Last updated: August 12, 2021

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Welcome! Today we are going to talk about the goniometer, a measuring instrument used in various applications, from mathematical calculations to analysing the mobility of joints.

There are two types of goniometer: a simpler one, called a degree protractor and the precision goniometer (also called Universal), the latter being found in two sizes: conventional or "finger".

Knowing what are the characteristics and applications of this instrument and its variations will make all the difference at the time of purchase. Therefore, if you are interested in buying a goniometer, keep reading this article.




Summary

  • The main indication for using a goniometer is to measure joint amplitude and mobility. Measuring the flexion and extension of a joint is called goniometry, a simple and very effective technique.
  • The precision goniometer, also called universal goniometer, is a device formed by two arms: one fixed and the other mobile, connected by a circular-shaped axis.
  • The protractor, both the 180º semi-circle and the 360º circle, is also considered a goniometer, although its use is indicated for situations where the need for precision is lower. The size also varies, and the conventional goniometer may measure 20, 25 or 35 cm, while the "finger" goniometer measures 7 cm.

The Best Goniometers: Our Picks

Buying Guide

The choice of a measuring tool depends on how you will use it and what accuracy you need to get the job done. So it is necessary to pay attention, because each instrument is specific to one need.

A versatile instrument that is worth investing in is a goniometer. You can use it in physiotherapy, carpentry, carpentry, construction, mechanics and even visagism. Want to know more about the goniometer? Then keep reading this article.

Imagem de um fisioterapeuta utilizando um goniômetro para medir a mobilidade da articulação de uma paciente.

The goniometer is an instrument widely used by physiotherapists. (Source: Elnur Amikishiyev / 123RF)

What is a goniometer?

The goniometer is an instrument used in measuring or checking angular measurements. This tool can have a semicircular or circular shape, or be presented as two rulers connected by an axis.
The goniometer is used for measuring and checking angular measurements

Among the types of goniometers is the protractor, a semicircle or graduated circle, with angles of 180 or 360 degrees. This instrument is widely used in loose angle measurements.

The protractor, either semicircle or circle, is usually part of the school material for children and adolescents in mathematics or geometry class, but it is also a working tool for many professionals.

For applications where precision and accuracy in calculations are required, a precision (also called universal) goniometer is used, an instrument consisting of a fixed or stationary arm, a movable arm and a circle.

The goniometer has the following features: a rivet connects the mobile arm to the fixed arm and to the central axis. This circle has four graduations, from 0 to 90º (or 110º in some cases).

What are the uses of the goniometer in physiotherapy?

Mobility, amplitude and flexibility of body movements are essential to maintain the quality of life, good posture and to prevent joint and muscle injuries and other orthopaedic diseases.

The evaluation and measurement of the amplitude of movements that each joint is capable of performing is done by a physiotherapist, through a technique called goniometry, which uses an instrument called goniometer.

The data obtained with the goniometer may establish whether or not there is dysfunction in the joints, quantify the limitations of joint angles and serve as a comparison between the initial and subsequent evaluations.

With the goniometry it is possible to establish a diagnosis, set goals with the treatment, evaluate the functional improvement or recovery and make possible changes in the treatment.

To make this measurement, the fixed arm (of the instrument) must be aligned with the segment adjacent to the joint being evaluated, in the initial zero degree position.

The mobile arm must be positioned in the region of movement of the joint and the intersection point of the goniometer must be positioned on the axis of the joint.

For the assessment to be correct and effective, it is important:

  • Stabilise the instrument before the assessment.
  • Allow a full and slow range of movement.
  • Know the anatomical points.
  • Follow the reference values for each joint.
  • Understand the bony limits.
  • Comparison with the contralateral side of the patient provides important data.

It is possible to perform the evaluation with the goniometer on the shoulder, elbow, hip and knee joints. For each joint studied, there are different assessment techniques: flexion, extension, abduction and adduction.

The goniometer is an effective, durable, reusable (just wash it) and low cost instrument.

Advantages
  • Several applications: from simple mathematical calculations to uses in medicine
  • Two versions: protractor and precision goniometer
  • You find plastic, acrylic, metal or steel models
  • It is a cheap instrument
Disadvantages
  • It is fragile, so avoid falls and do not store it with other instruments
  • You will need different sized instruments according to the measurement

What care should I take with the goniometer?

Because it is a precision instrument, the goniometer should not be subjected to falls. Another care you need to have is about the storage of the instrument: avoid storing it together with other materials.

It is also important to protect it from dust and humidity. With these basic precautions, the goniometer will last a long time.

Degree protractor or precision goniometer, which is the best instrument?

As mentioned earlier, the precision goniometer is part of the same category as another angle-measuring instrument: the protractor, but there are some differences between the two.

Imagem de um transferidor de grau ao lado de uma régua.

The protractor is also an angle measuring tool. (Source: succo / Pixabay)

Although both instruments have the same function, the goniometer goes beyond viewing, identifying or marking an angle... this tool has movement.

The movable arm makes it possible to measure the amplitude of a movement, for this reason this tool is widely used by orthopaedists and physiotherapists. In addition, the goniometer is a versatile tool with many applications.

Degree protractor Goniometer
Degree of accuracy Less precision High precision
Format Semicircle or circle Fixed and mobile arm united by an axis
Indication for use School or professional use Evaluation with a physiotherapist and other uses
Differential It is very easy to handle it It goes beyond the basic measurement, because it has movement

How much does a goniometer cost?

The price of a goniometer varies according to size, material and brand, but in general, this instrument has a very accessible cost. You will find models in small size between £ 10 and £ 25. The larger size instruments are a little more expensive and cost between £ 25 and £ 35.

Imagem de um fisioterapeuta utilizando um goniômetro para medir a mobilidade da articulação de uma paciente.

The goniometer costs between £ 10 and £ 35. (Source: Daniela Pelazza / 123RF)

Purchase criteria: Factors to compare the different goniometer models

After knowing the features and applications of a goniometer, you must be curious to test it. With that in mind, we have separated some tips on which features you should analyse when buying:

  • Model
  • Material
  • Size
  • Amplitude

We will explain each of the topics throughout this section.

Model

In addition to the conventional goniometer, of manual use, you can also find the digital goniometer.

With this tool, you can view the angle on an LCD display. Besides being easier to view and measure, the margin of error is very low (equal or less than 0.1 degrees) and you can save the markings.

Despite the advantages, this equipment is much more expensive than a conventional goniometer. Therefore, it is worth assessing whether there is a need to make this investment.

Material

You can find the goniometer in PVC plastic, acrylic, metal and steel. Most models are made of plastic or acrylic, because these materials are cheaper, modern and effective in measuring joint mobility.

Besides being cheaper, you can find a wide variety of plastic or acrylic goniometer models and find them more easily than models in other materials.

Size

You can find different sizes of goniometer, the choice is directly related to the use you will make of the instrument. The sizes vary:

  • Small: 7 cm
  • Medium: 20 or 25 cm
  • Large: 35 or 38 cm
Tip: If you are buying the product over the internet, check if the goniometer size refers to the open or closed instrument. This is a common confusion, but may lead you to need to buy another tool.

It is also possible to find larger goniometers, especially to measure the mobility of leg joints. The goniometer is a foldable instrument, so it is easy to store it.

Amplitude

It is important to establish what the applications with the goniometer will be: whether a circle with 360° amplitude is required or whether a semi-circle with 180° is sufficient.

Keeping this in mind is important, because one of the purchase criteria is the width of the instrument, some models open to 180º, while others open to 360º. This information is available in the product description.

(Featured image source: Wavebreak Media Ltd / 123RF)

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