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The Femur Length (FL)

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Focuses on the Femur Length (FL) for assessing skeletal development and gestational dating. Students will learn how to isolate the long bone, avoid acoustic shadowing, and place calipers precisely for a reliable biometric result.

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1. What does the Femur Length (FL) measurement actually include sonographically?
The entire femur including cartilaginous ends The ossified diaphysis and metaphysis only The diaphysis, metaphysis, and distal epiphysis The ossified shaft and femoral head
2. Which of the following structures is excluded from a standard FL measurement?
Ossified diaphysis Ossified metaphysis Distal femur epiphyseal (DFE) ossification center Mid-diaphyseal shaft
3. What is the first step to achieve a correct FL measurement plane?
Place the transducer perpendicular to the femur Align the transducer with the bone's long axis Measure the longest visible segment Identify the DFE center first
4. A trainee takes multiple FL measurements and accepts the longest result as the most accurate. This approach is:
Correct — the longest measurement always reflects best alignment Incorrect — other sources of error beyond misalignment cause undermeasurement Correct only in the third trimester Incorrect — the shortest measurement is always preferred
5. How do you confirm correct transducer alignment for FL measurement?
Verify the femoral length exceeds BPD Confirm both cartilaginous head/greater trochanter & distal condyle are visible Confirm the DFE ossification center is visible Use Doppler to locate the femoral artery
6. Where should the electronic cursors be placed when measuring FL?
At the outermost tips of the visible bone including the distal femoral tip At the bone-cartilage junction, excluding the distal femoral tip At the center of the diaphysis At the DFE ossification center
7. What is the correct anatomical landmark for measuring the femur length (FL)?
Proximal ossified end to distal cartilaginous tip Proximal ossified end to distal ossified end Medial edge of the femur to lateral edge Entire length of the femur including surrounding tissues
8. The femur must be perpendicular to the ultrasound beam for an accurate FL measurement.
True False
9. A sonographer obtains a femur length measurement of 10 mm at 14 weeks of gestation. What is the next step?
Accept the measurement as normal. Compare with gestational age-specific growth charts. Immediately suspect skeletal dysplasia. Repeat the measurement in the third trimester.
10. What is a possible clinical implication of a short femur length (FL)?
Intrauterine Growth Restriction (IUGR) Skeletal dysplasia Chromosomal abnormalities (e.g., Down syndrome) All of the above
11. Femur length alone is sufficient for determining gestational age in all cases.
True False
12. Which of the following conditions might be suspected with an abnormally long femur length?
Macrosomia Dwarfism Osteogenesis imperfecta Microcephaly
13. A fetus shows a consistently short femur length on multiple ultrasounds. What should be included in the differential diagnosis?
Constitutional short stature Skeletal dysplasia Trisomy 21 All of the above
14. Femur length should be measured from the proximal to distal ossified ends of the femur, avoiding cartilaginous areas.
True False
15. When measuring femur length (FL), the ultrasound probe should be:
Aligned parallel to the femur shaft. Aligned perpendicular to the femur shaft. Tilted at a 45-degree angle. Positioned at the maternal umbilicus.
16. If the femur appears shortened on ultrasound, what additional steps can help confirm an abnormality?
Measure other long bones (e.g., humerus). Cross-check with gestational age-specific charts. Assess for other markers of skeletal dysplasia or chromosomal abnormalities. All of the above.