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How a goniometer works

Updated March 21, 2017

A goniometer is a medical tool that is used to measure range of motion. This range is expressed as angles and listed in degrees.

Often, patients have reduced range of motion at a joint, such as a knee or elbow. A physical therapist can use a goniometer to measure the range of motion possible at that joint. Later, progress can be charted by taking frequent measurements as treatment continues.

Goniometer Basics

A goniometer is a medical tool that is used to measure range of motion. This range is expressed as angles and listed in degrees.

Often, patients have reduced range of motion at a joint, such as a knee or elbow. A physical therapist can use a goniometer to measure the range of motion possible at that joint. Later, progress can be charted by taking frequent measurements as treatment continues.

Goniometer Use

Like a compass, the circular portion of a goniometer is marked with degrees, from 0 to 360. Two arms extend from this circle, one of which can pivot freely. The arm that does not pivot is mounted at the zero-degree point.

When used, the goniometer's fulcrum, or centre, is placed at a joint, such as the elbow. Both arms of the device are aligned with the corresponding limbs. Using the elbow example, a patient might start with his elbow fully extended. The goniometer would indicate 180 degrees, and the arms of the tool would be opposite one another.

As the patient moves her limb, the arms of the goniometer move with it. Once the range of motion is complete, the dial of the device is checked. This indicates the new angle at the joint. Comparing the original and new angle readings shows the range of motion in degrees.

To continue the elbow example, if the patient can move her forearm only slightly, the goniometer might read 76.7 degrees C. If the original, outstretched elbow measurement was 180 degrees, the patient's range of motion is -12.2 degrees C.

Goniometer Advantages

Charting goniometer readings is useful in physiotherapy settings. Because physiotherapy often progresses slowly, frequent goniometer measurements on the affected joints can help the patient visualise improvements.

These changes may be slight from one day to the next, but when charted, seeing the steady increase in degree range can provide motivation and daily goals.

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About the Author

Benjamin Aries has been involved in digital media for much of his life and began writing professionally in 2009. He has lived in several different states and countries, and currently writes while exploring different parts of the world. Aries specializes in technical subjects. He attended Florida State University.