Flexor Tendon Injuries
Summary
Flexor tendon injuries to the hand are serious injuries requiring prompt diagnosis and surgical repair. The flexor digitorum profundus (FDP) flexes the DIP joint, while flexor digitorum superficialis (FDS) flexes the PIP joint. Injuries are classified by Verdan zones (1-5). Zone 2 — historically called "No Man's Land" — is particularly challenging due to the pulley system and risk of adhesions. Clinical examination involves isolating each tendon (holding other fingers in extension to test FDS; holding PIP straight to test FDP). Surgical repair should occur within 24-72 hours. The standard is a 4-strand core suture with epitendinous repair. Post-operative rehabilitation uses controlled active motion protocols (e.g., Kleinert, Duran) to balance tendon healing and prevent adhesions.
Key Facts
- FDS: Flexes PIP joint; Splits at Camper's chiasm to let FDP through
- FDP: Flexes DIP joint; Passes through FDS split
- Zones (Verdan): Zone 1 = distal to FDS insertion; Zone 2 = "No Man's Land"; Zone 3 = palm; Zone 4 = carpal tunnel; Zone 5 = forearm
- Examination: Hold other fingers in extension to test FDS; Hold PIP extended to test FDP
- Repair timing: Within 24-72 hours ideal
- Suture: 4-strand core + epitendinous
- Rehab: Early active motion protocols essential
Clinical Pearls
"Zone 2 Is No Man's Land": Zone 2 extends from the A1 pulley to the FDS insertion. Both tendons travel through a tight fibro-osseous sheath — repair here risks adhesions and is technically demanding.
"FDS Test — Block the Others": To test FDS, hold the other fingers in full extension (blocks FDP via its shared muscle belly). If FDS is intact, the finger can flex at PIP.
"FDP Test — Block the PIP": To test FDP, hold the PIP joint straight and ask the patient to flex the DIP. If FDP is cut, no DIP flexion.
"4-Strand Core Is Standard": Modern repairs use at least 4-strand core sutures for strength, allowing early active motion without rupture.
"Early Motion Prevents Adhesions But Risks Rupture": Post-op rehabilitation is a balance. Controlled early active motion reduces adhesions but must be supervised to prevent rupture.
Why This Matters Clinically
Flexor tendon injuries can have devastating functional outcomes if misdiagnosed or poorly managed. Prompt referral, skilled repair, and structured rehabilitation are essential.[1,2]
Incidence
| Parameter | Data |
|---|---|
| Incidence | Common hand trauma |
| Mechanism | Laceration; Glass, knife |
| Risk | Young adults; Manual workers |
Anatomy
| Structure | Function |
|---|---|
| FDP | Flexes DIP; Only flexor distal to FDS |
| FDS | Flexes PIP; Splits (Camper's chiasm) to allow FDP through |
| A2 and A4 pulleys | Critical for tendon gliding; Must be preserved at surgery |
| Vincula | Blood supply to tendons in digital sheath |
Verdan Zones
| Zone | Location | Key Features |
|---|---|---|
| 1 | Distal to FDS insertion | FDP only (Jersey finger) |
| 2 | "No Man's Land" | A1 pulley to FDS insertion; Both tendons; Pulleys critical |
| 3 | Palm | Lumbrical origin |
| 4 | Carpal tunnel | Median nerve adjacent |
| 5 | Forearm | Muscle bellies |
The Pulley System
The flexor sheath acts as a retinacular tunnel to keep the tendons close to the bone (preventing "Bowstringing").
- Annular Pulleys (A1-A5): Thick, transverse fibres.
- A2 (Proximal Phalanx) and A4 (Middle Phalanx) are the "Critical Pulleys". They must be preserved to prevent bowstringing.
- A1 (MCPJ): Often cut in trigger finger release or to allow bulkier tendon repairs to glide.
- A3 (PIPJ) and A5 (DIPJ): Smaller pulleys.
