Measurement of ROM in a rehabilitation unit is traditionally performed with a little instrument called a goniometer.

‘Gon’ is a Greek prefix implying ‘knee’ so a ‘goniometer’ means an instrument for measuring the knee, although in practice it can be used for measuring the range-of-motion - or ROM - of any joint.

Goniometers are traditionally plastic, with two arms connected at a central pivot point. At the centre is a flat disc with the angles marked on it and this is contiguous with one of the arms. The other arm is mobile in relation to the central disc.


How to measure range of motion (ROM)


Please note that there is no absolute standard for positioning of the patient - some people prefer to measure with the patient lying on their back and some prefer the patient to lie on their stomach. The important thing is to always use the same system with each subsequent measurement.

When it comes to taking the measurement, the stationary arm is pointed towards the bony lump right at the side of the hip - the greater trochanter - while the centre of the disc is positioned at a reference point on the side of the knee - the lateral epicondyle. This is the little bony lump on the lower outer side of the femur. Holding the goniometer carefully at these two reference points, the mobile arm is then moved so that it points to the bony bump of the outer ankle - the lateral malleolus. The measurement is recorded.

This is done for both flexion and extension and the ROM is calculated from the difference.​


Gender differences in range of motion

There is a difference between the normal range of motion for men and women:

  • for men - normal ROM is usually minus 6 to 140 degrees
  • for women - normal ROM is usually minus 5 to 143 degrees

range of knee motion

This video is from our Udemy course on the stiff knee, and it explains the terminology related to ROM and to knee stiffness.


Types of goniometer

The little cheap plastic goniometers are the most common, but they tend to have rather short arms. If you are going to buy a plastic one, try and find a version with longer arms. There is also a more robust metal goniometer with extendable arms.

You can also get apps that you download to your smartphone, and use it as an inclinometer to get an assessment of the angle of the limb.

This YouTube video might be useful in showing you how to use it properly.