Orthopaedic Surgery - Flexor Tendon Laceration

Basics

Flexor tendon lacerations may occur anywhere along the volar surface of the fingers, palm, wrist, or forearm.

They are commonly described according to the anatomic zone of injury because tendon anatomy, repair technique, rehabilitation, and prognosis vary substantially by location.

Flexor Tendon Zones

For the fingers, flexor tendon injuries are traditionally divided into Zones I through V.

The thumb has a corresponding three-zone classification.

Zone I

Zone I extends from the fingertip proximally to the proximal interphalangeal (PIP) flexion crease.

In this region, the flexor digitorum profundus (FDP) is the principal flexor tendon because the flexor digitorum superficialis (FDS) inserts more proximally.

Zone II

Zone II extends from the PIP flexion crease proximally to the distal palmar transverse crease near the A1 pulley.

Both the FDS and FDP tendons travel together within the flexor sheath in this region.

Zone II: “No-Man’s Land”

Zone II was historically called “no-man’s land” because repairs in this region were associated with a particularly high risk of postoperative adhesions, scarring, and poor tendon gliding.

The anatomy is complex because both the superficial and deep flexor tendons pass through a confined fibro-osseous pulley system.

Modern repair techniques and early mobilization protocols have substantially improved outcomes, but Zone II injuries remain technically demanding.

Zone III

Zone III extends from the distal palmar transverse crease proximally to the distal wrist flexion crease or transverse carpal ligament.

Zone IV

Zone IV corresponds to the carpal tunnel.

Multiple flexor tendons and the median nerve are closely packed within this confined space, so associated injuries may be substantial.

Zone V

Zone V is located proximal to the carpal tunnel, extending into the distal forearm.

Lacerations in this region may involve multiple tendons together with the median or ulnar nerves and major vessels.

Classification

Flexor tendon injuries are described according to both the specific tendon injured and the zone of injury.

They may involve the FDS, FDP, flexor pollicis longus, or combinations of these structures.

Function

Each flexor tendon contributes to finger strength, coordinated motion, and independent digital control.

The FDS primarily flexes the PIP joint, whereas the FDP flexes the DIP joint and also contributes to flexion of more proximal joints.

Epidemiology

Approximately 25% of flexor tendon lacerations occur in the workplace.

Males are affected substantially more often than females, with reported male-to-female ratios of approximately 3–6:1.

Risk Factors

The principal risk factor is occupational or recreational exposure to sharp objects or machinery.

Etiology

Most injuries result from a sharp penetrating mechanism such as a knife, broken glass, sheet metal, or other cutting object.

Crush or high-energy injuries may produce more extensive tendon and soft-tissue damage and generally have a worse prognosis.

Associated Injuries

Flexor tendon lacerations may occur with injuries to adjacent structures.

Digital Nerve Injury

Digital nerve laceration accompanies approximately one-quarter of flexor tendon injuries in some series.

Digital Artery Injury

Digital arteries may also be disrupted, potentially compromising perfusion of the involved finger.

Pulley Injury

The annular or cruciate pulley system may be damaged, particularly in deeper lacerations.

Pulley loss can impair tendon gliding and produce bowstringing.

Joint Injury

A laceration may penetrate the flexor tendon sheath or enter the interphalangeal or metacarpophalangeal joint, producing a traumatic arthrotomy.

Fracture

Associated phalangeal or metacarpal fractures may occur, particularly with high-energy mechanisms.

Diagnosis

Signs and Symptoms

The typical injury is a laceration over the palmar aspect of the finger, hand, or wrist.

Loss of tendon continuity alters the resting posture of the finger.

Change in Finger Posture

The injured finger may rest in greater extension than the adjacent digits because normal flexor tendon tension has been lost.

Comparison with the opposite hand and neighboring fingers is useful.

Loss of Active Flexion

The patient may be unable to actively flex the joint controlled by the injured tendon.

The exact deficit depends on whether the FDS, FDP, or both have been divided.

Loss of Tenodesis

Normally, passive wrist extension causes the fingers to flex because of the tenodesis effect.

Loss of this automatic finger flexion may indicate flexor tendon disruption.

