Gull Wing Deformity (Seagull Sign): Erosive Osteoarthritis

Answer:

Gull wing deformity is a central subchondral erosion of a distal interphalangeal joint flanked by marginal osteophytes, so the joint contour resembles a gull in flight. It points to erosive osteoarthritis. The central erosion is the finding that counts: marginal erosions turn up in ordinary hand osteoarthritis as well, so they do not separate the two.

Two central-erosion patterns are described and they sort by joint, not by disease: gull wing predominates at the distal interphalangeal joints, saw-tooth at the proximal interphalangeal joints [1]. In the same series marginal erosions were present in 100% of erosive and 80% of non-erosive hands [1], so it is the central defect, not erosion as such, that is worth describing.

Neither pattern is specific. A gull wing contour has been reported in late psoriatic arthritis at the interphalangeal joints and in rheumatoid arthritis at the proximal interphalangeal joints [4], so treat it as a pointer that narrows the differential rather than as a diagnosis.

Why is it called so?

The wings are the marginal osteophytes and the body is the central erosion between them: one concave dip with a raised spur on either side, tracing the silhouette of a gull in flight. The metaphor describes the contour of a single joint, not a pair of erosions.

Pathophysiology

Synovial inflammation erodes the subchondral cortex at the centre of the articular surface, the site primarily affected in erosive osteoarthritis and the reason it separates from the bare-area erosions of psoriatic arthritis [3]. The joint periphery responds with osteophytes and sclerosis, so destruction and repair run together. Repair can go further: eroded joints may remodel and occasionally ankylose, so a joint scored erosive at one visit can look reconstructed at the next [2,6]. In Framingham the age-standardised prevalence was 9.9% in women and 3.3% in men [5], the basis for calling it a disease of women around the menopause [2].

Alternative names: Seagull sign, gull-wing sign, seagull erosions. Saw-tooth is often listed as a synonym but is better treated as the separate proximal interphalangeal pattern [1]; the unrelated colonic sawtooth sign shares only the name.

Other associated named signs: pencil-in-cup deformity, ivory phalanx and whiskering, all of which point to psoriatic rather than erosive osteoarthritis.

Which arthritis is it? Where the bone is lost decides

Scoring progression: the Verbruggen-Veys phases

Erosive osteoarthritis is followed joint by joint through anatomic phases rather than a global score [6]:

A joint may pass from erosive to remodelled, so a single radiograph underestimates how active the disease has been [6].

Reporting it

• Say central erosion explicitly, and say which joints. Marginal erosion alone does not distinguish erosive from non-erosive hand osteoarthritis [1].
• Do not call it specific. Report it as favouring erosive osteoarthritis, having checked for a single-ray distribution, periostitis or a resorbed tuft [3,4].
• Note remodelling or ankylosis, which places the joint at the late phase rather than excluding the diagnosis [2,6].
• If the presentation is inflammatory, add ultrasound or MRI. Power Doppler activity is found mainly in erosive disease, and radiographic progression is about 2.5 times more likely with it [10].

Frequently asked questions

What does a gull wing deformity on an X-ray mean?

It favours erosive osteoarthritis. A central subchondral erosion in a distal interphalangeal joint, with marginal osteophytes rising on either side, produces the gull wing contour [1]. It is not specific, having also been described in late psoriatic and rheumatoid disease [4].

Is the seagull sign the same as gull wing deformity?

Yes. Seagull sign, gull wing sign, gull wing appearance and seagull erosions all name the same contour. Saw-tooth is the exception: although often listed as a synonym, it is a distinct central-erosion pattern that predominates in the proximal interphalangeal joints [1].

Which joints does erosive osteoarthritis affect?

The interphalangeal joints, with central erosions commoner at the distal than the proximal interphalangeal joints [1]. The metacarpophalangeal joints are relatively spared while the trapeziometacarpal joint at the thumb base is frequently involved [4].

How common is erosive osteoarthritis, and who gets it?

In the Framingham general-population cohort the age-standardised prevalence was 9.9% in women and 3.3% in men [5], and it predominantly affects women around the menopause [2].

References

1. Addimanda O, Mancarella L, Dolzani P, Punzi L, Fioravanti A, Pignotti E, et al. Clinical and radiographic distribution of structural damage in erosive and nonerosive hand osteoarthritis. Arthritis Care Res (Hoboken). 2012;64(7):1046-53.
2. Favero M, Belluzzi E, Ortolan A, Lorenzin M, Oliviero F, Doria A, et al. Erosive hand osteoarthritis: latest findings and outlook. Nat Rev Rheumatol. 2022;18(3):171-83.
3. Martel W, Stuck KJ, Dworin AM, Hylland RG. Erosive osteoarthritis and psoriatic arthritis: a radiologic comparison in the hand, wrist, and foot. AJR Am J Roentgenol. 1980;134(1):125-35.
4. Scutellari PN, Orzincolo C. [Erosive arthrosis of the hand. Criteria of the differential diagnosis]. Radiol Med. 1985;71(5):292-7.
5. Haugen IK, Englund M, Aliabadi P, Niu J, Clancy M, Kvien TK, et al. Prevalence, incidence and progression of hand osteoarthritis in the general population: the Framingham Osteoarthritis Study. Ann Rheum Dis. 2011;70(9):1581-6.
6. Wolski M, Podsiadlo P, Turkiewicz A, Ishijima M, Saarakkala S, Englund M, et al. Associations of trabecular bone texture with anatomical phases of osteoarthritis evolution and its progression in finger joints: results from the Nor-Hand study. Osteoarthritis Cartilage. 2026;34(11):1653-60.
7. Day MS, Nam D, Goodman S, Su EP, Figgie M. Psoriatic arthritis. J Am Acad Orthop Surg. 2012;20(1):28-37.
8. Zelnio E, Taljanovic M, Manczak M, Sudol-Szopinska I. Hand and wrist involvement in seropositive rheumatoid arthritis, seronegative rheumatoid arthritis, and psoriatic arthritis: the value of classic radiography. J Clin Med. 2023;12(7):2622.
9. Jacques T, Michelin P, Badr S, Nasuto M, Lefebvre G, Larkman N, et al. Conventional radiology in crystal arthritis: gout, calcium pyrophosphate deposition, and basic calcium phosphate crystals. Radiol Clin North Am. 2017;55(5):967-84.
10. Haugen IK, Mathiessen A, Slatkowsky-Christensen B, Magnusson K, Boyesen P, Sesseng S, et al. Synovitis and radiographic progression in non-erosive and erosive hand osteoarthritis: is erosive hand osteoarthritis a separate inflammatory phenotype? Osteoarthritis Cartilage. 2016;24(4):647-54.