Extensor Tendon Injuries

1. Clinical Overview

Summary

Extensor tendon injuries of the hand represent a spectrum of conditions ranging from simple lacerations to complex closed injuries with delayed deformity. The extensor apparatus is anatomically divided into nine zones based on the Kleinert and Verdan classification system, with odd-numbered zones corresponding to joint levels and even-numbered zones to inter-joint segments. [1,2] Zone I injuries at the distal interphalangeal (DIP) joint produce mallet finger, characterised by terminal extensor tendon disruption and inability to extend the DIP joint. Zone III injuries involve the central slip at the proximal interphalangeal (PIP) joint, which if unrecognised leads to boutonniere deformity with PIP flexion and compensatory DIP hyperextension. Zone V injuries over the metacarpophalangeal (MCP) joint deserve special attention when caused by "fight bites" (clenched fist injuries from punching teeth), as they carry exceptionally high infection risk requiring urgent surgical washout. [3,4]

The extensor mechanism differs fundamentally from the flexor system: extensors form an interconnected aponeurotic network rather than discrete tendons in sheaths, making them more vulnerable to adhesion but also allowing partial function despite complete laceration through juncturae tendinum connections. [5] Management is zone-specific: closed mallet finger responds well to continuous extension splinting for 6-8 weeks, whilst open injuries and most central slip disruptions require surgical repair with post-operative rehabilitation protocols. [6,7] Complications include extensor lag, adhesions (particularly in Zone IV over the proximal phalanx), and secondary deformities including swan neck and chronic boutonniere patterns. Early recognition and appropriate zone-specific treatment are critical to prevent permanent functional impairment and deformity. [8]

Key Facts

• Zones: 9 zones (Odd = joints: I=DIP, III=PIP, V=MCP, VII=wrist; Even = between joints)
• Zone I (DIP): Mallet finger from terminal tendon rupture or avulsion; treat with continuous extension splinting 6-8 weeks [6,9]
• Zone III (PIP): Central slip injury leads to boutonniere deformity (PIP flexion + DIP hyperextension) if untreated [10]
• Zone V (MCP): Fight bite (clenched fist injury) = high-risk human bite requiring urgent surgical washout + IV antibiotics [3,4]
• Anatomy: Aponeurotic network with juncturae tendinum connecting EDC tendons; sagittal bands stabilise tendons at MCP [5]
• Repair: Open injuries require core suture (figure-of-8 or horizontal mattress) with non-absorbable sutures [11]
• Rehabilitation: Dynamic splinting or early controlled motion protocols reduce adhesions compared to static immobilisation [12,13]
• Complications: Extensor lag, adhesions, swan neck deformity (from untreated mallet), chronic boutonniere (from missed central slip) [8,14]

Clinical Pearls

"Odd Zones = Joints": Zone I = DIP; Zone III = PIP; Zone V = MCP; Zone VII = Wrist; Zone IX = Muscle bellies. This mnemonic helps rapid localisation and predicts specific injury patterns for each zone.

"Mallet Finger = Splint 6-8 Weeks Continuously": Closed mallet finger is treated with extension splinting (Stack or Alumafoam splint) worn continuously without removal for minimum 6 weeks. If the DIP flexes even once during this period, healing resets and the clock restarts. [6,9]

"Boutonniere = Central Slip + Lateral Band Migration": Acute central slip rupture at PIP may appear benign initially. Over 2-3 weeks, the lateral bands migrate volarly (palmar to the PIP axis of rotation), converting from extensors to flexors, creating the classic boutonniere posture: PIP flexion with DIP hyperextension. [10,15]

"Fight Bite = Emergency Until Proven Otherwise": Any laceration over the MCP joint following a punch is a human bite (fight bite/clenched fist injury) until proven otherwise. The clenched fist position at impact allows tooth penetration deep to tendon/joint capsule; when hand relaxes, skin closes over contaminated deep structures. Requires urgent surgical exploration, washout, and IV antibiotics covering Eikenella corrodens. [3,4]

"Test Extensors in Isolation": Due to juncturae tendinum connections between EDC tendons over the metacarpals (Zone VI), a completely lacerated extensor can still demonstrate some extension when adjacent fingers extend. Always test active extension with neighbouring fingers held in flexion to isolate the injured tendon. [5]

"Swan Neck from Mallet, Boutonniere from Central Slip": Untreated mallet finger redirects extensor force proximally to hyperextend the PIP (creating swan neck deformity). Untreated central slip injury allows lateral bands to slip volar, flexing the PIP whilst the terminal tendon hyperextends the DIP (boutonniere). The two deformities are pathophysiologic opposites. [14]

Why This Matters Clinically

Extensor tendon injuries are frequently encountered in emergency departments and hand clinics but carry significant risk of missed diagnoses and suboptimal outcomes. Mallet finger accounts for approximately 60% of closed extensor injuries, yet up to 25% of patients treated conservatively develop persistent extensor lag or secondary swan neck deformity due to inadequate splinting compliance or duration. [9,16] Central slip injuries are notoriously difficult to diagnose acutely because initial PIP extension may appear intact through intact lateral bands; boutonniere deformity develops insidiously over weeks as lateral bands migrate volarly, and once established, surgical reconstruction yields inferior results compared to early PIP extension splinting. [10,15]

Fight bite injuries represent true hand surgery emergencies with infection rates approaching 30-50% when treatment is delayed beyond 12 hours, often resulting in septic arthritis, osteomyelitis, and permanent stiffness. [3,4] The superficially innocuous appearance of a small MCP laceration belies deep contamination with oral flora including Streptococcus, Staphylococcus, anaerobes, and Eikenella corrodens, a fastidious gram-negative organism resistant to many first-line antibiotics. Delayed presentation or inadequate debridement can necessitate multiple operations, prolonged antibiotics, and occasionally ray amputation.

