SWAN NECK DEFORMITY
PIPJ Hyperextension + DIPJ Flexion
Nalebuff Classification (RA)
Critical Must-Knows
- Characterized by PIPJ Hyperextension and DIPJ Flexion.
- Driven by dorsal subluxation of the lateral bands (opposite of Boutonniere).
- Can be Primary (Volar plate laxity/Intrinsic tightness) or Secondary (Mallet finger).
- Bunnell's Intrinsic Tightness Test discriminates Type I from Type II.
- Conservative management involves blocking PIPJ hyperextension (Figure-of-8 splint).
- Surgery ranges from soft tissue balancing (FDS tenodesis) to salvage (Fusion).
Examiner's Pearls
- "If the PIPJ is stiff, tenodesis will NOT work. You must release the contracture first.
- "In Mallet-induced Swan Neck, treating the DIPJ often corrects the PIPJ (if flexible).
- "Intrinsic tightness is defined as less PIP flexion when the MCP is extended vs flexed.
Clinical Imaging
Imaging Gallery
The Intrinsic Trap
The Problem
Intrinsic Tightness In Rheumatoid Arthritis, the intrinsic muscles often become fibrotic and tight. This pulls the lateral bands taut and hyper-extends the PIPJ. If you simply perform a capsulodesis or tenodesis without releasing the intrinsics, the deformity will recur or the finger will be stiff.
The Solution
Bunnell's Test You MUST assess intrinsic tightness. Passive PIP flexion is checked with MCP Extended (tightens intrinsics) and MCP Flexed (relaxes intrinsics). If Flexion with Extended MCP is LESS than Flexion with Flexed MCP, the test is POSITIVE.
| Condition | PIPJ | DIPJ | Lateral Bands | Volar Plate |
|---|---|---|---|---|
| Swan Neck | Hyperextended | Flexed | Dorsal Subluxed | Lax/Ruptured |
| Boutonniere | Flexed | Hyperextended | Volar Subluxed | Normal/Contracted |
| Mallet | Normal | Flexed | Normal | Normal |
| Jersey | Normal | Extended (cannot flex) | Normal | Normal |
DOVEPathomechanics
Memory Hook:The Swan flies like a DOVE.
FLIDNalebuff Classification
Memory Hook:The lid (FLID) is on the deformity.
SOFTSurgical Options
Memory Hook:Keep the finger SOFT.
Overview
Swan Neck deformity consists of hyperextension of the PIPJ and reciprocal flexion of the DIPJ. It is caused by an imbalance where the extensor mechanism subluxates dorsally at the PIPJ.
It is the reverse of a Boutonniere deformity. It requires laxity of the Volar Plate to permit hyperextension. The lateral bands displace dorsal to the axis of rotation of the PIPJ. Once dorsal, they act as extensors of the PIPJ, locking it in hyperextension. This tension is transmitted distally, but because the lateral bands are effectively shortened by the hyperextension, the DIPJ is pulled into flexion by the FDP (Passive Insufficiency). Or, the FDP causes DIPJ flexion because the extensor mechanism has no power at the DIPJ? Actually, the DIPJ flexion is usually passive due to the FDP pull exceeding the extensor pull (which is all used up at the PIPJ).
Pathophysiology and Mechanisms
Extensor Apparatus
- Lateral Bands: Normally lie dorsal to the axis of rotation of the PIPJ (extensors).
- Transverse Retinacular Ligament: Prevents dorsal migration. In Swan Neck, this ligament stretches or fails.
- Triangular Ligament: Becomes tight / shortened.
The interplay of these ligaments creates the balance.
Classification Systems
Nalebuff Classification (Rheumatoid)
- Type I: PIPJ is flexible in all positions. No intrinsic tightness.
- Type II: PIPJ is flexible, but intrinsic tightness is present (Bunnell +ve).
- Type III: PIPJ flexion is limited (Stiff). X-ray often normal.
- Type IV: PIPJ is stiff and X-ray shows joint destruction.
This classification guides treatment from splinting (I), release (II), manipulation (III), to fusion (IV).
Clinical Assessment
Examination
- Deformity: Obvious PIP Hyperextension / DIP Flexion.
- Passive Correctability: Can you reduce the PIPJ easily? (Type I/II vs III).
