J. Hecquet

Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves.

Abstract This paper proposes an anatomical parameter, the pelvic incidence, as the key factor for managing the spinal balance. Pelvic and spinal sagittal parameters were investigated for normal and scoliotic adult subjects. The relation between pelvic orientation, and spinal sagittal balance was examined by statistical analysis. A close relationship was observed, for both normal and scoliotic subjects, between the anatomical parameter of pelvic incidence and the sacral slope, which strongly determines lumbar lordosis. Taking into account the Cobb angle and the apical vertebral rotation confers a three-dimensional aspect to this chain of relations between pelvis and spine. A predictive equation of lordosis is postulated. The pelvic incidence appears to be the main axis of the sagittal balance of the spine. It controls spinal curves in accordance with the adaptability of the other parameters.

Three-dimensional study of pelvic asymmetry on anatomical specimens and its clinical perspectives

The aim of this study was to assess pelvic asymmetry (i.e. to determine whether the right iliac bone and the right part of the sacrum are mirror images of the left), both quantitatively and qualitatively, using three‐dimensional measurements. Pelvic symmetry was described osteologically using a common reference coordinate system for a large sample of pelvises. Landmarks were established on 12 anatomical specimens with an electromagnetic Fastrak system. Seventy‐one paired variables were tested with a paired t‐test and a non‐parametric test (Wilcoxon). A Pearson correlation matrix between the right and left values of the same variable was applied exclusively to values that were significantly asymmetric in order to calculate a dimensionless asymmetry index, ABGi, for each variable. Fifteen variables were significantly asymmetric and correlated with the right vs. left sides for the following anatomical regions: sacrum, iliac blades, iliac width, acetabulum and the superior lunate surface of the acetabulum. ABGi values above a threshold of ± 4.8% were considered significantly asymmetric in seven variables of the pelvic area. Total asymmetry involving the right and the left pelvis seems to follow a spiral path in the pelvis; in the upper part, the iliac blades rotate clockwise, and in the lower part, the pubic symphysis rotates anticlockwise. Thus, pelvic asymmetry may be evaluated in clinical examinations by measuring iliac crest orientation.

How is sagittal balance acquired during bipedal gait acquisition? Comparison of neonatal and adult pelves in three dimensions. Evolutionary implications

We compare adult and intact neonatal pelves, using a pelvic sagittal variable, the angle of sacral incidence, which presents significant correlations with vertebral curvature in adults and plays an important role in sagittal balance of the trunk on the lower limbs. Since the lumbar curvature develops in the child in association with gait acquisition, we expect a change in this angle during growth which could contribute to the acquisition of sagittal balance. To understand the mechanisms underlying the sagittal balance in the evolution of human bipedalism, we also measure the angle of incidence of hominid fossils. Fourty-seven landmarks were digitized on 50 adult and 19 intact neonatal pelves. We used a three-dimensional model of the pelvis (DE-VISU program) which calculates the angle of sacral incidence and related functional variables. Cross-sectional data from newborns and adults show that the angle of sacral incidence increases and becomes negatively correlated with the sacro-acetabular distance. During ontogeny the sacrum becomes curved, tends to sink down between the iliac blades as a wedge and moves backward in the sagittal plane relative to the acetabula, thus contributing to the backwards displacement of the center of gravity of the trunk. A chain of correlations links the degree of the sacral slope and of the angle of incidence, which is tightly linked with the lumbar lordosis. We sketch a model showing the coordinated changes occurring in the pelvis and vertebral column during the acquisition of bipedalism in infancy. In the australopithecine pelves, Sts 14 and AL 288-1, and in the Homo erectus Gona pelvis the angle of sacral incidence reaches the mean values of humans. Discussing the incomplete pelves of Ardipithecus ramidus, Australopithecus sediba and the Nariokotome Boy, we suggest how the functional linkage between pelvis and spine, observed in humans, could have emerged during hominid evolution.

