Comparison of pubo femoral distances in lateral versus supine positioning of the child

Introduction and Objective: Ultrasound screening for
developmental dysplasia of the hip (DDH) is conventionally
based upon the method developed by Graf. In 2013 the
pubo femoral distance (PFD) was proposed as a new ultrasound
screening measurement, defined as the minimally
measurable distance between the medial aspect of the femoral
head and the pubic bone, but no consensus exists on
the positioning of the child when performing the examination.
Our aim is to examine the agreement of PFD when
measured with the child in the lateral versus supine
position.
Materials and Methods: We included a consecutive
series of children referred for hip ultrasound suspect for
DDH during a period of two months. The PFD measurement
was obtained for each child for both hips, afterwards
the child was placed in the supine position and the PFD
measurement was repeated on both sides. Ultrasound
examinations were performed by two experienced pediatric
musculoskeletal radiologists. Mean PFD values for lateral
and supine positioning were compared using Student’s
paired t-test and controlled for age of the child using linear
regression. Agreement was analyzed using Bland Altman
plot.
Results: We included 30 children (15 boys), mean age at
examination was 34 days (range 13-83). Mean PFD in lateral
position was 3.5 mm 95%CI (3.2; 3.7) and did not
differ significantly from mean PFD in supine position at
3.6 95%CI (3.4; 3.9). Mean difference in PFD between
examination positions was 0.16 mm 95%CI (-0.31; 0.58)
and was not significantly correlated to the child’s age at
examination (p = 0.062). Inspection of the Bland Altman
plot did not reveal a systematic difference in PFD between
examination positions.
Conclusions: Shifting from lateral to supine examination
position of the child had no impact on PFD measurements.
These findings underline the versatility of the PFD measurement
as a screening tool for DDH.