Having full knee range of motion (ROM) is really important for day to day function.
The knee needs to be able to bend and straighten so we can walk and run, support our body weight, control our balance and is an important shock absorber for our body.
When knee movement is limited, it causes pain, impairs function and makes us predisposed to knee injuries.
When we talk about knee range of motion, we are looking at
how much movement there is at the knee. The main movements at the knee are
flexion and extension i.e. bending and straightening of the knee. There is also
a small amount of rotation.
There are three types of range of motion at a joint
Active Knee ROM: This is how much the knee can bend and straighten on its own i.e. knee muscles actively contracting without any external help
Passive Knee ROM: How far the knee can bend and straighten when moved by an external force, usually another person – the leg and knee muscles completely relaxed.
Active Assisted ROM: How far the knee can move when it is weak or in pain with some assistance – knee muscles are working to move the leg but with some help e.g. from a therapist
It is normal of passive range of motion to be slightly greater than active range of motion.
These three range of motions in a healthy, pain-free joint will be similar, but if you have injured your knee, have pain in your knee or a knee condition such as arthritis, chances are your range of motion will be less than normal with active range of motion being most affected.
Normal knee range of motion usually refers to how much the knee bends and straightens. There is also a small amount of rotation at the knee, typically measured when the knee is bent.
Normal active knee range of motion is:
Normal passive knee ROM is:
Functional range of motion is how much movement is needed for typically daily activities such as walking, climbing stairs and squatting down. At the knee joint, most functional activities require up to 120 degrees of knee flexion, rather than the full 135 degrees, however, virtually all functional activities require full knee extension.
Knee Range of Motion With Activities:
So as you can see, if knee flexion range of motion is slightly
limited, you should still be able to do most of your usual activities. But
losing just a few degrees of knee extension can have a massive impact on
The most accurate way to measure knee range of motion is to use a goniometer. A goniometer is essentially a specially designed protractor that measures joint angles.
There is a circle in the middle of a goniometer representing 360o of motion, out of which come two extending arms: a stationary arm (connected to the protractor) and a moveable arm.
When measuring knee range of motion, you need to identify three landmarks on the leg
Ideally, you will need someone to do the measuring for you – it is hard to get an accurate measurement if you try and do it yourself.
To find the greater trochanter, find the midpoint of the bony ridge on the top of your pelvis (the iliac crest) and bring your fingers down 15-20cm until you feel a bony lump. The greater trochanter is more towards the back of the thigh than the front due to the large muscle bulk of the quads on the front of the thigh. You will have to press in through the soft tissues of the thigh to feel it.
The best way to measure knee range of motion is to:
If you prefer, you can measure knee flexion in sitting, as long as your leg can move freely. It works best to sit on a high chair or the edge of a table. Line up the goniometer as described above and then bend your knee as much as you can
If you don’t have a goniometer, you can still assess your ROM. This can be really helpful for seeing what progress you are making with your rehab after a knee injury. It won’t be as accurate as using a goniometer, but it does give you somewhere to start.
If you are wanting to guestimate the range of movement at your knee, try this
Estimating Knee Extension:
Estimating Knee Flexion:
This doesn’t give you an actual measurement of flexion, but it does give you a measurement to compare with when monitoring you progress when trying to improve knee flexion.
There are also various apps that you can download that essentially turn your phone into a goniometer. They vary in quality but a study1 published in Physiotherapy Journal found that the "Knee Goniometer" App installed on an iphone was a reliable tool.
There are loads of things you can do to increase knee range of movement. Gaining even just a few degrees of movement, particularly knee extension, can make a massive difference.
Check out our article on How To Improve Knee Flexibility for loads of great ideas.
If you are trying to improve your knee range of motion through exercises and physical therapy, aim to check your ROM no more than one or twice a week.
It takes time for knee range of motion to improve so if you measure it too often, you are unlikely to notice much change which can be very disheartening.
Page Last Updated: 21/05/19
Next Review Due: 21/05/21
1. Physiotherapy Journal: The knee smartphone-application goniometer is a more reliable tool than the standard goniometer in acute orthopaedic settings. L. Pereiralow, L.Pereira, S. Rwkabayiza, E. Lécureux, B. Jolles. May 2015