Breech presentation is a risk factor for dysplasia of the femoral trochlea

Abstract

Background and purpose: Instability of the patellofemoral joint is a common disorder in children and young adults. Although it has multifactorial causes, a shallow femoral trochlea is the single most important factor for instability. There is no consensus as to the etiology of trochlear dysplasia. We assessed whether the presentation of the fetus at birth could be a predisposing factor for trochlear dysplasia.

Subjects and methods: We examined 348 knees in 174 newborns using ultrasonography, concentrating especially on the trochlea femoris. We measured the sulcus angle (SA) on a transverse scan. The way of fetal presentation at birth and standard parameters such as sex, gestational age, and length and weight at birth were registered. As breech presentation is a known risk factor for dysplasia of the hip, we also looked for an association between dysplasia of the femoral trochlea and dysplasia of the hips.

Results: The mean SA was 148°. 17 knees in 14 children had an SA of >159°, which was defined as the threshold value for dysplasia. The incidence of breech position in these children was 15-fold higher. Of the different groups of breech positions, a child in frank breech with the knees locked in extension had a 45-fold increased risk of having trochlear dysplasia.

Interpretation: For some newborns, a high sulcus angle can be found at birth, indicating that trochlear dysplasia can be found from birth. Breech presentation with knees extended appears to be a major risk factor for development of trochlear dysplasia.

Figures

Figure 1.

Collage demonstrating ultrasound examination of the knee of a 3-month-old girl, with a corresponding ultrasound screenshot and a line diagram for illustration of the sulcus angle (SA). With the knee flexed above 45° and the transducer held in a transverse plane perpendicular to the axis of the femoral diaphysis, an image of the femoral condyles with the trochlea was produced. The femoral ossification center is visible.

Figure 2.

The different categories of breech position. Complete breech is where the knees are held in a fixed flexed position. Incomplete breech is where one knee is kept flexed while the other is extended. The most frequent type is the frank breech position, where the knees are fixed extended while the hips are flexed.

Figure 3.

Flow chart illustrating the statistical analyses. These were performed in 3 main steps. In the first step, all 174 children were included, The sulcus angle (SA) was analyzed as a continuous variable. In the second step, 4 children with unknown birth presentation were excluded from further analysis. The SA was analyzed as a dichotomous variable when describing the odds ratio for dysplasia with respect to birth presentation. In the final step, knees of unknown position were excluded to obtain the odds ratio for dysplasia with respect to knee position.