Direct ultrasonographic measurement of femoral anteversion in newborns Thore Hinderaker 1, Alf Uden 1,2, Olav Reikerfis 1 1 Department of Orthopaedics, University Hospital, Tromso, Norway 2 Department of Orthopaedics, Malm5 General Hospital, University of Lund, Sweden
Abstract. A direct method of ultrasonographic measurement of the anteversion angle of the femoral neck is presented. Normal values based on measurements in 30 rand o m newborns with vertex presentation correspond well with figures from previous autopsy series. The femoral anteversion in breech presentation was found to be on average 10~ greater than in vertex presentation (p < o.ooo 1). Key words: Femoral anteversion - Measurements - Newborns - Ultrasonography
In the pathogenesis of hip joint instability, particular interest has been focused on the anteversion (AV) angle of the femoral neck [1, 2]. It is well established that the AV angle decreases during growth from 30o-40 ~ in infants to 5~ ~ in adults [9-11, 17, 21]. Individual variations are, however, considerable. A number of methods for measurement of femoral anteversion have been described [8, 15, 20]. All, however, have certain restrictions. Both conventional radiography and computed t o m o g r a p h y require ossification of the femoral head and neck, and both also give a rather high radiation dose to the gonads. These methods are, therefore, not desirable for use in the newborn, and nonionizing techniques should be employed . During recent years the technique o f ultrasonography has developed rapidly, and it is c o m m o n l y used for the evaluation of hip instability. The present study was carried out to assess the value o f ultrasonography for measuring the AV angles in the newborn and to compare values for those born in vertex presentation to those for babies born in breech presentation. Correspondence to: Dr. O. ReikerAs, National Hospital of Ortho-
paedics, Sophies Minde, Trondheimsvn. 132, N-0570 Oslo 5, Norway
Patients and methods On random days, babies who remained relaxed during ultrasound screening for hip instability were selected for measurement of the AV angle. The first 30 comprised 17 boys and 13 girls, all born in vertex presentation. Later, 19 breech presentations (6 boys and 13 girls) were selected. As some babies did not cooperate well enough, altogether 55 femurs were examined in the vertex group and 35 in the breech group. None of the babies had clinical or sonographic evidence of hip joint instability. A Siemens Sonoline SL-1 sonograph with a small-part probe of 7.5 MHz was used. The baby was placed supine towards the examiner who held the leg. The knee was flexed 90~ and the leg positioned perpendicular to the thigh with a foam rubber pillow (Fig. 1). A goniometer was attached to the probe to maintain its position during the measurement procedure. The probe was held with the right hand perpendicular to the long axis of the femur, along the long axis of the leg, and placed anteriorly in the groin. The centre of the femoral head was located and the probe was moved 2-4 mm distally to "freeze" the transverse section through
Fig. 1. Position of the baby and the probe for cross-sectional examination through the hip joint and femoral condyles. To secure mechanical alignment a goniometer was attached to the probe, and the baby was positioned on a foam rubber pillow as shown 9 1994 International Skeletal Society
T. Hinderaker et al. : Direct ultrasonographic measurement of femoral anteversion Fig. 2. Ultrasonographic cross-section through the proximal end of the femur in a newborn. The femoral head, neck and greater trochanter are indicated by a r r o w s Fig. 3. Measurement of femoral anteversion by ultrasonography in a newborn. The femoral head, neck and greater trochanter as well as the femoral condyles are indicated by a r r o w s
the distal half of the femoral head and the central part of the neck and greater trochanter (Fig. 2). Alongside this picture a transverse section through the centre of the femoral condyles permitted the Siemens angle measurement program to show and calculate the AV angle directly on the screen (Fig. 3). The angle between the posterior tangent to the condyles and the centre line through the head and neck represents the true AV angle, and it corresponds directly to the calculated AV angle of Dunlap et al.  and Rippstein . An intraobserver test was carried out on 12 babies (24 femora). These femora were not included in the main series. Data are expressed as means and standard deviations (SD). The two-tailed t-test was used for statistical comparisons (paired and non-paired), p < 0.05 was considered significant.