Wrist Squeeze Test

In children or uncooperative patients, squeezing the forearm or flexor muscle mass can produce passive finger flexion when the tendons are intact.

Failure of the expected motion raises concern for tendon injury.

Physical Examination

A careful examination should be completed before local anesthesia whenever possible so that motor, sensory, and vascular function can be accurately documented.

Flexor Digitorum Profundus Testing

To test the FDP, the examiner stabilizes the PIP joint and other proximal joints in extension while asking the patient to actively flex the DIP joint.

Ability to flex the DIP indicates an intact FDP tendon.

Failure suggests FDP disruption or dysfunction.

Flexor Digitorum Superficialis Testing

To isolate the FDS, the examiner holds the other fingers in full extension and asks the patient to flex the finger being tested.

With the other digits immobilized, the tested finger should primarily flex at the PIP joint.

Failure to flex the PIP suggests FDS injury, although anatomic variations must be considered.

Strength Testing

Each finger should be assessed individually for flexion strength.

Weakness may indicate a partial tendon injury even when active motion remains present.

Tenodesis Examination

The wrist is passively moved through flexion and extension while the examiner observes the normal cascade of the fingers.

Abnormal movement suggests disruption of the flexor mechanism.

Vascular Examination

Perfusion must be assessed carefully.

Evaluation may include capillary refill, skin color, temperature, pulse oximetry, and Doppler assessment.

A poorly perfused or dysvascular digit is a surgical emergency.

Sensory Examination

Adjacent digital nerves should be tested before anesthetic injection.

Light touch and two-point discrimination are particularly useful for identifying digital nerve injury.

Wound Exploration

The wound should be carefully evaluated for evidence of partial or complete tendon injury, pulley disruption, foreign material, fracture, and joint penetration.

Exploration should be performed in a controlled fashion to avoid additional damage.

Imaging

Plain Radiographs

Radiographs should be obtained when there is concern for fracture, dislocation, bony avulsion, or retained radiopaque foreign body.

Ultrasound

Ultrasound can identify tendon discontinuity and may be useful when the physical examination is uncertain.

MRI

MRI can also demonstrate flexor tendon injury but is rarely necessary when the history and examination clearly establish the diagnosis.

Differential Diagnosis

Phalangeal Fracture-Dislocation

A fracture or dislocation involving the phalanx or interphalangeal joint can produce pain and loss of active flexion that resembles tendon injury.

Tendon Avulsion

A tendon may be avulsed from its insertion without an open laceration.

An important example is FDP avulsion from the distal phalanx.

Tendon Rupture

Closed tendon rupture can also result in loss of flexion.

Pulley Rupture

Pulley disruption may cause pain and abnormal tendon mechanics while preserving some active flexion.

Initial Treatment

Vascular Assessment

The first priority is to determine whether the finger and hand are adequately perfused.

A dysvascular digit or hand requires emergent operative evaluation.

Severe Associated Injury

Open fractures, major tissue loss, vascular injury, or gross contamination also require urgent surgical management.

Tetanus Prophylaxis

Tetanus immunization status should be reviewed and prophylaxis administered when indicated.

Wound Irrigation

The wound should be thoroughly irrigated with normal saline and gross contamination removed.

Antibiotics

Antibiotic administration depends on contamination, mechanism of injury, open fracture, bite exposure, and other risk factors.

A perioperative intravenous dose may be given for selected injuries according to local protocols.

Elevation and Splinting

The hand should be elevated and placed in a protective splint until definitive surgical assessment is completed.

Specialist Consultation

Early consultation with a hand surgeon or orthopaedic surgeon experienced in tendon repair is appropriate.

Factors Affecting Management

Treatment planning should consider hand dominance, occupation, time since injury, injury zone, tendon involvement, associated neurovascular injury, contamination, and patient comorbidities.

Physical Therapy and Hand Therapy

Postoperative hand therapy is an essential part of treatment.

The goal is to protect the repair while restoring tendon glide and preventing stiffness and adhesions.

Timing

Passive motion is commonly initiated within approximately 3–5 days after surgery, depending on the strength of the repair and the rehabilitation protocol.

