Diseases, Disorders information » Osteoarthritis

Osteoarthritis:This is a disease mainly of the cartilage

Disorders — Wed, 03 Mar 2010 14:11:37 +0000

This is a disease mainly of the cartilage, but also the subchondral bone. If you look at the joint, and some like to think of osteoarthritis as a total joint failure. Again, it’s not a real synovial process but it probably starts in the cartilage. The cartilage is made up of chondrocytes, which are these little circles, then you have your proteoglycans which are very hygroscopic. They hold water in a gel state and give the cartilage its resiliency. And cartilage would expand even more if it wasn’t for this sort of retaining collagen framework that laces back and forth through the cartilage to give it some structure. It’s believed that the initial insult is some kind of damage to this collagen. Maybe what happens then is that when the collagen starts to break down these proteoglycans start to absorb more and more water, the cartilage begins to swell and it loses its typical helpful resilience. Once that is out of balance then the chondrocytes become injured and the cartilage does start to finally degrade. But often these patients have abnormalities of the subchondral bone, probably initially starting in the cartilage. The subchondral bone is not exactly like the rest of the bony structures. It’s designed to absorb some impact and if it starts to sclerose it’s not going to do a very good job of that. The last thing, that’s not shown in this slide, are these neurologic and mechanical factors. Any abnormalities of the ligaments, any alteration of the biomechanics of the joint because of muscle weakness or neurologic impairment, albeit subtle, may actually aggravate the pressure on the cartilage, accelerating the damage. Occasionally patients will have osteoarthritis and then they’ll sprain an ankle or twist a knee, nothing bad enough to require a cast or surgery, but then what you may notice is in that joint the osteoarthritis accelerates because of these probably subtle biomechanical changes.

If you look at it just in a schematic way, abnormalities of the collagen network, for whatever reason, swelling of the cartilage resulting in chondrocyte injury. Like most cells in the body, if the cells become injured, they try to somehow repair. So they actually have what we call “synthetic response”. They produce more of the matrix proteins. They also start to produce more of the proteolytic enzymes. There’s a balance between production of these matrix proteins and destruction. What may also be part of the picture, is that eventually when the chondrocytes can’t keep up the destructive enzymes start to get the upper hand, and finally when the cartilage breaks down you lose your chondrocytes. It’s not the kind of tissue that can repair itself. It’s not like skin or liver. Once it’s damaged to a certain point it does not recover. It doesn’t have any vascular supply. All its nutrients come from blood vessels or synovium so it really has a limited ability to repair. Again, you see that once the cartilage breaks down, that may lead to changes in biomechanical factors but the biomechanical factors may also have an initiating role, or aggravating role, so it becomes a vicious cycle and ultimately the patients develop osteophytes and the like.

Probably about 60 million people have x-ray evidence of osteoarthritis in this county. Any country that has a significant older population, it’s a significant problem. Obviously if you go to a country where the average life span is 45, I don’t think osteoarthritis is going to be on the top of their list of things to treat. But in this country it is a very significant medical problem. It’s not life-threatening, in a sense, but it certainly can be very disabling. I think 500 years ago osteoarthritis probably was a cause of death. People couldn’t keep up, they couldn’t work in the fields or whatever it is that they did, and basically if you didn’t work you didn’t eat and you were just sort of left to die if the culture you were in didn’t have the ability to care for you. In our culture we do, but it is a major health problem, major expense. Over half a million joint replacements are done every year and probably better than 90% of those are done for osteoarthritis. If you think how much these things cost – and also there is some morbidity, occasionally mortality, it’s not a benign procedure – but I’ll tell you the surgeons are getting really good. Most of the patients I see are out in two or three days unless they have a lot of other medical or arthritis problems to go on with it. They just get all their stuff at home, their low molecular heparin and physical therapy all at home. A lot of these patients, of the 60 million that I quoted, may just have x-ray evidence. If you do x-rays of people that are 80 years or older you are going to see a lot of osteophytes, maybe you’ll see some cartilage loss. A lot of these patients really won’t have many symptoms. I’m sure you all have done a flat plate of the abdomen or a chest x-ray, or an x-ray of a knee that got banged up, and you see a little bit of osteoarthritis that is really of no clinical significance. It would be of clinical significance if we had some kind of therapy to prevent progression. But since we don’t, it’s of little importance.

