Our hands have 1/4th of the bones in our bodies, and are full of membranes and tiny muscles that hold the many hand bones together, giving them a sturdy form. 

The fingers are moved by long tendons with muscle bellies that wrap around the forearm bones, some crossing the elbow for leverage.

The wrists are tightly wrapped by ligaments, like bracelets, to hold close all those tendons, blood vessels, and nerves crossing the amazing wrist joint. 

Elbows are moved by muscles from above and below. 

Restrictions, knots, or injuries in any of these parts of the arm and hand can cause pain in any of the others.