Understanding zone-specific anatomy and treatment protocols enables clinicians to deliver evidence-based care, avoid common pitfalls, and counsel patients realistically about outcomes, recovery timelines, and the critical importance of compliance with splinting regimens and hand therapy.

---

2. Epidemiology

Incidence and Demographics

Extensor tendon injuries are common, accounting for approximately 30-40% of all hand tendon injuries, though exact incidence is difficult to determine as many minor injuries are managed in primary care without specialist referral. [17] Unlike flexor tendon injuries which predominate in the palm and digits, extensor injuries occur across all zones from fingertip to forearm. Males are affected 3-4 times more frequently than females, with peak incidence in the 20-40 age group reflecting occupational and recreational exposure. [2,17]

Risk Factors

• Occupational: Manual labourers, food service workers (laceration injuries), healthcare workers (needlestick and sharp injuries)
• Sports: Ball sports (cricket, basketball, volleyball) for mallet finger; rugby, martial arts for central slip injuries [16]
• Violent trauma: Assault-related injuries including fight bites disproportionately affect young males in urban settings [3]
• Age-related: Bony mallet finger more common in older patients with osteoporotic bone; tendinous ruptures predominate in younger active individuals [9]

---

3. Anatomy and Pathophysiology

Extensor Tendon Zone Classification

The Kleinert-Verdan classification divides the extensor mechanism into nine zones, each with distinct anatomy and treatment implications. [1,2]

Functional Anatomy

The Extensor Mechanism: An Aponeurotic Network

Unlike flexor tendons which function as discrete "ropes in tubes" (pulleys and sheaths), the extensor system is a complex interconnected aponeurotic web. [5] This architecture has critical clinical implications:

Advantages:

• Injury to one tendon may not completely abolish extension due to interconnections (juncturae tendinum)
• Simpler surgical repair compared to flexor tendons (no critical pulley system)

Disadvantages:

• Broad flat tendons adhere readily to underlying bone and subcutaneous tissue
• Complete tendon division may be missed on examination if juncturae maintain partial extension
• Zone IV injuries (extensor directly on bone) have particularly high adhesion rates

Zone-Specific Anatomy

Zone I: Terminal Tendon The terminal extensor tendon is remarkably thin (approximately 1mm diameter) and inserts onto the dorsal base of the distal phalanx. [5] Disruption results in unopposed flexion by flexor digitorum profundus (FDP), creating the classic mallet posture. The proximal extensor force is redirected to the central slip, predisposing to secondary PIP hyperextension (swan neck deformity) if the volar plate is lax. [14]

Zone III: Central Slip and Lateral Bands Over the proximal phalanx, the extensor digitorum communis (EDC) trifurcates:

• Central slip: Inserts onto the dorsal base of middle phalanx; primary PIP extensor
• Lateral bands (medial and lateral): Pass around the sides of PIP to merge distally as the terminal tendon [5]

Central slip rupture eliminates active PIP extension. Over subsequent weeks, the lateral bands migrate volarly (palmar to the PIP axis of rotation) due to loss of central restraint. Once volar, they become paradoxical PIP flexors whilst simultaneously hyperextending the DIP through their terminal tendon insertion—the boutonniere deformity. [10,15]

Zone V: Sagittal Bands and the Fight Bite Mechanism At the MCP joint, sagittal bands form a sling from the volar plate, wrapping around the EDC tendon to centralise it over the metacarpal head. [5] Sagittal band rupture (usually radial-sided) allows EDC subluxation into the ulnar gutter ("boxer's knuckle").

In fight bite injuries, the clenched fist position at impact flexes the MCP joint, tightening skin over the metacarpal head. A tooth easily penetrates skin, extensor tendon, and MCP joint capsule. When the hand relaxes post-impact, the tendon retracts proximally, dragging oral bacteria beneath intact skin into deep structures. The wound may appear trivial externally whilst harbouring deep contamination. [3,4]

Zone VII: Extensor Retinaculum and Six Dorsal Compartments

1. Abductor pollicis longus (APL) + Extensor pollicis brevis (EPB)
2. Extensor carpi radialis longus (ECRL) + Extensor carpi radialis brevis (ECRB)
3. Extensor pollicis longus (EPL) — pivots around Lister's tubercle
4. Extensor digitorum communis (EDC) + Extensor indicis proprius (EIP)
5. Extensor digiti minimi (EDM)
6. Extensor carpi ulnaris (ECU)

Zone VII repairs require release or reconstruction of the retinaculum to prevent bowstringing and adhesions. [11]

Pathophysiology of Deformities

---

4. Clinical Presentation

Zone I: Mallet Finger

Mechanism of Injury

Forced flexion of the extended DIP joint is the hallmark mechanism. [9] Common scenarios include:

• Ball striking the extended fingertip (cricket, basketball, volleyball)
• Tucking in bedsheets (forced flexion against resistance)
• Blunt trauma to fingertip

Clinical Features

Classification of Mallet Finger

Tendinous vs Bony:

• Tendinous mallet: Rupture of terminal tendon substance (more common in younger patients) [9]
• Bony mallet: Avulsion fracture of dorsal distal phalanx base (more common in older patients; seen on lateral X-ray) [6]

Wehbe-Schneider Classification (for bony mallet): [6]

• Type I: Transverse fracture with small dorsal fragment (less than 30% articular surface)
• Type II: Fracture with 30-50% articular involvement
• Type III: Fracture with > 50% articular surface ± volar subluxation of distal phalanx

Surgical fixation is indicated for Type II/III injuries due to DIP joint instability. [6,9]

Zone III: Central Slip Injury

Mechanism of Injury

• Forced flexion of extended PIP joint
• Direct laceration over dorsal PIP
• Volar PIP dislocation (central slip avulsed during reduction) [10]

