgeon should repair all flexor tendon lacerations.
Primary repair should occur within 12 hours. Secondary repair can
occur up to 4 weeks after the injury. Avulsion of the flexor digitorum
profundus tendon from its insertion on the distal phalanx is another
common flexor tendon injury. This typically results from a grasping
motion against high-speed resistance. The patient will be unable
to flex the distal phalanx. Prognosis depends on the size of the
bony fragment, the length of time from injury to repair, and the
blood supply to the tendon.
Flexor tendon injuries are relatively rare in children. Emergent
management of these patients is the same as for adults. However,
postoperative return to motion is quicker than in adults.3
The extensor tendons are the most common site of tendon injuries
because of the superficial nature of the tendons on the dorsum of
the hand. A separate zone classification system (I to VIII) for
extensor tendon injuries has been developed for assessing injury
patterns, repair techniques, and rehabilitation.4
Zone I involves the area over the distal phalanx and distal interphalangeal
joint. Injury can occur from blunt or sharp trauma. Complete laceration
or rupture of the tendon at this level will result in the distal
interphalangeal joint flexed 40 degrees. This injury after
blunt trauma is often referred to as “mallet
finger,” and it is the most common tendon injury
in athletes. This injury has been classified as type I if
there is tendon only rupture, type II if there is a small avulsion
fracture, and type III if >25% of the articular surface
is involved. Types I and II can be treated with the distal interphalangeal
joint immobilized in continuous slight hyperextension for 6 to 10
weeks. Some hand surgeons may prefer operative treatment. Chronic
untreated mallet finger may result in a swan-neck deformity (Figure 265-9). This occurs when the lateral
bands are displaced proximally and dorsally, resulting in increased
extension forces on the proximal interphalangeal joint.
Zone II involves the area over the middle phalanx. Injuries are usually
a result of laceration. Treatment is similar to zone I injuries.
Zone III involves the area over the proximal interphalangeal joint.
The central tendon is the most commonly injured
structure. Complete disruption of the central tendon may result in
the volar displacement of the lateral bands, causing them to be
flexors, along with the unopposed flexor digitorum profundus. Additionally,
the extensor hood retracts, causing extension of the metacarpophalangeal and
the distal interphalangeal joints, resulting in the boutonnière
deformity (Figure 265-10). Controversy
exists regarding whether treatment of type III injuries should be
conservative or operative. Closed injuries are initially treated
with the proximal interphalangeal joint immobilized in extension
for 5 to 6 weeks and should be followed closely by a hand specialist.
Zone IV involves the area over the proximal phalanx. These injuries
have clinical findings similar to zone III injuries. These injuries
are often less problematic because the joint is not involved, and
the tendon at this level is broad and flat.
Zone V involves the area over the metacarpophalangeal joint. Open
injuries to this area should be considered human bites until proven otherwise.
Wounds from human bites should have delayed repair following a course
of broad-spectrum antibiotics to ensure a minimum risk of infection.
This injury typically requires operative washout and admission for
IV antibiotics. Clean wounds can be repaired primarily using mattress
sutures to reapproximate tendon edges.
Zone VI involves the area over the dorsum of the hand. Because
the tendons in this area are so superficial, even minor-appearing lacerations
may be associated with one or more tendon injuries. If the laceration
is proximal to the junctura tendineae, the patient may be able to
extend the involved metacarpophalangeal joint, because weak extensor
forces are transmitted to the junctura from adjacent extensor tendons.
Injuries to zones VI, VII, and VIII typically require operative fixation
with K wires and advanced suture techniques.5
Zone VII involves the area over the wrist. Repair can be difficult
because of the presence of the extensor retinaculum. This thick,
fibrous structure on the dorsum of the wrist contains 12 extensor
tendons and six synovial lined retinacular compartments.
Zone VIII involves the area of the distal forearm. Injuries to this
area require a thorough exploration to identify all injured structures. The
tendons frequently retract into the forearm and must be retrieved and
repaired. As a general principle, lacerations of <25% do
not require repair; 25% to 50% need simple suture
repair, and >50% need specialized repair. After
repairs in zones V through VII, splinting should occur with the
wrist in 15-degree extension, the metacarpophalangeal joint in 15-degree
flexion, and the interphalangeal joint in 15-degree flexion in the
involved and adjacent digit.
Pediatric patients with extensor injuries should be treated similarly
to adults with the same injury. However, greater emphasis should
be placed on hand surgery follow-up within 24 hours to maximize
function and minimize morbidity.6