OSTEOCHONDRODYSPLASIAS

Bone is formed from collagen. Bone dysplasias predominantly involve one type of collagen (Figure 15.1). Terms used in the description of bone dysplasias according to the defect in collagen are shown in Table 15.1.

The normal growth plate or physis consists of four zones:

1. resting cartilage;

2. proliferative cartilage;

3. hypertrophic cartilage;

4. zone of provisional calcification.

The revised international classification of osteochondrodysplasias encompasses those disorders that are perinatally lethal and/or amenable to prenatal diagnosis (Table 15.2). Prenatal diagnosis has been made in most of the lethal forms of ostechondrodysplasia (Table 15.3). The osteochondrodysplasias include the infant or fetus with dwarfism. Most are lethal. For most convenience in diagnosis they can be divided into the following groups:

1. ■ Osteochondrodysplasias with platyspondyly

2. ■ Osteochondrodysplasias with short trunk

3. ■ Short rib osteochondrodysplasias

4. ■ Osteochondrodysplasias with defective bone density

5. ■ Miscellaneous group

Osteochondrodysplasias with Platyspondyly (Table 15.4)

Although the trunk of the infants in this group is not significantly short, the vertebral bodies in the radiograph are markedly flattened. Histopathologically the physeal growth zones are usually disorganized and may be retarded, but the resting cartilage is mostly unremarkable.