Hand & Wrist

Swan Neck and Boutonnière Finger Deformities

Most swan neck and boutonnière deformities are caught early enough to treat with splinting alone. Dr. Peter FitzGibbons evaluates and treats both traumatic and rheumatoid finger deformities in Bethesda and Germantown, Maryland.

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What is swan neck and boutonnière finger deformities?

Swan neck and boutonnière deformities are opposite finger postures caused by an imbalance in the extensor tendon mechanism, from trauma or inflammatory arthritis such as rheumatoid arthritis. Boutonnière causes a bent middle joint with a hyperextended fingertip; swan neck causes a hyperextended middle joint with a bent fingertip. Splinting is first-line; surgery treats deformities that fail conservative care.

The finger extends through a coordinated network of tendons and ligaments called the extensor mechanism. As the extensor tendon crosses the top of the proximal phalanx, it splits into three parts: a central slip, which attaches to the base of the middle (middle interphalangeal, or PIP) joint's neighboring bone and straightens the PIP joint, and two lateral bands, which join fibers from the small intrinsic hand muscles and travel on to straighten the fingertip (DIP) joint (Elzinga & Chung via ASHT; Orthobullets). Two supporting ligaments, the triangular ligament and the transverse retinacular ligament, hold the lateral bands in their correct position on top of and to the sides of the joint.

A boutonnière deformity is a bent (flexed) PIP joint combined with a hyperextended (backward-bent) DIP joint (JAAOS). It begins when the central slip tears or stretches, most often from a direct blow or a "jammed finger" in ball sports, or from joint swelling in rheumatoid arthritis. Without the central slip holding them in place, the lateral bands slide below the joint's axis of rotation. The pulling force that should straighten the middle joint now bends it instead, while over-tensioning the tendon at the fingertip pulls that joint into hyperextension. This is classified as a Zone III extensor tendon injury.

Swan neck deformity is the mirror image: a hyperextended PIP joint with a bent DIP joint, often with the knuckle (MCP) joint bent as well (StatPearls). It can start at either end of the finger. If the tendon at the fingertip fails first, as in an untreated mallet finger, the extensor pull that used to straighten the tip gets redirected up to the middle joint, which gradually hyperextends. Alternatively, tightness of the small intrinsic muscles or the central slip itself can overpull the middle joint into hyperextension directly, with the fingertip curling in response. A stretched-out volar plate, the ligament that normally checks the middle joint from bending backward, is a key contributor once hyperextension develops (StatPearls).

Why These Deformities Happen

Both deformities have two broad causes: trauma and inflammatory arthritis, and the distinction matters because treatment differs between them (JAAOS). Boutonnière deformity follows a laceration or traumatic avulsion of the central slip, or capsular swelling from rheumatoid synovitis; up to half of rheumatoid arthritis patients develop a boutonnière deformity in at least one finger (Orthobullets). Swan neck deformity related to rheumatoid arthritis is more common in women, while the traumatic form shows no strong age or sex pattern (StatPearls); swan neck deformities are reported to occur more often overall than boutonnière deformities (Elzinga & Chung). In the rheumatoid hand, synovitis, tendon damage, ligament rupture, joint subluxation, and eventual joint fusion combine to produce either pattern depending on which structures fail first (Chikkatur & Halim, PubMed). Untreated mallet finger, spasticity from stroke or brain injury, and primary intrinsic muscle tightness are additional recognized causes of swan neck deformity (StatPearls).

Symptoms — do you recognize these?

Boutonnière: the middle joint sits bent while the fingertip bends backward, sometimes with pain and swelling right after a jamming injury
Boutonnière: loss of active straightening at the middle joint, though grip and fist-making are often still possible
Swan neck: the middle joint hyperextends while the fingertip curls forward
Swan neck: difficulty making a full fist because the middle joint "locks" straight during attempted bending
Progressive stiffness or a fixed deformity if the condition goes untreated
A visibly abnormal finger posture that is often more noticeable than it is painful

If your finger will not straighten fully after a jamming injury, or you notice a new bent or backward-curving posture in a joint, call our office promptly. Delayed treatment increases the chance that a flexible, correctable deformity becomes a fixed one requiring surgery.

How we diagnose it

Boutonnière, the Elson test. This is the most reliable way to catch an acute central slip injury before the classic deformity is visible. With the PIP joint bent 90 degrees over the edge of a table, the patient is asked to straighten the middle phalanx against resistance. Weak or absent straightening at the PIP joint with a rigid, involuntary straightening of the DIP joint indicates a torn central slip (Orthobullets; JAAOS).

Swan neck, the Finochietto-Bunnell test. This test tells us whether the limitation comes from tight intrinsic muscles or from a stiff joint capsule. The knuckle joint is held straight while we passively bend the middle joint and note how far it goes, then the test is repeated with the knuckle bent. If PIP bending improves when the knuckle is bent, intrinsic muscle tightness is the likely driver; if there is no change, capsular tightness is more likely (StatPearls).

Imaging. X-rays are not required to diagnose or begin treating an acute boutonnière deformity, but we obtain them in chronic cases to check for arthritis or a bony fragment, and always before considering reconstructive surgery (Orthobullets). For swan neck deformity, X-rays help us evaluate joint damage, arthritis, or wrist collapse, which is particularly relevant in rheumatoid arthritis (StatPearls).

Treatment options

Treatment depends on how long the deformity has been present, whether the joint is still passively flexible, and whether the underlying cause is a one-time injury or ongoing inflammatory arthritis. Splinting is the first-line approach for both deformities (Elzinga & Chung).

