In order to appreciate this article from Dr. Craig Liebenson, we must first define regional interdependence.
"Regional Interdependence: Seemingly unrelated impairments in a remote anatomical region may contribute to, or be associated with, the patient's primary complaint. (Wainner 2007)" You must look both proximally and distally to the site of pain. It is important to note that this term is not the same as referred pain.
This article poses the question: could a neck dysfunction be related to a problem in the lower extremities? The forward head posture is commonly seen in many of our patients. They often present with hypertonus in the upper trapezius and suboccipital muscles. BUT is the neck hypertonicity the primary problem? What if the patient's symptoms are greatly different in sitting vs. standing? If the tension is lessened by sitting (without changing the upper quadrant in any manner), then the patient's symptoms changed simply by altering the position of the lower extremity. The author also states that you must look at other possible causes of neck dysfunction, such as faulty respiration. Potentially the patient breathes differently in sitting vs. standing so the common denominator may not be the lower extremity after all.
In all cases, it is extremely important to assess- correct (perform an intervention)- then reassess in order to determine to true origin of a patient's symptoms.
Wainner RS, Whitman JM, Cleland JA, Flynn TW. Regional interdependence: a musculoskeletal examination
model whose time has come. The Journal of orthopaedic and sports physical therapy. Nov