INTRA-UTERINE FEMORAL GROWTH

Abstract

Background: Lower limb buds appear during the second week of embryonic life and are well differentiated by the end of the 8th week. Primary ossification centres of femur and tibia appear by the end of the 8th week and by 12 weeks the cartilaginous anlage is complete. By 14 weeks primary ossification is sufficient to allow accurate ultrasonographic measurement of femoral length.

There are many established database for estimating fetal femoral length ultrasonagraphically. There is little data however on radiological measurements of fetal femoral lengths. The aim of our study was to introduce radiologically measured fetal femoral lengths in order to improve our understanding of normal fetal femoral growth.

Methods: A group of 40 post-mortem foetal radiographs ranging from 14 weeks to 39 weeks gestation were retrieved from our radiology department having excluded all cases with associated lower limb deformation. Femoral lengths were measured and plotted against gestational age. A standard growth curve was constructed and compared to the currently available data on ultrasonographic measurements. A growth velocity chart, growth remaining and an antenatal multiplier chart was also constructed.

Results: At 14 weeks the length of the femur was 14mm and the tibia 11mm. At birth the femoral diaphyseal length was 75mm and the tibia 62mm.

Using the standard growth curve there was a strong correlation between our radiological measurements and previously published ultrasonographic measurements (R2= 0.9492)

The femoral growth velocity curve demonstrated a rapid growth acceleration phase peaking at 12 cm/annum at 16 weeks, followed by a rapid deceleration phase reducing to a growth rate of 5 cm/annum at birth.

The growth remaining was calculated for each week. At 24 weeks the growth achieved is 10% thus giving a multiplying factor of 10. At birth the growth achieved is 20% giving a multiplying factor of 5.

Discussion: Modern 3D and 4D ultra-sonography has lead to an increasingly accurate detection of antenatal deformities. Antenatal orthopaedics is an advancing sub-specialty. The understanding of normal intra-uterine growth is essential knowledge of a paediatric orthopaedic surgeon when advising on antenatally detected deformities. This correlation of ultrasonographic and radiographic measurements further deepens our understanding of foetal femoral growth.