Why would neck adjustment have an effect on anything other than neck pain?

Pain or discomfort in one area of the body may be linked functionally to discomfort arising from another area. Consequently, addressing dysfunction in one part of the body may relieve symptoms in another part. If you look at a model of the spine, you can see that the spine is one continuous structure. Adjustment at various points along the structure may be needed to help reduce biomechanical stresses on other parts of the spine and to relieve discomfort when it is clinically necessary.

The spine is also the protective channel that surrounds the spinal cord and tensions on the "dura mater", a membrane that covers the spinal cord, can create torsion and strain on the nerves resulting in pain.