Swan neck deformities in the fingers are most commonly caused by which condition?

Swan neck deformities, characterized by hyperextension of the proximal interphalangeal joint and flexion at the distal interphalangeal joint, are most commonly associated with rheumatoid arthritis. This autoimmune condition causes chronic inflammation in the joints, which can lead to stretching and damage of the surrounding ligaments and tendons. As a result, the normal alignment and function of the fingers are compromised, leading to the characteristic swan neck appearance.

In contrast, while osteoarthritis can lead to various hand deformities, it typically results in more osteophyte formation and joint degeneration rather than the specific flexion and extension patterns seen in swan neck deformity. Post-traumatic abnormalities typically arise from specific injuries or accidents and do not generally follow the pattern of joint involvement seen in rheumatoid arthritis. Similarly, although neuromuscular disorders can result in hand deformities, they do not specifically cause swan neck deformities in the same manner as rheumatoid arthritis does. Hence, the association of swan neck deformities with rheumatoid arthritis is well established in clinical practice.