[Cadaver study of acetabular cup mobility in the healthy hip and prosthesis by monopodal pressure simulation ]

The purpose of this study was to quantify relative displacement of anterior and posterior horn of the acetabulum lunate surface using Omega strain gauges while increasing loads were applied to the hip joint. Measurement were performed on fresh cadaver bones in unipodal stance using experimental method before and after socket's implantation.

[corrected] Nine skeletons, from fresh non-embalmed cadavers, including pelvis, the three last lumbar vertebrae and both femurs were maintained in unipodal equilibrium using metallic cables for muscle passive simulation. Loads were applied up to 700 N. Specific extensometric Omega strain gauges were created and tested, with 5 mu of sensibility. Measurement of displacement between horns were studied on two sides of each pelvic before and after implantation of conventional and prototype cemented or press fit implants.

Among 81 loads on 18 acetabulum healthy and implanted, displacement was significant in 58 cases with a spacing of horn of 7 to 140 mu with average 31.1 mu and non significant in 25 cases. On healthy acetabulum, spacing was variable from 12 to 140 mu (average 43.2 mu) in 18 of 26 loads. On implanted acetabulum by different sockets, spacing was variable from 7 to 100 mu (average 27.4 mu) in 40 of 55 loads. Displacement was function of rotation hip, smaller in internal rotation and larger in external rotation. Spacing of horns was reduced in oversize sockets.

The data obtains by omega strain gauge suggest acetabular displacement is not univocal under load. There were a widening of the acetabular notch on load. This can be explained by the modification of primary incongruity of the two components of the hip joint because of acetabular deformation. Such results are in agreement with recently published data obtained about length of the transverse acetabular ligament.