Coupling is very common in spinal function. Frequently, three motions will simultaneously take place during normal physiological movement. Pure motion in one plane perhaps does not exist. Only sagittal motion unit movements roughly approximate to motion in one plane, assuming that no abnormal or other curves exist. After the first degree or two of motion, one induces a portion of the other, and they are inseparable.
Extension also reduces the range of lateral flexion and rotation.
This appears to be a function of rib cage stiffness and patient individuality. Clearly, from the work of White and Panjabi, we cannot use the rotation of the middle and lower thoracic spinous as a constant. Rotation restricts flexion and extension, and is invariably accompanied by a degree or two of lateral flexion. This statement warrants further clarification as traditional, and historical motion palpation does not address this issue. The lumbar region shows certain cross-coupling of all three rotations.