The term goniometer comes from the Greek gonia (angle) and metron (measure). This instrument therefore makes it possible to measure angles. Goniometers are used in medicine to measure range of motion and joint size.

The medical goniometer, also called a coxometer, is used in orthopedics and rehabilitation to measure the angle of a joint. This can be to measure a fixed angle or the amplitude of a movement. One of the advantages of using a goniometer is that the results obtained are objective.

Composition

The goniometers usually used in medicine are mechanical and operate on the same principle as protractors. There are different models that are suitable for different types of measurement. They are plastic or metal.

Who use a goniometer?

Goniometers are used in medicine by physiotherapists, osteopaths, physiotherapists, orthopedic surgeons, chiropodists and radiologists, all professionals involved in bone and joint care.

Goniometers are used to report the opening capacity of a joint or its deformation. They are particularly useful within the framework of the study of an articular pathology, to follow the functional recovery of a limb after an accident and / or a surgical intervention, or within the framework of the fitting of a prosthesis.

Measure angles

Depending on the joint studied, the angles measured are not the same: some joints offer little possibility of movement (knees, elbows), while others allow more complex movements (shoulders, wrists , the neck).

Joint movements studied

Each joint is characterized by the movements it allows to perform:

• flexion – extension: of the leg, of the arm;
• adduction – abduction: lateral displacement of the arm;
• internal – external rotation: of the head, of the lower limb;
• pronation – supination: action of turning the forearm;
• inversion – éversion.

Joint pathologies

The amplitude of a joint can be affected for different reasons:

• due to abnormal ligament tension;
• due to “stiffness” of the skin due to the presence of scars following surgery or a burn;
• by the presence of muscle contractures;
• following a fracture, a sprain;
• when placing a prosthesis.

The stages of operation

The goniometer is used to measure the limit angle of a joint, that is, the maximum opening angle of the joint.

The results are interpreted as a function of the angle in the natural position, at rest. For example, legs or arms stretched out and relaxed.

When to use it?

The goniometers used after a joint operation (knee, hip, wrist, etc.) make it possible to check the correct progress of the operation carried out and to monitor recovery during the subsequent rehabilitation.

Precautions to take

The difficulty in using the goniometer is to fix reference points with respect to which the angles are measured, in order to be able to repeat the measurements and follow the evolution of the measurement over time. Usually, the practitioner relies on bony landmarks.

The goniometer will be chosen according to the joint to be studied.

The different models

There are three types of goniometers:

• the compass with protractor, which is by far the most widely used. The 4 existing models are presented below;
• the goniometer for prosupination;
• the goniometer using gravity.

The Cochin goniometer

This plastic model is equipped with two flat rulers which revolve around a central protractor. It is not very precise.

Houdre’s goniometer

The branches of this model are much longer and allow the angles of large joints (knees, elbows) to be measured with good precision.

Labrique’s goniometer

In this metal model one of the two branches is fixed, which makes it possible to refer to the vertical.

Balthazar’s goniometer

It consists of a protractor on which is fixed a branch, while a second pivots around the center of the protractor. This model, invented by Professor Balthazar, allows the measurement of small joints (hand, fingers).

The first goniometers

The first goniometer used would be that of the mineralogist Niels Steensen in 1696 who used it to measure the angles of crystals. In 1878, we find for the first time a goniometer in a medical catalog (the Krohne and Sesemann catalog), where it is presented as being useful to “check the angle in the cases of deformities, to compare one case with another, or the same cases at different stages of the disease ”.

Other fields of application

Goniometers are useful for measuring angles in many fields: in optics to study the deflection of light beams, in radiocrystallography, in navigation, etc.