Pelvic rotation

Posterior Pelvic Rotation Theory This concept grows out of an appreciation for the dynamic forces that are applied to the lumbosacral joint when the human body is in motion. After reading this article, you have had some exposure to the complexity of the interactions which are occurring at the lumbosacral junction. It is an amazing mechanical system that is able to function and transfer enormous loads applied in a repetitive, pulsating fashion (Fig. 6). 

Pelvic rotation. The pelvis rotates on the swing side, approximately 4 degrees on either side of the central axis. Because the pelvis is a semi-rigid structure, this rotation occurs alternately at each hip joint as the hip passes from relative internal rotation to external rotation during stance phase. 

During these motions, the lumbar spine rotates to the right and flexes laterally to the left, compensating for the right sacral flexion created by pelvic rotation toward the left with right pelvic tilt The relationship of the rotated right L5 to the left-on-left sacral rotation completes the picture... 

The gluteus maximus follows the law oj muscle detorsion. Therefore, to increase hip extension, as in ballet movement, the ilium must be rotated. Somatic dysfunction of the lumbar spine will limit lumbar regional motion, pelvic rotation, and hip extension... 

An additional late scan 120-180 s after intravenous contrast administration may be helpful to exclude deep pelvic vein thrombosis or if there is poor visualization of pelvic veins on the arterial phase scans (Fig. 2.2). Depending on the patient s pelvic circumference, the late scan may be acquired with a reduced tube current, e.g. 50 mAsec. Late scans obtained after 3-5 min are also suitable for evaluation of the bladder, which, at this time, contains part of the renally eliminated contrast medium. Even filling of the bladder with contrast medium is achieved by rotating the patient about her longitudinal axis. 

Anteriorly the sacroiliac, sacro-spinous and sym-physeal ligaments are transversely orientated to support the pelvic floor and resist external rotation. There are superior symphyseal ligaments which support the pubic symphysis. 

Avulsion fractures of the posterior inferior iliac spine and the transverse process of the 5 lumbar vertebra are rare but indicative of severe trauma. The former occurs as a result of external rotation of the hemi-pelvis which avulses the sacrospinous ligament at its insertion. The latter injury results when the ilio-lumber ligament is avulsed from the tip of the transverse process of L5 by shearing forces in the vertical plane. These injuries should arouse suspicion of pelvic instability. 

This classification system aims to link management and prognostic evaluation with the imaging findings. It is based on the work of Tile and the Association for Osteosynthesis and relates to the site of fractures within the pelvic ring (Fig. 12.15a-c). There are three classifications, A, B and C. In type A fractures, the pelvic ring is stable, type B is partially stable this includes the open-book and bucket-handle fractures which are caused by external- and internal-rotation forces, respectively. In type C injuries, there is complete disruption of the posterior sacroiliac complex. In adults, type A lesions represent 52%, type B 27% and type C 21% (Theumann et al. 2002). The classification is shown in Table 12.1. 

Anterior fractures include the anterior wall and anterior column and they are often associated with other pelvic fractures. They are the result of a lateral blow to the greater trochanter when the leg is externally rotated. This is a relatively uncommon injury and typically causes minimal displacement, so surgical fixation is not usually required. 

Review of some everyday activities demonstrate their effect on the pelvic structures. In the standing position, body weight is transmitted through the fifth lumbar vertebra to the sacrum, where the force vector splits in two. One force vector drives the sacrum into its articulation, and the other rotates the sacrum anteriorly. The greater the lumbosacral angle, the greater is the anterior vector force, which in turn increases the lumbosacral strain (Fig. 57-2). 

The tests for pelvic dysfunctions have fair specificity and variable sensitivity. The presence of a sacral dysfunction can obscure or exaggerate the findings for pelvic dysfunction. The standing flexion test can be falsely positive if there is an overwhelmingly positive seated flexion test and sacroiliac dysfunction. The depth of the sacral sulcus is not specific to pelvic dysfunction because a deep sulcus can also indicate a forward sacral torsion with the axis opposite to the deep sulcus, a unilateral sacral shear, as well as a posteriorly rotated ilium on the same side. A shallow sulcus can also indicate sacral dysfunction in addition to an anterior rotated ilium on that side. 

Anomalies of renal position and rotation are well demonstrated by the high resolution anatomic images. Horseshoe and ectopic kidneys can be easily separated from the background and overlying tissues. Pelvic kidneys in particular, which often are significantly smaller than the normally positioned kidney, are well demonstrated with MR urography (Fig. 1.2.13). Hypoplastic kidneys associated with ureteric ectopia and supernumerary kidneys, which have been difficult to demonstrate with other imaging modalities, can usually be demonstrated even if there is minimal renal function. 

Fig. 9.6. Pelvic X-ray of a male baby with classic exstrophy split symphysis is present. The pubic and iliac bones are rotated outwards with an increase in the inter-triradiate distance...

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