Swan neck deformity is a finger deformity where the middle joint bends too far backward (hyperextends) while the fingertip joint bends downward into a fixed flexed position. The knuckle joint also tends to flex. The result is a finger that curves into a shape resembling the S-curve of a swan’s neck. It can affect one finger or several, and it develops when the tendons and ligaments that normally balance finger movement fall out of alignment.
How It Looks and Feels
The hallmark of swan neck deformity is visible at two joints in the same finger. The middle joint (called the PIP joint) pushes upward into hyperextension, while the fingertip joint (the DIP joint) droops downward. In early stages, the finger may still move relatively normally, though you might notice the middle joint locking or catching when you try to bend it. Over time, the hyperextension can become fixed, making it difficult or impossible to curl the finger into a fist or grip objects.
Daily tasks that require fine motor control, like buttoning a shirt, turning a key, or washing your hair, become progressively harder. Pain isn’t always the primary symptom. Functional loss is. Many people first notice the deformity when gripping becomes unreliable or the finger starts getting stuck in the extended position.
What Causes the Imbalance
Each finger relies on a delicate balance between tendons that straighten it (extensors) and tendons that curl it (flexors), held in check by small ligaments. Swan neck deformity develops when something disrupts that balance, and it can start from multiple points along the finger.
One common pathway begins at the fingertip. An untreated mallet finger, where the tendon that straightens the fingertip is torn or stretched by a direct blow, shifts extensor force away from the tip and toward the middle joint. Over time, this redistribution causes the middle joint to hyperextend and the fingertip to droop. A structure called the volar plate, a thick ligament on the palm side of the middle joint that normally prevents it from bending backward, gradually loosens under this abnormal pressure.
The deformity can also begin at the middle joint itself. When the central slip of the extensor tendon is damaged, the volar plate becomes lax and a nearby ligament (the triangular ligament) tightens. The small muscles within the hand contract, pulling the middle joint into hyperextension while the fingertip is left unsupported and drops into flexion.
Rheumatoid Arthritis
Rheumatoid arthritis is one of the most common causes. Chronic inflammation weakens the extensor tendons at the fingertip joint, causing them to stretch or slip out of position. The inflammation also damages the volar plate and tightens the intrinsic muscles of the hand. Because RA is a systemic condition, multiple fingers on both hands are often affected, and the deformity tends to progress alongside the disease if inflammation isn’t well controlled.
Trauma and Hypermobility
A deep laceration to the extensor tendon, a direct blow to the fingertip, or a crushing injury can all trigger the cascade. People with hypermobility syndromes, including Ehlers-Danlos syndrome, are also susceptible because their ligaments are naturally looser. In these cases, the volar plate may be lax from the start, making the middle joint vulnerable to hyperextension even without significant trauma or inflammation.
How It Differs From Boutonniere Deformity
Swan neck deformity is often confused with boutonniere deformity because both involve the same two finger joints but in opposite directions. In a boutonniere deformity, the middle joint is stuck in a bent (flexed) position while the fingertip hyperextends. Swan neck is the mirror image: the middle joint hyperextends and the fingertip flexes. Both result from damage to the extensor mechanism, but they originate at different points and require different treatment approaches. If you’re unsure which you’re dealing with, the simplest way to tell them apart is the position of the middle joint: bent down means boutonniere, bent up means swan neck.
How It Progresses
Swan neck deformity generally worsens in stages. Early on, the middle joint moves freely in all directions and the hyperextension can be corrected by gently pushing the joint into a normal position. At this stage, the deformity is flexible and intermittent, sometimes appearing only during certain hand movements.
As the imbalance persists, the middle joint may begin to limit flexion in certain hand positions. The finger might only bend fully when the knuckle is pushed into a specific angle. Eventually, the middle joint becomes stiff in hyperextension regardless of hand position. In the most advanced stage, the joint surfaces themselves deteriorate, with X-rays showing cartilage loss and joint destruction. At that point, the deformity is fixed and the finger is essentially non-functional for gripping.
Splinting and Hand Therapy
In the early, flexible stages, the primary goal is to prevent the middle joint from snapping into hyperextension while still allowing you to bend the finger. Ring-style splints worn over the middle joint do exactly this. They sit on the finger like a piece of jewelry, blocking full extension but allowing you to curl the finger normally. These work well for people with hypermobility or mild deformity, and many people wear them throughout the day during regular activities.
Static splints that hold the finger in one position are also used, though they come with trade-offs. A rigid splint can prevent hyperextension effectively, but it also blocks flexion, which limits function during tasks like gripping or washing. Some therapists use a dynamic splint design that incorporates a rubber band between the fingertip and wrist. This keeps the finger gently flexed while allowing the patient to actively straighten the finger against resistance, building strength in the extensor muscles. A typical protocol involves extending the finger against the band’s tension about 10 times per hour.
Hand therapy also focuses on stretching the tight intrinsic muscles that contribute to the imbalance. Exercises that isolate the middle joint, bending and straightening it while the knuckle is held in different positions, help maintain mobility and can slow progression.
Surgical Options
Surgery is considered when the deformity progresses despite splinting, when the middle joint is becoming stiff, or when hand function is significantly impaired. The specific procedure depends on what’s causing the imbalance and how far it has advanced.
For flexible deformities, the most common approach is volar plate advancement, which tightens the loosened ligament on the palm side of the middle joint to restore its ability to block hyperextension. This is often combined with rebalancing the tendons around the joint. If the flexor tendon at the middle joint is intact, it can be used as an internal tether (a tenodesis) to prevent the joint from overextending. Another option involves reconstructing a ligament that links the extensor mechanism at the fingertip to the flexor mechanism at the middle joint, restoring the natural give-and-take between the two joints.
When the deformity is driven by excessive pull from the extensor tendon’s central slip, a procedure called a central slip tenotomy partially releases that tension. For late-stage deformities with joint destruction, joint fusion or replacement may be the only remaining options. Fusion locks the joint in a functional position, sacrificing movement for stability. Joint replacement preserves some range of motion but has a limited lifespan, particularly in fingers that take heavy use.
Recovery from these procedures typically involves several weeks in a splint followed by a structured hand therapy program. Regaining full finger mobility takes months, and the outcome depends heavily on how much joint damage was present before surgery.
The Role of Early Treatment
Swan neck deformity is far easier to manage when caught early. A flexible deformity that responds to splinting and exercise can often be kept functional for years. Once the joint stiffens or the cartilage deteriorates, options narrow considerably and outcomes are less predictable. For people with rheumatoid arthritis, controlling the underlying inflammation with appropriate medication is the single most important factor in preventing progression. For anyone who notices a fingertip drooping after an injury, prompt treatment of the initial mallet finger can prevent the chain reaction that leads to swan neck deformity down the line.