- Medullary bone:
- decreased in quantity, & trabecula are thin & irregular;
- feature that most sig helps to establish the dx is presence of layer of unmineralized bone (osteoid seam) surrounding mineralized segment;
- trabeculae & cortex have less bone, & is surrounded by a layer of unmineralized bone (osteoid seam)
- osteoid seams;
- refers to the layer of unmineralized bone which surrounds the mineralized trabeculae;
- osteoid seams may also be present in

- Epiphyseal Physis:
- epiphyseal plate is enlarged in height and width;
- hypertrophic cell zone:
- there is gross distortion of the hypertrophic cell zone (enlarged and distorted) & poorly defined zone of provisional calcification;
- normally orderly columns are lost and instead, there is a marked increased in axial height of zone, & there is disorderly & profligate profusion of cell
with only a small amount of intervening matrix;
- there is  failure of mineralization and vascular invasion;
- w/ exception of hypophophatasia and metaphyseal chondrodysplasia no other syndrome produces these changes;
- resting a proliferative zones are normal;
- zone of provisional calcification seen in pts w/ rickets is poorly defined with only a few of the defective bars between the almost non existant columns
of chondrocytes showing deposition of mineral;
- tongues of viable cartilage w/o evidence of active enchondral replacement