- Impact: Does the finger initiate flexion? Locking?
- Mallet: Check if the DIPJ can extend passively.
Always document the passive range of motion.
Investigations
Radiology
- Views: AP and Lateral.
- Findings:
- Joint Space: Look for narrowing/erosions (Type IV).
- Alignment: Degree of hyperextension.
- Fracture: Mallet fracture at DIPJ?
Crucial to rule out joint destruction before offering soft tissue reconstruction.
Management Algorithm
Splinting (Type I)
- Device: Figure-of-8 Splint / Oval-8 / Silver Ring Splint.
- Mechanism: Blocks the last 10-20 degrees of extension (prevents hyperextension) but allows full flexion.
- Mechanism: Blocks the last 10-20 degrees of extension (prevents hyperextension) but allows full flexion.
- Outcome: Highly effective for mobile deformities. Patients often wear silver rings permanently as jewelry.
Compliance is very high with silver rings compared to plastic.
Surgical Considerations
FDS Tenodesis (Swallow Tail)
- Indication: Type I (Mobile).
- Technique: One hemislip of the FDS tendon is divided proximally (in palm or P1).
- Routing: It is passed through the flexor sheath and anchored into P2 bone or looped.
- Effect: Creates a check-rein that prevents PIP hyperextension.
- Rehab: Dorsal block splint to protect the tenodesis.
The tenodesis must be tensioned with the PIPJ flexed 20-30 degrees.
Complications
Surgical Complications
- Recurrence: Common in RA due to progressive disease; occurs in up to 30% at 5 years.
- Stiffness: Correction of hyperextension often results in loss of full flexion; trade-off between stability and motion.
- Infection: Increased risk with silicone implants or immunosuppressive RA medications.
- Tendon Rupture: FDS tenodesis can fail if tensioned too tightly or if manipulation is forceful.
- Implant Failure: Silicone arthroplasty fractures over time (7-10 year lifespan).
- Neuroma: Risk of digital nerve injury with lateral approaches.
- Flexion Contracture: Over-correction can limit extension; reported in 15% of tenodesis cases.
Careful patient selection and setting realistic expectations are essential.
Rehabilitation
- Splint: Dorsal block splint (prevents extension past 20 deg).
- Motion: Active flexion allowed.
- Wean: Start gentle active extension.
- Check: Ensure no recurrence of hyperextension "snap".
- Strength: Grip strengthening using putty and Theraputty exercises.
- Splint: Night splinting often continued for 3-6 months to prevent recurrence.
- Dexterity: Fine motor tasks (picking up coins, buttons, writing).
- Goals: Functional ROM (30-80 degrees) is better than Full ROM.
- Work Simulation: Occupation-specific tasks to prepare for return to work.
- Long-term Splinting: Silver ring splints worn permanently in some cases.
- Monitoring: Regular hand therapy reviews to detect recurrence early.
- Disease Control: In RA, coordination with rheumatology for DMARD optimisation.
Prognosis
Expected Outcomes by Treatment
- Splinting (Type I): Excellent functional outcomes; 80-90% symptom control with ring splints.
- FDS Tenodesis: Good results in 70-80%; some loss of full flexion expected (10-20 degrees).
- Intrinsic Release: Effective for Type II; may need combined with tenodesis.
- Fusion (Type III/IV): Reliable pain relief; functional position (30-45 degrees) preferred.
- Arthroplasty: Fair function for 7-10 years; silicone fracture is inevitable long-term.
Patient satisfaction depends on realistic expectations and appropriate procedure selection.
Evidence Base
Classification Utility
- Classic paper describing the 4 types
- Tailored treatment algorithm based on mobility and X-ray
- Emphasized the importance of intrinsic tightness
FDS Tenodesis Outcomes
- Review of superficialis tenodesis for swan neck
- Corrected widespread deformity in majority
- Complication of flexion contracture in 15%
- Effective for Type I/II
Ring Splints
- RCT comparing silver ring splints to thermoplastic
- Silver rings had higher compliance and patient satisfaction
- Both effectively corrected deformity and improved dexterity
Spiral Oblique Retinacular Ligament
- SORL reconstruction uses a tendon graft to link DIP extension to PIP flexion
- Complex procedure
- Corrects both deformities theoretically but stretches out over time
Dermodesis
- Removing an ellipse of skin from volar PIPJ
- Shortens the volar skin to act as a check-rein
- Simple, low risk, but skin stretches over time
- Good for mild deformity
Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Rheumatoid Assessment
"A 60-year-old with RA has Swan Neck deformities in fingers 3, 4, 5. She wants surgery because they 'lock'. What is your assessment?"
