No abstract

ANNOTATIONSHowever, some recent studies8, l o seem to be reasonably reassuring. Nevertheless, until more is known about the possible harmful effects, it would seem advisable to reduce the number of scans carried out during pregnancy. This, of course, will apply more to scans in early pregnancy rather than t o measurements of the biparietal diameter. Assessments of the biparietal diameter are impossible before ten weeks since the fetal head is not formed and measurements are unsatisfactory before sixteen weeks. The most accurate time for maturity assessments is between twenty and thirty-four weeks. Accurate assessments of the duration of pregnancy can be made in the very early weeks, and such measurements would be of obvious value in doing serial estimations to assess fetal growth.Keeping in mind the possible inaccuracies, and limiting the number of scans done during pregnancy, ultrasonic measurement of the biparietal diameter is an extremely useful aid to the obstetrician. IAN MACGILLIVR.4Y . (1965) 'Fetal develoonient as deter-Gynaec. Brit. Cwlth, 71, 11. mined by ultrasonic pulse echo'techniques." Anivr.' J . Obsret. Gyitec., 92, 44. and complicated pregnancy.' Ann. Chir. Gynec, Fenn., 59, 71. diameter.'J. Ohstet. Gynaec. Brit. Cwlth, 76, 603. Gynec., 29, 842. 12, 114. detector.' Brit. nied. J . , 2, 92. Lancet, i, 11 33. 3 . Ojala, A., Ylostalo, P., Jouppila, P., Jarvinen, P. A. (1970) 'Fetal cephalometry by ultrasound in normal 4. Campbell, S. (1969) 'The prediction of fetal maturity by ultrasonic measurement of the biparietal 5. Hibbard, L. T., Anderson, G. V. (1967) 'Clinical applications of ultrasonic fetal cephalornetry.' Obster. 6. Kato, M . (1966) 'Visible mutation induced in Drosophila by ultrasonic vibration.' Bid/.

Human fingernail thickness was measured distally in 39 subjects using an adapted electronic micrometer and ultrasound transmission time was measured both distally and proximally. Distal ultrasound nail transmission time correlated well with micrometer measurements. There was a clear rank order of distal and proximal nail transmission times: thumb greater than index greater than middle greater than ring greater than little fingers. Male nails had greater transmission times than female nails on the ring and little fingers. Distal nail transmission time was 8.8% less than proximal transmission time.

A method for direct measurement of the local pressures in the acetabular cartilage is described. Pressure transducers were introduced into the subchondral bone and positioned there in contrast with the cartilage: the transducers were calibrated in situ. Twelve cadaveric hips were prepared in this way and the pressures were measured with the joint loaded in flexion, extension, abduction, adduction, and in lateral and medial rotation. The highest pressures were recorded in the anterior and posterior segments of the acetabulum; the lowest pressures were constantly found at the zenith of the joint. The relationship of these findings to the pathogenesis of osteoarthritis is considered.