Boutonniere Deformity

Boutonnière deformity is a characteristic finger deformity resulting from disruption of the central slip of the extensor mechanism at the PIP joint. The hallmark is a combination of PIP joint flexion and DIP joint hyperextension. Understanding the extensor mechanism anatomy is essential to understanding the deformity — the central slip normally extends the PIP joint, while the lateral bands (which pass dorsal to the PIP joint axis) extend the DIP joint; when the central slip is disrupted, the lateral bands migrate volarly, changing from DIP joint extensors to PIP joint flexors.

• Causes: traumatic (the most common cause — laceration over the dorsal PIP joint, forced volar PIP dislocation, or forced flexion injury to the extended PIP joint); inflammatory (rheumatoid arthritis — the most common cause of non-traumatic boutonnière; the chronic synovitis distends and attenuates the central slip and triangular ligament); post-burn; post-infection
• Anatomy of the deformity: the central slip inserts at the dorsal base of the middle phalanx; central slip disruption → PIP joint can no longer be actively extended → PIP joint falls into flexion; the transverse retinacular ligament (TRL) normally prevents the lateral bands from subluxing volarly; when the central slip is torn, the TRL also elongates; the lateral bands displace volarly below the PIP joint axis → they now flex the PIP joint (instead of extending it) AND hyperextend the DIP joint (their distal pull is unchecked); the triangular ligament (between the two lateral bands dorsally) also attenuates — allowing the bands to remain volarly displaced
• The name `boutonnière` (French: buttonhole) refers to the PIP joint `buttonholing` through the split between the volar-displaced lateral bands

• Mechanism: forced flexion of the extended PIP joint (avulses the central slip from its insertion); volar PIP dislocation (disrupts the central slip and often the volar plate); laceration over the dorsal PIP joint (divides the central slip directly)
• Acute traumatic central slip injury: the boutonnière deformity may not be immediately apparent at the time of injury — the lateral bands maintain PIP extension initially; over 2–3 weeks the lateral bands migrate volarly and the deformity develops; this is why all injuries over the dorsal PIP joint must be assessed for central slip integrity and treated with PIP extension splinting even if the deformity is not yet established — failure to immobilise in extension allows the boutonnière to develop
• Elson test: the most sensitive clinical test for central slip integrity; the finger is placed over the edge of a table with the PIP joint in 90° flexion; the patient is asked to extend the PIP joint against resistance; if the central slip is intact, the DIP joint remains floppy (the extension force is transmitted through the central slip to the middle phalanx, and the lateral bands remain relaxed distally); if the central slip is disrupted, the DIP joint becomes rigid (the patient attempts extension using only the lateral bands, which tighten over the DIP joint making it rigid) — a rigid DIP joint on the Elson test = central slip injury; this test allows differentiation of complete from partial central slip disruption in the acute setting
• Management of acute traumatic central slip injury: continuous PIP extension splinting for 6 weeks (the DIP joint is left free and actively flexed to maintain lateral band mobility and prevent DIP stiffness); the PIP joint must not be allowed to flex during this period — the central slip heals in extension; after 6 weeks, a programme of active PIP flexion with continued night splinting for a further 2 weeks
• Operative indications for acute traumatic boutonnière: open central slip laceration (requires direct repair); large avulsion fragment with bony displacement (>30% articular surface); failed conservative management for closed injury; irreducible volar PIP dislocation

• Prerequisites for surgical reconstruction: the deformity must be passively correctable (the PIP joint must be able to reach full extension passively before any reconstruction is attempted); passive correction is achieved by serial static splinting, dynamic extension splinting, or serial casting over weeks to months; any surgical reconstruction will fail if the PIP joint remains fixed in flexion — the reconstructed central slip will be under excessive tension and rupture
• Surgical options: central slip reconstruction (using a distally based slip of the lateral band or a tendon graft — weaves through the extensor mechanism to recreate the central slip insertion); the Dolphin technique (reefing/shortening of the attenuated central slip and releasing the volar-displaced lateral bands back to their dorsal position by dividing the transverse retinacular ligament); Littler`s technique (lateral band transfer)
• PIP arthrodesis: for severe fixed contractures (Stage III) or after failed reconstruction; the index and middle finger PIP joints are typically fused in approximately 40° of flexion (to maintain pinch function); the ring and little finger PIP joints are fused in approximately 45–50° to allow grip; PIP silicone arthroplasty is an alternative in the ring and little fingers where motion is more critical

• Rheumatoid boutonnière vs pseudo-boutonnière: rheumatoid boutonnière arises from synovitis distending the central slip and TRL — the disease begins at the PIP joint; pseudo-boutonnière occurs as a result of volar plate or PIP joint injury leading to PIP flexion contracture — the DIP joint hyperextension in this case is a compensatory phenomenon rather than true lateral band displacement; in pseudo-boutonnière, the DIP joint is passively correctable with the PIP in any position; in true boutonnière, DIP hyperextension is driven by the laterally displaced lateral bands and is not fully correctable with PIP in extension — this distinction is made on careful clinical examination
• Transverse retinacular ligament (TRL) and oblique retinacular ligament (ORL): the TRL runs transversely from the lateral bands to the flexor sheath at the PIP joint level; normally it prevents the lateral bands from displacing volarly; when attenuated (in boutonnière), the lateral bands drop below the PIP joint axis; the ORL (Landsmeer`s ligament) runs obliquely from the flexor sheath at the PIP joint to the terminal extensor over the DIP joint; it links PIP and DIP extension — when the PIP extends, the ORL tightens and extends the DIP; in boutonnière, the ORL is under greater tension (lateral bands are distal and volar), contributing to DIP hyperextension; release of the ORL is sometimes performed as part of boutonnière reconstruction to reduce DIP hyperextension

• Boutonnière deformity: PIP FLEXION + DIP HYPEREXTENSION; caused by central slip disruption → lateral bands migrate volar to PIP axis → flex PIP + hyperextend DIP
• Causes: traumatic (forced PIP flexion or dorsal laceration) — most common; rheumatoid (synovitis attenuates central slip); post-burn; post-infection
• Elson test: PIP at 90° flexion over table edge; ask patient to extend PIP against resistance; DIP rigid = positive (central slip disrupted, lateral bands doing the extension work); DIP floppy = negative (central slip intact)
• Acute closed central slip injury: deformity may not be apparent for 2–3 weeks; MUST splint PIP in extension for 6 weeks even without established deformity; DIP left free to flex (prevents lateral band adhesions)
• Conservative treatment: 6 weeks PIP extension splint; DIP active flexion during splinting; then gradual PIP mobilisation at 6 weeks; most acute injuries heal without surgery
• Nalebuff classification (RA): Stage I (<40° PIP, correctable) → splint/synovectomy; Stage II (40–70°, partially correctable) → serial splinting then reconstruction; Stage III (>70°, fixed) → PIP arthrodesis or arthroplasty
• Surgical reconstruction prerequisite: PIP must be passively correctable BEFORE surgery; achieve this with serial splinting first; reconstruction in a fixed joint will fail
• TRL: prevents lateral band volar subluxation at PIP level; attenuates in boutonnière; lateral bands drop volar to PIP axis = deformity established
• PIP arthrodesis fusion angles: index/middle ~40° flexion (pinch); ring/little ~45–50° flexion (grip); arthroplasty an option for ring/little where motion is more critical
• Key: boutonnière deformity from central slip disruption; mallet deformity from terminal extensor disruption — both are extensor tendon avulsion injuries at different levels