Ultrasound femoral anteversion (FAV) relative to tibial torsion (TT) is abnormal after screening for adolescent idiopathic scoliosis (AIS): evaluation by two methods

Abstract

In the scoliotic spine, torsion is generally evaluated in relation to axial rotation of the apical vertebra. In the lower limbs, the changes in torsion by age of femoral anteversion (FAV) relative to tibial torsion (TT) have been studied in dried bones, normal growing subjects and adults and subjects with osteoarthritis of the hip or the knee. This paper reports the application of real-time ultrasound to FAV and TT in normal children age 11–18 years and in scoliosis screening referrals with particular reference to how FAV relates to TT as 1) ratios, and 2) tibio-femoral index (TFI) of torsion, calculated as TT minus femoral FAV. The FAV/TT ratio findings show an abnormal normal relationship of FAV to TT both proximo-distally and in left-right asymmetry. These may express torsional abnormalities in femoral and/or tibial growth plates with left-right asynchrony suggesting the possibility of similar torsional abnormalities in vertebral end-plates and/or rib growth plates initiating the deformity of AIS. TFI of the right limb in the scoliosis girls is greater than in the normals that is interpreted as resulting from earlier skeletal maturation of FAV. FAV/TT ratios and TFI are unrelated to the spinal deformity (Cobb angle and apical vertebral rotation) except for boys where TFI is associated with apical vertebral rotation. FAV/TT ratios may be a more accurate method estimating the relationship of FAV to TT. than TFIs.