Acute Presentation (First 7-10 Days)

The classic boutonniere deformity is not present acutely. Initial presentation is subtle:

• Tenderness over dorsal PIP joint
• Swelling around PIP
• Weak but present PIP extension (lateral bands still intact and positioned dorsally)
• Difficulty distinguishing from PIP sprain

Delayed Presentation (2-4 Weeks)

As lateral bands migrate volarly, the boutonniere posture emerges: [10,15]

• PIP held in flexion (30-50°)
• DIP hyperextension (compensatory)
• Active PIP extension weak or absent
• Passive PIP extension may initially be full (before contracture develops)

Elson Test for Central Slip Integrity

The Elson test is the gold standard for diagnosing acute central slip rupture before deformity develops. [10,18]

Interpretation: Intact central slip directs extensor force to PIP extension. Ruptured central slip redirects all force through lateral bands to the DIP, which hyperextends rigidly. [18]

Zone V: Fight Bite (Clenched Fist Injury)

Mechanism and Clinical Context

A laceration over the MCP joint sustained by punching another person's teeth constitutes a fight bite. [3,4] Key features:

• History of punching (often denied initially; ask directly about altercation)
• Small laceration (often 5-10mm) over dorsum of MCP joint, usually index or middle finger
• Injury occurred with fist clenched; wound position changes when hand is extended vs flexed
• High suspicion if patient presents > 6 hours post-injury (delay suggests reluctance to disclose mechanism)

Examination

• Always examine with fist clenched: Wound position shifts; closed wound in extended hand may communicate with MCP joint capsule when fist clenched [3]
• Test extensor tendon function (active MCP extension)
• Assess for signs of infection: erythema, warmth, purulence, crepitus (subcutaneous gas from anaerobic bacteria)
• Check neurovascular status

Red Flags

• Fever, systemic signs: Suggests established sepsis; urgent surgical washout required
• Crepitus: Gas-forming organisms; requires broad-spectrum antibiotics including anaerobic cover
• Delayed presentation (> 12 hours): Infection rate increases dramatically; lower threshold for admission and IV antibiotics [4]

Zone VI-VII: Open Lacerations

Open extensor tendon lacerations typically present with:

• Loss of active extension at affected joint(s)
• Visible tendon ends (if laceration > 50% tendon width)
• Wound over dorsal hand, wrist, or forearm

Pitfall: Partial lacerations may retain some active extension through juncturae tendinum connections (Zone VI) or intact tendon fibres. Always test active extension with adjacent fingers flexed to isolate the injured tendon. [5]

---

5. Clinical Examination

Systematic Approach

1. Inspection

   • Resting posture: mallet droop, boutonniere, swan neck, or rotational deformity
   • Wound location (determines zone)
   • Swelling, ecchymosis, erythema

2. Active Extension Testing (Zone-Specific)

   • DIP joint: Ask patient to extend DIP from flexed position; mallet = complete failure
   • PIP joint: Test PIP extension in isolation; boutonniere = weak extension ± fixed flexion
   • MCP joint: Test MCP extension with wrist in neutral; complete laceration = loss of MCP extension
   • Wrist: Test wrist extension; multiple tendons may be affected in Zone VII injuries

3. Passive Range of Motion

   • Full passive extension distinguishes tendon injury from joint pathology (arthritis, contracture)
   • Fixed flexion contracture indicates chronic injury with secondary joint changes

4. Special Tests

   • Elson test: See above; for central slip integrity [18]
   • Central slip tenodesis test: Flex wrist maximally; intact central slip produces PIP extension; ruptured central slip = no PIP extension [10]

5. Neurovascular Examination

   • Digital nerve function (two-point discrimination; sensation to fingertip)
   • Vascular status (capillary refill, digital Allen test if concern for arterial injury)

Assessment of Wound Depth (Open Injuries)

For open lacerations, determine:

• Percentage of tendon width involved (less than 50% may be observed; ≥50% requires repair) [11]
• Joint capsule violation (especially Zone V fight bites)
• Bone or periosteal injury
• Foreign body presence (glass, tooth fragment)

---

6. Investigations

X-ray Imaging

Indications:

• All suspected mallet finger injuries (to identify bony avulsion) [6,9]
• Fight bite injuries (to exclude tooth fragment, metacarpal fracture, gas in soft tissues) [3,4]
• Open lacerations with high-energy mechanism (to exclude fracture, foreign body)

Views:

• Mallet finger: Lateral view of affected digit (best demonstrates bony fragment size and DIP joint subluxation)
• Fight bite: PA, lateral, and oblique views of hand (to identify tooth fragments which may be radiolucent)

Radiographic Findings:

Ultrasound

Not routinely used but may identify:

• Tendon rupture vs partial tear
• Tendon retraction distance
• Fluid in MCP joint (fight bite with septic arthritis)

MRI

Reserved for complex cases:

• Chronic boutonniere deformity (assessing lateral band position, central slip scarring)
• Suspected occult fracture with normal X-rays
• Pre-operative planning for tendon reconstruction

Laboratory Investigations (Fight Bite)

---

7. Management

General Principles

1. Zone-specific treatment: Each zone has distinct optimal management
2. Timing: Early repair (within 24 hours) yields best results for open injuries; fight bites require emergency washout [3,11]
3. Splinting: Foundation of closed injury management (mallet, boutonniere)
4. Rehabilitation: Early controlled motion protocols reduce adhesions [12,13]
5. Patient compliance: Critical for conservative management success (especially mallet splinting) [9]

---

Zone I: Mallet Finger

Conservative Management (Closed Tendinous Mallet)

Indications: [6,9]

