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

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.

Mapping of the femoral trochlea in a newborn population: an ultrasonographic study.

BACKGROUND: The anatomy of the femoral trochlea is of vital importance to the stability of the patellofemoral joint. Knowing the characteristics of the femoral trochlea in newborns might prove useful when considering the predisposing factors to patellar instability. PURPOSE: To define the normal anatomy and the natural variances of the femoral trochlea in a newborn population as well as evaluation of ultrasonography as a method of imaging. MATERIAL AND METHODS: The femoral trochlea of both knees of 174 newborns (82 girls and 92 boys) was examined using ultrasonography within 3 days after birth. For evaluation of the repeatability of the method, a separate population of 40 newborns was examined by two examiners. RESULTS: The sulcus angle (SA) and Trochlear Index (TI) proved to be the most reliable and reproducible parameters. The overall mean SA was 148° (SD 5.6). An angle of more than 159° was defined as dysplastic, and 17 of the knees were categorized in this group. The overall mean TI was 2.21 (SD 0.05). A value of less than 2.11 was defined as dysplastic and 11 of the newborns fell into this category. CONCLUSION: As a method of visualizing the newborn femoral trochlea and the position of the patella, ultrasonography is a reliable tool and might be of vital importance. In a further perspective, knowledge of the anatomy of a normal versus a dysplastic newborn trochlea renders it possible to study the predisposing factors to patellar instability and methods of treatment. Our results indicate that dysplasia of the femoral trochlea may be congenital.