As I mentioned in Knee Replacement Surgery – What Every Patient Should Know, over 650 000 total knee replacements are carried out annually in the USA alone. Other developed countries also see high numbers of surgeries being undertaken, and the numbers are steadily increasing worldwide year after year. The mean age for a knee replacement in the UK is 70, although it is not uncommon for people in their 50s to be faced with this decision. Interestingly, more women seem to undergo knee replacements than men, and there does not seem to be any signs of this changing.
Astonishingly the rates of total knee replacement have increased over ten times in the past 25 years. With such a huge rise in the number of surgeries, we have to ask ourselves are they all necessary? There are numerous possible reasons for this increase and they probably all play a part in the rising numbers. More people are suffering from arthritis, medical techniques are improving, healthcare is more accessible, people’s expectations are higher, marketing of and recommendation for knee replacements has increased, and so on. With all these factors resulting in an increase in the number of people being classed as ‘suitable’ for a knee replacement, we need ways of determining if someone actually needs the procedure or we just think they need it.
The main clinical reason people undergo a knee replacement is for Osteoarthritis. Over 95% of knee replacements are carried out for this reason, with the rest being for conditions such as inflammatory arthritis (this series of articles is only addressing knee replacements done in context of osteoarthritis). There are many risk factors that delicately interplay in increasing the risk of developing arthritis such as bone density, sex, hormones, trauma, meniscal damage and bone morphology, but by far obesity and age are the two most significant risk factors.
The older you are the more likely it is that your arthritis progresses to the stage that you require a knee replacement. There are some people who may require knee replacements in their fifties but they are in the minority. Obesity is one of the reasons someone may need a knee replacement earlier. Although it maybe true that obesity results in increased bone mineral density, it also takes it’s toll on the joints and results in an acceleration of the development of osteoarthritis.
So we have established that osteoarthritis is the main reason that people have knee replacements, but how do we know when the arthritis is advanced enough that a knee replacement is warranted?
It is widely thought that X-rays are the best way to see how bad someone’s arthritis is. Patients will often ask me for a repeat X-ray to see if their increasing pain is due to worsening arthritis. X-rays are great for diagnosis of osteoarthritis, but once diagnosed their usefulness is fairly limited. There are a few hallmarks of disease that can be seen on X-ray and some signs that indicate end-stage arthritis, but X-ray findings (other than confirming diagnosis osteoarthritis) do not generally play a role in deciding if someone requires a replacement or not. There is also limited use of CT or MRI scans in osteoarthritis so be wary if these are suggested.
So if the X-rays aren’t really useful in telling us if surgery is required, what is? The answer is patient symptoms. This is the most significant indication for the requirement for surgery. In general someone should be suffering from significant, persistent pain, either at night or on weight bearing or both. Mobility is often widely affected, to different degrees, but this is variable and pain is still the major indication for needing surgery. I often tell patients that if they are asking me if they require a knee replacement, they likely don’t need one yet. They will know when they need it!
Although pain is a strong indication, the symptoms of arthritis can be responsive to some treatments. As such before considering surgery all patients should undergo a 6 month course of non-operative treatment to see if symptoms improve enough to make surgery unnecessary. These treatments range from analgesia to steroid joint injections to hydrotherapy and are outlined in the Osteoarthritis Research Society International guidelines (http://www.oarsi.org/index2.cfm?section=Publications_and_Newsroom&content=OAGuidelines). Only after failure of these treatments to control symptoms should surgery be seriously considered. There is currently no clear consensus on the severity of pain required to indicate surgery and each patient is treated on an individual basis.
Another thing to consider when deciding if surgery is suitable is age. Those patients less than 55 have more varied outcomes than those over 55, and are more likely to require a revision of the knee replacement in the future. Morbid obesity also leads to more variable surgical outcomes. Not only can obesity lead to a higher chance of the knee replacement failing but it can also lead to a higher risk of complications during surgery. Those who are significantly overweight should strongly consider losing weight prior to surgery. Not only will it reduce the risk of surgery and possibly make the replacement have more chance of succeeding, but it could also lead to surgery no longer being needed as the reduced load on the knee could significantly improve symptoms.
Another important point to be aware of is regarding arthroscopy. If your arthritis is advanced enough that is is causing persistent considerable pain, arthroscopy is not really of any use and knee replacement is generally the surgical option to consider. If this describes you and someone tries to sell you arthroscopy or hyaluronic acid or glucosamine injections, be very careful as they are not really going to be of any benefit and will just result in more trauma to the knee and unnecessary expense.
So in conclusion, the main indication for a knee replacement in radiographically confirmed osteoarthritis is the presence of persistent, severe (as judged by the patient) pain. Before progressing to surgery you should first trial at least 6 months of non-operative treatment, and if you are overweight you should make the effort to lose weight as it will reduce risk and increase the chances of the knee replacement being successful.
Now you know who should seriously consider a knee replacement, you should go on to read the following article to learn more about what to expect immediately and in the years after a knee replacement.