Early Active Motion

Early active-motion protocols are increasingly used when a sufficiently strong repair has been achieved and the patient can follow restrictions reliably.

Immobilization

Children, cognitively impaired patients, or adults who cannot comply with movement restrictions may require more prolonged immobilization to protect the repair.

Surgery

Timing of Repair

Primary repair generally provides the best functional outcome.

Repair is preferably performed during the acute period, often within approximately 7–10 days of injury.

Delayed primary repair may still be possible, but direct repair becomes more difficult as tendon retraction, scarring, and muscle shortening develop.

Chronic Injuries

Injuries older than approximately 3–4 weeks often cannot be treated with straightforward primary repair and may require tendon grafting, staged reconstruction, or other reconstructive techniques.

Anesthesia

Repair may be performed under general anesthesia, regional anesthesia, or wide-awake local anesthesia without tourniquet (WALANT), depending on injury pattern and surgeon preference.

Flexor Tendon Sheath Injury

When the flexor tendon sheath is also disrupted, timely repair is desirable because excessive scarring can impair tendon gliding and worsen the functional result.

Surgical Exploration

The wound is extended as necessary to identify the full extent of injury.

The surgeon evaluates the tendon, pulley system, nerves, vessels, joints, and bone.

Minimizing Tissue Trauma

Meticulous technique is important because additional surgical trauma promotes scar formation and adhesions.

Sequence of Repair

After all injuries have been identified, flexor tendon repair is generally completed before nerve and vascular repair.

Tendon Repair Technique

A variety of core suture patterns can be used.

The repair must provide enough strength for early motion while remaining sufficiently smooth and compact to glide through the tendon sheath and pulley system.

Core Sutures

Repair strength generally increases with the number of core suture strands crossing the repair site.

Modern repairs commonly use at least four core strands, with some techniques using six or more.

Epitendinous Suture

An additional circumferential epitendinous suture is commonly placed to improve repair strength and smooth the tendon surface.

Zone II Repair

Zone II injuries require particular attention because both the FDS and FDP pass through the pulley system.

FDP

The FDP is repaired to restore DIP flexion and overall digital function.

FDS

Depending on tendon damage, available space within the sheath, and intraoperative tendon gliding, the surgeon may repair both FDS slips, one slip, or neither, balancing strength against the risk of excessive bulk and adhesions.

Postoperative Splinting

A dorsal blocking splint is typically applied after repair.

The wrist is generally maintained in neutral to slight flexion, the MCP joints are flexed to approximately 70°, and the interphalangeal joints are kept near extension.

Hand Therapy

The splint is removed or adjusted under controlled conditions during supervised hand therapy, which commonly begins within 3–5 days.

The exact rehabilitation protocol depends on the injury zone and strength of repair.

Follow-Up

Prognosis

Outcome depends strongly on the location, mechanism, severity, and associated injuries.

Clean sharp lacerations generally have a better prognosis than crush, avulsion, contaminated, or high-energy injuries.

Zone II Prognosis

Zone II injuries remain particularly prone to postoperative stiffness and adhesion formation because of the complex tendon-pulley anatomy.

Complications

Loss of Motion

Reduced range of motion may result from scar formation, tendon adhesions, joint stiffness, or inadequate rehabilitation.

Adhesions

Adhesions can tether the repaired tendon to surrounding tissue and limit active flexion despite preserved passive motion.

Loss of Strength

Persistent weakness may occur even after successful healing.

Infection

Infection may complicate contaminated wounds, open fractures, joint injuries, or tendon sheath injuries.

Tendon Rerupture

The repair may rupture if excessive force is applied before adequate healing occurs.

Rerupture may require repeat repair or reconstruction.

Delayed Reconstruction

Severe scarring, chronic tendon loss, failed primary repair, or rerupture may necessitate tendon grafting, staged tendon reconstruction, or tendon transfer.

Patient Monitoring

Follow-up should closely assess wound healing, vascular status, tendon integrity, active and passive range of motion, scar formation, adhesion development, strength, and compliance with splinting and therapy.

Early recognition of excessive stiffness or repair failure allows rehabilitation or surgical planning to be modified before permanent functional loss develops.