SWAN NECK DEFORMITY

Swan neck deformity was possibly first described by Thomas Sydenham in 1676, although the first comprehensive clinical observations were given by Charcot and Garrod. The finger malformation is characterized by proximal interphalangeal (PIP) joint hyperextension and distal interphalangeal (DIP) joint flexion, which produces a “kink” in the digit resembling the shape of a swan’s neck while in flight. The deformity occurs in ~50% of patients with rheumatoid arthritis (RA).  Swan neck deformity can also be secondary to muscle imbalance secondary to disorders like cerebral palsy, excessive ligamentous laxity secondary to Ehlers-Danlos syndrome, ligamentous laxity and tendon imbalance secondary to SLE, and to chronic injuries such as a mallet finger, volar plate rupture, or attenuation of the Landsmeer’s spiral oblique retinacular ligament. ^1-4

Pathophysiology

• Primary pathology occurs at a single joint with secondary changes at the other; metacarpophalangeal (MP) joint flexion does not have to be present
• Stretching of the extensor tendon or weakening of tendon attachment to the base of the distal phalanx leads to laxity of DIP joint, as evidenced by mallet finger and to subsequent hyperextension at the PIP joint produces classic swan neck deformity
• Attenuation or rupture of the volar plate can also produce a swan neck deformity
• In RA, fixed swan’s neck deformity is thought to be initially triggered by the adhesion of extensor tendons to the dorsum of the PIP joint, followed by attenuation of the transverse retinacular ligament and/or volar plate secondary to synovitis.³

Related Anatomy

• DIP joint
• PIP joint
• Palmar plate
• Extensor tendon
• Intrinsic muscles
• Volar plate
• Landsmeer’s spiral oblique retinacular ligament 
• Triangular ligament which tightens in swan neck deformity

Classification

• Although swan neck deformity arises from initial laxity of the DIP joint or the PIP volar polate, the deformity is classified according to the class of hyperextension at the proximal joint
  • Extrinsic type: muscle fibrosis, spasm, tendon adhesions and pathologic flexion of the wrist and metacarpophalangeal joint tighten extrinsic extensor tendons
  • Intrinsic type: intrinsic muscular contraction overpowers extrinsic flexors due to poor blood flow, tendon adhesion or volar subluxation of the metacarpophalangeal joint
  • Articular type: synovitis, trauma, surgical interventions, congenital joint laxity, partial flexor tendon rupture or the formation of subcutaneous scar tissue may weaken, stretch or degrade joints leading to instability and force imbalances
• In rheumatoid arthritis the swan neck deformities can also be classified by four types: 1. Swan neck deformity with full range of motion; 2. Swan neck deformity with intrinsic tightness; 3.Swan neck deformity with a fixed PIP contracture; 4.Swan neck with severe PIP joint arthritis.

Incidence and Related Conditions

• Associated with rheumatologic diseases, neurologic and vascular lesions and some heritable connective tissue disorders such as Ehlers Danlos syndrome
• Approximately 50% of RA patients exhibit swan neck or boutonniere deformity of varying severity
• Congenital swan neck deformity is uncommon and results from laxity of the palmar plate of the PIP joint
• swan neck deformity is the most common joint deformity in patients with system lupus erythematosus and Jaccoud arthropathy
• May be a complication of some surgical interventions, resulting from joint fibrosis after fixation to treat fracture and/or dislocation of the PIP joint

Differential Diagnosis

• Boutonniere deformity
• Mallet finger
• Volar plate rupture
• Hyperligamentous laxity

In most cases, swan neck deformity develops in the later stages of clinical syndromes or as the result of injury or post-operative interventions. Patients will typically already be under medical observation before the presentation of the deformity.  Patients sometimes decide to seek medical attention when it becomes difficult to initiate active PIP joint flexion.

