April 11, 2024

Flexor Tendon injury is common when the injury occurs in the volar aspect of the hand and forearm which is mostly associated with neurovascular injury.

Flexor Tendon Anatomy
Flexor Tendon Anatomy

Pulley anatomy

Anatomy of flexor tendon pulley
Anatomy of flexor tendon pulley

A1, A3, and A5 lie in the volar plate of MP, PIP, and DIP joint

Most important annular pulleys

A2: Proximal Portion of Proximal Phalanx

A4: Middle 3rd of middle phalanx

If all pulleys are divided keeping A2 and A4 intact flexion can be achieved which will permit the finger to touch the palm but if one of the 2 pulleys is not intact, even on maximum clenching the fist, it will remain away from the palm creating tip to palm distance.

In thumb: 2 annular pulleys separated by an oblique pulley

A2 Pulley: Prevent Bowstring

A4 Pulley: Reducing the angle of attack

Primary repair is possible: Only if care has been taken to deliver the tendon through an L-shaped incision across the pulley


The damaged pulley will be reconstructed using

  1. Extensor retinaculum sheath
  2. Palmaris longus tendon graft

Zones of Flexor tendon(Verdan)

Zones of flexor tendon
Zone 1Insertion of FDS tendon in a terminal phalanx to middle phalanx (Only 1 tendon)
Zone 2Zones of pulley: Insertion of FDS to the proximal edge of pulley over MCP joint
Zone 3From the proximal edge of the pulley to the distal edge of the carpal tunnel
Zone 4Within carpal tunnel
Zone 5Proximal to carpal tunnel

Observing finger flexion cascades

  • Allowing the wrist to drop free into the extension
  • Passive tenodesis effect of long flexors that brings all 4 fingers into a smooth flexion cascade
  • Increment of flexion from IF to LF + Flexion of IP joint of the thumb

If injured

Jersey finger: If suspected avulsion with no history of cut injury

Other Possible injuries

Cut injuries at both tendons in Zone 2: Associated with neurovascular injury

Zone 3: Digital nerve and superficial arch injuries

Zone 4: Median nerve injury

At FCU cut: Ulnar neurovascular injury

No man’s land

  • Introduced by Bunnel’s
  • Zone 2: Due to poor results of primary repair
  • Limited Space: Fibrocartilagenous tunnel containing 2 tendons multiple pulleys and minimal areolar tissue to allow gliding despite best of repairs
  • With small swelling fibrosis of epi-tendinous structures
  • No good outcome

So, Proper exposure using [midlateral incision/ Brunner’s incision]

Minimal tissue handling

Avoid revascularization to tendons

Avoid bunching

Strong enough repair for early mobilization

Maintaining or reconstructing pulley system

FPL Injury

Zone I injuries: Distal to IP Joint

Zone II injuries: Between IP and MCP joints

Zone III injuries: Deep to thenar muscles

Bruner’s incision

  • Extensile zig-zag incision
    • Keeps away scar site from repair
    • Do not produce function limitation wound contracture
Primary repair< 24 hr
Delayed primary repair24 hr – 10 days
Secondary repair> 2 weeks
Duration of repair

For partial injury

Different types of partial tears

4 Strand Techniques

More the number of suture filaments cross the repair site the more is the strength of the initial repair (time zero)

It is believed that 14.7 N Strength is required to flex the finger against moderate resistance. So, 3-5 times (around 45 N) strength is required after repair from [ time-zero]

More 4-core easily surpass 45 N + Epitendinous technique add (10-50%) So,

2 strand: weak

8 Strand: Too bulky

Zone I: Tendon injury

Mostly blunt injury

Associated with avulsion fractures of the terminal phalanx

Jersey’s finger

3 Types (Leddy and Packer)

Type I

  • No bony avulsion
  • Tendon retracts in palm
  • Vincula disrupted and health collapse in few days

Type II

  • Usually no bony avulsion or a small amount of avulsion fragment
  • Tendon found at A3
  • Vinculum longus- Intact

Type III

  • Large bony fragment avulsion
  • Rotated to face volar
  • Stock in A4 pulley

Treatment of Zone 1 tendon injury

Type I

  • Usually, repair as tendon degeneration and myostatic contractures are highly likely
  • Delayed presentation (>21 days) required DIP fusion, FDS reconstruction around FDS (not through charisma) or excision of FDP

Type II

  • Tendon retracts to and repaired to bone

Type III

  • ORIF with pull out sutures or sutures anchor

Superficialis finger

For small distal stump in cut FDP tendon in zone 1

  • The proximal stump is sutured to the middle phalanx
  • The proximal end of the distal stump is sutured to the neck of the middle phalanx (to prevent hyperextension deformity of DIP)

This method is used for non-reconstructable pulley in zone 2 with a bowstring of FDP

Quadriga Effect

Quadriga Effect of flexor tendon
Quadriga Effect of flexor tendon

Syndrome explained by Verdan (1960)

  • The Tendon of FDS arises from a common belly, it has a mass action on all 4 fingers
  • If one of the 4 tendons is sutured too tightly or shortened too much, the other tendon becomes relatively longer; Rendering them ineffective
  • And, muscle belly can contract effectively only if excursion of all the tendons is normal
  • If one of the tendons is fixed or its amplitude altered then a proportional effect will be evident in all the other slips ( reduced flexion)= Often producing forearm pain
  • Pseudoquadriga is produced by fixed contracture of IP joints

1 cm advancement has been found clinically to produce a quadriga effect

Lumbrical Plus finger

Paradoxical extension at IP joint (action of lumbricals) on attempted flexion

Seen in

  1. Tendon graft is either too long
  2. Sutured in laxed tension
  3. Has ruptured in attempted reconstruction for zone 2 are sometimes repaired using a tendon graft

The force in these cases is transmitted through the lumbrical muscles tendon unit instead of the flexor tendon and hence paradoxical movement is produced.

( It is important to demonstrate full passive flexion before making the diagnosis of a lumbrical plus finger)

Post operative

Rehabilitation is done using Modified Duran’s Protocol or Kleinert methods.

Kleinert protocol is a dynamic splinting, allowing for active digit extension and passive digit flexion.

Duran protocol, on other hand, used to perform passive digital flexion exercises

However, both methods will avoid active flexion for up to 6 weeks.