Goniometer for Measuring a Joint's Range of Motion

Photo of a knee getting measured with a goniometer.
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How does your physical therapist get an accurate measurement of how your body is moving? How does he or she know how much a joint moves? Easy: your PT uses a device called a goniometer.

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.

Technology and Goniometers

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.

Recently, a number of goniometer apps on portable devices like smartphones have become available. These use your device's accelerometer and gyroscopic technology to measure changes in the position of the phone. You simply open the app, place your phone in the correct position on your body part, and move your body through its available range of motion. The app will then measure the amount of motion that occurred around the specific joint. Remember, only a trained professional should be using information about goniometric measurements to make medical decisions.

Are There Ways to Improve My Range of Motion?

If your PT uses a goniometer to measure your range of motion and notes a decreased motion from your baseline, he or she can help you improve your joint's ability to move. Specific range of motion exercises can be done for various body parts, and techniques called mobilizations can be performed to help your joints move better.

Flexibility exercises may also be prescribed by your physical therapist to help improve your range of motion. If loss of mobility is due to tightness in muscles surrounding a joint, stretching those muscles can help improve the range of motion. Your PT can use his goniometer to measure your successes with stretching. Increased range of motion equals effective stretching.

It is important that your PT uses a goniometer correctly. There may be variances in measurement if a goniometer is used incorrectly. Generally, it is accepted that goniometric measurements have good inter-tester and intra-tester reliability.

Goniometric measurements should be only one small component of your overall rehab program and assessment. While a goniometer can be used to measure joint range of motion, the quiality of that motion—how things are moving—may be of equal importance. Your PT should take both quantity and quailty of motion into account when assessing your condition.

A Word From Verywell

When you go to physical therapy, there may be a lot of tools that are used, and these may seem strange or unusual. By learning about the different tools of the trade—like goniometers—you can go to PT with an understanding of what to expect.

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