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Prenatal Ultrasonography in Antenatal Orthopaedics: A New Subspecialty

Medical ultrasonography was initially developed for pregnancy management and prenatal diagnosis. It has had an accelerating role in orthopaedic practice in the past two decades, with proven good results in the diagnosis and management of developmental dysplasia of the hip (23), slipped capital femoral epiphysis (14), rotational profile of limbs (13), joint pathology (10), tendinitis (27), and osteomyelitis (16). Only recently have orthopaedic surgeons become involved in prenatal counseling when a fetal abnormality is recognized by ultrasound; hence, the new subspecialty of antenatal orthopaedics. In our institution, the Antenatal Diagnosis and Counseling Service has a weekly multidisciplinary meeting to consider methods of obtaining further information about and options for management of fetal anomalies. Clinical and autopsy follow-up findings after delivery and after abortion act as quality controls for antenatal ultrasound diagnoses. Prenatal ultrasound detection of anomalies is affected by operator skills, the quality of ultrasound equipment, gestational age, maternal body habitus, and the problems of scanning a mobile target with limited access. Transvaginal scanning allows detection of skeletal anomalies up to 4 weeks earlier than transabdominal scanning because of proximity to the fetus (8,29). Color Doppler ultrasound is used to assess the cardiac blood flow and blood flow in a limb with a constriction band. The role of three-dimensional ultrasound is being evaluated. One cannot assume that the recognized anomaly is the only one present. There are limited published data regarding detection rates of conditions other than aneuploidies, neural tube defects, and cardiac abnormalities. Detection rates from tertiary referral centers that see high-risk populations should not be considered indicative of the accuracy of routine screening studies in low-risk populations. Many of the comments in this article are based on our center’s experience. In most developed countries, an ultrasound scan between 18 and 24 weeks of pregnancy (by menstrual age) is routine, the timing directed by the upper age limit of legal termination of pregnancy in each country. The detection rate of fetal anomalies is enhanced by adding an early-pregnancy ultrasound scan (e.g., transvaginal ultrasound at around 13 weeks) and a third-trimester ultrasound scan. The incidence of congenital defects of all pregnancies is 1:50, and the incidence of musculoskeletal anomalies 0.4% to 0.6% (4). The frequency of congenital skeletal anomalies in the general population is 0.024% (22); in other words, substantially less. This discrepancy reflects the high incidence of perinatal death in fetuses with multisystem or chromosomal abnormalities and the high elective termination rate for fetuses with major abnormalities in countries where second-trimester ultrasound is routine and termination is legal. In South Australia, about 90% of pregnancies with ultrasound-recognized myelodysplasia and almost all with lethal skeletal dysplasias are terminated (11). In general, we find that with adequate information and counseling about the condition, parents are more willing to accept major abnormalities of one or two extremities. Even with such intervention, however, most parents remain unwilling to accept major abnormalities involving three or four extremities. The time available to assess the fetus and its surroundings is finite, and the focus of the operator is primarily on major anomalies and markers for aneuploidy. Although a substantial amount of information is being accumulated on the ultrasound detection and evaluation of musculoskeletal anomalies in the fetus, there is still much to learn about normal in utero development and the natural history of developmental conditions.