Angulated Bones

Janice L. B. Byrne, MD

DIFFERENTIAL DIAGNOSIS

Common

Thanatophoric Dysplasia
Osteogenesis Imperfecta
Diabetic Embryopathy

Less Common

Campomelic Dysplasia
Kyphomelic Dysplasia
Abnormal Joint Angulation

Rare but Important

Hypophosphatasia
Fetal Trauma

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Are there fractures?
Is the ossification normal?
Is the angulation mid-shaft or at a joint?
Is the distal limb normal?
Is one limb affected or all?
Are both segments of the limb affected?
Are the abnormalities limited to the long bones or are other skeletal elements affected?
Are there other structural anomalies?

Helpful Clues for Common Diagnoses

Thanatophoric Dysplasia
- Micromelia
- Normal ossification
- No fractures
- Short ribs with bell-shaped thorax
- Platyspondyly
- Lumbar kyphosis common
- “Telephone receiver” femur in type I
- Normal calvarium in type I
- Femora less curved in type II
- Cloverleaf-shaped skull (Kleeblattschädel) in type II
- Polyhydramnios often severe and progressive in the second trimester
- Other anomalies rare
- Lethal within first few hours-to-days of life
Osteogenesis Imperfecta
- Fractures a prominent feature
- Decreased ossification of all bones
- Type II (perinatal lethal) with extensive in utero fractures, limb deformities
- “Beaded” ribs due to healing fractures
- Deformable skull with pressure from ultrasound transducer
- Non-lethal types associated with less severe limb shortening, fewer in utero fractures
- Progressive deformation, shortening may occur in type III/IV
- Type III/IV may present with isolated bent femur in utero
- Size of chest correlated with risk of lethal outcome
Diabetic Embryopathy
- Uncontrolled diabetes most prevalent human teratogen
- Abnormal femur common
  - Usually bilateral femur abnormality, but often discordant
  - Short, angulated or curved femur
- Associated tibia-fibula abnormality
- Preaxial polydactyly
- Other structural defects common in uncontrolled diabetes
  - Cardiac
  - Central nervous system: Anencephaly, holoprosencephaly, spina bifida
  - Anorectal malformation

Helpful Clues for Less Common Diagnoses

Campomelic Dysplasia
- Severe angulation of femora, tibiae, fibulae
  - Anterolateral bowing especially common
- Scapula absent or hypoplastic
- XY sex reversal (male to female) or ambiguity
  - Genotypic males appear phenotypically as females
- Normal ossification
- No fractures
- Bell-shaped chest
- Kyphoscoliosis
- 1st trimester cystic hygroma or increased nuchal translucency
- Characteristic skin dimpling over area of angulation
Kyphomelic Dysplasia
- Normal chest size
- Less severe long bone shortening
- Angulation or curvature of long bones
- Normal ossification
- No fractures
Abnormal Joint Angulation
- Fixed vs. moveable joint
- Normal distal extremity associated with dislocated joint
  - Knees, hips most commonly affected
  - Movement at the joint often observed in utero despite dislocation
  - May be unilateral or bilateral
  - May be associated with fetal malpresentation
  - Prolonged dislocation may result in dysplastic joint
- Abnormal distal extremity often associated with abnormal joint or proximal bone
  - Joint usually without spontaneous movement
  - Wrist most commonly affected, but ankle also possible
  - Angle of deviation predicts which bone is hypo- or aplastic; angulation is toward the hypoplastic element
  - Radial deviation associated with hypoplasia or aplasia of radius and thumb
  - Ulnar deviation less common; associated with ulnar hypoplasia
  - Tibial or fibular hypoplasia or aplasia associated with fixed angulation of ankle
  - Associated oligodactyly common

Helpful Clues for Rare Diagnoses

Hypophosphatasia
- Multiple sub-types including perinatal lethal, infantile and late onset (adult)
- In general the later the onset, the less severe the clinical course
- Undermineralization of calvarium results in brain being seen “too well” on ultrasound
- Perinatal lethal type with prominent midtrimester ultrasound findings of severe undermineralization and micromelia of all long bones and calvarium
- In general long bones thin and bowed with absent posterior shadowing
- Spurs often seen along mid-shaft of long bones
Fetal Trauma
- Isolated fractures due to fetal trauma rare in absence of severe maternal trauma

Other Essential Information

Distinguish between angulated bones and angulated joints when evaluating the fetus
Curvature of multiple bones predicts generalized osteochondrodystrophy
- Severity of associated limb length shortening and chest size will predict lethal vs. non-lethal skeletal dysplasia

Alternative Differential Approaches

Presence of fractures of major importance
- Consider osseous fragility syndromes including osteogenesis imperfecta and hypophosphatasia
- Severity and number of in utero fractures may help distinguish lethal vs. non-lethal disorder
- Rib fractures without long bone fractures seen in type IA achondrogenesis