Total knee replacement may be done on people, usually over 55, whose knees have been damaged by arthritis, trauma, or other destructive diseases of the joint resulting in severe limiting knee pain and significant stiffness, instability (constant giving way) and deformity (lock-knees or bowlegs) of the knee.
The Mexican government has a Federal District, which houses the federal government. The Federal District is a physical place and a territory, bordering Mexico City, which is the country's capital city. This is not counted as one of the states, and is much like the United States' District of Columbia.
The Distrito Federal (DF, Federal District) is the capital of Mexico. (Most of its territory is occupied by Mexico City.) It has an area of 1,547 square kilometers (597 square miles). It is about ten times the size of the District of Columbia, the US capital. Although there are no municipalities in Mexico's Distrito Federal, there are sixteen political districts.