- Cruciate Pulleys (C1-C3): Thin, criss-cross fibres. Allow the sheath to collapse/expand during flexion.
Zone 1: "Jersey Finger"
Distal to the FDS insertion. Only the FDP is cut.
- Mechanism: Forced extension of a flexed DIPJ (e.g., grabbing a rugby shirt).
- Classification (Leddy and Packer):
- Type 1: Tendon retracts into palm (Vincula broken). Blood supply compromised. Emergency (<7 days).
- Type 2: Tendon retracts to PIPJ (held by vincula). Good blood supply. Repair <3 weeks.
- Type 3: Bony avulsion caught at A4 pulley.
- Repair: Button repair (pull-out suture) or Suture Anchor into the distal phalanx.
Zone 2: "No Man's Land" (Bunnell)
From A1 pulley to FDS insertion.
- Challenge: Both FDS and FDP lie in tight sheath. Swelling = stuck. Scarring = stuck.
- The Chiasm: The FDS splits into two tails, spirals violently (Camper's Chiasm), and inserts. The FDP passes through this split. Restoring this relationship is difficult.
- Modern Repair:
- Core Suture: 4-strand (e.g., Modified Kessler, Cruciate, Adelaide) increases strength to allow early motion.
- Epitendinous Suture: A fine running suture (6-0 Prolene) around the edge. Smooths the repair sites (gliding) and adds 20% strength.
- Venting: Often we open the A2/A4 pulley laterally ("venting") to allow the swollen repair to pass.
Zone 3: "The Lumbrical Origin"
- Palm. Better prognosis as no tight sheath.
- Caution: The Digital Nerves and Vessels closely accompany the tendons here (Common digital nerve bifurcation).
Zone 4: Carpal Tunnel
- Usually massive trauma (glass/suicide attempt).
- Spaghetti Wrist: Median Ulnar Nerves + 9 Flexor Tendons + Arteries.
- Priority: Stabilise skeleton -> Revascularise -> Nerve Repair -> Tendon Repair.
Zone 5: Forearm
- Musculotendinous junction.
- Easier to repair (good blood supply).
- Risk: Myotendinous junction holds sutures poorly (cheese wire). Use mattress sutures.
History
| Feature | Notes |
|---|---|
| Mechanism | Usually laceration (glass, knife) |
| Loss of flexion | "Finger won't bend" |
| Wound location | Indicates zone |
Signs
| Sign | Notes |
|---|---|
| Resting posture | Injured finger lies in relative extension |
| Loss of PIPJ flexion | FDS injury |
| Loss of DIPJ flexion | FDP injury |
| Wound | May be small; Deep structures can be damaged |
Red Flags
[!CAUTION]
- Active bleeding or haematoma (vascular injury)
- Numbness (digital nerve injury)
- Contaminated wound (infection risk)
- Delay >24 hours (poor outcome)
Tendon Testing
| Tendon | Test |
|---|---|
| FDS | Hold all other fingers in extension → isolates FDS → Ask to flex PIP |
| FDP | Hold affected finger's PIP extended → Ask to flex DIP |
Important Notes
- Test EACH finger individually
- Always assess neurovascular status
- Document wound characteristics
Jersey Finger
| Feature | Notes |
|---|---|
| Mechanism | Forced extension against FDP contraction (grabbing jersey) |
| Finding | Cannot flex DIP; Tendon may retract into palm |
| Zone | Zone 1 |
| Urgency | Early repair before retraction |
| Investigation | Purpose |
|---|---|
| Clinical examination | Primary diagnosis |
| X-ray | Bony avulsion (Zone 1); Foreign body |
| Wound exploration | In theatre; Assess tendon, nerve, vessel |
Management Algorithm
FLEXOR TENDON INJURY MANAGEMENT
↓
┌───────────────────────────────────────────────────────────┐
│ INITIAL ASSESSMENT │
