Swan neck deformity is an orthopedic condition that changes the normal alignment of the joints in a finger, resulting in a characteristic, curved appearance. This deformity occurs when the balance between the flexor and extensor tendons that control finger movement is disrupted. While it can affect a single finger, it is often a sign of a chronic condition affecting multiple joints in the hand. The structural changes significantly impact a person’s ability to use their hands for everyday tasks.
Defining the Characteristic Appearance
The name “swan neck” comes from the visual resemblance of the affected finger to the outstretched neck of a swan. This distinctive shape involves an abnormal posture in two of the three main joints. The middle joint, known as the Proximal Interphalangeal (PIP) joint, is forced into hyperextension, bending backward beyond its normal straight position.
The final joint, the Distal Interphalangeal (DIP) joint (closest to the fingertip), compensates by curling downward into flexion. This opposing movement creates an “S” shape when the finger is viewed from the side. This pattern of hyperextension at the PIP joint and flexion at the DIP joint differentiates it from a Boutonnière deformity, where the opposite joint pattern occurs. The deformity results from a mechanical imbalance in the finger’s complex extensor mechanism, the network of tendons and ligaments responsible for straightening the finger.
Primary Causes
The most common underlying factor leading to swan neck deformity is chronic inflammation associated with Rheumatoid Arthritis (RA). In RA, the chronic synovitis, or inflammation of the joint lining, weakens the tissues and ligaments surrounding the PIP joint, particularly a strong ligament on the palm side called the volar plate. This weakening allows the PIP joint to hyperextend, which then shifts the lateral stabilizing tendons above the joint axis, further perpetuating the hyperextension.
This mechanical change creates an imbalance in the extensor mechanism, which transmits excessive force to the DIP joint, causing it to flex. The deformity can also arise from a direct injury, such as hyperextension trauma to the PIP joint that ruptures the volar plate. Traumatic damage to the extensor tendon at the DIP joint, like an untreated mallet finger injury, can also lead to secondary development of the deformity over time.
Other Contributing Factors
Neurological conditions, such as stroke or cerebral palsy, can cause muscle spasticity and imbalance, where overactive extensor muscles pull the finger into the hyperextended position. Connective tissue disorders like Ehlers-Danlos Syndrome (EDS) are also a factor, as generalized joint hypermobility and ligamentous laxity make the joints prone to hyperextension.
Functional Limitations and Associated Symptoms
The structural change in the finger directly translates into significant limitations in hand function. The hyperextension of the middle PIP joint severely impairs the ability to flex the finger inward, making it difficult or impossible to form a complete fist. This inability to bend the finger properly makes it challenging to grasp or pinch objects, directly affecting grip strength.
Individuals frequently experience difficulty performing fine motor tasks that require precision and dexterity, such as buttoning a shirt, picking up small coins, or using a pen. The unbalanced tension in the tendons can also cause a snapping sensation when the finger is moved. As the condition advances, the joints may become stiff and painful, especially during movement or when pressure is applied to the affected area.
Treatment and Management Strategies
Management of swan neck deformity often begins with conservative, non-surgical approaches, especially when the joint remains flexible and can be passively corrected. Physical and occupational therapy are important components, focusing on maintaining the range of motion and improving muscle strength.
A primary non-surgical strategy involves specialized splints or orthotics, such as silver ring splints or figure-eight splints. These splints are designed to be worn over the PIP joint to physically block hyperextension while still allowing the necessary flexion for grasping. If the deformity is rigid or severe, or if conservative methods fail to restore function, surgical intervention may be necessary.
Surgical Options
For flexible deformities, soft tissue reconstruction procedures, such as the Littler procedure, can be performed to create a volar restraint that prevents the PIP joint from bending backward. For severe or long-standing deformities where joint damage is extensive, a surgeon may recommend arthrodesis (joint fusion to stabilize the finger) or arthroplasty (replacing the damaged joint).