Differences in the rates of penetration determined from radiographic and shadowgraphic measurements of acetabular sockets.

Abstract

A number of previous studies have observed a marked difference in the penetration depths recorded between direct and radiographic measurement, although no assessment of how these discrepancies affect the rates of penetration has been undertaken. In this report, the penetration depth of 95 sockets was determined from both prerevision radiographs and casts of the retrieved sockets using the uniradiographic and shadowgraphic techniques, respectively. It was observed that the mean discrepancy between the penetration rates derived from the two measurement methods was 0.046 (SE 0.017) mm yr(-1), which was significantly different from zero at P = .007. It was concluded that the penetration rates derived from this method of radiographic assessment seriously underestimated the true value as measured by a direct method by approximately 20%. As a consequence, the discrepancy in penetration rates between those sockets that are loose at revision surgery (direct measurement) and the general population of acetabular components (radiographic measurement) may not be as large as previously thought.