Knee Pain, Anatomy and Why It Hurts

If your knee is severely damaged by arthritis or injury, it may be hard for you to perform simple activities, such as walking or climbing stairs. You may even begin to feel pain while you are sitting or lying down. If nonsurgical treatments like medications and using walking supports are no longer helpful, you may want to consider total knee replacement surgery. Joint replacement surgery is a safe and effective procedure to relieve pain, correct leg deformity, and help you resume normal activities.

Knee replacement surgery was first performed in 1968. Since then, improvements in surgical materials and techniques have greatly increased its effectiveness. Total knee replacements are one of the most successful procedures in all of medicine. According to the Agency for Healthcare Research and Quality, more than 600,000 knee replacements are performed each year in the United States.

The knee is the largest joint in the body and having healthy knees is required to perform most everyday activities. The knee is made up of the lower end of the thighbone (femur), the upper end of the shinbone (tibia), and the kneecap (patella). The ends of these three bones where they touch are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily.

The menisci are located between the femur and tibia. These C-shaped wedges act as "shock absorbers" that cushion the joint. Large ligaments hold the femur and tibia together and provide stability. The long thigh muscles give the knee strength. All remaining surfaces of the knee are covered by a thin lining called the synovial membrane. This membrane releases a fluid that lubricates the cartilage, reducing friction to nearly zero in a healthy knee. Normally, these components work in harmony. But disease or injury can disrupt this harmony, resulting in pain, muscle weakness, and reduced function.

Total Knee Replacement

The first step when making the decision about knee replacement is to meet with your surgeon to see if you are a candidate for total knee arthroplasty (TKA). Your surgeon will take your medical history, perform a physical examination, and X-ray your knee. Even if the pain is significant, and the X-rays show advanced arthritis of the joint, the first line of treatment is nearly always non-operative. This includes weight loss if appropriate, an exercise regimen, medication, injections, or bracing. If the symptoms persist despite these measures, then you could consider TKA.

The decision to move forward with surgery is not always straightforward and usually involves a thoughtful conversation with yourself, your loved ones, and ultimately your surgeon. The final decision rests with you based on the pain and disability from arthritis influencing your quality of life and daily activities. Those who decide to proceed with surgery commonly report that their symptoms keep them from participating in activities that are important to them like walking, taking stairs, working, sleeping, etc., and non-operative treatments have failed.

These are some frequently asked questions regarding total knee replacement (TKR):

How long does a TKR last?

A common reply to this question is that total joint replacement lasts 15-20 years. A more accurate way to think about longevity is via the annual failure rates. Most current data suggest that both hip and knee replacements have an annual failure rate of 0.5-1.0%. This means that if you have your total joint replaced today, you have a 90-95% chance that your joint will last 10 years, and an 80-85% that it will last 20 years. With improvements in technology, these numbers may improve.

What types of implants are there?

The orthopedic implant industry has developed a number of innovative technologies in an effort to improve the outcomes of TJA. In recent years, these technologies have been marketed directly to patients, which have increased awareness as well as confusion on what these different designs mean. The most important message is that while a certain manufacturer may claim that their design is better, almost all the available registry data (large collections of data from countries that track TJA) show that there is no clear advantage to any of these designs when it comes to improving outcomes.

Here are specific implant design terms:

• Gender-specific: This refers to a modified implant design that accounts for average anatomic differences between men’s and women’s knees. Most manufacturers have incorporated similar modifications in their newer designs, which allow for more sizing options so that the prosthesis can be more accurately fit the patient’s native anatomy and recreate the natural function of the knee.

• Rotating platform: This refers to a plastic bearing that independently rotates on a metal tray on which it is seated. More often, the plastic bearing locks into the metal tray — referred to as a “fixed bearing.” Some theoretical advantages to the rotating platform concept when it was initially designed was that it could reduce the wear of the plastic bearing, reduce the rate of loosening of the metal parts, and better replicate how a patient’s knee works (kinematics). Most current data show that after 5-10 years in use, there does not appear to be any difference between rotating platform and fixed bearing designs in any of these outcomes.

Will my surgeon use a computer, robot, or custom cutting guide in my surgery?

There are many studies attempting to evaluate these emerging technologies and their influence on the success of surgeries. Each of these technologies has a specific goal that has fueled its development (i.e. more accuracy in implant placement, more efficient or faster surgery, etc.). To date, there appears to be both pros and cons to each of these technologies, but more research is required to determine what advantage, if any, these may offer. The best approach is to discuss this topic with your surgeon. You may want to know if they use one of these technologies, why they have chosen to do so, and what their experience has been in using it.

Can a Partial Knee/Unicompartmental Knee Replacement (UKR) relieve my knee pain?

There are many kinds of arthritic conditions that can affect the human body. Osteoarthritis, or degenerative joint disease, is the most common form of arthritis. The bones in a joint are covered with a tough, lubricating tissue called cartilage (the cushion in the joints) to help provide smooth, pain-free motion to the joint. As the layer of cartilage wears away, bone begins to rub against bone (“bone-on-bone”), causing the irritation, swelling, stiffness, and discomfort commonly associated with arthritis.

In some patients, only one part of the knee is damaged, while the remaining parts are completely healthy. In these cases, it is possible to replace only the damaged part of the knee with a metal and plastic implant. With a partial knee, only the damaged cartilage of the knee is replaced. The healthy parts are preserved. In the past decade, there has been a major increase in the use of unicompartmental knee replacement (UKR/partial knee replacement) as surgical techniques have been refined. UKR has shown to be a reliable operation for isolated unicompartmental arthritis. UKRs now account for 8% to 10% of knee replacement procedures. Recent studies have suggested excellent medium- and long-term results of UKR. Overall, results have shown 85% to 90% survivorship at 10 years, with as many as 90% of patients reporting that they are very satisfied with the procedure and they have reported excellent subjective and objective outcomes. Recent studies suggest that unicompartmental replacement allows a high percentage of patients to return to pre-surgical sport and activity participation.

If you have additional questions about knee pain or would like more information about treatment options please contact our office at 972-543-1250.

Tags:   Joint Replacement Joint Replacement Program Knee Replacement