Flexor Tendon Injuries

Andrew Campbell

Hisham M. Awan

INTRODUCTION

Anatomy
- Flexor tendons
  - Flexor carpi ulnaris
  - Flexor carpi radialis (FCR)
  - Flexor pollicis longus (FPL)
  - Flexor digitorum superficialis (FDS)
  - Flexor digitorum profundus (FDP)
- Important anatomic relationships
  - FCR is the closest tendon to the median nerve in the forearm.
  - There are nine tendons (FDS ×4, FDP ×4, and FPL) and one nerve (median nerve) in the carpal tunnel.
  - FPL is the most radial tendon in the carpal tunnel.
  - In the forearm, wrist, and hand, the FDS tendons lie superficial to FDP. At the level of the metacarpophalangeal (MCP) joints, FDS splits and FDP becomes superficial. FDS slips rejoin at Camper Chiasm and insert on the middle phalanx. FDP inserts on the distal phalanx (Figure 34.1).
- Tendon anatomy
  - Structure
    - Composed of bundles of collagen fascicles surrounded by epitenon, a surface that is crucial for gliding
  - Nutritional supply
    - Arterial supply—vinculae from digital arteries
    - Synovial diffusion
  - Pulley system
    - Prevents bowstringing of flexor tendon
    - A2 and A4 are most important in fingers.
    - Oblique pulley is most important in the thumb.
Mechanism of injury
- Most commonly results from penetrating trauma or lacerations to the palmar aspect of the hand or volar wrist/forearm
- Jersey finger (see Chapter 35)—avulsion of FDP insertion on the distal phalanx due to forceful distal interphalangeal (DIP) joint extension during FDP contraction

FIGURE 34.1 Relationship of flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDp) on the palmar aspect of a finger. CC, Camper’s Chiasm; MC, metacarpal; P1, proximal phalanx; P2, middle phalanx; P3, distal phalanx.

EVALUATION

History
- Penetrating trauma or laceration to palmar hand or volar wrist/forearm
- Weak or absent flexion of digit
Physical examination
- Inspection
  - Assess wounds for foreign bodies, identify injured structures, evaluate for evidence of arthrotomy.
  - Assess digital cascade.
    - Digit with a flexor tendon injury is held extended at rest relative to other fingers.
    - Persistent extension at proximal interphalangeal (PIP) or DIP joints during passive wrist extension is indicative of flexor tendon injury.
      - ▲ Passive wrist extension normally causes flexion at MCP, PIP, and DIP joints (tenodesis effect).
- Strength/range of motion
  - Loss of active flexion of digit
  - Test FDS and FDP for each finger (Figure 34.2)
- Neurovascular examination
  - Given proximity of nerves and vessels to finger flexor tendons, concomitant neurovascular injuries are common.
  - Document a thorough examination at the time of injury.
    
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