Technically, the most efficient way to carry out spinal mobilizations would be a direct anterior-posterior (AP) approach of the vertebrae. However, anatomical constraints (such as the presence of soft tissue organs like the stomach etc. directly overlying the spine) prevent this approach. It is therefore much more common to have most spinal mobilizations (including the lumbar vertebrae and sacroiliac joints) performed using the posterior-anterior (PA) approach by manipulating the parts of the individual vertebrae such as the spinous processes or transverse processes etc. that are much more accessible from behind.
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