Can back pain caused by symptom-giving sacroiliac joint relaxation ...

contribute to this locking mechanism as they increase the pressure on the joint when
contracted:
o the transverse abdominal muscle
o the middle part of the internal oblique abdominal muscle
o the piriformis muscle
o the coccygeal muscular structures and the pelvic floor
1.2.3. The pelvic shear
according to Klein and Sommerfeld [24]
The pelvic shear is a model which represents the pelvis as a buffer system in a
sagittal plane. This model presumes certain mobility in the SIJ.
In the upright standing position, the two levers sacrum and innominate bone
introduce a nutational motion in the SIJ. This nutation is slowed down by the
sacrotuberous and the sacrospinal ligament. As they have a favourable leverage,
they are the most effective dampers of the nutational motion, even though they act
only passively. The following muscles are able to
function as active nutation dampers:
o iliac muscle
o straight muscle of the femor, tensor
fasciae latae muscle, sartorius muscle
o piriformis muscle
o muscles of the pelvic floor
During pregnancy the relation between the
different levers changes and the stabilising Fig. 1F: The pelvic shear [24]
ligaments get softer. Therefore the model of the pelvic shear can slightly deviate from
its normal scheme.
Master’s Thesis Wolfgang Aspalter 19