Swan neck deformity vs Boutonniere deformity

Alterations in the relationships between the balanced extrinsic and intrinsic musculature of the hand due to trauma or secondary to the effects of systemic disease may cause the development of functional deformities such as a boutonnière or swan-neck deformity.

	Swan-neck deformity		Boutonniere deformity
Deformity	PIPJ	Hyperextension	PIPJ	Flexion
	DIPJ	Flexion	DIPJ	Hyperextension
	MCPJ	Flexion	MCPJ	Extension
Thumb	Not affected		May be affected
Function	Impaired	Inability to make fist due to PIPJ hyperextension	More of aesthetic concern	Able to make fists
Causes and Biomechanics	Wrist synovitis	Carpal collapse, supination and ulnar translation lengthens/weakens extrinsic tendons which are then overpowered by intrinsic tendons resulting in MCPJ flexion and PIPJ extension	Central slip dysfunction from tear (trauma) or attenuation (synovitis in RA)	Triangular ligament stretches
	MCPJ synovitis	Weakened extensor tendon insertion at P1 increases extensor force on P2 leading to PIPJ hyperextension		Lateral bands sublux in volar direction maintaining a persistent PIPJ flexion
	MCPJ volar plate	Weakened volar plate leads to MCPJ subluxation and shortened intrinsics which causes PIPJ hyperextension		Concentration of extensor force on DIPJ
	PIPJ synovitis	Attenuates volar plate and triangular retinacular ligament (TRL) resulting in dorsal translation of lateral band and destruction of FDS insertion leading to PIPJ hyperextension and DIPJ flexion due to increase in FDP tension and decrease in lateral band tension		In chronic cases, fixed contracture develops
	PIPJ volar plate	Lax volar plate allows for PIPJ hyperextension
	DIPJ mallet injury	Extensor power is concentrated on the central slip resulting in PIPJ hyperextension and volar plate weakens over time
Classification and management	Nalebuff’s		Nalebuff and Miller’s
1	Flexible	1. PIPJ extension block splints (Figure of 8 or Murphy ring) 2. FDS sling/tenodesis i.e. Beckenbaugh technique (FDS slip is transected and brought over A2 pulley and sutured back to itself) 3. Littler ORL reconstruction (creation of ORL using lateral band) 4. Lateral band mobilization and skin release (Nalebuff and Millender)	Extensor lag of 10-15 degrees, passively correctable	1. Splinting (DIP in full extension) 2. Dolphin or Folwer tenotomy (Releasing lateral tendons near their insertion into distal phalanx)
2	Intrinsic tightness	Intrinsic release at MCPJ	Extensor lag of 30-40 degrees, passively correctable	Shorten central slip or Centralize lateral bands
3	Fixed hyperextension deformity of PIP	1. MUA 2. Intrinsic release	Fixed flexion deformity with retinacular tightness (ORL and TRL)	ORL (which maintains DIP extension and prevents flexion) stretching and then proceed as in stage 2 when PIP is fully extended
4	Arthritic	1. Arthrodesis of PIPJ 2. Arthroplasty	Arthritic	Arthrodesis or Swanson type arthroplasty