Zone 2 (No Man's Land) | 4-Strand Repair | Early Motion
Flexor Tendon Zones
Critical Must-Knows
- Zone 2 = 'No Man's Land' - both tendons in fibrous sheath
- A2 and A4 pulleys are critical (prevent bowstringing)
- 4-strand core suture minimum for early active motion
- Epitendinous suture adds 10-20% strength, improves gliding
- Early active motion reduces adhesions, better outcomes
Clinical Pearls
- "FDP alone if lacerated distal to FDS insertion
- "Core suture 2mm from cut end = optimal strength
- "Early motion: controlled active flexion, passive extension
- "Rupture peak at 7-10 days (weakest point in healing)
Clinical Imaging
Imaging Gallery
Critical Flexor Tendon Exam Points
Zone 2 Challenge
'No Man's Land': Both FDP and FDS in tight fibro-osseous sheath. Limited space, high adhesion risk. Historically poor outcomes, now improved with modern techniques and early motion.
Critical Pulleys
A2 pulley (proximal phalanx) and A4 pulley (middle phalanx) are critical for mechanical advantage. Preserve or reconstruct to prevent bowstringing.
Repair Principles
4-strand core suture minimum. More strands = stronger repair allowing earlier motion. Epitendinous suture adds strength and improves gliding. Suture 2mm from edge for optimal strength.
Rehabilitation
Early active motion protocols reduce adhesions. Controlled active flexion, full passive extension. Synergistic exercises. 6 weeks protected motion.
1-5 Fingers to ForearmFlexor Zones
| 1 | Distal to FDS insertion FDP only (Jersey finger) |
| 2 | FDS insertion to A1 No Man's Land (both tendons) |
| 3 | Palm (lumbrical origin) NV bundle at risk |
| 4 | Carpal tunnel Median nerve in tunnel |
| 5 | Forearm Muscle repairs |
| 1 | Distal to FDS insertion FDP only (Jersey finger) | 4 | Carpal tunnel Median nerve in tunnel |
| 2 | FDS insertion to A1 No Man's Land (both tendons) | 5 | Forearm Muscle repairs |
| 3 | Palm (lumbrical origin) NV bundle at risk |
Hook:Zone 1 is finger tip, Zone 5 is forearm - numbers go proximal!
A2-A4Critical Pulleys
| A2 | Over proximal phalanx Most critical pulley |
| A4 | Over middle phalanx Second most critical |
| A2 | Over proximal phalanx Most critical pulley |
| A4 | Over middle phalanx Second most critical |
Hook:A2 and A4 are even numbers = critical pulleys. A1, A3, A5 are odd = can sacrifice.
STRONGRepair Checklist
| S | Strands (4-6 core) Multi-strand resists gapping, allows early motion |
| T | Tension the core Slightly snug to prevent gap at repair site |
| R | Repair both if possible FDP and FDS in zone II; excise one FDS slip only if crowded |
| O | Open (vent) pulleys Judicious A2/A4 venting to allow gliding |
| N | Nerve & vessel check Digital NV bundles lie adjacent in zones II-III |
| G | Glide test Intraoperative extension-flexion (often WALANT) before closure |
| S | Strands (4-6 core) Multi-strand resists gapping, allows early motion | R | Repair both if possible FDP and FDS in zone II; excise one FDS slip only if crowded | N | Nerve & vessel check Digital NV bundles lie adjacent in zones II-III |
| T | Tension the core Slightly snug to prevent gap at repair site | O | Open (vent) pulleys Judicious A2/A4 venting to allow gliding | G | Glide test Intraoperative extension-flexion (often WALANT) before closure |
Hook:A STRONG repair earns an early-motion programme; a weak one earns a splint.
Overview & Epidemiology
Flexor tendon injuries are common hand-trauma injuries, typically in young working-age men from glass, knives and occupational sharp objects. Zone II is the most frequently injured and most studied zone. Understanding the zone system, repair biomechanics, and rehabilitation principles is essential for optimal outcomes — a digit that does not flex represents a time-sensitive surgical problem.
Pathophysiology & Anatomy
Tendon healing occurs by combined intrinsic (tenocyte-mediated, within the tendon) and extrinsic (from the sheath/surrounding tissue) pathways. Extrinsic healing forms adhesions that restrict gliding — the central biological problem in zone II. Repairs are weakest at roughly 7-10 days as collagen remodels, the period of peak rupture risk. Controlled tendon excursion biases healing toward the intrinsic pathway, which underpins early-motion rehabilitation.
