Pathoanatomy: (The Problem)
Cartilage has several important characteristics. It has very little, if any, blood supply so its nourishment must come from the fluid of the joint. It is relatively acellular so that repair, when it is damaged, is very slow and usually limited. It is somewhat soft, yet it must last a lifetime as it does not replenish itself like our skin, for instance, is able to do.
When cartilage is damaged therefore, it can be a permanent problem. Despite much research, we have difficulty replacing human cartilage after injury. As the cartilage wears, the debris created causes inflammation in the joint. Inflammatory fluid is produced which itself is somewhat detrimental. Pain from swelling and inflammation results and is progressive. Bone spurs or “osteophytes” may develop and pieces of bone and cartilage will occasionally break off and become loose within the joint. Eventually bone will start to contact bone, creating significant friction, inflammation, and pain.
Symptoms and Signs: (What it feels like)
The initial symptoms may be mild with only an occasional ache after extensive activity. Progressively though, the inflammation and aching become more intense and longer lasting. Patients note increased warmth and swelling. They can often feel a roughness or a catching sensation within the knee. Activities increase the pain and rest decreases it.
Anti-inflammatories like aspirin or ibuprofen often decrease the pain and inflammation. As the disease progresses, the patient may begin to notice deformity of the joint such as a bull-legged appearance.
Cartilage damage is difficult to see on plain x-rays and even on MRI scans initially. Arthroscopically, however, it is quite evident. Once the osteoarthritis progresses, the plain x-rays start to show bony changes. The space between the bones narrows and bone spurs start to form.
Occasionally, pieces of bone will break off and become loose within the joint, causing pain and catching. The joint eventually becomes stiff and frequently swollen.
Natural History: (What happens with no treatment)
Osteoarthritis is a progressive disease process that gradually worsens over time. It may take many years to become symptomatic, but once it does, it usually progresses steadily. Some patients have relatively significant evidence of osteoarthritis on x-ray but yet have few symptoms. Others have few signs of the disease yet have significant pain. It is therefore difficult to predict for any particular patient what to expect of their osteoarthritis.
Treatment and Options:
Like most other diagnoses in orthopaedics, treatment begins conservatively and progresses as necessary in accordance with the patient’s response. Initially, rest and activity modification is helpful. Decreasing the stress on the knee by methods such as weight reduction and avoidance of stairs or long walks may allow the inflammation to decrease. Heating pads or, occasionally, ice packs may also feel good. As the patient exercises, repetitive stress that increases the irritation to the knee must be avoided.
Medications which decrease inflammation can give pain relief from osteoarthritis. Aspirin, ibuprofen, and many newer so-called “nonsteroidal anti-inflammatories” are in this category. There are risks and potential side effects from these medications which must be watched for. Injections of steroid medication directly into the knee joint can sometimes reduce the symptoms for extended periods of time. This too has its own set of risks such as infection, pain from the injection, and occasionally, skin discoloration and dimpling.
When the symptoms are mechanical in nature such as those from a loose piece of bone getting caught within the joint, arthroscopy and removal or debridement of the cause can be very helpful. Other problems such as meniscal tears and rough cartilage also occur in osteoarthritis and can be treated arthroscopically as well. Newer techniques allow us to regenerate articular cartilage or at least fibrocartilage. In some cases we now have the ability to transplant healthy articular cartilage from one part of the knee where it is not needed to another part where it is. It is important to realize that the osteoarthritis itself cannot be cured arthroscopically and that it will continue to progress despite arthroscopic examination and debridement.
Finally, once the joint cartilage becomes significantly thin or worn-out and the pain is not responsive to other forms of treatment, consideration can be made for either osteotomy or joint replacement. An osteotomy changes the weight bearing axis of the knee, shifting the weight from the more damaged side to the less involved side. Like rotating the tires on a car, this can decrease the symptoms for many years but is only an option if there is a relatively uninvolved side. If both sides are significantly involved, a joint replacement becomes a better option. Joint replacement, or “arthroplasty”, involves resurfacing the arthritic joint with a combination of metal and plastic components. Pain relief is often remarkable, but the risks and options must be considered. An artificial knee has a limited life span and therefore is less appropriate for young patients and those who are very active since, predictably, it may wear out. In addition, the operative risks include infection, bleeding, nerve or blood vessel damage, fracture, blood clots, pulmonary embolism, and mechanical failure such as loosening. Despite these risks, greater than 90% of joint our replacements do very well.
Surgical Intervention:
If an osteotomy is chosen, hospitalization averages 1 to 2 days. A cast or brace is worn 6-8 weeks. For joint replacement hospitalization averages 2 to 3 days after which many patients either transfer to a rehab facility or go home with home health care assistance. The surgery can be performed with either a general or an epidural anesthetic and takes about 1 hour to complete. Initial physical therapy is designed to regain range of motion and strength in the knee and to assist the patient in walking. Usually a walker or crutches are used to assist in this process.