Knee Range Of Motion

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.

What Is Knee Range of Motion?

There are three different ways of looking a knee range of motion:

• 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 for passive knee 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.

What is Normal Knee Range of Motion? 

What Is Normal Functional Knee ROM?

Functional range of motion is how much movement is needed for typical 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.

How To Measure Knee Range Of Motion

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 360^o 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:

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:

• Lie down on your back with your leg straight, on a flat, preferably hard surface
• Place the axis of the goniometer over the lateral femoral epicondyle
• Line the stationary arm of the goniometer up with the greater trochanter along the outer thigh
• Line the other arm of the goniometer up with the lateral malleolus of the ankle
  

• To measure knee extension, gently push your knee down into the floor (using your leg muscles not your hands) so the knee is as straight as it goes and measure


• To measure knee flexion, bend the knee as far as you can, by sliding your foot up towards your buttocks, keeping the arms and axis of the goniometer in place, then measure

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

How To Measure Knee ROM Without A Goniometer

If you don’t have a goniometer, you can still assess your knee 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 ROM

• Lie on your back on a firm surface
• Push your knee down into the floor (using your leg muscles not your hands)
• Slide your hand, palm down, underneath your knee. If you can:
  a. Just get a couple of your fingers underneath with difficulty = 0^o extension
  b. Just slide all your fingers underneath = +5^o degrees i.e. lacking 5^o extension
  c. Easily slide your whole hand underneath = +10^o i.e. lacking 10^o extension
  d. Can’t get any of your fingers underneath = -5^o or more i.e. hyperextension

Estimating Knee Flexion ROM

• Lie on your back on a firm surface
• Slide your heel along the floor towards your bottom
• Measure the distance from the back of your heel to your bottom

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.

Measure Knee ROM With Your Phone

There are also various apps that you can download that essentially turn your phone into a goniometer. They vary in quality but a study* published in Physiotherapy Journal found that the "Knee Goniometer" App installed on an iPhone was a reliable tool.

What Restricts Knee ROM?

There are a number of things that can restrict normal knee range of motion, the most common being:

• Swelling: increased fluid inside the knee joint restricts movement. Find out how to reduce knee swelling to regain knee ROM
  
  
• Pain: when pain is bad, it can stop us wanting to move the knee. 
  
  
• Impingement: where something gets stuck inside the joint and blocks movement e.g. meniscus tear
  
  
• Muscle Tightness: tight muscles may limit how much the knee can bend or straighten. Knee strengthening exercises can really help
  
  
• Muscle Weakness: if there is sufficient loss of muscle power, then you might not be able to fully bend or straighten your knee. Knee stretches can help to improve your flexibility and knee ROM
  
  
• Wear & Tear: degeneration of the knee bones and the formation of bone spurs can impede knee movement, most typically due to knee arthritis

How To Increase Knee ROM

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.

Assessing Progress With Knee ROM

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: 12/02/21
Next Review Due: 12/02/23

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References

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