Overview of Femur Length Test | Physiotherapy

Femur Length Test

What is femur length (FL)?

The length of the femur measures the longest bone in the body and reproduces the longitudinal growth of the fetus. Its utility is similar to the biparietal diameter (BPD, which is the diameter between the 2 sides of the head.

The length of the femur increases from approximately 1.5 cm at 14 weeks to approximately 7.8 cm at term. Similar to DBP, dating using the length of the femur should be done as soon as possible.

Why are fetal measurements important?

First, an ultrasound can help determine your due date. Based on the measurement results, the gestational age of the baby will be calculated based on the average size of other babies scanned during the 20th week of pregnancy. However, the range of calculations at this time of pregnancy is within 2-3 weeks of the actual delivery date, whereas an earlier ultrasound is more reliable in calculating the delivery date.

More importantly, however, if fetal abnormalities are found during an initial ultrasound, further investigation can be done, and if any treatment is warranted, they can be started all over again.

Measurement of the length of the femur

Among the markers used to assess fetal health and growth is the length of the baby’s femur, the long bone of the thigh. Slow from the blunt end of the bone to the chute, the length of the femur is generally measured in millimeters.

Discovery of the short length of the femur on ultrasound may designate the need for further testing to rule out certain conditions. But it is also important to take into account the limitations inherent in using femur length as a marker of poor pregnancy outcomes.

When the length of the femur is below the fifth percentile, parents can be warned of a number of possible atypical pregnancy outcomes.1 A short femur length identified on ultrasound in the second or third trimester raises concern about conditions that Are detailed below.

But this measurement has many limitations, from a human error to outdated ultrasound equipment to normal variations. The length of the femur is just one mutable among many that should be used to make willpower about a baby’s health.


Only the first ultrasound examination amid 12 and 42 weeks of each fetus with a clearly established gestational age was used for the analysis. No exclusions were made on the basis of small birth weight for a date, prematurity, or other events several weeks after the examination. Separate regression models were tailored to approximation the mean and standard deviation at each gestational age for each parameter.

Femur length test: Procedure: PRONE

  • The patient is in the prone position
  • The patient’s knees and hips are flexed, with the plantar surfaces of the feet on the table
  • Your uniform medial malleolus and knees together

To compare the lengths:

  • Tibia: The therapist stands at the foot of the table to compare the heights of the patient’s tibial plateaus to find the shortest tibia
  • Femur: The therapist then stands beside the table to compare the positions of the kneecaps looking for the shorter femur

Results of femur length test

A total of 5,807 mean abdominal diameters and abdominal circumferences were derived from fetal anteroposterior and transverse fetal abdominal diameter measurements. The length of the fetal femur was measured in 5860 cases. The graphs, tables, and regression formulas of the biometric measurements are presented. A comparison of our charts with others showed no significant differences. Solitary the Merz1 centiles for abdominal biometry were lower and for femur length advanced than ours.

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