Trochlear dysplasia - congenital anomaly or biomechanical development

. The aim of this study was to investigate the appearance of the trochlear groove in infants and to present the possible causes for the development of trochlear dysplasia as one of the most severe pathologic findings in patients with patellar instability. Material and Methods. Knee ultrasonography was per-formed in 200 infants, 3 to 6 months of age. The measurements were made at 30 and 60 degrees of knee flexion, in order to measure the trochlear bone and cartilaginous sulcus angle on the patellar surface of the femur and to determine the degree of trochlear dysplasia. A 7-megahertz probe was used for measurements, which was tangentially placed with the reference to the posterior femoral joint. Results. A completely flat trochlear bony sulcus angle was registered in all infants aged 3 to 6 months. The mean cartilaginous sulcus angle was between 149 ± 5.4° and 19 infants had a sulcus angle over 159°. Eleven infants with trochlear dysplasia were in breech presentation at birth. Conclusion. Our study showed that the cartilaginous part of the trochlear groove was already well developed at birth. Breech presentation of the fetus could be a predisposing factor for dysplasia of the cartilaginous part of the trochlear groove. The bony part of the trochlear groove is dysplastic in infants and it gradually gets deeper, later getting a shape of the overlying articular cartilage. The influence of the Delpech law, with lower pressure in the trochlear groove, could be the possible mechanical theory explaining the development of the trochlear dysplasia in the later stage of the childhood.