Mildly Short Femur/Humerus
Karen Y. Oh, MD
DIFFERENTIAL DIAGNOSIS
Common
Idiopathic
Chromosome Abnormality
Trisomy 21
Turner Syndrome (XO)
Early Onset IUGR
Less Common
Heterozygous Achondroplasia
Osteogenesis Imperfecta
Proximal Focal Femoral Dysplasia
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Is the short femur or humerus present bilaterally versus isolated asymmetric?
Measure humerus and femur on both sides to compare
Consider measuring all extremity bones if humerus/femur is dramatically short
More likely a skeletal dysplasia
If isolated to one long bone, could be focal defect of that limb
Check morphology of affected extremity to exclude in utero amputation/amniotic bands
Assess morphology of osseous structures
Are the long bones straight versus bent?
Bent bones suggests in utero fractures and/or abnormal bone density
Skull shape
Abnormal can aid in assessment of skeletal dysplasia
Bone density
Can be difficult to assess in utero until later in gestation
Poor ossification of skull can be useful clue for abnormal bone density
Many syndromes are associated with mildly short long bones
Ranges from chromosomal abnormalities to multisystem disorders
Helpful Clues for Common Diagnoses
Idiopathic
Often constitutional if symmetric and parents are short
May be seen in fetuses of Asian or Hispanic descent
Shorter average femur and humerus than white or African American pregnancies
Biologic inherent variation has most impact in the third trimester
Trisomy 21
Minor marker for trisomy 21 (T21)
Short humerus length (HL) more sensitive than short femur length (FL)
FL and HL compared to BPD
Expected FL = -9.3 + 0.90 (BPD)
Expected HL = -7.9 + 0.84 (BPD)
Abnormal
measured:expected FL ≤ 0.91 or HL ≤ 0.90
Look for other signs of trisomy 21
≥ 1 minor markers seen in 50-70% of T21 fetuses
Major anomalies in 25-30% (cardiac, duodenal atresia, etc.)
Correlate with serum screen and first trimester ultrasound
Serum screen risk for T21 reported for maternal serum quadruple test or integrated screening
Nuchal translucency in first trimester always should be < 3 mm
Turner Syndrome (XO)
Mild rhizomelia present at time of second trimester screening
Nuchal cystic hygroma is the predominant obvious finding
Usually large fluid collection in lateral and posterior neck
Can have multiple thin septations
Can present with non-immune hydrops
Associated with cardiovascular anomalies (60%)
Coarctation of aorta
Hypoplastic left heart
May have early symmetric growth restriction
Early Onset IUGR
All biometric parameters should be equally affected
Symmetric IUGR has strong association with aneuploidy
Search carefully for anatomic abnormalities to correlate
Unlike asymmetric IUGR, more often fetal etiology rather than maternal/placental
Oligohydramnios may be present
Especially in cases of trisomy 13, 18
Helpful Clues for Less Common Diagnoses
Heterozygous Achondroplasia
Long bone shortening noted in late second or third trimester
Early scan may be normal with progressively discrepant bone growth
Humerus affected more severely than femur
Normal ossification and morphology
No fractures or bowing
Look for other signs to make diagnosis
Macrocephaly, frontal bossing
Thoracolumbar kyphosis
Trident hands
Autosomal dominant
Check parental chromosomes to assess for recurrence risk
80% are new mutations
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