Anatomy
Flexor Digitorum Profundus (FDP): Inserts on distal phalanx base. Flexes DIP joint.
Flexor Digitorum Superficialis (FDS): Splits around FDP (Camper's chiasm), inserts on middle phalanx. Flexes PIP joint.
Pulley System: A1-A5 (annular) and C1-C3 (cruciate) pulleys. A2 and A4 are critical for mechanical advantage. Others can be sacrificed if necessary.
Zone Classification
Zone 2 (A1 pulley to FDS insertion): The "No Man's Land." Both FDP and FDS tendons lie within the tight fibro-osseous sheath. Historically poor outcomes due to adhesions. Modern repair techniques and early motion have improved results.
Repair Principles: Repair both tendons if possible. Some surgeons debride one slip of FDS if space is tight. Protect A2 and A4 pulleys.
Clinical Presentation
Clinical Examination
FDP Test: Hold PIP extended, ask patient to flex DIP. Tests FDP independently.
FDS Test: Hold other fingers extended (blocking FDP contribution), ask to flex PIP. Tests FDS independently.
Cascading Posture: Normal resting hand has fingers in cascade of increasing flexion. Loss of cascade suggests laceration.
Wound Examination: Location indicates zone. Explore wound if tendon injury suspected (after tourniquet, in OR).
Investigations
Flexor tendon laceration is largely a clinical and operative diagnosis — imaging is adjunctive.
- Plain radiographs: Mandatory after any sharp injury to exclude retained glass/foreign body, fracture or a bony avulsion fleck (suggests FDP avulsion / Jersey finger).
- Ultrasound: Useful for closed or doubtful injuries — confirms tendon continuity, identifies the level of a retracted proximal stump, and is operator-dependent.
- MRI: Reserved for complex, chronic or reconstructive planning (gap, sheath scarring, pulley integrity).
- Intraoperative assessment remains the reference standard.
Tendon Evaluation
Look for:
- Complete vs partial laceration (greater than 60% width = functionally complete)
- Level of laceration vs skin wound (tendons may have retracted with the digit position at injury)
- Associated injuries (digital nerves, vessels, bone)
Management
Principles:
- Minimum 4-strand repair for early active motion (more strands = stronger)
- Suture placed 2mm from cut end for optimal strength
- Locking suture configuration adds strength
- 3-0 or 4-0 braided non-absorbable suture
Common Techniques: Modified Kessler, Strickland, Savage, cruciate.
Strength: 2-strand ≈ 20N, 4-strand ≈ 40N, 6-strand ≈ 60N. Early active motion requires ~40N.
Rehabilitation
Principle: Controlled early motion reduces adhesion formation and improves final range of motion. Requires strong repair (4+ strands).
Protocol (Typical):
- Dorsal blocking splint (wrist flexed 20-30°, MCP 50-70°, IP extended)
- Active flexion, full passive extension
- 4-6 times daily exercises
- Progress to place-and-hold, then active motion
- 6 weeks protected, then progressive strengthening
Outcomes: Superior to immobilization with reduced adhesions.
Complications
Adhesions: Most common problem. Limit gliding. May require tenolysis.
Rupture: Peak at 7-10 days (weakest point in healing). Requires re-repair.
Stiffness: From adhesions or joint involvement. Address with therapy/tenolysis.
Bowstringing: If critical pulleys (A2, A4) not preserved or over-vented. Reduces mechanical advantage and excursion.
