Figure 4.

Stages of evolution of LCPD. The original Waldenström classification had four stages; stage of avascular necrosis (I), stage of fragmentation (II), stage of reconstitution (III), and healed stage (IV). In the modified classification, Stages I, II, and III are subdivided into early (a) and late (b) parts of the respective stages. Fragmentation commences with a vertical fissure, perpendicular to the articular surface (vertical white arrow—Stage IIa). In Stage II, metaphyseal cysts (black arrows) may be seen. Appearance of “wooly” new bone at the periphery of the epiphysis signals the beginning of Stage IIIa (horizontal white arrow).