9 The m e a n difference between the first and second measurement o f the intraobserver test was 0.2 ~ _+ 5.7 ~ T h e values for the 30 r a n d o m babies in vertex presentation are s h o w n in Table 1. T h e overall m e a n was 25 ~ _+ 8 ~. N o significant differences were shown, neither between the right a n d left sides n o r between the sexes. T h e values for breech versus vertex presentation are s h o w n in Table 2. The m e a n A V angle was 10 ~ higher in the breech-delivered babies (p < 0.0001).
Table 1. Femoral anteversion angle (degrees) of newborns in vertex presentation
Table 2. Femoral anteversion angle (degrees) of breechborns versus vertex presentation n
P < 0.0001
The aim o f the present study was two-fold: firstly to evaluate the s o n o g r a p h i c m e t h o d for m e a s u r e m e n t o f femoral anteversion and, secondly, to c o m p a r e the A V angle in breech-delivered infants to those b o r n in vertex presentation. The latter idea is based on D u n n ' s theories o f postural deformities . D a h l s t r 6 m et al.  observed the A V angle during s o n o g r a p h i c screening for hip instability by an anterior a p p r o a c h , b u t gave no figures. Several authors have m e a s u r e d the A V angles in infants by plain r a d i o m e t r y [8, 15] a n d c o m p u t e d t o m o g r a p h y . Such m e t h o d s c a n n o t be used in n e w b o r n s because o f the high radiation to the gonads, a n d are certainly n o t suitable as a screening m e t h o d . Until now, then, there has been no safe a n d accurate m e t h o d for m e a s u r e m e n t o f femoral anteversion in the newborn. In the present study, the anteversion o f the femoral neck was m e a s u r e d as the angle between the posterior tangent o f the femoral condyles a n d the central line t h r o u g h the femoral h e a d a n d neck, projected on a plane perpendicular to the long axis o f the femur. This corresponds to the A V angle m e a s u r e d by D u n l a p et al. , which is the usual definition for femoral anteversion. F o r reasons m e n t i o n e d a b o v e our m e t h o d could n o t be controlled by r a d i o g r a p h i c gold standards; its accuracy,
T. Hinderaker et al. : Direct ultrasonographic measurement of femoral anteversion therefore, could not be established. However, the ultrasound scanning was performed in exactly the same manner as c o m p u t e d t o m o g r a p h y , and this technique has proved to be reliable . An accurate record of the two ultrasonic images depends on a constant orientation of the transducer, and this was secured by the goniometer. Measuring anatomical parameters in healthy newborn babies implies challenges concerning precision. As our method is based on "free hand technique", an intraobserver test is crucial; our results demonstrate a reasonable precision. Furthermore, there should be no systematic errors produced by the method. We therefore assume that it is reliable to c o m p a r e mean results in two groups of newborns as in the present study. In autopsy series the AV angle at 40 weeks' gestation is reported to be 25~ ~ with considerable individual variation [11, 18, 19]. The satisfactory correspondence of our values to these figures indicates the reliability o f the method. The well-known higher risk of neonatal hip instability in breech-delivered babies [1, 13, 16] indicates a mechanical effect o f the breech presentation on the hip joint. We wanted to examine whether this influence could also be shown by the AV angle. Fetuses in extended breech position often have the hip joint internally rotated. This produces greater pressure between the posterior aspect o f the femoral head and the acetabulum. According to D u n n ' s theories of postural deformities , a higher AV angle in breech-delivered infants seems logical. In conclusion, we have described a method for direct measurement of femoral anteversion in the newborn by ultrasonography. A significantly higher AV angle was found in breech-delivered babies, supporting the concept o f a mechanical effect on the proximal end o f the femur in babies b o r n by breech presentation otherwise have normal hip joints.
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