Evidence Base
- Cadaver zone II in situ model (12 hands), each specimen its own control
- Ultimate tensile strength: 2-strand 33.9N, 4-strand 43.0N, 6-strand 78.7N
- 2-strand gapped 2.75mm after 1000 cycles vs 0.30mm (4-strand) and 0.31mm (6-strand)
- Gliding resistance increase after repair was small and not significant
- 72 cadaver FDP tendons, 4-strand modified Kessler, progressive cyclic loading
- All constructs exceeded the ~27N threshold for early active range of motion
- 3-0 suture failed by pullout in 63.5% (looped) and 38.9% (single-strand) of repairs
- 4-0 suture pulled out in only 11.1% (looped) and 0% (single-strand)
- Core suture purchase no shorter than 0.7-1cm in each tendon end, well tensioned
- A2 may be partially vented (incision under 1.5-2cm); A4 may be vented entirely
- Judicious venting did not cause loss of hand function or bowstringing
- Intraoperative extension-flexion test (often WALANT) confirms gliding before closure
- 60 zone II FDP repairs with tensioned 4- or 6-strand core and only 3-4 peripheral stitches
- Pulleys vented as needed; early active flexion started postoperatively
- No repairs ruptured during follow-up of 8-33 months
- 52/60 (87%) fingers achieved good or excellent function by Tang criteria
- Systematic review/meta-analysis: 7 studies, 569 zone II digits
- Early active motion gave greater total active motion than early passive motion
- Higher rupture risk when active flexion-extension was used with a 2-strand repair
- 2-strand technique judged insufficient for active flexion-extension protocols
- Retrospective cohort, 86 fingers, zone I/II primary flexor repair
- Good/excellent 12-week ROM in 56% (WALANT) vs 31% (traditional) — not statistically significant
- Overall rupture rate 11.6%, tenolysis 3.5%, reoperation 9.3%
- Small sample and poor follow-up (41%) limit strength of conclusions
Differential Diagnosis & Mimics
A digit that will not flex is not always a tendon laceration. Distinguishing causes changes the operation, the timing and the consent.
Why a Finger Will Not Flex — Distinguishing the Causes
| Entity | History / mechanism | Examination clue | Key discriminator | Action |
|---|---|---|---|---|
| Complete flexor laceration | Sharp cut (glass, knife), open wound | No active flexion of relevant joint; loss of cascade | Wound over flexor surface; tendon ends visible/retracted | Surgical exploration and repair |
| Partial flexor laceration | Sharp cut, weak/painful flexion | Flexion present but weak or triggering | Greater than 60% width = functionally complete | Repair if over 60%; otherwise trim/observe |
| FDP avulsion (Jersey finger) | Forced extension of flexed DIP (rugby/jersey grab) | No active DIP flexion, often no skin wound | Closed injury; Leddy-Packer type; possible bony fleck on X-ray | Urgent reinsertion (type I/II earliest) |
| Trigger finger / stenosing tenosynovitis | Atraumatic, gradual catching/locking | Palpable A1 nodule, painful clicking | No wound; intermittent locking not fixed loss | Splint/steroid; A1 release if refractory |
| Nerve injury (median/ulnar) | Laceration proximal to muscle, or compression | Motor loss with sensory deficit in nerve territory | Tendon intact on exploration; sensory map abnormal | Nerve repair; treat cause |
| Fixed joint contracture / dislocation | Old injury, Dupuytren, prior trauma | Passive AND active motion both lost | Tendon glides but joint will not move passively | Address joint, not tendon |
Controversies & Areas of Uncertainty
Flexor tendon surgery is one of the most opinion-driven areas in hand surgery; examiners use these debates to separate safe from outstanding candidates.
- How critical are A2 and A4 really? The classic teaching that A2 and A4 must never be touched has softened. Tang's principle of judicious venting (A2 partially under 1.5-2cm, A4 entirely) reports no bowstringing or functional loss and is now mainstream, yet the safe limit of venting before mechanical disadvantage appears is still debated.
- Strand number — strong enough vs too bulky. More strands increase strength and resist gapping, but extra core passes add bulk and gliding resistance and prolong surgery. Many units now favour a well-tensioned 4- or 6-strand repair rather than chasing maximal strand counts.
- Suture caliber. Larger 3-0 suture intuitively seems stronger, but cadaver data show it fails by pulling through the tendon; 4-0 may give a more reliable suture-tendon interface in average-sized tendons.
- How much (and what kind of) peripheral suture? A formal circumferential epitendinous suture adds strength and smooths the repair, but tensioned strong-core series suggest only sparse peripheral stitches are needed, questioning routine elaborate epitendinous work.
- Should the FDS be repaired in zone II? Repairing both tendons restores independent PIP/DIP control but crowds the sheath and risks adhesions; some surgeons excise one FDS slip to make room. Evidence does not clearly favour either approach.
- Rehabilitation regime. True early active motion, place-and-hold, relative-motion-flexion orthoses and early passive motion all have advocates; the best protocol for a given repair strength and patient reliability is not settled.
- Anaesthesia. WALANT permits intraoperative active testing and is cost-effective, but high-quality comparative outcome data versus traditional anaesthesia remain limited.
Management Algorithm
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Scenario 1: Zone 2 Flexor Tendon Laceration
"A 30-year-old man cuts his right ring finger on broken glass. He cannot flex his DIP or PIP joints. How do you manage him?"
