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

1.4.4. Posture and postural changes
During pregnancy the organs in the upper abdomen such as liver, stomach and
spleen have to make way for the enlarging uterus with its growing placenta and fetus
and are therefore moved cranially and slightly laterally. Likewise, the third lumbar
vertebra, representing the apex of lordosis, offers more space to the uterus when
shifted posteriorly. This shift occurs by a lowering of the lordosis in the lumbar spine,
and this lowering can only take place if the pelvis straightens up. This straightening
up advantageously enables the SIJ to withstand the considerably greater pressure on
this joint due to weight gain in pregnancy (see chapter 1.2.). If such a flattening of the
lumbar lordosis is not possible, the forces within the pelvic ring increase according to
the model of the pelvic shear (see chapter 1.2.3.), and that alone can lead to
increased strain in the SIJ. [34]
In the course of the ninth month of pregnancy the anterior weight increases in
relation to the posterior weight due to the size of the uterus, so that the muscular
structures are not able any more to keep the pelvis in an upright position. In most
cases this leads to an increased lordosis in the last stages of pregnancy. As a
compensatory mechanism, the thoracic spine and the nape are stretched; in other
words, these two curves of the spine are flattened and the shoulders are pulled
backwards. [25]
1.4.5. Uterus
During pregnancy the uterus undergoes a twenty-fold increase in weight from 50 g to
1,100 g at term. It grows from 7 cm to a length of 30 cm and the cavity expands from
some 40 ml to 4,000 ml. [68]
The uterus consists of bundles of smooth muscle cells separated by thin sheets of
connective tissue. Myometrial growth is almost entirely due to muscle hypertrophy,
although some hyperplasia may also occur. The stimulus for myometrial growth and
development is derived from the direct effects of the growth processes in the uterus
and from the effects of oestrogen and progesterone produced by the ovaries and the
placenta. The muscle cells are arranged in three layers with muscle bundles running
Master’s Thesis Wolfgang Aspalter 27