My knee feels stiff after replacement surgery – is that normal?

You’ve had a total knee replacement (TKR). You’re back home to start your recovery. But your new knee is feeling stiffer and more difficult to bend than you expected. Should you be concerned?

Joint stiffness is actually one of the most common questions people have around knee replacements. When it does happen, patients often describe it as a feeling of tightness, like a belt or waistcoat around the knee. How normal is that? The short answer is that experiencing some stiffness after surgery is to be expected – it’s part of the healing process, and usually temporary. But what temporary means can vary a bit from person to person. Let’s look at the issue in more detail…

How much should I be able to bend my knee?

The medical term for this is your range of motion (ROM). You might also hear it called “degrees of flexion.” Flexion simply means the amount of bending you can achieve in your leg. As a quick guide:

0° – is when your leg is completely straight (“zero degrees of flexion”)
90° – is what we generally need in order to sit down comfortably
110° – is roughly what you would need for cycling
120° – is the approximate flexion when someone sits cross-legged
145° – is, roughly, the maximum flexion most people can achieve in normal circumstances

What about people who’ve just had a knee replacement? Most post-TKR patients can expect to get about 90 degrees of flexion within the first few days or weeks of their operation. On day one, for example, you might get about 50° of flexion. On day two, 60°. On day three, 80° – and your ROM gradually increases from there. But the process can take longer for some people, especially if you were getting a poor range of motion before your operation. Flexion varies a lot from person to person. The important thing, though, is that you’re progressing in the right direction.

What causes stiffness after knee replacement?

There are a few reasons why knees can feel stiff after a replacement. The primary reason is the inflammatory response. This is your body’s natural reaction to trauma. You’ve been through a major operation. The tissues in your knee have been disrupted. So your body triggers an immune response to protect the joint and start the healing process, releasing fluid and chemicals that will cause the whole area to tighten and swell (oedema). Over the first few days, your body is also busy generating scar tissue – a kind of “emergency collagen” that helps your wound heal quickly, but can also cause short-term pain and stiffness. Another thing to factor in is muscle weakness (atrophy). Although the nurses will have encouraged you to get moving as soon as possible, your body will be resting more and moving less than usual as you recover. This causes muscles fibres to slacken (surprisingly quickly), which in turn makes the joint stiffer and less mobile; think of that stiff-leg feeling you get after a long slouch on the sofa. A further problem with pain and swelling is the deconditioning trap. This is when we avoid exercise in order to avoid the discomfort that comes with it… which leads to weaker muscles, more stiffness, and more discomfort: a vicious cycle.

What can I do to reduce stiffness and improve my range of motion?

So it’s fair to expect a certain degree of stiffness in your knee after the operation. But is there anything you can do to accelerate the recovery process? Fortunately, there is. We mentioned movement just now, and this is key. Regular movement combats joint stiffness in many different ways. It rebuilds weakened muscles (reducing the pressure on your new joint), improves blood flow (bringing more oxygen and nutrients to your knee tissues), increases your brain’s pain tolerance (by releasing endorphins, the body’s natural painkillers, during exercise), and even boosts energy levels (by encouraging your muscle cells to produce more mitochondria, the “engines” of cells). Other important factors are:

Pain management – regularly taking the medication you’ve been given, to make activity and exercise easier for you

Physiotherapy – getting a programme of exercises and stretches that’s tailored to you and your knee

Elevation – lying down and raising your leg for about 30 minutes, once or twice a day

Hydration – drinking water regularly supports tissue health and helps you to avoid muscle cramps

Circulation – gently rotating your ankles encourages the blood to keep flowing freely in your legs

Ice therapy – regularly applying ice packs to your knee helps to reduce pain, inflammation and tissue-bleed

Consistency – keeping up with the exercises you’ve been given, even when it feels frustrating

What happens if my knee still won’t loosen up?

There are lots of things we can do to help you regain your ROM, including one-to-one physiotherapy, which is highly effective for many patients. So, if you’re concerned about your progress, it’s worth checking in with your surgeon to see what they can arrange for you. In some rare cases, excessive scar tissue can form around the new knee and make it difficult to flex. This is, obviously, a mechanical issue rather than a problem with weak muscles or pain – and in these cases we can use an arthroscopic operation to clean out the excess scar tissue and restore flexibility. But, as we say, this is quite rare. The important thing to bear in mind about post-surgical joint stiffness is that it’s common, and it usually gets better with time and consistent exercise. Some patients are still seeing improvements 1-2 years after their operation. For others, the journey to better flexion can be faster. What’s “normal” for one person isn’t necessarily normal for another. But with persistence, patience and proper support, most people see huge improvements.