The Fundamental Importance of Knee Range of Motion

Fundamentally, your knee range of motion (ROM) determines the activities you can engage in, not just following surgery, but for the rest of your life. This is why it is so important for you to pay attention to your ROM. In the table here we give sample activities and the ROM required to engage in those activities. We hasten to note that having the specified ROM only means that you have the potential to engage in the activity—it does not indicate that you have the strength to do so (link to strength).

ROM (Extension and Flexion)

Range of motion is a composite parameter. It is made up of extension (the ability to straighten your leg) and flexion, the ability to bend your leg. When we put the two together we get your range of motion. Ideally, this should be from 0º extension (completely straight leg) to 130º, a fully flexed leg. Some prostheses stop a little short of 130, and that is okay.

The Importance of Knee Extension

Knee extension is important for two critical reasons: 1) if you don’t have full extension, you are much more likely to fall, falling is one of the most dangerous things you can do, and 2) if your legs cannot go completely straight then your quadriceps muscles are always activated and tire very quickly, limiting what you can do.

The Importance of Knee Flexion

Knee flexion is important is because it is the primary determinant of what you can do. For example, you must be able to bend your leg so your feet are underneath a chair to stand up from the chair without using the chair’s arms.

Range of Motion and Edema

Range of motion is inversely related to the amount of fluid in your knee. After surgery your knee swells, and as little as one ounce of fluid can completely immobilize your knee. So as fluid is pumped out of your knee (and into the lymph) your range of motion increases. You want to get the fluid out for several reasons:

  1. Fluid in the knee limits your ROM
  2. It is the fluid in the knee that puts pressure on neural receptors in the knee and the brain interprets this pressure as pain. Quite literally, it is the fluid that is causing your pain. Get rid of the fluid and the pain stops.
  3. The fluid in and around the knee inactivates the neural communication between your brain and your leg muscles. If you have about 1 ounce of fluid in the knee, you will lose control of your major leg muscles. You need to control these muscles to walk normally, climb and descend stairs and engage in many activities of daily living. Get rid of the fluid and the communication is restored.
  4. The fluid in the knee contains chemicals that promote the formation of scar tissue. When the scar tissue is first forming it is easy to disrupt and if you get rid of the fluid, the scar promoting chemicals will go with it. But, if the fluid persists and scar tissue is allowed to form thick fibers of collagen, these fibers will limit your range of motion for life. To prevent this from happening Doctors will do what is called a manipulation under anesthesia, (MUA) where they put you to sleep and then bend and straighten your leg until they no longer feel the scar tissue ripping. Then you have to restart therapy.

Push the Play Button below to watch a super (and short) video that explains the importance of knee flexion and extension.

Getting to 90º

Gaining a good ROM >90 degrees in the first few weeks will enable you to rapidly gain ROM, get the fluid out and put in a position where you are well past the critical ROM for a Manipulation Under Anesthesia. Nothing removes fluid and restores ROM (and strength) faster than the X10 Knee Recovery System™. This, and the fact that it has minimal to no pain, is why we so strongly recommend it.

Knee Range of Motion

Our clinical team is ready to help you at any time with your knee surgery recovery. You can reach us with a phone call at 1-855-910-5633 or an email at To schedule a 15 minute call with us click on the Want to Learn More? image on this page.