Skeletal fluorosis is a health effect of excessive accumulation of fluoride in bones leading to changes in bone structure and making them extremely weak and brittle. The early stages of skeletal fluorosis are characterized by increased bone mass, detectable by x-ray. If very high fluoride intake persists over many years, joint pain and stiffness may result from the skeletal changes. The most severe form of skeletal fluorosis is known as "crippling skeletal fluorosis," which may result in calcification of ligaments, immobility, muscle wasting, and neurological problems related to spinal cord compression.