• Tendinous mallet (no fracture or small avulsion less than 30% articular surface)
• Acute presentation (less than 4 weeks from injury)
• No DIP joint subluxation

Splinting Protocol: [9,16]

1. Splint type: Stack splint (Alumafoam) or Zimmer splint; immobilises DIP in 0-10° hyperextension
2. Duration: Continuous wear for 6-8 weeks without removal
3. Critical instruction: DIP must never flex during treatment period; single flexion episode resets healing, requiring restart of 6-8 week protocol
4. Weaning: After 6-8 weeks, continue night splinting for additional 4-6 weeks
5. Skin care: Remove splint weekly for cleaning and reapplication; maintain DIP extension during splint changes (use volar support)

Outcomes: [6,9,16]

• Success rate: 60-85% achieve less than 10° extensor lag
• Failure predictors: Poor compliance, delayed presentation (> 4 weeks), chronic injuries

Surgical Management

Indications: [6,9]

• Bony mallet with fragment > 30% articular surface (Wehbe-Schneider Type II/III)
• Volar subluxation of distal phalanx
• Failed conservative management with persistent extensor lag > 30°
• Open injuries with tendon laceration

Surgical Options:

1. K-wire fixation (closed bony mallet with large fragment):

   • Longitudinal K-wire across DIP joint holding joint in extension
   • Fragment fixation with separate transverse K-wire if needed
   • Remove at 6 weeks

2. Open repair (tendinous rupture or open laceration):

   • Direct tendon repair with figure-of-8 or horizontal mattress suture (4-0 non-absorbable)
   • Temporary K-wire fixation of DIP in extension for 6 weeks [11]

3. Ishiguro technique (chronic mallet with bone fragment):

   • Extension block K-wire technique
   • Reduces fragment whilst maintaining DIP extension [9]

Post-operative: DIP splinting in extension for 6 weeks; then progressive mobilisation with hand therapy

---

Zone III: Central Slip Injury / Boutonniere Deformity

Conservative Management (Acute Injury with Positive Elson Test)

Indications: [10,15]

• Acute central slip rupture (within 2 weeks)
• Closed injury
• PIP joint passively correctable to full extension

Splinting Protocol: [10,18]

1. Splint type: PIP extension splint (static or dynamic); allows DIP flexion (important to prevent lateral band contracture)
2. Duration: 6 weeks continuous PIP immobilisation in full extension
3. DIP exercises: Encourage active DIP flexion during splinting period (pulls lateral bands dorsally, counteracting volar migration) [15]
4. Weaning: Progressive reduction in splinting time over 2-4 weeks

Outcomes:

• Success rate: 70-80% if initiated within 2 weeks of injury [10]
• Failure: Progressive boutonniere deformity requires surgical reconstruction

Surgical Management

Indications: [15,18]

• Open injuries with central slip laceration
• Chronic boutonniere deformity (> 6 weeks) unresponsive to splinting
• Fixed PIP flexion contracture

Acute Repair (open injuries): [11]

• Direct central slip repair with figure-of-8 or horizontal mattress suture (4-0 non-absorbable)
• Temporary K-wire fixation of PIP in extension (controversial; some advocate dynamic splinting instead)
• Post-operative: PIP extension splinting for 6 weeks; DIP mobilisation encouraged

Chronic Boutonniere Reconstruction: [15,18] Multiple techniques described:

1. Terminal tendon tenotomy (Fowler procedure): Releases tight lateral bands allowing them to migrate dorsally to aid PIP extension
2. Central slip reconstruction: Using lateral band tissue or palmaris longus tendon graft
3. Lateral band mobilisation and centralisation: Surgically repositioning lateral bands dorsal to PIP axis

Outcomes: Chronic boutonniere has guarded prognosis; residual stiffness and incomplete correction common [15]

---

Zone V: Fight Bite / MCP Injuries

Fight Bite Management (Clenched Fist Injury)

This is a hand surgery emergency. [3,4]

Emergency Department Management:

1. Do not close wound: Leave open for delayed primary closure post-washout
2. X-ray: Rule out tooth fragment, fracture, gas in tissues
3. Tetanus prophylaxis: Update if > 5 years since last booster
4. IV antibiotics: Initiate immediately (see below)
5. Splint in position of safety: Intrinsic plus (MCP flexion, IP extension) to prevent joint stiffness
6. Urgent surgical referral: Operative exploration and washout within 12 hours [3,4]

Antibiotic Regimen: [4]

• First-line: Co-amoxiclav 1.2g IV TDS (covers Streptococcus, Staphylococcus, Eikenella, anaerobes)
• Penicillin allergy: Clindamycin 600mg IV QDS + ciprofloxacin 400mg IV BD (Eikenella coverage)
• Duration: 5-7 days IV, then switch to PO for total 14 days if joint penetration confirmed

Operative Management: [3,4]

1. Exploration: Extend wound proximally and distally; examine with fist clenched to identify true depth of penetration
2. Washout: Copious irrigation (≥3L saline); debride devitalised tissue
3. Tendon repair: If EDC lacerated, repair with core suture (see below)
4. Joint inspection: Open MCP joint capsule if any suspicion of penetration; washout joint thoroughly
5. Specimen culture: Send deep tissue/joint fluid for culture (polymicrobial: expect Streptococcus viridans, Staphylococcus aureus, Eikenella corrodens, anaerobes)
6. Wound management: Leave open; plan delayed primary closure at 3-5 days if no infection
7. Post-operative: Splint in intrinsic plus position; elevation; IV antibiotics; hand therapy once wound healed

Outcomes and Complications: [4]

• Infection rate: 15-30% despite appropriate treatment
• Septic arthritis: 10-15% (higher if delayed presentation > 12 hours)
• Chronic stiffness: Common even with optimal treatment
• Osteomyelitis: 5-10% if bony involvement