Access to a three-dimensional measure of vertebral axial rotation.

Abstract Scoliotic curvatures can only be assessed through three-dimensional (3D) procedures. Measurement of the axial vertebral rotation appears to be of primary importance for such techniques. Nevertheless, traditional methods are based only on 2D data, obtained through antero-posterior radiographic projections of the spine. A 3D method is described in this study, taking into account the sagittal tilt of the vertebrae. Only such a measurement provides a real 3D method for a true appraisal of the scoliotic spine. The practical implications are developed.

[Two key describers of the sacro-acetabular relationships: the angles of sacral and acetabular incidence].

PURPOSE OF THE STUDY Implantation of total hip arthroplasties raises several important questions concerning the relationship between the orientation of the lumbosacral joint and the acetabular-femoral joint; in other words, between the position of the patients trunk and the orientation of the acetabula. To elucidate better these complex relationships, we conducted a morphometry study on a sample of 51 dry pelves: pelv 26 female and 25 male specimens. MATERIAL AND METHODS Three-dimensional coordinates of 47 homologous points were recorded for each pelvis. Data were then processed with De-Visu, a graphic visualization software. Seven parameters were compared: sacral slope, sacral incidence, and five parameters quantifying the three-dimensional orientation of the acetabula. RESULTS The graphic modelization enabled an integral 3-D visualization of each pelvis. The sagittal view enabled simultaneous visualization of the sacrum, the sacroiliac joints, the acetabula, and their alignments, as well as the variability of their spatial relation. The position reference chosen to simulate the upright position aligned the anterior iliac spines and the superior 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 slope was the most strongly correlated with the acetabular parameters. It exhibited a positive correlation with sagittal acetabular slope (r=0.59) and acetabular inclination (r=0.59). It exhibited a negative correlation with acetabular anteversion (R=0.45). The correlation with the sagittal acetabular 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 correlation between this angle and inclination was very high in males (r=-0.88) and non-significant in females. There was however a very strong correlation with anteversion in females (r=-0.74) which was non-significant in males. This contrasting finding was related to the wide spread of the inclination values in males and anteversion values in females. DISCUSSION We demonstrated a new sagittal parameter: the acetabular incidence. The summit of this angle is the center of the acetabulum. The sides are the pelvic thickness and the acetabular axes. This parameter was negatively correlated with the sacral incidence. It account simultaneously for the sagittal position of the sacrum in relation to the acetabula and for the degree of acetabular anteversion and inclination. We have demonstrated that the geometric sum of these two angles, sacral incidence and acetabular incidence, is equivalent to the sacro-acetabular angle demonstrated by Lazennec and Saillant. These authors showed that the sacro-acetabular angle is the sum of two positional parameters, the sacral slope and the sagittal acetabular tilt (or slope). The three angles -- sacral incidence, acetabular incidence, sacro-acetabular angle -- are anatomic angles which do not vary with the pelvic position.

Deux descripteurs clé des relations sacro-cotyloïdiennes : les angles d’incidence sacrée et cotyloïdeMise en évidence par le logiciel De-Visu

