Influence of pelvic position on radiographic measurements of the prosthetic acetabular component. An experimental study on a pelvic model.

A change in the position of a prosthetic acetabular component between two different radiographic examinations indicates loosening, and may be observed as tilting or migration of the socket. To determine the apparent changes in socket position caused by improper positioning of the pelvis, a full-scale model of a pelvis with attached prosthetic sockets was examined radiographically in different positions. The projected alignment of the Charnley socket indicator wire against the inter-tuberosity line was markedly influenced by the positioning of the pelvis. An alternative way of measuring the alignment is to use the long axis of the projected ellipse of the outer circumferential groove in the socket polyethylene. The thus defined socket alignment was not influenced by the positioning of the pelvis within the investigated range. No apparent socket migration was recorded within the range of pelvic rotation and inclination studied.