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Swan neck deformity (SND) is often caused by conditions such as rheumatoid arthritis which cause inflammation in the joints
Swan neck deformity (SND) may be caused by a variety of conditions, especially those that involve muscles, tendons, or nerves:
- Rheumatoid arthritis
- Cerebral palsy
- Lupus
- Parkinson’s disease
- Marfan syndrome
- Scleroderma
- Stroke
- Ehlers-Danlos syndrome
- Psoriatic arthritis
- Flexor tendon ruptures following an injury
- Ischemic injuries
- Tightened hand muscles secondary to injury
- Muscle spasm caused by nerve damage
- Malformation post fracture of the finger
- Untreated mallet finger
What is swan neck deformity?
Swan neck deformity affects the fingers and occurs when joints between the small digital bones become abnormal and the fingers bend to form a curved shape similar to a swan neck:
- Proximal interphalangeal joint (middle knuckle of the finger) hyperextends (bends backward).
- Distal interphalangeal joint (topmost knuckle in the finger) flexes (bends forward).
In some cases, flexion in the metacarpophalangeal (MCP) joint may be seen. The MCP joint is the lowermost knuckle of the finger that attaches to the wrist.
SND may cause difficulty bending the middle joint and a cracking sensation when the finger is bent forcefully. The finger may become stiff, leading to physical impairment.
The condition can occur in all fingers except the thumb because it has only two knuckles, whereas all the other fingers have three knuckles.
What are the different types of swan neck deformity?
There are two proposed classifications of swan neck deformity:
- Nalebuff: Based on the mobility of the proximal interphalangeal (PIP) joint; helps in identifying the severity of the deformity and determining the type of surgical treatment.
- Type I: PIP joints are flexible, and the finger can be moved in all directions.
- Type II: PIP joint flexion is limited in some positions; for example, the finger has restricted movement.
- Type III: PIP joint flexion is limited in all positions, which means the finger is stiff. However, articular surfaces of the PIP joint remain normal.
- Type IV: PIP joints are destroyed; the finger is stiff and has a poor radiographic appearance.
- Welsh: Based on the condition of the muscles present in the fingers.
- Type I: Caused by a deformity or disease in the PIP joint.
- Type II: Caused by a deformity or disease in the metacarpophalangeal joint.
Diagnosis of SND is made by looking at the appearance of the finger as well as radiographic imaging such as X-rays.
How is swan neck deformity treated?
Swan neck deformity is treated based on the severity of the condition.
Non-invasive treatment
- Physical therapy: First-line treatment of SND is physical therapy (PT) or occupational therapy (OT). PT and OT involve exercises and massages that target proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints to help the finger regain its strength and mobility. PT and OT are done post surgery to speed up recovery.
- Splints: A ring splint, also called a figure eight splint, is placed around the PIP joint for a few weeks. The advantage of a ring splint over other splints is that the finger can be bent down freely.
Surgical treatment
- In moderate cases, soft tissue such as the skin, tendons, and ligaments near the PIP joint are repaired.
- In severe cases, the PIP joint may be replaced through arthroplasty, and it is done when the joint is stiff.
- Sometimes, finger joint fusion surgery may be done to fuse the joints together, and the finger becomes immovable in that joint. It is usually done at the DIP joint but may also be done at the PIP joint.
