Please can you give a brief introduction to rheumatoid arthritis (RA) and osteoarthritis (OA)?
Arthritis translates to “joint inflammation.” The most common form of arthritis is osteoarthritis (OA), which affects 12-15% of North Americans over the age of 60, and will increase in prevalence as our population ages. OA is more common among women, and persons with lower socioeconomic status. It tends to affect large weight-bearing joints such as the hips and knees, but also affects the spine, including the neck, and joints in the hands and feet. The traditional view of OA was that it was a natural part of aging, a degenerative process, but this view is antiquated.
We now know that rather than a single entity, OA is the final common end-point of a heterogeneous group of disorders which ultimately results in failure of the joint. This process affects the entire joint: the cartilage, the synovium and muscles around the joint, the capsule which surrounds the joint, and the bones which make up the joint. As the disease progresses, movement becomes more painful, impeding the patient’s ability to exercise, and to function in general. As you might expect, there is an association between OA and cardiovascular disease, endocrine disorders like diabetes, and depression. In persons with hip or knee OA, the pain is worse with weight-bearing, so these patients tend to avoid activities which exacerbate the pain. However, this lack of activity reduces muscle fitness and worsens the disease.
Meanwhile rheumatoid arthritis (RA) is a systemic inflammatory disease, and affects far fewer people, between 1-2% of North Americans. It affects patients a lot earlier in life; more than 80% of these patients will develop their disease between the ages of 35 to 50. Women are three times more likely than males to be affected by RA. It is an autoimmune disease, which means that the body’s immune system starts attacking healthy tissue. These effects are not limited to joints, and the immune system may also attack the hearts, lungs, blood vessels, and skin.
Not surprisingly, RA is associated with increased mortality. Small joints in the hands and feet are most commonly affected, but larger joints such as the hips, knees, shoulders and elbows are also affected in many cases. While joint changes are not apparent at the onset, the eventual destruction of these joints is more rapid than in OA. In some patients, the joint itself will look a lot like OA in the operating room.
The medical management of OA and RA are also different. In OA the medical management is focussed on pain control, for example taking over-the-counter painkillers. In fact, painful OA accounts for the highest use of non-steroidal anti-inflammatory drugs. But for RA, the patient takes disease-modifying anti-rheumatic drugs, such as methotrexate, or biologics, such as adalimumab, which work by attenuating the immune system and have more severe side effects than the medications used for OA.
Overall, OA is more common, and while it can be very severe, the joint destruction is less rapid than in RA, and tends to affect patients later in life. As well the systemic features of RA can be much more severe, and because these patients are affected earlier in life, they have to live with the disease for a longer period of time.
What is total joint arthroplasty and when is it needed?
Total joint arthroplasty is surgical replacement of the joint surface with an artificial weight-bearing surface. There are several materials used, with the most common being some combination of a metal and polyethylene. It is most commonly performed electively, which means it is scheduled well-ahead of time, typically for what we generically call end-stage arthritis.
End-stage arthritis is when the pain in the joints and the resulting functional limitation is unacceptable to a patient, despite medical management. We’ve all known people (perhaps our parents or grandparents) who have complained about pain in a joint, but not necessarily to the point where it has limited their ability to perform their daily functions or to enjoy life – such as shopping, golfing, or playing with their grandchildren. In some cases, patients can’t even climb a flight of stairs!
Once the patient feels that their function is limited to an unacceptable degree, due to their arthritis, total joint arthroplasty is indicated. Patients usually do really well after joint replacement, with hip replacement in particular demonstrating vast improvements in quality of life following surgery.
What are the main complications that can occur with joint arthroplasty?
The complication rate following surgery is actually quite low; typically fewer than 3% of patients will have any complication whatsoever. The biggest risk for patients is the occurrence of deep vein thrombosis (DVT) or pulmonary embolism, but patients are typically given some sort of prophylaxis, so rates still remain low.
The most disappointing complication, in my mind, is the need for a revision arthroplasty – essentially meaning the surgeons have to go back and replace the joint replacement, often with a larger prosthesis, with more bone loss and a higher risk of further complications. It is estimated that the lifespan of joint replacements is 10-15 years – maybe more depending on how active the patient is. So a younger patient is more likely to need a revision in their lifetime than an older patient. As such, revision is only a complication when it occurs earlier than expected. The most common reasons for early revision are infection, poor positioning of the components, or dislocation.
In our paper we talked about several phases:
revision under 5 years
revision between 5-10 years
revision occurring >10 years from surgery
I think it is fair to say that revision within 5 years is an extremely sub-optimal outcome.