├───────────────────────────────────────────────────────────┤
│ ➤ ABC if major trauma │
│ ➤ Test FDS and FDP (each finger) │
│ ➤ Assess neurovascular status │
│ ➤ X-ray for bony injury / foreign body │
│ ➤ Photograph and document wound │
│ ➤ Tetanus prophylaxis │
│ ➤ Antibiotics if contaminated │
└───────────────────────────────────────────────────────────┘
↓
┌───────────────────────────────────────────────────────────┐
│ REFERRAL │
├───────────────────────────────────────────────────────────┤
│ ➤ Urgent referral to hand surgeon / plastics │
│ ➤ Primary repair within 24-72 hours ideal │
│ ➤ Delayed repair (>2 weeks) has worse outcomes │
└───────────────────────────────────────────────────────────┘
↓
┌───────────────────────────────────────────────────────────┐
│ SURGICAL REPAIR │
├───────────────────────────────────────────────────────────┤
│ ➤ General or regional anaesthesia + tourniquet │
│ ➤ Careful wound extension (preserve A2, A4 pulleys) │
│ ➤ Retrieve tendon ends │
│ ➤ 4-strand core suture (Kessler, cruciate) │
│ ➤ Epitendinous (running) suture │
│ ➤ Repair digital nerves/vessels if injured │
│ │
│ ZONE 1 (FDP avulsion): │
│ ➤ Reinsertion to distal phalanx (button/anchor) │
│ │
│ ZONE 2 (No Man's Land): │
│ ➤ Most technically demanding │
│ ➤ Preserve A2/A4 pulleys │
│ ➤ May need pulley reconstruction │
└───────────────────────────────────────────────────────────┘
↓
┌───────────────────────────────────────────────────────────┐
│ REHABILITATION │
├───────────────────────────────────────────────────────────┤
│ ➤ Hand therapy referral essential │
│ ➤ Early active motion protocols (Kleinert / Duran) │
│ ➤ Dorsal blocking splint │
│ ➤ Balance: Prevent adhesions vs avoid rupture │
│ ➤ 6-12 weeks protected motion │
│ ➤ Full activity at 12 weeks │
└───────────────────────────────────────────────────────────┘
A good repair with bad rehab will fail. (Rupture or Adhesion). The tendon has roughly no strength for the first 3 weeks. Strength starts at week 3 and maximizes at week 12.
1. Kleinert Protocol (Active Ext/Passive Flex)
- Mechanism: Uses rubber bands glued to the fingernails, attached to the wrist band.
- Action: Rubber bands pull fingers into flexion (Passive). Patient actively extends against the bands (Active Extension).
- Pros: Easy to understand.
- Cons: High flexion contracture rate (PIP). Rarely used now.
2. Duran Protocol (Passive Flex/Passive Ext)
- Mechanism: Patient uses their other hand to passively flex the fingers.
- Action: Controlled passive motion.
- Pros: Safe.
- Cons: Doesn't create much tendon excursion (gliding). Risk of adhesions.
3. Belfast / Sheffield Protocol (Early Active Motion) - Standard of Care
- Requirement: Needs a strong repair (4-strand).
- Action: Patient actively flexes the finger gently (half-fist) within the splint.
- Pros: Best tendon gliding. Least adhesions. Strongest final tendon.
- Cons: Higher risk of rupture if patient is non-compliant/forceful. "Place and Hold" exercises used.
4. Manchester Short Splint
- Innovation: Allows wrist extension (instead of blocking it).
- Theory: Wrist extension reduces the work of flexion (tenodesis effect).
- Use: Becoming more popular for cooperative patients.
1. Rupture (The Disaster)
- Incidence: 3-5%.
- Cause: Patient using hand too early, or catching it on a door handle.
- Timing: Week 2-3 is the danger zone (Softening phase of healing).
