The pelvic section is designed to correct pelvic tilt and pelvic torsion. The pelvic tilt presents as a protrusion of the pelvis. Usually, the hemipelvis is higher on the thoracic convex side. The pelvic tilt is corrected by a 3-point pressure system that consists of pressure zones 41, 2 and 30 and expansion zone 16. The location of pressure zone 41 is on the iliac fossa, which is on the high side of the pelvic tilt. Pressure zone 2 is on the opposite side to pressure zone 41 and is located approximately 3cm above the iliac crest. Pressure zone 30 is on the opposite side to pressure zone 41, and is located on the greater trochanter. Expansion zone 16 has a window and is required on the low side of the hemipelvis. This provides a space for the hemipelvis to move into during correction.
Pressure zone 41 has a concave shape, which mimics the anatomical dimple-shape of the iliac fossa. Its inferior lateral trimline is at the caudal aspect of the iliac fossa. The pressure zone 30 is shaped so as to apply slight pressure on the greater trochanter, without causing discomfort. The trimline extends to the greater trochanter so that the counterforce works with pressure zone 2. Pressure zone 2 is shaped as previously mentioned in the lumbar section. The pelvic grip of the brace is designed so that it is higher on the side in which the pelvis is tilted lower, hence it has an asymmetrical shape.
The functions of these forces are to work together as a 3-point pressure system. Pressure zone 41 pushes the contralateral hemipelvis upward and the expansion zone 16 provides a space for the hemipelvis to move into for correction, (figure 3.22).
Figure 3.22 Posterior view of a right thoracic and left lumbar curves in the coronal plane. Pressure zones 41, 2, 30 and expansion zone 16 are represented in the figure as 41, 2, 30 and 16 respectively. The upward moment is represented as M. The thoracic convexity is to the right, therefore the pelvis tilt is to the left side. Pressure zone 41 pushes the pelvis between the two counterforces 2 and 30, therefore M is produced. This moves the left hemipelvis upward into expansion zone 16, as a result the pelvis is levelled, (Master by thesis, Wood, G 2003). .
Pelvic torsion consists of iliac rotation and pelvis transversal rotation. The iliac rotation refers to a position of relative anteversion of the concave side of the lumbar curve and retroversion of the convex side of the lumbar curve. Anteversion is an abnormal position of the hemipelvis that is rotated and torsioned anteriorly therefore the ASIS is more prominent than usual, (figure 3.23). The contralateral hemipelvis would be in retroversion. Retroversion is an abnormal position of the hemipelvis, which is rotated and torsioned posteriorly therefore the ASIS is less prominent than usual, (figure 3.24). The contralateral hemipelvis would be in anteversion.
Rigo and Chêneau (1997, 2000) reported that this could be the consequence of passive tension of the lumbar fascicles of the erector spinae (longisimus thoracis and iliocostalis). Rigo (1999a) found that sometimes, combined or substituting iliac rotation causes a true three-dimensional iliac torsion (a bone deformity). Iliac rotation is corrected by pressure zones 37 and 34 as well as expansion zones 36 and 6 on the hemipelvis that is in anteversion. Pressure zones 38 and 2 as well as expansion zones 35 and 33 are applied to the hemipelvis that is in retroversion. Also by correction of the lumbar curve, the pelvis automatically assumes an anteversion position and therefore corrects itself.
The hemipelvis that is in anteversion, has its ventral inferior trimline of the brace that extends inferiorly to cover the ASIS and pressure zone 37. However it is not as low as the contralateral side because expansion is required by expansion zone 36 for the correction of anteversion. The dorsal inferior trimline, for the same hemipelvis, extends inferiorly to the gluteus maximus. This trimline is sufficiently inferior to apply pressure zone 34.
The hemipelvis that is in retroversion, has its ventral inferior trimline of the brace that extends inferiorly to above the symphysis pubis to apply pressure zone 38. This is much lower than the contralateral side because pressure is required by pressure zone 38 for the correction of retroversion. The dorsal inferior trimline, for the same hemipelvis, is higher than the contralateral side because expansion is required by expansion zone 33 for the correction of retroversion. These inferior ventral and dorsal trimlines are asymmetrical and depend on the position of the pelvis.