Scenario 2: Partial FDP Laceration - Repair Decision
"A 35-year-old carpenter presents 6 hours after a knife injury to the volar aspect of his left index finger in Zone 2. He has weak but present DIP flexion and full PIP flexion. In theatre, you find the FDS is intact but the FDP has approximately 70% of its width lacerated with 30% still in continuity on the radial side. The A2 pulley is intact. He is reliable and motivated for therapy. How would you manage the FDP and what would you counsel him about rehabilitation?"
Scenario 3: Re-rupture After Primary Repair - Salvage Options
"A 28-year-old builder returns to clinic 3 weeks after Zone 2 FDP and FDS repair of his middle finger. He admits he returned to light work against advice and felt a pop 2 days ago. He now has no active DIP or PIP flexion. X-ray shows no bony injury. In theatre, you find both tendons have completely ruptured and the proximal ends have retracted into the palm with significant fraying and degeneration of the tissue at the previous repair site. The tendon ends are mushy and will not hold suture. What are your management options and what would you recommend?"
MCQ Practice Points
Zone 2
Q: Why is Zone 2 called "No Man's Land"? A: Both FDP and FDS tendons are within the tight fibro-osseous sheath. Limited space leads to high adhesion risk and historically poor outcomes (now improved with modern techniques).
Critical Pulleys
Q: Which pulleys are critical for flexor tendon function? A: A2 (proximal phalanx) and A4 (middle phalanx). These must be preserved or reconstructed to prevent bowstringing. A1, A3, A5 can be sacrificed if necessary.
Repair Strength
Q: What is the minimum core suture for early active motion protocol? A: 4-strand repair. Provides approximately 40N strength needed for controlled early active motion. 2-strand is insufficient (only 20N).
Guidelines, Registries & Global Practice
Global epidemiology: Flexor tendon lacerations are common hand-trauma injuries, predominantly affecting young working-age men, most often from glass, knives and occupational sharp objects. Zone II is the most frequently injured and most studied zone. The dominant injury pattern reflects manual work and domestic glass injuries worldwide, so the burden is highest in working populations and in regions with high rates of interpersonal and occupational sharp trauma.
Side-by-side guidance (recommendations converge more than they differ):
How Major Bodies Frame Flexor Tendon Care
| Body / source | Emphasis | Practical position |
|---|---|---|
| BSSH / BOA (UK) | Timing and specialist referral | Primary repair ideally within days; refer to a hand unit; structured therapy-led rehabilitation |
| ASSH / AAOS (US) | Repair strength and protected motion | Multi-strand core repair supporting early controlled motion; hand-therapy partnership |
| IFSSH / global consensus (Tang) | Strong tensioned core + venting + EAM | Well-tensioned 4-6 strand core, judicious A2/A4 venting, intraoperative gliding test, early active motion |
| FESSH / European practice | WALANT and out-of-splint motion | Increasing use of wide-awake repair with intraoperative active testing and freer early motion |
Registry note: There is no dedicated international flexor-tendon registry equivalent to the arthroplasty registries (NJR, AJRR, AOANJRR, SHAR). Best evidence therefore comes from multicentre cohorts and meta-analyses, which consistently report rupture rates of roughly 4-12% and good/excellent outcomes around 70-90% with modern strong-core repair and early active motion.
High- vs limited-resource practice variation: In well-resourced settings, repair is performed under loupe/microscope magnification with hand-therapy-supervised early active motion and, increasingly, WALANT. In limited-resource or remote settings, delayed primary or staged repair, simpler 2-strand techniques and immobilisation-based rehabilitation are more common because of restricted theatre access and limited specialist hand therapy — a recognised driver of higher adhesion and stiffness rates rather than a difference in principle.
FLEXOR TENDON LACERATIONS
Clinical summary
Zone Classification
- •Zone 1: Distal to FDS (FDP only)
- •Zone 2: No Man's Land (both in sheath)
- •Zone 3: Palm (NV at risk)
- •Zone 4: Carpal tunnel
- •Zone 5: Forearm
Repair Principles
- •4-strand core suture minimum
- •Suture 2mm from cut end
- •Epitendinous suture adds 10-20%
- •Preserve A2 and A4 pulleys
Rehabilitation
- •Early active motion reduces adhesions
- •Dorsal blocking splint
- •Active flexion, passive extension
- •6 weeks protected motion
Complications
- •Adhesions (most common)
- •Rupture (peak 7-10 days)
- •Stiffness
- •Bowstringing