Abnormal Ossification

Janice L. B. Byrne, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Are there fractures?
- Presence or absence of fractures most important clue for differential
Are the fractures generalized or limited to a portion of the skeleton (e.g., ribs)?
Do the long bones appear short?
If short long bones, is there micromelia?
Is there angulation or curvature of the long bones without fractures?
Is the underossification generalized or limited to part of the skeleton?
Is the calvarium involved?
Does the fetus move normally or is there evidence of arthrogryposis/akinesia?

Helpful Clues for Common Diagnoses

Arthrogryposis, Akinesia Sequence
- Lack of movement → decreased mineralization
- Fractures rare in utero; may occur at the time of birth
Osteogenesis Imperfecta
- Perinatal lethal form with multiple fractures in utero
- “Beaded” appearance of ribs due to multiple fractures
- Deformable calvarium due to underossification

Helpful Clues for Less Common Diagnoses

Achondrogenesis
- Large calvarium, micromelia
- Severely decreased ossification of spine, calvarium in IA, IB
- Rib fractures in type IA; none in IB
- Normal cranial ossification, absence of rib fractures in type II
Hypochondrogenesis
- Part of a spectrum of achondrogenesis type II, but less severe findings
- Fractures rare

Helpful Clues for Rare Diagnoses

Hypophosphatasia
- Generalized lack of ossification
- Calvarium poorly ossified
- Small thorax, short limbs
- Fractures rare, but may involve ribs which may have a “rachitic rosary” appearance
Atelosteogenesis
- Severely underossified humerus, fibula, femur; bowed tibia
- Narrow thorax, proximal limb shortening