RECOMMENDED HAND SURGEON THERAPY ORDERS

• Edema control
• Patient education on prevention
• PIP flexion splinting limiting 30 degrees of flexion for prolonged conservative management.
• Isolated active range of motion exercises, blocking exercises for PIP and DIP
• Post-operative Massage with bacitracin until 48 hours after suture removal, then switch to vitamin E cream
• Tendon gliding exercises when allowed
• Begin strengthening exercises at 8-10 weeks after splinting has been discontinued
• Scar conformer splinting if scar is hypertrophic if applicable
• Progressive PROM stretches when applicable which may include dynamic splinting or straps
• Work Hardening / work simulation if necessary

REVIEW OF THERAPIST CONSERVATIVE INTERVENTIONS FOR SWAN NECK DEFORMITY

Therapy for non-operative patient to include:

For acute onset, full time splinting of PIP in 30 degrees of flexion for 6 weeks.  Following full time splinting, switch to part time day and full night in slight flexion splinting.  This can be maintained for a total of 3 months if necessary to counterbalance flexion postures during the day.

• Prefab, alumo-foam, or custom splint fabrication by an Occupational Therapist or Physical Therapist, Certified Hand Therapist.  Custom splints may provide a more proper fit and comfort, to immobilize DIP, but allow full DIP AROM. (see image)
• Patient should return 1x per week for splint checks and skin checks, until week 6.
• At week 1, full AROM is initiated during to encourage DIP and MCP joint gliding only.  Follow up visits weekly to monitor progress, skin inspection and compliance.
• At week 6, initiate PIP AROM; tendon gliding & blocking exercises for PIP within comforts range and gradually progress to PIP extension to approximately 10-15 degrees flexion over the next 2 weeks. (limit full extension to prevent early overstretching).  This technique may not provide any correction in certain cases.
• Encourage towel wringing exercises with warm water to full functional use.
• Take breaks, ice x 10 minutes intermittently throughout the day.
• At 8-10 weeks, gentle PRE’s may be initiated.

REVIEW OF POST OPERATIVE INTERVENTIONS FOR BOUTINNIERE DEFORMITY - NOT INCLUDING SHORT ARC EARLY AROM (ZONE 3 EXTENSOR TENDON INJURY)

Early hand therapist assistance and intervention:

• At week 1-4, dressing assessment and changing with oil embedded dressings to keep the surgical site clean and dry.  Check skin for signs of infection and educate patient.
• Edema control – encourage elevation, encourage early gentle finger ROM, watch for RSD/CRPS signs.
• Very light compressive sleeves for fingers and/or hand.  Be aware of the tourniquet effect causing distal edema accumulation and restricted blood flow to the surgical site.
• Patient education – teach signs of infection, avoid maceration of surgical site, encourage a smoke free recovery, avoid excessive exercise to minimize scarring.
• Encourage AROM to uninvolved fingers as tolerated to optimize AROM and minimize edema.
• At week 4, referral to an Occupational Therapist or Physical Therapist / Hand Therapist for protective splinting.  Custom splint fabrication may provide 35-40 degrees in flexion posture with a circumferential gutter PIP, DIP is allowed full AROM. (see image)
• At week 4, initiate AROM blocking exercises for the PIP and DIP, focusing on isolated joint motion for each.  Reverse blocking (Active PIP extension while supporting MCP’s in flexion) may also be initiated to focus on regaining some PIP extension. (see image)
• At week 4, initiate tendon gliding exercises only within patients’ comfort to avoid early tendon overstretching. (see image)
• At week 6, initiate gentle PROM to involved finger(s) to maximize functional grasp and AROM. Introduce tendon gliding exercises a few times per day to minimize stiffness from the splinting, with intermittent splinting as depicted in the conservative management section.
• At week 7-8, if necessary, initiate self stick flexion wrapping, static progressive or dynamic splinting with MCP block splint, velcro flexion strap, or flexion golf glove to maximize PROM and ultimately AROM.   Be sure to look out for an extensor lag at the PIP (see image)
• Continue extension splinting for night time to compensate for all the flexion activities and postures during the day.  Introduce light extension assist spring loaded splint for 10 minute intervals 3x per day for PIP extension
• At week 8, progress to full unrestricted AROM and PROM of fingers, thumb and wrist while. 
• At week 8-10, initiate light strengthening as tolerated with no pain and to patients’ comfort as they progress (gripper, putty, clips, web, dowel grasps, towel wringing, etc).