PURPOSE OF THE STUDY Implantation of total hip arthroplasties raises several important questions concerning the relationship between the orientation of the lumbosacral joint and the acetabular-femoral joint; in other words, between the position of the patients trunk and the orientation of the acetabula. To elucidate better these complex relationships, we conducted a morphometry study on a sample of 51 dry pelves: pelv 26 female and 25 male specimens. MATERIAL AND METHODS Three-dimensional coordinates of 47 homologous points were recorded for each pelvis. Data were then processed with De-Visu, a graphic visualization software. Seven parameters were compared: sacral slope, sacral incidence, and five parameters quantifying the three-dimensional orientation of the acetabula. RESULTS The graphic modelization enabled an integral 3-D visualization of each pelvis. The sagittal view enabled simultaneous visualization of the sacrum, the sacroiliac joints, the acetabula, and their alignments, as well as the variability of their spatial relation. The position reference chosen to simulate the upright position aligned the anterior iliac spines and the superior 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 slope was the most strongly correlated with the acetabular parameters. It exhibited a positive correlation with sagittal acetabular slope (r=0.59) and acetabular inclination (r=0.59). It exhibited a negative correlation with acetabular anteversion (R=0.45). The correlation with the sagittal acetabular 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 correlation between this angle and inclination was very high in males (r=-0.88) and non-significant in females. There was however a very strong correlation with anteversion in females (r=-0.74) which was non-significant in males. This contrasting finding was related to the wide spread of the inclination values in males and anteversion values in females. DISCUSSION We demonstrated a new sagittal parameter: the acetabular incidence. The summit of this angle is the center of the acetabulum. The sides are the pelvic thickness and the acetabular axes. This parameter was negatively correlated with the sacral incidence. It account simultaneously for the sagittal position of the sacrum in relation to the acetabula and for the degree of acetabular anteversion and inclination. We have demonstrated that the geometric sum of these two angles, sacral incidence and acetabular incidence, is equivalent to the sacro-acetabular angle demonstrated by Lazennec and Saillant. These authors showed that the sacro-acetabular angle is the sum of two positional parameters, the sacral slope and the sagittal acetabular tilt (or slope). The three angles -- sacral incidence, acetabular incidence, sacro-acetabular angle -- are anatomic angles which do not vary with the pelvic position.

Deux descripteurs clé des relations sacro-cotyloïdiennes : les angles d’incidence sacrée et cotyloïde

PURPOSE OF THE STUDY Implantation of total hip arthroplasties raises several important questions concerning the relationship between the orientation of the lumbosacral joint and the acetabular-femoral joint; in other words, between the position of the patients trunk and the orientation of the acetabula. To elucidate better these complex relationships, we conducted a morphometry study on a sample of 51 dry pelves: pelv 26 female and 25 male specimens. MATERIAL AND METHODS Three-dimensional coordinates of 47 homologous points were recorded for each pelvis. Data were then processed with De-Visu, a graphic visualization software. Seven parameters were compared: sacral slope, sacral incidence, and five parameters quantifying the three-dimensional orientation of the acetabula. RESULTS The graphic modelization enabled an integral 3-D visualization of each pelvis. The sagittal view enabled simultaneous visualization of the sacrum, the sacroiliac joints, the acetabula, and their alignments, as well as the variability of their spatial relation. The position reference chosen to simulate the upright position aligned the anterior iliac spines and the superior 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 slope was the most strongly correlated with the acetabular parameters. It exhibited a positive correlation with sagittal acetabular slope (r=0.59) and acetabular inclination (r=0.59). It exhibited a negative correlation with acetabular anteversion (R=0.45). The correlation with the sagittal acetabular 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 correlation between this angle and inclination was very high in males (r=-0.88) and non-significant in females. There was however a very strong correlation with anteversion in females (r=-0.74) which was non-significant in males. This contrasting finding was related to the wide spread of the inclination values in males and anteversion values in females. DISCUSSION We demonstrated a new sagittal parameter: the acetabular incidence. The summit of this angle is the center of the acetabulum. The sides are the pelvic thickness and the acetabular axes. This parameter was negatively correlated with the sacral incidence. It account simultaneously for the sagittal position of the sacrum in relation to the acetabula and for the degree of acetabular anteversion and inclination. We have demonstrated that the geometric sum of these two angles, sacral incidence and acetabular incidence, is equivalent to the sacro-acetabular angle demonstrated by Lazennec and Saillant. These authors showed that the sacro-acetabular angle is the sum of two positional parameters, the sacral slope and the sagittal acetabular tilt (or slope). The three angles -- sacral incidence, acetabular incidence, sacro-acetabular angle -- are anatomic angles which do not vary with the pelvic position.