Non-Fight Bite Zone V Lacerations

Indications for surgical repair: [11]

• Laceration involving ≥50% tendon width
• Complete tendon division

Repair Technique:

• Core suture: Figure-of-8 or horizontal mattress with 4-0 non-absorbable suture (e.g., Ethibond, Prolene)
• Epitendinous running suture (optional): 6-0 monofilament for smooth tendon gliding
• Post-operative: Dynamic extension splinting or static splint for 4 weeks; then progressive hand therapy [12,13]

---

Zone VI-VII: Metacarpal and Wrist Lacerations

Surgical Repair Technique: [11]

• Suture: Core suture (figure-of-8 or horizontal mattress) with 3-0 or 4-0 non-absorbable
• Zone VII (wrist) specific: Divide extensor retinaculum to prevent bowstringing and adhesions; may require retinaculum reconstruction at case conclusion
• Multiple tendon lacerations: Repair all divided tendons; balance tension to prevent differential extension

Post-operative Splinting: [12,13]

• Static splinting: Wrist 30-40° extension, MCP 0° extension, IP joints free for 4 weeks
• Dynamic splinting: Outrigger splint with elastic traction maintaining extension; allows controlled flexion against resistance
• Early controlled motion: Preferred protocol to reduce adhesions (see Rehabilitation section)

---

Zone IV: Proximal Phalanx Injuries

Zone IV has the highest risk of adhesions (tendon lies directly on bone with no sheath). [5,11]

Surgical Repair:

• Standard core suture technique
• Post-operative: Early controlled motion protocol essential to prevent adhesions [12,13]

Secondary Tenolysis:

• Indicated if significant adhesions cause extensor lag > 30° despite hand therapy
• Timing: Minimum 3-6 months post-repair to allow scar maturation

---

8. Rehabilitation and Splinting Protocols

Philosophy

Extensor tendons have lower tensile strength than flexor tendons but heal with greater tendency to adhesion formation, particularly in Zone IV and over dorsal hand. [5,12] Modern rehabilitation emphasises early controlled motion to balance tendon healing with adhesion prevention. [13]

Static Splinting

Indications:

• Mallet finger (Zone I)
• Acute central slip injuries (Zone III)
• Patients unable to comply with complex dynamic protocols

Protocol:

• Immobilise affected joint(s) in extension
• Duration: 6-8 weeks (Zone I), 6 weeks (Zone III), 4 weeks (Zones V-VII)
• Advantages: Simple, low cost, good compliance
• Disadvantages: Stiffness, adhesions, loss of flexion [12]

Dynamic Extension Splinting

Indications:

• Zones V-VII open repairs
• Motivated patients with access to hand therapy

Protocol: [12]

• Outrigger splint with elastic bands maintaining finger extension
• Patient actively flexes against elastic resistance; elastics return finger to extension
• Duration: 4-6 weeks
• Advantages: Reduces adhesions, maintains flexion, improved outcomes vs static splinting
• Disadvantages: Bulky, expensive, requires hand therapist supervision

Early Controlled Motion (Short Arc Motion / Evans Protocol)

Indications:

• Zones III-VII repairs
• Gold standard for Zone IV (high adhesion risk) [12,13]

Protocol: [13]

• ICAM (Immediate Controlled Active Motion) splint: Blocks full flexion but allows 30-40° active flexion
• Tendon excursion of 3-5mm occurs without gapping repair site
• Duration: 4 weeks; then progressive unrestricted mobilisation
• Outcomes: Superior grip strength and lower adhesion rates compared to static splinting [13]

Rehabilitation Milestones

---

9. Complications

Extensor Lag

Definition: Difference between passive and active extension (e.g., passive full extension but 20° active extension deficit) [8]

Causes:

• Tendon repair gap/stretch (inadequate suture technique or early failure)
• Adhesions preventing full tendon excursion
• Chronic injury with tendon scarring and lengthening

Management:

• less than 10°: Observation; often improves with hand therapy
• 10-30°: Intensive hand therapy; consider dynamic splinting

• 30°: Surgical options (tendon shortening, tenolysis, reconstruction) [8]

Adhesions

Risk factors:

• Zone IV injuries (tendon on bone)
• Delayed repair (> 7 days)
• Static immobilisation > 6 weeks
• Infection or wound complications [12]

Prevention:

• Early controlled motion protocols
• Atraumatic surgical technique
• Minimise post-operative inflammation

Management:

• Hand therapy: Scar massage, stretching, dynamic splinting
• Tenolysis: Surgical adhesion release if plateau reached after 3-6 months of therapy; unpredictable results

Swan Neck Deformity (Secondary to Chronic Mallet)

Pathophysiology: Untreated mallet finger redirects extensor force to central slip, hyperextending PIP; DIP remains flexed [14]

Management:

1. Mild (passively correctable): Serial splinting; SORL (Spiral Oblique Retinacular Ligament) reconstruction [14]
2. Moderate (fixed deformity): Volar plate advancement, lateral band mobilisation
3. Severe (arthritic changes): DIP joint arthrodesis in functional position (10-15° flexion)

Chronic Boutonniere Deformity

Management: [15,18]

• Supple PIP (passively correctable): Prolonged PIP extension splinting (3-6 months); if fails, surgical lateral band mobilisation + central slip reconstruction
• Stiff PIP (fixed contracture): Requires stepwise release: volar capsulotomy, lateral band lengthening/repositioning, central slip reconstruction; outcomes guarded [15]

Infection (Fight Bite Specific)

Complications: [3,4]

• Septic arthritis (10-15%)
• Osteomyelitis (5-10%)
• Flexor tenosynovitis (spread to volar compartment)
• Chronic stiffness despite infection eradication
• Amputation (rare; reserved for overwhelming sepsis with necrosis)

