Fig. 1.

Photomicrographs of Osteonecrosis-Free and Osteonecrosis-Positive Distal Femoral Epiphyses

A&B- Representative 5 μm thick H&E-stained parasagittal section of an ON-free distal femoral epiphysis. B is higher magnification photomicrograph of box in A. Note abundant hematopoietic marrow with occasional adipocytes and trabeculae with most osteocyte lacunae showing healthy nuclei. Occasional, isolated empty lacunae exist randomly in normal bone due to the relative size of lacunae, 5 μm section thickness, and positioning of nuclei in neighboring sections. Scale bars = 1 mm (A) and 200 μm (B).

C&D- Representative section from an ON-positive distal femoral epiphysis. D is higher magnification photomicrograph of box in C. A positive diagnosis of ON in a DFE required the presence of both fatty marrow or necrotic bone marrow stroma that surrounded trabeculae, and multiple confluent empty osteocyte lacunae (Kawedia et al., 2012; Janke et al., 2013; Liu et al., 2016; Yang et al., 2009). Most ON-positive DFE's had only a portion, occasionally as little as 10%, of the epiphysis involved with ON. Nonetheless, note copious amount of fatty marrow in D, with trabeculae containing multiple confluent empty lacunae. Fields with fatty marrow or stromal necrosis surrounding trabeculae that contained only lacunae with healthy osteocyte nuclei were not uncommon. Only when fat or marrow necrosis-enveloped trabeculae also had multiple confluent empty osteocyte lacunae was the specimen designated as ON-positive. Multiple confluent empty osteocyte lacunae in trabeculae were never observed in the midst of healthy, hematopoietic marrow. Scale bars as for A&B = 1 mm (C) and 200 μm (D).