- Management: Urgent re-exploration. If tendon ends are shredded, may need a Tensor Fascia Lata (TFL) graft or 2-stage reconstruction (Hunter Rod).
2. Adhesions (The Stiffness)
- Incidence: Common in Zone 2.
- Mechanism: Tendon sticks to the sheath.
- Management:
- Therapy: Aggressive physio.
- Tenolysis: Surgical release of scar tissue. (Wait at least 6 months post-injury).
- Warning: Tenolysis carries a huge risk of rupture (devascularises tendon).
3. Bowstringing
- Cause: Destruction/Cutting of A2/A4 pulleys.
- Effect: Tendon pulls away from bone like a bow string. Loss of mechanical advantage. Finger stays flexed.
- Management: Pulley reconstruction (using a tendon graft loop).
4. Quadriga Effect
- Cause: FDP tendons of Middle, Ring, and Little share a common muscle belly. If one FDP is advanced too much (shortened), it tethers the muscle.
- Sign: The patient cannot fully flex the other fingers because the muscle hits the "short leash" of the repaired finger.
5. Lumbrical Plus Finger
- Cause: FDP graft is too long (lax).
- Mechanism: When patient tries to flex, the force goes through the lumbrical (which originates on the FDP). The lumbrical pulls on the extensor hood.
- Sign: Paradoxical extension of the PIPJ when attempting flexion.
If the A2 or A4 pulleys are destroyed, they must be rebuilt to prevent bowstringing.
- Technique: Loop of tendon graft (Palmaris Longus) wrapped around the phalanx bone.
- Or use a slip of the FDS tendon (if FDS is being sacrificed).
Key Studies
- Strickland et al.: Demonstrated 4-strand repairs are >50% stronger than 2-strand.
- Silfverskiold: Proved that epitendinous sutures add 20% strength and reduce gapping.
- Gelberman: Showed that early motion stimulates intrinsic tendon healing (pumping fluid).---
What is a flexor tendon injury?
The flexor tendons bend your fingers. If a tendon is cut (usually by something sharp like glass or a knife), you can't bend that finger properly.
What are the symptoms?
- Cannot bend the finger tip (FDP injury)
- Cannot bend the middle joint (FDS injury)
- A cut or wound on the finger or palm
How is it treated?
- Surgery to stitch the tendon back together (usually within a few days)
- Hand therapy to help the tendon heal and move properly
- A splint to protect the repair
How long does recovery take?
Full recovery takes 3-6 months. You'll need to do exercises regularly. Too little movement causes stiffness; too much risks breaking the repair.
- Tang JB. Recent evolution in flexor tendon surgery. J Hand Surg Eur Vol. 2018;43(5):469-489. PMID: 29673302
High-Yield Exam Topics
| Topic | Key Points |
|---|---|
| Zone 2 | "No Man's Land"; Both tendons; Pulley system |
| FDS test | Hold other fingers in extension |
| FDP test | Hold PIP extended; Flex DIP |
| Repair | 4-strand core + epitendinous |
| Rehab | Early active motion; Dorsal blocking splint |
| Jersey finger | Zone 1 FDP avulsion; Urgent repair |
Sample Viva Question
Q: A patient has a laceration to the palm and cannot flex the DIP of the index finger. How would you assess and manage?
Model Answer: This suggests FDP injury. Assessment: Test FDP by holding PIP extended — patient cannot flex DIP. Test FDS by holding other fingers extended — may or may not be intact. Check sensation (digital nerve) and capillary refill (vessels). X-ray to exclude bony injury or foreign body.
Management: Urgent referral to hand surgery for primary repair within 24-72 hours. Repair involves 4-strand core suture + epitendinous repair, with preservation of A2/A4 pulleys if Zone 2. Post-op: Dorsal blocking splint and early active motion protocol (Kleinert/Duran) with hand therapy. Complications include adhesions, stiffness, and rupture.
Last Reviewed: 2025-12-24 | MedVellum Editorial Team