Boutonniere Deformity: Central Slip Rupture, Volar Lateral Band Migration, and Capener Splinting
In short
Disruption of the central slip permits lateral bands to slide volar to the PIP joint; serial static or Capener splinting restores extensor balance before contractures fix.
In this guide (4 sections)
The Biomechanics and Pathoanatomy of Boutonniere Deformity
Boutonniere deformity (from the French for 'buttonhole') is a classic digital deformity characterized by proximal interphalangeal (PIP) joint flexion accompanied by distal interphalangeal (DIP) joint hyperextension. It represents the biomechanical mirror image of the swan-neck deformity and is commonly triggered by blunt trauma, forced flexion of an extended PIP joint, laceration within Verdan Zone 3, or rheumatoid synovial pannus.
The primary pathological event is disruption or attenuation of the central slip of the extensor tendon at its insertion onto the base of the middle phalanx. Once the central slip fails, the triangular ligament tears, allowing the lateral bands to subluxate volar to the transverse axis of rotation of the PIP joint. In this volar position, the lateral bands convert into active flexors of the PIP joint while exerting continuous, exaggerated extension force on the DIP joint, locking the head of the proximal phalanx through the extensor hood like a button through a buttonhole.
Elson's Test and Boutonniere Staging Matrix
| Clinical Stage / Test | Physical Examination & Joint Mobility | Pathological Tissue Mechanics | Rehabilitation & Orthotic Directive | |
|---|---|---|---|---|
| Elson's Test (Acute Central Slip) | PIP flexed 90° over table edge; extend middle phalanx against resistance | Weak/absent PIP extension; rigid DIP hyperextension (positive Elson's) | PATHOGNOMONIC: Confirms complete central slip rupture before deformity fixes | |
| Stage 1 (Mild / Flexible) | Mild PIP extensor lag (< 15°); PIP joint completely passively correctable | Central slip attenuated; lateral bands dynamically migrate volar during flexion | Continuous static PIP extension splinting for 6 weeks; active DIP flexion | |
| Stage 2 (Moderate / Correctable) | PIP flexion contracture 30-40°; passively correctable with firm manual force | Volar subluxation of lateral bands fixed; triangular ligament attenuated | Dynamic Capener spring splint or serial casting to regain full passive extension | |
| Stage 3 (Fixed Fibrotic Contracture) | Fixed PIP flexion contracture; oblique retinacular ligaments contracted | Volar plate contracture; collateral ligament shortening; joint adhesions | Surgical reconstruction: Fowler central tenotomy, Matev procedure, arthrodesis |
Standardized Clinical Rehabilitation Protocols and Splinting Regimen
- Strict Uninterrupted Static PIP Extension Splinting (Weeks 0 to 6): Fabricate a custom thermoplastic or aluminum gutter splint holding the PIP joint in complete 0-degree extension while leaving the MCP and DIP joints completely free; maintain continuous wear 24 hours a day for 6 weeks; do not allow the PIP joint to bend even once.
- Isolated Active DIP Joint Flexion Drills (Curtis Protocol): With the PIP joint securely locked in 0-degree extension by the splint, instruct the patient to actively flex their DIP joint against light resistance; this active pull draws the subluxated lateral bands dorsally and stretches contracted oblique retinacular ligaments.
- Dynamic Capener Wire-Spring Splinting for Residual Extension Lags: Introduce a dynamic wire-spring Capener splint at Week 6 if an active extensor lag persists; the spring mechanism delivers low-load prolonged stress (LLPS) to overcome joint contracture without tissue trauma.
Frequently Asked Questions
What is a 'buttonhole' or Boutonniere deformity?
When the main tendon on top of your middle finger joint tears, the two side tendons slip down around the sides of your finger. The bone pops up through the torn tendon like a button popping through a buttonhole, locking your middle knuckle bent down and your fingertip bent backward.
What is Elson's test, and how does it spot a torn tendon before the finger deforms?
Your therapist bends your finger over the edge of a table at a 90-degree angle and asks you to push your middle bone straight up against their finger. If the tendon is torn, you will have zero power in the middle joint, while your fingertip becomes rock-hard and stiff.
Why do I have to bend my fingertip while wearing a splint that holds my middle joint straight?
Bending your fingertip while the middle joint is locked straight pulls the slipped side tendons back up to where they belong on top of your finger. It also stretches out stiff ligaments and stops your finger from locking into a permanent deformity.
Related condition guides
Related recovery guides & articles
BookPhysio.in Editorial Team
The BookPhysio.in editorial team writes and maintains this content, checking it against reliable clinical sources. Content follows our medical review policy: general information only, and no page claims a clinical review until a named registered physiotherapist has signed it off.
Read our medical review policy