Chamberlain line is a measurement near where the spinal cord connects to the brain. Physicians use this line to measure the position of the dens of C2 . Normally, the tip of the dens should be at or just below the Chamberlain line. If the dens sticks above the Chamberlain line, usually more than 3 to 5 millimeters, it suggests a condition called basilar invagination.
Basilar invagination is a condition where the top of the spine pushes up into the skull, which can put pressure on the brainstem and spinal cord.