Scenario 2: The Mallet Swan
"A patient presents with a chronic Mallet finger and a secondary Swan Neck deformity. The PIPJ is flexible. How do you treat the Swan Neck?"
Scenario 3: Post-Traumatic Stiff Swan Neck
"A young carpenter had a hyperextension injury. Now has a fixed Swan Neck (Type III). X-ray is normal. He needs strength."
Scenario 4: Multiple Digits in RA
"A 55-year-old woman with well-controlled rheumatoid arthritis presents with Swan Neck deformities in all fingers of her dominant hand. She is an artist and cannot hold a brush. Radiographs show preserved joint spaces. What is your approach?"
MCQ Practice Points
Diagnosis
Q: What constitutes a positive Bunnell test? A: Decreased PIP flexion when the MCP joint is extended (vs flexed).
Anatomy
Q: Which ligament normally prevents dorsal subluxation of the lateral bands? A: Transverse Retinacular Ligament.
Classification
Q: In Nalebuff Type II, what is the defining feature? A: Intrinsic muscle tightness.
Treatment
Q: What is the primary function of a Figure-of-8 splint in Swan Neck? A: To block PIP hyperextension while allowing flexion.
Surgical Indication
Q: What is the surgical treatment for Nalebuff Type II Swan Neck? A: Intrinsic release (Littler procedure) to address the underlying intrinsic muscle tightness.
Secondary Swan Neck
Q: How does a Mallet finger cause Swan Neck deformity? A: Loss of the terminal tendon anchor causes proximal retraction of the extensor mechanism, concentrating extension force at the PIPJ.
Australian Context
Splinting and Therapy:
- Silver Ring Splints (Oval-8, Murphy) are often imported from the USA or custom-made by specialized jewelers.
- Australian Hand Therapy Association (AHTA) members provide specialized splinting services.
- NDIS may fund splints and hand therapy for eligible patients with permanent disability from RA.
- Medicare rebates available for hand therapy under Enhanced Primary Care (EPC) referrals.
Epidemiology and Access:
- Rheumatoid arthritis affects approximately 1.9% of Australians, with higher prevalence in older females.
- Indigenous Australians have higher rates of untreated trauma leading to chronic deformities (Mallet to Swan Neck progression).
- Hand surgeons with specialized RA experience are concentrated in major metropolitan centres.
- Public hospital waiting lists for elective hand surgery can be Category 3 (up to 365 days).
Telehealth Considerations:
- Assessment of intrinsic tightness (Bunnell's test) is difficult via video consultation.
- Pre-operative counselling can be effectively done remotely.
- Post-operative follow-up may use hybrid models with local allied health support.
Occupational and Legal:
- WorkCover claims arise from repetitive strain or crush injuries causing secondary deformity.
- Return-to-work programs should involve hand therapist and occupational physician collaboration.
- Functional capacity evaluations may be required for workers' compensation cases.
Multidisciplinary Care:
- Rheumatology, Hand Surgery, and Hand Therapy must communicate regarding disease control.
- Arthritis Australia provides patient support groups and educational materials.
- Climate considerations: Heat can reduce splint compliance; breathable materials preferred.
Cost Considerations:
- Silver ring splints cost $100-200+ each (not PBS subsidised).
- Silicone arthroplasty implants have significant cost implications in public hospital budgets.
- Early referral and conservative management reduce overall healthcare costs.
High-Yield Exam Summary
Classification (Nalebuff)
- •Type I: Mobile
- •Type II: Intrinsic Tight
- •Type III: Stiff
- •Type IV: Arthritis
Management
- •Splint: Oval-8 / Ring
- •Sx I: Tenodesis
- •Sx II: Intrinsic Release
- •Sx III/IV: Fusion
Mechanics
- •Volar Plate Laxity
- •Lateral Bands Dorsal
- •Bunnell Test Positive
- •Mallet drive