Final answer:
In lumbar spine extension, the sacrum moves slightly upward; this motion is part of the nutational movement. The cervical region has the greatest range of rotation while the lumbar region is limited in rotation but allows for flexion, extension, and lateral flexion.
Step-by-step explanation:
When there is extension in the lumbar spine, the sacrum undergoes a movement commonly known as nutational motion. In the context of lumbar extension, the sacrum moves in conjunction with the lumbar vertebrae, which leads to the top of the sacrum moving slightly forward or anteriorly, and the base of the sacrum moving upward or superiorly. This movement can be described as a slight upward motion of the sacrum.
To provide additional context, rotation in the vertebral column varies by region. The cervical region allows for the greatest range of motion for rotation, while the thoracic region allows for considerable rotation due to its flattened and vertically positioned articular processes. The lumbar region, which is directly associated with the sacrum, allows for flexion, extension, and lateral flexion, but is limited in rotation due to the orientation of its articular processes. During extension, the paralleled alignment of the lumbar and sacral regions contributes to the aforementioned upward movement of the sacrum.