Extensor tendon injuries are among the most frequently encountered hand tendon injuries. In a 10-year US population-based study, acute traumatic hand/wrist tendon injuries occurred at 33.2 per 100,000 person-years, with extensor injuries more common than flexor injuries, peaking at age 20-29 with a male predominance (de Jong 2014).

• Most common closed tendon injury: mallet finger (Zone I), typically from a forced flexion (ball-sport "jamming") of the extended DIPJ.
• Most common extensor injury site overall: Zone III of the index finger.
• ~25% are work-related (construction, food preparation, transport) — relevant for return-to-work counselling.
• Mechanisms: lacerations (glass, knives) dominate open dorsal injuries; closed avulsions cause mallet and Boutonnière; direct blows cause sagittal band rupture.

The extensor mechanism is a thin, broad, low-excursion system — unlike the round, gliding flexors. Key points that drive management:

• Extrinsic extensors (EDC, EIP, EDM, EPL, ECRL/B, ECU) arise in the forearm; intrinsic muscles (lumbricals, interossei) contribute the lateral bands.
• Over the proximal phalanx the EDC splits into a central slip (inserts on the base of the middle phalanx, extends the PIPJ) and two lateral bands (join the intrinsics to form the conjoined lateral bands → terminal tendon at the distal phalanx, extends the DIPJ).
• Sagittal bands at the MCPJ tether the EDC centrally over the joint — rupture allows ulnar subluxation ("boxer's knuckle").
• Triangular ligament (dorsal, distal) keeps the lateral bands dorsal; transverse retinacular ligament (volar) restrains them. Central slip loss tips this balance so the lateral bands fall volar to the PIP axis → Boutonnière.
• Juncturae tendinum interconnect the EDC tendons over the dorsum of the hand; an adjacent intact tendon can extend a finger with a proximal (zone V-VI) laceration, masking the injury.
• Extensor tendons have little excursion and tolerate little gapping — even 1-2 mm of repair-site lengthening produces clinically significant extensor lag.

Odd numbers are joints; even numbers are bones. Treatment and prognosis vary by zone — odd-numbered (joint-level) zones have thin tendons, little surrounding tissue, and the highest adhesion risk.

Extensor tendon injuries are classified by Verdan zones (I-IX)—odd numbers are joints, even numbers are bones. Zone I (DIP/Mallet finger) is the most common closed tendon injury: treat with Stack splint in extension for 6-8 weeks. Zone III (PIP/Boutonnière) involves central slip rupture causing lateral band volar migration; requires extension splinting for 6 weeks with active DIP flexion exercises to prevent deformity. Elson's test diagnoses central slip injury: with PIP flexed 90°, if the central slip is torn, the DIP becomes rigid (lateral bands tighten). Zone V (MCP) sagittal band rupture ("Boxer's knuckle") causes extensor subluxation into the valley between knuckles. Unlike flexors, extensors are flat with less excursion and prone to gapping.

Extensor injuries are largely a clinical diagnosis, but targeted investigations refine management:

• Plain radiographs (AP + true lateral): mandatory for any suspected mallet — quantify fragment size (% articular surface) and look for volar subluxation of the distal phalanx (the key surgical trigger). Also excludes associated fracture/dislocation and radiopaque glass foreign bodies in lacerations.
• Wound exploration is the definitive "investigation" for open dorsal injuries — examine through the full range of motion, as a tendon divided in flexion retracts out of the wound when the finger is extended.
• Bedside tests: Elson's test (central slip integrity, Zone III) and assessment of active extension against gravity/resistance at each zone. Test each digit independently to defeat juncturae masking.
• Ultrasound / MRI: reserved for chronic, occult, or zone VII-VIII injuries where the level of disruption or adhesion is unclear; not routine in the acute setting.

The cardinal sign of an extensor injury — inability to actively extend a digit — has several mimics. Distinguishing them changes management entirely.