Full-time PIP extension splinting (boutonnière)

The PIP joint is splinted straight full-time for six weeks, eight weeks for chronic cases, while the DIP joint is deliberately left free to move. Active DIP motion draws the lateral bands back into their correct dorsal position and stretches the tightened ligament beneath them, which helps reverse the deformity itself (Orthovellum; St. Cloud Orthopedics protocol).

When used: Acute, closed, flexible deformities, sometimes combined with temporary pin fixation across the PIP joint in more severe cases before transitioning to splinting alone.

Serial casting (boutonnière)

A series of casts is applied at progressively greater extension to gradually stretch a chronic but still supple deformity back toward straight.

When used: Chronic, flexible boutonnière deformities that have not fully responded to a standard extension splint.

Relative motion flexion orthosis (boutonnière)

A splint that holds the affected finger's knuckle in slightly more bending relative to its neighbors, unloading the central slip during normal hand use rather than immobilizing the finger completely. A controlled study of 28 patients with chronic Burton Stage I boutonnière deformity found this orthosis improved PIP extension while preserving flexion (ASHT Research Update).

When used: Chronic, mild, still-supple boutonnière deformities as an alternative to full-time splinting.

Figure-of-8 or ring splint (swan neck)

A small splint, sometimes a silver or gold ring splint, that blocks the PIP joint from hyperextending while still allowing it to bend normally for grip and pinch (Wheeless' Textbook of Orthopaedics; ASHT PDF).

When used: Patients who retain full active PIP motion but rest in a hyperextended posture; frequently used long-term in rheumatoid arthritis.

Hand therapy and joint protection

Structured range-of-motion exercises, corrective splinting progressions, and education on joint-protective hand use. Before any surgical rebalancing procedure, passive PIP motion must be optimized through therapy first (Elzinga & Chung). Our physical therapy partners in Rockville work closely with our surgeons on these programs.

When used: Alongside splinting for both deformities, and as a required preliminary step before considering surgery.

Recovery & rehabilitation

Complete correction of either deformity is difficult to achieve, but meaningful improvement in both function and appearance is realistic with the right combination of splinting and, when needed, surgery (Elzinga & Chung). For an acute, closed boutonnière injury treated promptly with splinting, outcomes are generally good. The longer treatment is delayed, the more likely the deformity becomes fixed and requires surgery instead of splinting alone.

Surgery carries a genuine tradeoff that we discuss with every patient beforehand: improving extension at the PIP joint can come at the cost of some flexion, since the same structures that were overpulling the joint into a deformed position were also, in a sense, keeping it mobile. We only recommend surgery after a thorough conversation about this risk, and only in joints confirmed to be supple and free of significant arthritis on preoperative X-ray.

After surgical reconstruction, hand therapy is essential and typically continues for two to three months, progressing from protected splinting to active and then resisted motion as the repair matures. Patients in Montgomery County who need ongoing therapy are seen by our physical therapy team in Rockville, working in coordination with the operating surgeon.

Frequently Asked Questions

What is the difference between swan neck and boutonnière deformity?

They are opposite postures of the same finger joints. In boutonnière deformity, the middle joint is bent and the fingertip is hyperextended. In swan neck deformity, the middle joint is hyperextended and the fingertip is bent. Both come from an imbalance in the extensor tendon system that runs along the back of the finger, but the imbalance runs in opposite directions. Because the mechanics differ, the splints and surgical procedures used for each are different as well, even though both conditions affect the same two joints.

Can a jammed finger really cause a lasting deformity?

Yes. A jamming injury during a ball sport can tear the central slip tendon over the middle joint. If that injury is missed or undertreated, the deformity that follows, called boutonnière deformity, can become fixed within weeks. This is why any finger that will not fully straighten after a jamming injury should be evaluated rather than assumed to be a simple sprain. Early splinting, usually six to eight weeks, resolves most acute cases without surgery.

Does rheumatoid arthritis always cause finger deformities?

Not always, but it is common. Up to half of people with rheumatoid arthritis develop a boutonnière deformity in at least one finger, and swan neck deformity is also frequent, particularly in women. The mechanism differs from a traumatic injury: joint swelling and long-term synovitis gradually damage the tendons and ligaments that balance the finger joints. Because rheumatoid disease is progressive, we monitor these hands over time and intervene with splinting, and sometimes surgery, before a flexible deformity becomes fixed.

Will I need surgery for my finger deformity?

Most people do not. Splinting is the first treatment for both boutonnière and swan neck deformities, and many acute or mild cases resolve without an operation. Surgery becomes reasonable when the deformity is fixed rather than flexible, when splinting has failed over a reasonable trial, or when there is a structural injury like a tendon laceration that will not heal on its own. We confirm with an X-ray beforehand that the joint is free of significant arthritis, since surgery works best on a joint that still moves well.

Why does my finger lock straight when I try to make a fist?

This is the hallmark complaint of swan neck deformity. The middle joint is hyperextending rather than bending as it should, so when you try to close your hand, that joint "locks" backward instead of flexing forward with the rest of the finger. A figure-of-8 or ring splint that blocks the joint from hyperextending, while still allowing normal flexion, often resolves this immediately without surgery, provided the joint itself still has good passive motion.

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Peter G. Fitzgibbons, MD

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Medically reviewed by Peter G. Fitzgibbons, MD, MD

Last reviewed August 5, 2026