Single x-ray of the toes revealing increased density throughout the osseous structures of the involved digit in a person with psoriatic arthritis. Sclerosis of an entire phalanx, typically the great toe, is likely the result of bony proliferation as an exaggerated healing response to injured bone in patients with seronegative spondyloarthropathy.
Reference
Resnick D, Broderick TW: Bony proliferation of terminal toe phalanges in psoriasis: the "ivory" phalanx. J Can Assoc Radiol 1977 Sep;28(3):187-9.