Deux descripteurs clé des relations sacro-cotyloïdiennes : les angles d'incidence sacrée et cotyloïde Mise en évidence par le logiciel De-Visu Two key describers of the sacro-acetabular relationships: The angles of sacral and acetabular incidence Analysis by the software De-Visu

SummaryPurpose of the study.„Implantation of total hip arthroplasties raises several important ques-tions concerning the relationship between the orientation of the lumbosacral joint and theacetabular-femoral joint; in other words, between the position of the patients trunk and theorientation of the acetabula. To elucidate better these complex relationships, we conducted amorphometry study on a sample of 51 dry pelves: pelv 26 female and 25 male specimens.Material et methods.„ Three-dimensional coordinates of 47 homologous points were recordedfor each pelvis. Data were then processed with De-Visu, a graphic visualization software. Sevenparameters were compared: sacral slope, sacral incidence, and “ve parameters quantifying thethree-dimensional orientation of the acetabula.Results.„ The graphic modelization enabled an integral 3-D visualization of each pelvis. Thesagittal view enabled simultaneous visualization of the sacrum, the sacroiliac joints, the ace-tabula, and their alignments, as well as the variability of their spatial relation. The positionreference chosen to simulate the upright position aligned the anterior iliac spines and the super-ior pubic point. This position was found pertinent because the mean value of the sacral slope(41.8 ) and the sacral incidence (54 ) were not different from published series. The sacral slopewas the most strongly correlated with the acetabular parameters. It exhibited a positive corre-lation with sagittal acetabular slope (r=0.59) and acetabular inclination (r=0.59). It exhibiteda negative correlation with acetabular anteversion (R=0.45). The correlation with the sagittalacetabular slope was very strong for anteversion (r=0.92), and rose with acetabular inclination(r=„0.66). The angle formed by the two acetabular axes was highly variable (37 ). The corre-lation between this angle and inclination was very high in males (r=„0.88) and non-signi“cantin females. There was however a very strong correlation with anteversion in females (r=„0.74)which was non-signi“cant in males. This contrasting “nding was related to the wide spread ofthe inclination values in males and anteversion values in females.Discussion.„We demonstrated a new sagittal parameter: the acetabular incidence. The sum-mit of this angle is the center of the acetabulum. The sides are the pelvic thickness andthe acetabular axes. This parameter was negatively correlated with the sacral incidence. Itaccount simultaneously for the sagittal position of the sacrum in relation to the acetabulaand for the degree of acetabular anteversion and inclination. We have demonstrated thatthe geometric sum of these two angles, sacral incidence and acetabular incidence, is equi-valent to the sacro-acetabular angle demonstrated by Lazennec and Saillant. These authorsshowed that the sacro-acetabular angle is the sum of two positional parameters, the sacralslope and the sagittal acetabular tilt (or slope). The three angles „sacral incidence, acetabu-lar incidence, sacro-acetabular angle„ are anatomic angles which do not vary with the pelvicposition.© 2008 Elsevier Masson SAS. Tous droits reserves.