Management:

• Repeat surgical washout if infection not controlled
• Prolonged IV antibiotics (2-6 weeks) for osteomyelitis/septic arthritis
• Intensive hand therapy once infection eradicated

Nail Deformity

Zone I injuries involving the germinal matrix may cause nail ridging or deformity; warn patients pre-operatively

Juncturae Syndrome

Over-tight repair of EDC in Zone VI can restrict flexion of adjacent fingers via juncturae tendinum connections [5]

Prevention: Adjust tendon tension intra-operatively; ensure adjacent fingers achieve full flexion

---

10. Prognosis and Outcomes

Zone I: Mallet Finger

Conservative management: [9,16]

• Good outcome (extensor lag less than 10°): 60-85%
• Residual lag 10-20°: 15-30% (often functionally acceptable)
• Failure requiring surgery: 5-15%

Predictors of poor outcome:

• Poor compliance with splinting
• Delayed presentation (> 4 weeks)
• Large bony fragments
• Age > 50 years

Functional impact: Most patients tolerate mild extensor lag (less than 15°) without significant functional limitation

Zone III: Boutonniere Deformity

Acute management (splinting within 2 weeks): [10,15]

• Good outcome: 70-80%
• Progression to chronic boutonniere: 15-20%

Chronic boutonniere reconstruction: [15]

• Good outcome (PIP extension to within 20° of normal): 40-60%
• Residual stiffness common
• Patient satisfaction variable

Zone V: Fight Bite

Outcomes with early treatment (less than 12 hours): [3,4]

• Infection rate: 15-20%
• Full recovery of function: 60-70%

Outcomes with delayed treatment (> 12 hours):

• Infection rate: 30-50%
• Chronic stiffness: 40-60%
• Need for multiple procedures: 20-30%

Zone VI-VII: Open Lacerations

Outcomes with surgical repair + early mobilisation: [11,12,13]

• Excellent outcome (full ROM, strength > 80% contralateral): 60-75%
• Good outcome (ROM > 80%, mild extensor lag): 20-30%
• Poor outcome (significant lag, adhesions): 5-15%

Predictors of poor outcome:

• Zone IV injuries (adhesion risk)
• Multiple tendon injuries
• Delayed repair (> 7 days)
• Wound infection
• Non-compliance with hand therapy

---

11. Special Populations

Paediatric Patients

Bony mallet in children: Often Salter-Harris Type III physeal injury; requires anatomic reduction and fixation to prevent growth arrest [9]

Splinting compliance: Challenging in young children; consider K-wire fixation for acute mallet if compliance doubtful

Athletes

Return to sport: [16]

• Mallet finger: Protective splinting allows return to non-contact sport at 4-6 weeks; contact sport at 8-12 weeks
• Zone V-VII repairs: Return to contact sport at 12 weeks minimum; protective taping for additional 3 months

High-level athletes: Lower threshold for surgical management to expedite return and optimise outcome

Older Patients

Bony mallet more common: Osteoporotic bone; fixation challenging

Functional expectations: Lower demand; conservative management often appropriate even with residual lag

---

12. Evidence and Guidelines

Landmark Studies

1. Kleinert et al. (1967): Described extensor tendon zone classification system; remains standard [1]
2. Evans & Burkhalter (1986): Dynamic splinting protocol for extensor repairs; demonstrated improved outcomes vs static immobilisation [12]
3. Doyle (1993): Comprehensive classification and treatment algorithm for extensor injuries [2]
4. Newport et al. (2005): Biomechanical analysis of extensor tendon repair strength; advocated stronger repair techniques and early motion [13]
5. Peng et al. (2023): Systematic review of mallet finger management; no significant difference between surgery and splinting for closed tendinous injuries [6]

Current Guidelines

British Society for Surgery of the Hand (BSSH): [11]

• Mallet finger: 6-8 weeks continuous extension splinting for closed injuries
• Fight bite: Emergency washout within 12 hours; IV co-amoxiclav
• Open repairs: Consider early controlled motion protocols to reduce adhesions

American Society for Surgery of the Hand (ASSH): [17]

• Zone-specific treatment essential
• Early motion protocols preferred for Zones III-VII to minimise adhesions
• Multidisciplinary hand therapy integral to optimal outcomes

---

13. Patient Education and Layperson Explanation

What is a mallet finger?

Mallet finger occurs when the tendon that straightens the end of your finger (the DIP joint) is torn or pulled off the bone. The fingertip droops downward and you cannot straighten it actively, though someone else can straighten it for you (passive extension is full).

Common causes:

• Ball hitting the end of your finger (cricket, basketball, volleyball)
• Jamming your finger tucking in bedsheets or catching on clothing

Treatment: A special splint holds the fingertip straight for 6-8 weeks continuously. This is the most important part: the finger must not bend even once during this time, or healing resets and you start over. After 6-8 weeks, you wear the splint at night for another month while gradually using the finger during the day.

Success rate: About 70-80% of people heal well with splinting alone if they follow instructions carefully.

What is a boutonniere deformity?

Boutonniere (French for "buttonhole") is when the middle joint of the finger (PIP joint) bends down and the fingertip (DIP joint) bends up. It happens when the central tendon over the middle joint is torn. At first, the finger may look nearly normal, but over 2-4 weeks the deformity develops as the side tendons slip out of position.

Treatment: If caught early (within 2 weeks), a splint holding the middle joint straight for 6 weeks often works. If the deformity becomes fixed, surgery is needed, but results are less predictable.

What is a fight bite?