When Applicable:

• Education the patient to limit heavy strengthening tasks, lifting and heavy use until week 10 post-op.
• Encourage finger food tasks, in hand manipulation and coin stacking, and palm scratch exercises to optimize AROM and function.
• Encourage towel wringing exercises for incorporating fingers and wrist into HEP and functional re-integration.
• When available, find a Certified Hand Therapist to provide additional splinting

*Wound healing may be prolonged in diabetic patients and smokers.

*There are short ARC protocols in review by several researchers which allow earlier introduction of controlled AROM.

• Operative: flexible implant arthroplasty has high complication rates.
• Volar tenodesis may stretch out with time and cause recurrent swan neck deformity

• Management decisions should be based on classification and staging
• Patient's overall medical status, corticosteroid use and the condition of other large joints and deformities also should be considered
• In later stages, soft-tissue procedures alone may not produce lasting operative correction
• Volar plate tenodesis is useful and can be done by using a flexor digitorum sublimis (FDS) tenodesis.  In this procedure a single slip of the FDS tendon is left attached to its insertion site on the base of the middle phalanx while it is cut proximally to separate it from the intact portion the FDS tendon. The PIP joint is temporarily blocked in flexion with a K-wire.  The FDS slip is passed under the flexor tendons and attached to the edge of the A-2 pulley or anchored to the bone in this area. The tension is set to create a 20-30 degree flexion contracture of the PIP joint. the k-wire is removed at 3-4 weeks.
• When intrinsic tightness is associated with a swan neck deformity, an intrinsic release should be considered during planning of the surgical  reconstruction. 
• Triangular ligament tightness is always part of the swan neck deformity
• Swan neck deformities are frequently associated with SLE

New Articles

1. Carlson E, Carlson M. Treatment of swan neck deformity in cerebral palsy. J Hand Surg Am 2014;39(4):768-72. PMID: 24613587
2. Ko J, Kalainov D, et al. Double lateral band transfer for treatment of traumatic hyperextension instability of the proximal interphalangeal joint: a report of two cases. Hand (N Y) 2012;7(1):108-13. PMID: 23450120
3. Wei DH, Teronno AL. Superficialis sling (flexor digitorum superficialis tenodesis for swan neck reconstruction. J Hand Surg Am 2015; 40(10): 2068-2074.
4. Lin JD, Strauch RJ. Closed soft tissue extensor mechanism injuries (mallet, boutonniere, and sagittal band).  J Hand Surg Am 2014: 39(5): 1005-1011.

Reviews

1. Dreyfus J, Schnitzer T. Pathogenesis and differential diagnosis of the swan-neck deformity. Semin Arthritis Rheum 1983;13(2):200-11. PMID: 6673115
2. Smith G, Amirfeyz R. The flexible swan neck deformity in rheumatoid arthritis. J Hand Surg Am 2013;38(7):1405-7. PMID: 23455410

Classics

1. Welsh R, Hastings D. Swan neck deformity in rheumatoid arthritis of the hand. Hand 1977;9(2):109-16. PMID: 914085

Hand Therapy References

1. Cannon, et al. (2001).  Diagnosis and Treatment Manual for Physicians and Therapists, Upper extremity Rehabilitation (4^th ed).  The Hand Rehabilitation Center of Indiana.
2. Mackin, Callahan, Skirven, Schneider, and Osterman, (2002). Rehabilitation of the Hand and Upper Extremity, 1, (5^th ed). St Louis, MO: Mosby Year Book, Inc.
3. Cooper, (2014). Fundamentals of Hand Therapy; Clinical Reasoning and Treatment Guidelines for Common Diagnoses of the Upper Extremity, (2^nd ed). Mosby, imprint of Elsevier Inc.
4. Stanley and Tribuzi. (1992).  Concepts in Hand Rehabilitation.  F. A. Davis Company