Goniometer: A Tool for Measuring a Joint's Range of Motion

Photo of a knee getting measured with a goniometer.
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A goniometer is a device used in physical therapy to measure a joint's range of motion (ROM). There are two "arms"—one that is stationary and one that is movable—that are hinged together. Each is positioned at specific points on the body with the center of the goniometer aligned at the joint of interest. Hash marks on the hinge allow the therapist to precisely measure ROM in degrees.

Though you can easily purchase one yourself, a goniometer is meant for properly trained health professionals who know how to use it for best results. For example, a therapist may use the tool to obtain a baseline range of motion measurement of a specific joint after an injury. After an intervention, they may measure again to ensure that the treatment is effective.

The word goniometer is derived from the Greek words gonia and metron, which mean angle and measure, respectively.

Types of Goniometers

A traditional goniometer is pretty basic. It is usually made of clear plastic, sometimes metal, and some cost just a few dollars.

They come in different sizes: Small goniometers are meant to measure range of motion around the joints of your fingers, thumbs, and hands. Large goniometers are used to measure your hips or knees.

While the most basic form of goniometer is a physical piece of equipment, new forms have been developed. Most notably:

  • Goniometers that strap to a body part to measure range of motion while you move
  • Digital goniometers: Studies have shown that they're as accurate or better than the basic versions.
  • Goniometer apps on portable devices like smartphones: 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. One study found this method to be equally effective to basic goniometers in terms of measuring range of motion.

Remember, only a trained professional should be using information about goniometric measurements to make medical decisions.

Why Goniometers Matter

While strength receives a lot of attention, range of motion is an often-ignored measurement of it fitness. It is an indicator of flexibility as one ages.

If your therapist uses a goniometer to measure your range of motion and notes a decreased motion from your baseline, they can help you improve your joint's mobility with stretching and other interventions. Repeat use of a goniometer can help measure your improvement.

A study in the Journal of Aging Research found that as men and women hit retirement age, they lose an average of five to seven degrees of range of motion in their shoulders and hips each decade.

Increased (or preserved) range of motion means better mobility and injury prevention long term.

A Word From Verywell

One thing to ask any physical therapist: How do goniometric measurements figure into your overall rehab program and assessment? While a goniometer can be used effectively to measure joint range of motion, the quality of that motion—how things are moving—may be of equal importance. Your PT should take both quantity and quality motion into account when assessing your condition.

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  1. Hancock GE, Hepworth T, Wembridge K. Accuracy and reliability of knee goniometry methodsJ Exp Orthop. 2018;5(1):46. doi:10.1186/s40634-018-0161-5

  2. Behnoush B, Tavakoli N, Bazmi E, et al. Smartphone and Universal Goniometer for Measurement of Elbow Joint Motions: A Comparative StudyAsian J Sports Med. 2016;7(2):e30668. doi:10.5812/asjsm.30668

  3. Stathokostas L, Mcdonald MW, Little RM, Paterson DH. Flexibility of Older Adults Aged 55–86 Years and the Influence of Physical ActivityJ Aging Res. 2013;2013. doi:10.1155/2013/743843

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