A "fight bite" is a cut on your knuckle caused by punching someone's teeth. Though the cut may look small, it is extremely high risk for serious infection because:

• Teeth carry many bacteria deep into the joint
• The wound closes over contaminated tissue
• Infection can spread to bone and joints

Treatment: Fight bites are hand surgery emergencies. You need:

• Urgent surgery to wash out the wound and remove contaminated tissue
• IV antibiotics for at least 5-7 days
• Leaving the wound open initially (closed later once infection risk passes)

Never ignore a knuckle injury after a punch—seek medical attention immediately.

---

14. Examination Focus

High-Yield Exam Topics

Sample Viva Questions with Model Answers

Q1: A 35-year-old cricketer presents with inability to extend the DIP joint of his right index finger after the ball struck his fingertip. Describe your management.

Model Answer: "This is a classic presentation of mallet finger, a Zone I extensor tendon injury. I would first confirm the diagnosis by examining active and passive DIP extension—mallet finger has absent active extension but full passive extension, distinguishing it from joint pathology. I would obtain a lateral X-ray to identify a bony avulsion fragment.

For closed tendinous mallet or small bony fragment involving less than 30% of the articular surface, I would treat conservatively with continuous extension splinting using a Stack or Alumafoam splint for 6-8 weeks without removal. Critical patient education includes that the DIP must never flex during this period or healing resets. After 6-8 weeks, I would wean with night splinting for an additional 4-6 weeks.

Surgical indications include bony fragments exceeding 30% of the articular surface or volar subluxation of the distal phalanx, as these represent unstable injuries. Success with conservative management is 60-85% achieving less than 10 degrees of extensor lag, but compliance is the most important factor." [6,9]

Q2: How would you diagnose an acute central slip injury?

Model Answer: "Acute central slip injury is challenging because the classic boutonniere deformity typically develops over 2-4 weeks, not immediately. Initially, the patient presents with PIP tenderness, swelling, and weakened but present extension through intact lateral bands.

The gold standard diagnostic test is the Elson test. With the PIP flexed 90 degrees over the edge of a table, I ask the patient to extend the PIP against resistance. With an intact central slip, strong resistance is felt at the PIP and the DIP remains floppy. With a ruptured central slip, there is weak or absent resistance at the PIP, and the DIP becomes rigidly hyperextended as all extensor force is diverted through the lateral bands to the terminal tendon.

If diagnosed acutely, I would initiate PIP extension splinting for 6 weeks while encouraging active DIP flexion exercises, which pull the lateral bands dorsally and prevent volar migration. Early treatment yields 70-80% good outcomes; once chronic boutonniere is established, surgical reconstruction has much poorer results." [10,15,18]

Q3: A 22-year-old man presents 8 hours after punching someone in the mouth with a 7mm laceration over the dorsum of his right middle finger MCP joint. Describe your management.

Model Answer: "This is a fight bite or clenched fist injury, which is a hand surgery emergency due to extremely high infection risk. The mechanism involves the fist being clenched at impact, allowing tooth penetration through skin, extensor tendon, and potentially the MCP joint capsule. When the hand relaxes, the tendon retracts, dragging oral bacteria beneath intact skin into deep structures.

I would examine the wound with the fist clenched to identify the true depth of penetration and test extensor function. I would obtain X-rays to rule out tooth fragments, fractures, or subcutaneous gas. I would initiate IV co-amoxiclav immediately (or clindamycin plus ciprofloxacin if penicillin-allergic) to cover Streptococcus, Staphylococcus, Eikenella corrodens, and anaerobes. Tetanus prophylaxis should be updated.

This patient requires urgent surgical exploration and washout within 12 hours. In theatre, I would extend the wound to fully visualise the extensor tendon and MCP joint, perform copious irrigation with at least 3 litres of saline, debride devitalised tissue, repair any tendon laceration, and leave the wound open for delayed primary closure at 3-5 days. Deep tissue cultures would guide antibiotic therapy. Post-operatively, the hand is splinted in the intrinsic plus position with strict elevation.

The infection rate is 15-30% even with appropriate treatment and increases dramatically if presentation is delayed beyond 12 hours. Complications include septic arthritis, osteomyelitis, and chronic stiffness." [3,4]

Q4: What are the complications of extensor tendon injuries and how do you manage them?

Model Answer: "Extensor tendon injuries have several important complications:

Extensor lag: This is the difference between passive and active extension. For example, full passive extension but a 20-degree active deficit. Causes include tendon gapping or stretching from inadequate repair, adhesions, or chronic tendon lengthening. Management depends on severity: less than 10 degrees may be observed, 10-30 degrees warrants intensive hand therapy and dynamic splinting, whilst greater than 30 degrees may require surgical tendon shortening or reconstruction.

Adhesions: Particularly common in Zone IV where tendon lies directly on bone. Prevention involves early controlled motion protocols. If significant adhesions develop, tenolysis can be performed after 3-6 months, though results are unpredictable.

Swan neck deformity: Secondary to chronic untreated mallet finger. The extensor force redirects proximally, hyperextending the PIP whilst the DIP remains flexed. Management ranges from serial splinting and SORL reconstruction for mild cases to DIP arthrodesis for severe arthritic changes.

Chronic boutonniere: Results from untreated central slip injury. The lateral bands scar in a volar position with PIP capsular contracture. This is very difficult to correct surgically, with guarded outcomes. Prevention through early recognition and splinting is key.

Infection: Specific to fight bites, with rates of 15-50% depending on treatment delay. Can progress to septic arthritis, osteomyelitis, and chronic stiffness requiring prolonged antibiotics and multiple procedures." [8,14,15]

Q5: Describe the rehabilitation principles following extensor tendon repair.

Model Answer: "Extensor tendon rehabilitation has evolved significantly. Traditionally, static immobilisation was used, but this resulted in high rates of adhesions and stiffness. Modern approaches emphasise early controlled motion, which balances tendon healing with adhesion prevention.

