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

Abstract

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.

Fig. 1

Coronal views of the pelvis. 1, acetabular diameter; 2, sacral–acetabular diameter; 3, upperplate S1-acetabulum; 4, sacroiliac–acetabulum; 5, scalenion–acetabulum; 6, sacroiliac–acetabulum angle; 7, pelvic oblique diameter; 8, lateral sacral mass/pelvic breadth (A/C); 9, lateral sacral mass/sacral breadth (A/B); 10, symphysis pubis–apex iliac crest.

Fig. 6

Anterior views (A,B) of pelvis. (A) 67, semi-pelvic spacer; 68, Wiberg angle; 69, Hilgenreiner angle (superior lunate surface obliqueness). (B) 70, acetabulum sphericity; 71, lateral incidence.

Fig. 7

The 15 significant homologous variables on the abscissa axis (among the 71 homologous variables) and the difference between right–left on the ordinate axis: the degree of asymmetry (positive and negative) is displaced with respect to the abscissa axis and the perfect symmetry (or the asymmetry is zero) is the abscissa axis. 1, sacroiliac–acetabulum (length); 2, lateral sacral mass/pelvic breadth; 3, pubis symphysis; 4, great axis obturator foramen; 5, scalenion–acetabulum; 6, apex iliac crest–acetabulum; 7, anterior medial iliac buttress; 8, medio-superior iliac buttress; 9, postero-inferior iliac buttress; 10, wing ilium slope; 11, centre–edge angle of Wiberg; 12, acetabulum axis; 13, Hilgenreiner angle; 14, sacraoiliac–acetabulum (angle); 15, iliac crest orientation.

Fig. 3

Sagittal views of right iliac bone. 26, ilio-ischium angle; 27, ilio-pubic angle; 28, ischio-pubic angle; 29, orientation of wing ilium; 30, iliac crest tubercle (apex) thickness; 31, iliac crest tubercle (anterior) thickness; 32, iliac crest tubercle (posterior); 33–44 (•), thickness of iliac buttress (anterior, posterior, medium); 45, greater sciatic notch.

Fig. 4

Coronal view of pelvis (A), sagittal view of right iliac bone (B), lateral right view of sacrum (C). (A) 46, postero-medial upper sacral plate–ischial tuberosity; 47, postero-medial upper sacral plate–supero-medial ischio-pubic ramus; 48, postero-medial upper sacral plate–infero-medial ischio-pubic ramus; 49, postero-medial upper sacral plate–obturator foramen; 50, postero-medial upper sacral plate–ilio-pubic ramus; 51, medial upper sacral plate–ischial tuberosity; 52, medial upper sacral plate–ischio-pubic ramus; 53, sacral plane breadth (PSIS-scalenion); 54, lateral sacral mass orientation. (B) 55–57, growth factor (sum of ilium, pubis, ischium and iliac axises). (C) 58, sacro-iliac height; 59, auricular surface angle.

Fig. 5

Anterior view of pelvis. 60, acetabulum axis; 61, central cosine of acetabulum axis (x); 62, central cosine of acetabulum axis (y); 63, central cosine of acetabulum axis (z); 64, acetabulum axis (bis); 65, slope of iliac blade; 66, ilio-sacral angle.

Fig. 8

Correlation coefficient between right and left for significant asymmetric variables. 1, sacroiliac–acetabulum (angle); 2, postero-inferior iliac buttress; 3, scalenion–acetabulum; 4, anterio-medial iliac buttress; 5, wing sacral/pelvic breadth; 6, acetabulum axis; 7, Hilgenreiner angle; 8, medio-superior iliac buttress; 9, sacroiliac–acetabulum (length); 10, iliac crest orientation; 11, centre–edge angle of Wiberg; 12, great axis obturator foramen; 13, wing ilium slope; 14, pubis symphysis (height); 15, apex iliac crest-acetabulum.

Fig. 9

The six significant (▪) ABGi positive (acetabulum axis, iliac crest orientation) and negative (Hilgenreiner angle, sacroiliac–acetabulum (angle), Wiberg angle, lateral sacral mass/pelvic breadth) among 71.

Fig. 2

Sagittal views of right iliac bone. 11, hipbone length; 12, symphysis pubis height; 13, symphysis pubis slope; 14, horizontal greater sciatic notch; 15, pelvic general index (C/11); 16, superior iliac spines length; 17, apex iliac crest–ischial tuberosity; 18, anterior–superior iliac spine–ischial tuberosity; 19, postero-superior iliac spine–ischial tuberosity; 20, great axis of obturator foramen; 21, anterior iliac crest; 22, apex iliac crest–acetabulum; 23, minimal ilium breadth; 24, pubis length; 25, antero-superior iliac spine–acetabulum.

Fig. 10

Pelvic asymmetry: a spiral path in the pelvis, the upper part with the iliac blades rotating clockwise and the lower part with the pubic symphysis rotating anticlockwise.

Fig. 12

The pelvis clinical asymmetry measurement: the right iliac crest angle is greater than the left. Then the right iliac crest is unfolded whereas the left one is folded. Therefore, the left iliac crest vertex is higher than the right. Thus, pelvis asymmetry can lead to confusion with pelvis imbalance. ASIS, anterior superior iliac spine; PSIS, posterior superior iliac spine; TIC, tubercle of iliac crest.

Fig. 11

The pelvis in the transverse plane and the effects of the asymmetry.