Osteoarthritis:Metabolic and neurologic factors

Disorders — Fri, 25 Dec 2009 09:50:49 +0000

Metabolic factors: certain metabolic diseases are associated with an increased incidence of osteoarthritis. Acromegaly, for instance. Obviously this is very uncommon but there may be more common subtle metabolic factors that play a role in the development of primary osteoarthritis.
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Neurologic factors: this is a disease of older patients. It’s unusual to see a primary osteoarthritis in patients under age 50. What happens when people age is that things just don’t work as well as they used to, in general, and the neurologic system is no different. This is becoming an area of great interest to several of the major centers studying osteoarthritis. Actually, if you look at the number of centers studying osteoarthritis it is much less common. So unfortunately it’s not a disease that rheumatologists and orthopedists are always that interested in, even though it is much more common. But these neurologic factors may be a subtle loss of proprioception or some weakness of some muscles that help support the joint, and people have shown that these things do occur and certain measures can affect that and make the patients symptomatically better. Aging and obesity, clearly osteoarthritis is associated with aging, but whether it is the cause of it is not clear. And obesity; there have been a number of studies. It’s hard to show that obesity actually causes osteoarthritis but certainly if someone weighs 450 pounds there is going to be a lot more stress on their knees, and especially their hips. So it does appear to be an aggravating factor but whether or not it’s a primary cause is not clear.
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Of course osteoarthritis can occur secondarily to other diseases. Trauma. Someone who had a broken hip or a torn anterior cruciate ligament may be predisposed to develop osteoarthritis in that joint later. Inflammation, either chronic inflammation as in rheumatoid disease or acute inflammation, as in a patient with septic arthritis that just didn’t respond well or get treated adequately. Again, metabolic factors, AVN, avascular necrosis, sometimes by the time you see the patient you can’t tell what the cause was in a single joint, but maybe they have a history of AVN in another joint. Of course if you follow a patient with AVN that is very early in the course and you don’t operate right away, they will eventually develop osteoarthritis in that joint. Neurologic disorders, less subtle, such as syringomyelia where you get neuropathic joints, which is just basically a very severe degenerative process. Obviously, congenital or developmental defects. We followed one patient with spondylo-epiphyseal dysplasia, or something like that, and she has abnormalities in the structure of many of her joints, particularly the hip and the back, and I think the knees, and she’s had several joint replacements because this disorder that she was basically born with basically leads to premature osteoarthritis. There are a number of other rarer diseases that can occur and then predispose to osteoarthritis. I think one common thing that pediatricians may see is hip dysplasia, and if that’s not treated properly, those patients get an osteoarthritic joint. If it’s treated properly then the acetabular cup forms normally and the children do much better.

Osteoarthritis

Disorders — Wed, 23 Dec 2009 17:08:11 +0000

Osteoarthritis is one of the most common rheumatic diseases in this country. Actually, for most rheumatologists it may not be the biggest part of their practice -probably rheumatoid arthritis is – because often these patients have mild disease or it’s treated either by the primary care physician or they end up going directly to the orthopedic surgeon who can, in some instances, cure the disease. It’s a slowly progressive, usually polyarticular disease, involving certain joints. Usually weight-bearing joints and certain joints in the hand, especially the DIP joints, PIP joints and also the first carpometacarpal or CMC joint. This is a woman who actually had giant cell arteritis and I was following her for that and she really never complained about any articular manifestations, unless her associated polymyalgia rheumatica flared up. So she had had these little nodules, Heberden’s nodes, for a number of years, thought they were ugly but other than that didn’t seem to care too much about them. I always wondered, why, if it involves weight-bearing joints, would it involve the DIP joints particularly. Evidently there is quite a bit of force because of the tendons crossing these joints, that there is actually quite a bit of force generated across these joints and that’s probably why the arthritis is predisposed to occur in this area.
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As opposed to rheumatoid arthritis, this is the disease that basically starts in the cartilage, whereas rheumatoid arthritis is a synovitis and then secondarily involves the cartilage. With osteoarthritis, for whatever reason, you have a breakdown of this cartilage and the cartilage is lost in a non-uniform fashion. Focal areas wear out first, and in this instance you also have these little bony outgrowths which clinically you can palpate, and these are osteophytes. Presumably these osteophytes are some halfhearted attempt at repair of the joint. Some of the major hallmarks are this focal loss of cartilage and osteophyte formation. Sometimes you also get subchondral cysts, which can also occur in other types of arthritis but they are particularly prominent in osteoarthritis. What happens is when you have a severe loss of cartilage in an area, sometimes a subchondral bone cracks and synovial fluid is literally forced into this area. When you take an x-ray it looks just like a lucency. That’s all it is, just a little bit of synovial fluid that’s been forced into the subchondral bone.
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There’s a lot of etiologic factors in primary osteoarthritis. Hereditary factors do appear to be important. Maybe some sort of abnormality of collagen production in the cartilage. Certainly the type of osteoarthritis involving the hands, if you talk to a patient a lot of times they will tell you that their parents and grandparents may have had the same thing. Stress from impact loading. This is probably more of an aggravating factor. They’ve actually done studies looking at professional basketball players and showing that they didn’t have an increased incidence of osteoarthritis later in life, unless they had had a major knee injury, like a torn ACL.