In this short section I would like to help you build up a few new words to accurately describe the extent and severity of knee stiffness.

This will assist you with the rest of this course and also help you when talking to your doctor. 



Transcript of the video

When the knee is out straight, that is when it is extended. The movement towards it being out straight is called extension. If the knee can extend so much that it actually seems to bend a bit backwards, that is called hyperextension.

When the knee is bent, that is when it is flexed. The movement towards more bending is called flexion. We would only really talk of hyperflexion if the knee was forcibly bent beyond what would be normal.

The range from as flexed as one can go to as extended as one can go is called the ‘range-of-motion’ or ROM for short. We are going to talk a lot about ROM in this course. When we talk about active range-of-motion (or AROM for short) we are referring to the range that the patient can achieve without help. On the other hand the passive range-of-motion (or PROM) would involve using a device or an assistant to see if the range could actually go a little bit further.

Now let’s cover the terminology that might be used if there is a reduction in the range of motion of the knee, which may affect the ability to fully extend or to fully flex, or both.

If a patient is unable to actively extend the knee as fully as the good one, but an assistant can passively move it further, then the difference between the two ranges is referred to as the amount of extensor lag. This may be because of weak musculature or a damaged tendon, for example.

If the assistant was not passively able to achieve full extension either, then the patient would be considered to have an extension deficit, implying that there is something structural blocking that movement. This might, for example, be a badly healed bone break or a badly-sized knee replacement implant, or some kind of soft tissue impediment. If the block to full extension is due to tight scarring of soft tissues such under the kneecap or around the back of the joint, then one could use the term flexion contracture.

The opposite would apply to problems with flexing the knee. If a patient is unable actively to flex the knee as fully as it should, but an assistant can flex it further, then that is called a flexion lag. A flexion deficit would be present if an assistant could not make it flex fully either, and if this turned out to be due to soft tissue scarring, such as in or under the quads muscles, then this would be called an extension contracture.