• Surgery vs splinting for bony mallet — the long-held "greater than 1/3 articular surface" rule is increasingly questioned. In fractures without volar subluxation, comparative data show splinting matches surgery for outcome at lower cost and complication (Gumussuyu 2020). The strongest surgical indication is now DIPJ subluxation/instability, not fragment size alone.
• Optimal mallet splint and duration — the Cochrane review (Handoll 2004) found no splint type superior; 6-8 weeks continuous is convention rather than high-level evidence, and the trade-off between rigid adherence and skin maceration is unresolved.
• Relative-motion (yoke/ICAM) vs traditional dynamic/static splinting for zone IV-VII repairs — relative-motion protocols allow immediate hand use and appear to reduce adhesions, but most evidence is Level IV; high-quality randomised comparison data are still limited.
• Acute primary repair of central slip vs splinting for closed zone III injuries — closed acute injuries are generally splinted, but the threshold for operative repair (e.g. with displaced bony avulsion or open injury) varies between units.
• Extent of capsular exploration in zone V lacerations — whether every dorsal MCP laceration mandates formal joint exploration, or only those with a "fight-bite" mechanism or visible capsular breach, remains a point of judgement; the cost of a missed septic joint drives a low threshold.

1. Elson RA. Rupture of the central slip of the extensor hood of the finger. A test for early diagnosis. J Bone Joint Surg Br. 1986;68(2):229-31. PMID 3958008.
2. Handoll HHG, Vaghela MV. Interventions for treating mallet finger injuries. Cochrane Database Syst Rev. 2004;(3):CD004574. PMID 15266538.
3. de Jong JP, Nguyen JT, Sonnema AJM, et al. The incidence of acute traumatic tendon injuries in the hand and wrist: a 10-year population-based study. Clin Orthop Surg. 2014;6(2):196-202. PMID 24900902.
4. Gumussuyu G, Asoglu MM, Guler O, et al. Extension pin block technique versus extension orthosis for acute bony mallet finger; a retrospective comparison. Orthop Traumatol Surg Res. 2020;107(5):102764. PMID 33333280.
5. Burns MC, Derby B, Neumeister MW. Wyndell Merritt immediate controlled active motion (ICAM) protocol following extensor tendon repairs in zone IV-VII. Hand (N Y). 2013;8(1):17-22. PMID 24426888.
6. Merritt WH. The relative motion concept in acute and chronic boutonniere deformity: invited commentary. J Hand Ther. 2023;36(2):258-268. PMID 37045641.
7. Rocchi L, Fulchignoni C, De Vitis R, et al. Extension block pinning vs single Kirschner wiring to treat bony mallet finger. Acta Biomed. 2022;92(S3):e2021535. PMID 35604272.
8. Doyle JR. Extensor tendons: acute injuries. In: Green's Operative Hand Surgery.

Global Epidemiology

• Acute traumatic hand/wrist tendon injuries occur at ~33 per 100,000 person-years (10-year US population study); extensor injuries are more common than flexor, peaking at age 20-29 with male predominance (de Jong 2014).
• Zone III of the index finger is the most common extensor injury site; mallet finger (Zone I) is the most common closed tendon injury and a frequent ball-sport (cricket, basketball, baseball) and occupational injury worldwide.
• ~25% of hand tendon injuries are work-related, concentrated in construction/extraction, food preparation, and transport occupations — relevant for return-to-work planning in any health system.

Side-by-Side Guidance

There is broad international agreement: closed soft-tissue mallet and acute Boutonnière are splinted; open lacerations are repaired; relative-motion rehabilitation is favoured for zone IV-VII. Differences are mainly in operative thresholds for bony mallet and in availability of certified hand therapy.

Registry & Outcome Notes

• Unlike arthroplasty, extensor tendon injuries are not tracked in implant registries; evidence rests on cohort series and the single Cochrane review (Handoll 2004), which highlights the lack of high-level trial data — a recognised research gap.
• Outcome reporting uses Strickland-Steichen / Miller criteria, extensor lag, and total active motion (TAM); standardised PROMs (e.g. MHQ) increasingly supplement these.

High- vs Limited-Resource Practice

• Well-resourced settings: certified hand therapists, custom thermoplastic and relative-motion orthoses, early-active-motion protocols, and ready microsurgical repair.
• Limited-resource settings: reliance on prefabricated/improvised extension splints (aluminium-foam, Stack), static immobilisation when therapy is scarce, and longer travel for specialist repair — making adherence-friendly, low-cost splinting and clear patient education disproportionately important.
• Universal first principles: tetanus status, wound irrigation and prophylactic antibiotics for contaminated/bite wounds, and a low threshold to exclude joint penetration in dorsal lacerations.