A goniometer is a device used in physical therapy to measure the range of motion around a joint in the body. The word goniometer is derived from the Greek terms gonia and metron, which mean angle and measure, respectively.
A goniometer is usually made of plastic and is often transparent. Occasionally goniometers are made of metal. There are two "arms" of the goniometer: the stationary arm and the moveable arm. Each arm is positioned at specific points on the body and the center of the goniometer is aligned at the joint to be measured. There are hash marks on the center of the goniometer that your physical therapist uses to precisely measure joint range of motion.
When first starting physical therapy, your physical therapist may use a goniometer to obtain a baseline range of motion measurement around a specific joint. After a specific intervention or treatment, he or she may measure again to ensure that the treatment is effective.
Goniometers come in different sizes. Small goniometers are available to measure range of motion around the joints of your fingers, thumbs and hands. Large goniometers are used to measure the range of motion around your hips or knees.
There are also goniometers that strap to your body part that can measure range of motion while you move. Digital goniometers are also available, but these are rarely seen in a typical physical therapy clinic as they are quite expensive.
My physical therapist used a goniometer to accurately measure the joint range of motion around my knee after I had a total knee replacement surgery.