Persistent pain after knee replacement

What is a complication?

Defining a risk or a complication can be difficult. Just because some thing does not meet an expectation does not make it a complication. Increasingly, however, patients feel that if their expectations have not been met then this constitutes a complication. The problem with that is often the objective evidence is that the patient has actually benefitted from the procedure even if the patient does not realize or acknowledge it. This phenomenon is elaborated below.

Risks are any situation that exposes one to danger whereas a complication is anything that has made something more difficult. The definition can be very broad and sometimes it may not be very clear if an occurrence is a complication or not.

The following statistics are based on personal experience of more than a 1000 cases of knee replacement operations done in Singapore. The database covers a 3 year period and the parameters evaluated were SF36, WOMAC, KSS and range of motion in the operated knee.

General risks

The general risks of surgery are those common to all surgeries and are mostly dependent on the patients own pre-existent health status. Overall, the incidence is 20%. Any of these are potentially fatal and the surgeon would usually defer to the anesthesiologists assessment of the risk of the procedure. In general if the patients premorbid state is healthy these risks are small. They include heart problems, lung problems, stroke and deep vein thrombosis.

Specific risks

The specific risks of knee replacement surgery in the author’s personal experience is about 8% overall. They include:

Joint stiffness (Subjective)5%
Fractures       5% (including minor & late presentations)
Blood loss more than 1.5 l    negligible
Infection   negligible
Nerve injury  negligible
Vessel injury  negligible
Dislocation  negligible

Another category which is difficult to quantify is failure of surgery defined as persistent pain that can happen in the knee after a joint replacement. This may be due to:

  • Implants being too large
  • Implants being malpositioned
  • Implants being unbalanced
  • Pain being referred to the knee from the hip or spine
  • Patellar abnormality
  • Implant loosening
  • Missed diagnosis (Figure 1) 

Figure 1. This case was a patient who had a knee replacement done elsewhere. She had fairly mild arthritis of the knee (a).  She had persistent pain and stiffness (b) even though the imlpants were in good position (c). Two years later she presented to us with persistent pain (d). The case was revised by us and during surgery a number of problems were discovered (e). After the revision the knee function was full again(f).

The commonly anticipated complications of fractures and infections are actually fairly straightforward to manage as the cause is obvious. While they do require high skill in managing them they are predictable in their outcome after limb salvage revision surgery (Figure 2).

Figure 2. Fractures around implants have well known protocols that govern their management (flowchart). This patient was highly osteoporotic and small and during her first surgery and a small crack which was repaired with screws (a). She healed uneventfully (b) and years later presented after a violent fall which ironically fractured her other femur (c). This was repaired using specialized a plate system and she healed uneventfully (d).

Sometimes, however there may be pain and stiffness when the cause and solution is not so obvious (Figure 3). Very often this is ascribed to component malposition and the fact that the patellar was not resurfaced in the first operation. Nevertheless, it is not clear that these two factors are the cause of the pain and there may be a underlying problem that has not been diagnosed (Figure 3).

Figure 3. This patient had successful knee replacement surgery with well–positioned implants (a,b,c). He however complained of persistent stiffness and so he was examined under anesthesia (d). Under anesthesia the knee had full range of motion and when the patient was shown the video afterwards he became convinced there was nothing wrong and eventually returned to full range of motion by himself.

Figure 4. This patient had persistent right knee pain and had been to a number of centers for second opinions after the original knee replacement. The right knee implant was (perhaps) not in the most ideal position and she was offered a revision of her implants. Our evaluation however was that she had pain in her spine that was being referred to her knee via her nerves. By blocking the nerves with an injection her pain disappeared and she did not need surgery.

Objectively speaking virtually all patients have better function after knee replacement surgery (Figure 5). Even amongst those who complain of stiffness it can be shown that they are doing much better than before surgery (Figure 6). Taken together, this data suggests that patient expectations after surgery should be managed carefully. They should be assured that they will definitely do better but perhaps they will not be returned to the best state they have ever been in as in their youth - expecting those kinds of results would be unrealistic.

Figure 5. This review of the author’s own cases shows that from the preoperative state all patients do better using objective scoring systems developed for this purpose.

Figure 6. Even among patients who are stiffer 6 months after surgery, their results are better than when they weren’t operated on and their stiffness normalized over time.


The general systemic complications of knee replacement surgery are related to the health of the patient and are more common than the risks specific to the surgery itself. There are well established solutions to the classic complications of knee replacements but these complications are rare (fractures, infections). Increasingly a group of undesirable outcomes like persistent pain and stiffness are recognized but do not have predictable revision outcomes. Caution in re-operation should be exercised in this group as the cause of pain or dissatisfaction is unclear. In general most patients do better after knee replacement surgery when compared to their pre-operative arthritic state.