For Zone I mallet finger and Zone III central slip injuries, static splinting in extension remains the gold standard due to the specific anatomy and healing requirements.

For Zones IV through VII, I prefer early controlled motion protocols, particularly the Evans short arc motion or ICAM protocol. This uses a splint that blocks full flexion but allows 30-40 degrees of active flexion, producing 3-5mm of tendon excursion—enough to prevent adhesions without gapping the repair. Evidence demonstrates superior grip strength and lower adhesion rates compared to static splinting.

Dynamic extension splinting with outrigger devices is an alternative, using elastic bands to maintain extension whilst allowing active flexion against resistance.

The rehabilitation timeline progresses through protection (0-4 to 6 weeks), mobilisation (4-8 weeks), strengthening (8-12 weeks), and return to unrestricted activity (12+ weeks). Multidisciplinary hand therapy input is integral to optimal outcomes, particularly for Zone IV injuries which have the highest adhesion risk." [12,13]

---

15. References

1. Kleinert HE, Schepel S, Gill T. Flexor tendon injuries. Surgical Clinics of North America. 1981;61(2):267-286.

2. Doyle JR. Extensor tendons – acute injuries. In: Green's Operative Hand Surgery, 6th edition. Elsevier. 2011:159-188.

3. Talan DA, Abrahamian FM, Moran GJ, et al. Clinical presentation and bacteriologic analysis of infected human bites in patients presenting to emergency departments. Clinical Infectious Diseases. 2003;37(11):1481-1489. doi:10.1086/379331

4. Kennedy CD, Lauder AS, Pribaz JR, et al. Differentiation between pyogenic flexor tenosynovitis and other finger infections. Hand. 2017;12(6):585-590. doi:10.1177/1558944716675291

5. Tubiana R, Thomine JM, Mackin E. Examination of the Hand and Wrist, 2nd edition. London: Martin Dunitz; 1996.

6. Peng C, Huang RW, Chen SH, et al. Comparative outcomes between surgical treatment and orthosis splint for mallet finger: a systematic review and meta-analysis. Journal of Plastic Surgery and Hand Surgery. 2023;57(1-6):235-244. doi:10.1080/2000656X.2022.2164291

7. Jablecki J, Syrko M. Zone 1 extensor tendon lesions: current treatment methods and a review of literature. Ortopedia, Traumatologia, Rehabilitacja. 2007;9(3):227-237.

8. Newport ML, Blair WF, Steyers CM Jr. Long-term results of extensor tendon repair. The Journal of Hand Surgery. 1990;15(6):961-966. doi:10.1016/0363-5023(90)90023-7

9. Alla SR, Deal ND, Dempsey IJ. Current concepts: mallet finger. Hand (New York, NY). 2014;9(2):138-144. doi:10.1007/s11552-014-9609-y

10. El-Sallakh S, Aly T, Amin O, et al. Surgical management of chronic boutonniere deformity. Hand Surgery. 2012;17(3):319-323. doi:10.1142/S0218810412500311

11. Arvind V, Hong DY, Strauch RJ. Extensor tendon repair. JBJS Essential Surgical Techniques. 2024;14(3):e23.00082. doi:10.2106/JBJS.ST.23.00082

12. Neuhaus V, Wong G, Russo KE, et al. Dynamic splinting with early motion following zone IV/V and TI to TIII extensor tendon repairs. The Journal of Hand Surgery. 2012;37(5):933-937. doi:10.1016/j.jhsa.2012.01.017

13. Newport ML, Tucker RL. New perspectives on extensor tendon repair and implications for rehabilitation. Journal of Hand Therapy. 2005;18(2):175-181. doi:10.1197/j.jht.2005.02.011

14. Suroto H, Aprilya D, Prajasari T, et al. Treatment of chronic mallet finger with swan neck deformity using a modified Spiral Oblique Retinacular Ligament (SORL) reconstruction procedure: A case series and technical note. International Journal of Surgery Case Reports. 2023;103:107945. doi:10.1016/j.ijscr.2023.107945

15. Bellemere P. Treatment of chronic extensor tendons lesions of the fingers. Chirurgie de la Main. 2015;34(4):155-181. doi:10.1016/j.main.2015.06.002

16. Chauhan A, Jacobs B, Andoga A, et al. Extensor tendon injuries in athletes. Sports Medicine and Arthroscopy Review. 2014;22(1):45-55. doi:10.1097/JSA.0000000000000011

17. American Society for Surgery of the Hand. Extensor Tendon Injuries. Available at: www.assh.org/handcare/safety/extensor-tendon-injuries. Accessed January 2026.

18. Smith PJ, Ross DA. The central slip tenodesis test for early diagnosis of potential boutonniere deformities. Journal of Hand Surgery (British and European Volume). 1994;19(1):88-90. doi:10.1016/0266-7681(94)90057-4

19. Toci GR, Tecce ER, Katt BM, et al. Splinting versus percutaneous pinning for the treatment of soft tissue mallet finger: a retrospective cohort analysis. The Journal of Hand Surgery Asian-Pacific Volume. 2022;27(6):886-891. doi:10.1142/S2424835522500886

20. Tolkien Z, Potter S, Burr N, et al. Conservative management of mallet injuries: a national survey of current practice in the UK. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2017;70(8):1045-1052. doi:10.1016/j.bjps.2017.04.005

21. Canham CD, Hammert WC. Rehabilitation following extensor tendon repair. The Journal of Hand Surgery. 2013;38(8):1565-1567. doi:10.1016/j.jhsa.2013.03.025

22. Howell JW, Peck F. Rehabilitation of flexor and extensor tendon injuries in the hand: current updates. Injury. 2013;44(3):397-402. doi:10.1016/j.injury.2013.01.022

---

Last Reviewed: 2026-01-09 | MedVellum Editorial Team | Topic 760/1071