My knee still hurts after knee replacement surgery – is this normal? (2024)

Most patients having a knee replacement will have had a total knee replacement – effectively a complete resurfacing of the knee joint. It is an invasive operation that results in a lot of soft tissue inflammation, swelling and pain which takes a quite long time to settle down – so it is normal for patients to have some pain (although it should be improving) for 4 – 6 months after the operation is done.

A successful knee replacement operation:

• Resurfaces the damaged ends of the bone where the cartilage surface has worn away so that these no longer rub together.
• Re-aligns the leg if there has been deformity.
• Recreates the normal tension in the main knee ligaments which guide smooth bending movement.
• Gains a strong (and longstanding) fixation of the metal and plastic components onto the bone.

If all these aims are achieved with a good degree of accuracy, then most patients will have a well-functioning settled knee. But there are many studies that show that about 15% of patients will be dissatisfied after surgery. Sometimes this will be due to persisting discomfort or pain, sometimes tightness or limited range of bend, sometimes instability or lack of confidence – and often a combination of those features.

Causes of persisting pain

There are a variety of causes of persisting pain, and it is common for these to co-exist:

1. Referred pain – this is where you might feel pain around the knee, but it is coming from another source, typically the hip joint or the lower spine. It is vital that these are assessed carefully before knee replacement surgery, as degenerative joint problems often co-exist, and if your knee pain was mainly coming from your arthritic hip, then it will certainly not be improved by a knee replacement!
2. Leaving the kneecap unresurfaced – this is a source of much debate between knee surgeons, and there are reasons for and against which I won’t go into now, but if you leave the natural surface of the kneecap rubbing against the metal artificial component, then there is a chance that you will have persisting pain at the front of the knee, especially when the kneecap comes under greater loading force (walking on slopes and stairs). The most recent UK guidelines recommend that the kneecap (patella) should be resurfaced during a total knee replacement.
3. Poor tensioning of the soft tissues – one of the challenges for the surgeon is to position and fix the replacement components so that the main knee ligaments are under the correct tension, in all positions of movement. This can be difficult, and different designs of replacement achieve this in different ways. A patient may be left with a knee that feels too loose and unstable, especially when trying to walk on an uneven surface, or alternatively too tight in certain positions – and both of these can result in pain from ligaments and other soft tissues that are not evenly loaded.
4. Scarring – A small proportion of patients have a response to soft tissue trauma (including surgery) that generates excessive scar tissue. This is known as arthrofibrosis, and can result in a knee that was well-balanced at the time of surgery becoming progressively more stiff and uncomfortable over the first few months. This is more common when there has been significant previous trauma (such as a fracture around the knee) or multiple previous knee operations.
5. Nerve pain – The surgical incision that is made through the skin and underlying layers to get into the knee joint also cuts through small nerves that pass through these tissues. Commonly this leaves the outer aspect of the knee feeling a bit numb or tingly after surgery, or a feeling of a “tight band” around the knee. In most patients, this improves with time, and even if they are left with a different sensation to touch, this isn’t painful or annoying. But some will have a persistent nerve irritability that can include scar sensitivity and discomfort with any contact (including clothes). In more extreme forms, this is known as “complex regional pain syndrome”, which is a rare consequence of an operation (or any other traumatic episode).
6. Infection – this occurs in around 1% of knee replacements and (like other risks) will have been discussed with you prior to surgery. Sometimes this is obvious, with redness, swelling, and even wound breakdown. But often this is more subtle, with discomfort and tightness. Some patients are more vulnerable to infection than others – in particular smokers, those with diabetes, and conditions like rheumatoid arthritis (and the medications that these patients are on) which can depress the immune system.

So if you are having problems what should you do?

The first course of action will be to return to see your surgical team. The surgeon or experienced therapist should carefully assess your ongoing symptoms (pain, swelling, stiffness, tightness, stability etc) and then undertake a careful examination, looking for:

• Is the pain coming from the knee, or could it be referred from elsewhere?
• Has the alignment been restored to the pre-operative state?
• Is the knee well-balanced throughout range of movement?
• Does the kneecap track well, and has it been resurfaced?
• Are there any subtle signs of infection?
• Has the muscle function (particularly the quads muscle) recovered well?
• Is there excessive scar sensitivity, and has there been an exaggerated nerve injury response?

And also, were the expectations of knee replacement surgery realistic? If you were expecting to jog any distance, or return to higher level sport, then you are likely to be disappointed by an artificial knee.

Normally a new set of Xrays will be taken. These should include a “patella skyline” view to assess that part of the knee replacement. The xray images be used to assess the size, position and alignment of the replacement components, and to check secure fixation between metal, plastic and bone. A standard set of blood tests is also normally done, looking for any signs of infection (a raised white cell count, or raised inflammatory markers).

If infection is suspected, or if no other cause of pain has been identified, then a fluid sample will often be taken via a needle and syringe into the knee. This can be observed under a microscope to look for any bacteria, and then incubated to see in any organisms are present (the inside of the knee should be a completely sterile environment).

What can be done to help?

If the Xrays are satisfactory, and there is no infection or abnormal nerve response, and no alternative source of referred pain, then the symptoms are likely to be due to subtle imbalances in the soft tissue sleeve around the knee, coupled with inadequate muscular control. Many patients can improve with a targeted programme of exercises guided by an experienced physiotherapist, and this should be the first course of action if no other problem has been identified.

If a problem is identified with the replacement, then it is important that you are seen by a knee specialist who has experience with re-do knee replacement surgery in order to fully understand what the likely outcome of further surgery would be, and the risks.

Repeat (revision) surgery may be an option, but is not as predictable as primary surgery. It is crucial that the source of problems is correctly identified before making this decision – if not, you are at risk of undergoing another big operation and getting the same poor outcome.