Assessment of the distal femoral and proximal tibial ossification center in newborns by ultrasound

introduction: In full term infants the distal femur-and proximal tibia-epiphysis are the only secondary ossification centers seen roentgenographically. Therefore they have a certain Value as indicators of skeletal development. These two ossification centers can as well be evaluated easily by sonography. Patients and method: In a prospective study the ossification centers of the knee were studied by ultrasound (Acuson 128 and XP/10 system). The biological age (gestational and chronological age added) of the 210 infants examined (101 males and 109 females) was 42 weeks (mean; minimum 33 weeks, maximum 55 weeks). Infants with inborn errors of metabolism or hypothyroidism were excluded. The sonographically visible begin of mineralisation and the size of ossification centers (craniocaudal, transverse, and anterior-posterior) were recorded. Results: In infants with a biological age of 44 weeks and older allways both epiphysis were well mineralised, whereas only one of 9 babies of the 33rd week examined had a visible mineralisation of the distal femur epiphysis. The begin of the mineralisation is side independent and in all cases earlier and larger in the epiphysis of distal femur than in the proximal tibia. The craniocaudal diameter of the distal femur epiphysis of infants aged 40 weeks is 4.7 mm. The ratio of volume of the distal femurepiphysis and the bodyweight related to age is 0.0247 ml/kg in males and 0.0275 in females. Discussion: These results are similar to previous X-ray results known to the literature. The x-ray examination of the knee for skeletal development can easily be replaced by ultrasound.