Your recent review found that people with RA had an increased risk for hip dislocations after hip replacement surgery compared to those with OA. What do you think was the reason for this?
There are several possible reasons why patients with RA may be at a higher risk of dislocation. Since RA is systemic disease, with a significant impact on soft tissues around joints, it is possible that the soft tissue envelope around the hip joint, which normally helps keep the joint replacement in place, is less strong in RA patients.
Another possible reason is that, perhaps, patients with RA were systematically more likely to receive a smaller prosthesis than OA patients. Smaller hip prostheses have a smaller head to neck ratio, which increases the risk of dislocation. However, some of the studies included in the review actually accounted for head size - they adjusted for variable head size - and they still found that patients with RA had an increased risk. So, this explanation is less satisfactory at this point.
At the end of the day, both of these explanations are conjecture; firstly, the findings of this review need to be confirmed in a large-scale cohort study, and if the increased risk for dislocation persists, it will still require further exploration before we can definitively determine the cause.
Your research also found that RA patients have a higher infection risk following total knee replacement than patients with OA. Why do you think this is the case?
It is hard to know, but as I mentioned earlier, patients with RA tend to be treated with fairly harsh drugs, which modulate the immune system and limit its ability to attack the body. They may contribute to an increased risk for wound infection following surgery. Previous research into this issue has produced conflicting results. As with the findings around dislocation, this needs to be confirmed in a large-scale study.
Did your research find that OA patients were at an increased risk of any particular complications following total joint arthroplasty?
Well in our paper we were using patients with OA as the comparator group, so our findings are around patients with RA. We do know from previous research, however, that younger patients and males who have joint replacements are at a higher risk of certain complications, including early revision following joint replacement.
What impact do you think your study will have?
Well hopefully it will spur more research into outcomes following joint arthroplasty for patients with RA. We identified a few gaps in the research that’s been done so far, particularly around the definitions used for RA. This can be a very challenging diagnosis to establish, and while some studies used validated criteria to identify these patients, most of them did not.
We also noticed that a lot of studies did not account for important confounders, such as age and gender. Patients with RA tend to be younger, and are more likely to be female. Any study which identifies a differential risk for RA patients needs to determine if it persists after adjusting for these confounders.
None of the studies we looked at accounted for the effects of clustering by surgeon or hospital. Patients who are treated by Surgeon X are likely to be more similar to each other than to patients treated by Surgeon Y. Hopefully any future research into this population, and their risks following joint replacement will avoid these pitfalls.
In addition, I think that any time you can provide more information to caregivers and to patients, particularly when it is around risks following elective surgery, you are helping them make a more informed decision.
Do you have any plans for further research into this field?
Certainly! Now that we have identified these gaps in the literature, and have findings that indicate a greater risk following joint replacement for RA patients, we will try to answer these questions using a large cohort of patients. Perhaps even look specifically at RA patients, and look at predictors for complications specifically for this population.
Would you like to make any further comments?
The rates of total joint replacement are increasing rapidly in North America. In the last decade alone, the rates of knee replacements almost doubled. Furthermore, there is a demographic shift in the age of patients – people are having joint replacements earlier in life. And while patients with RA probably make up less than 5% of arthroplasty recipients in North America, we are still talking about thousands of patients.
I think it is very important that we continue to identify risk factors for complications and poor outcome following joint replacement in all recipients, and that we also look specifically for risk factors in recipients with RA.
Where can readers find more information?
They can find our paper in the Arthritis and Rheumatism journal: http://onlinelibrary.wiley.com/doi/10.1002/art.37690/abstract
They can find more information on the Women’s College Hospital: www.womenscollegehospital.ca
About Dr Bheeshma Ravi and Dr Gillian Hawker
Dr Ravi is a resident in orthopaedic surgery at the University of Toronto, and is currently pursuing a doctoral degree in clinical epidemiology, at the Institute of Health Policy, Management and Evaluation at the University of Toronto, under the supervision of Dr. Gillian Hawker.
Dr Hawker is Professor of Medicine and Health Policy, Management and Evaluation in the Faculty of Medicine, University of Toronto. She is the Physician-in-Chief of Medicine at Women's College Hospital, where she holds the F.M. Hill Chair in Academic Women's Medicine.
She is a clinical epidemiologist / health services researcher whose research has focused on improving access to and outcomes for care for people with osteoarthritis and osteoporosis. She has published almost 200 peer-reviewed articles and has served as a member of numerous academic and governmental advisory committees.
She is currently a member of the Performance Measurement Advisory Board of the Ontario Health Quality Council, and serves on the Board of the International Society for Osteoarthritis Research.