Pathogenesis and differential diagnosis of the swan-neck deformity.

T HE MECHANISMS and clinical settings of the swan-neck deformity (SND) have interested physicians for more than a century. Archibald E. Garrod, son of the famed Sir Alfred Garrod, in his 1890 Treatise on Rheumatism and Rheumatoid Arthritis,’ published an illustrated description of an arthritic deformity of the hand, characterized by “[flexion of] the terminal phalanges upon those of the second row . . , [hyperextension of] the second phalanges upon the first, . . . and [flexion of] the first phalanges upon the metacarpal bones” (Fig. 1). This description, which he derived from the work of Charcot 30 years earlier,’ would now be recognized as similar to the modern term SND. Garrod elaborated that