Knee Anatomy and Function

Are You Considering Knee Replacement Surgery?

Each patient is unique, but generally candidates for knee replacement surgery have:

  • Pain severe enough to restrict not only work and recreation, but also the routine activities of daily living
  • Pain that is not relieved by more conservative methods of treatment, such as reduced activity, medication or physical therapy
  • Significant joint stiffness and loss of mobility
  • X-rays that show advanced arthritis or other degenerative problems

The National Institutes of Health (NIH) has concluded that knee replacement surgery is “a safe and cost-effective treatment for alleviating pain and restoring function in patients who do not respond to non-surgical therapies.”1 According to the American Academy of Orthopaedic Surgeons, knee replacement procedures have resulted in significant restoration of function and reduction of pain in about 90% of patients.2 As you read,make a note of anything you don’t understand. Your doctor will be happy to answer your questions so that you’ll feel comfortable and confident with your chosen treatment plan.

Knee Basics: What You Need to Know

 

Knee Anatomy and Function
The knee is the largest joint in the body and is central to nearly every routine activity. The knee joint is formed by the ends of 3 bones: the lower end of the thigh bone (femur), the upper end of the shin bone (tibia), and the kneecap (patella). Thick, tough tissue bands called ligaments connect the bones and stabilize the joint. A smooth, plastic like lining called cartilage covers the ends of the bones and prevents them from rubbing against each other, allowing for flexible and nearly frictionless movement. Cartilage also serves as a shock absorber, cushioning the bones from the forces between them. Finally, a soft tissue called synovium lines the joint and produces a lubricating fluid that reduces friction and wear.

Arthritis: The Leading Cause of Knee Pain
One of the most common causes of knee pain and loss of mobility is the wearing away of the joint’s cartilage lining. When this happens, the bones rub against each other, causing significant pain and swelling — a condition known as osteoarthritis. Trauma or direct injury to the knee can also cause osteoarthritis. Without cartilage there is no shock absorption between the bones in the joint. This allows stress to build up in the bones and contributes to pain.

Understanding How the Knee Works

A joint is formed by two or more bones that are connected by thick bands of tissue called ligaments. The knee is the largest joint in the body and is made up of three main parts:

  • The lower end of the thigh bone, or femur.
  • The upper end of the shin bone, or tibia.
  • The kneecap, or patella.

The thigh bone (femur) turns on the upper end of the shin bone (tibia), and the kneecap (patella) slides in a groove on the end of the thigh bone. Ligaments, which are bands of tissue, connect the thigh bone and the shin bone to help keep the knee joint steady. The quadriceps, the long muscles on the front of the thigh, help strengthen the knee.

A smooth substance called articular cartilage covers the surface of the bones where they touch each other within the joint. This articular cartilage acts as a cushion between the bones. The rest of the surfaces of the knee joint are covered by a thin, smooth tissue liner called synovial membrane, which makes a small amount of fluid that acts as a lubricant so that the joint bones will not rub against each other.

What Causes Knee Pain?

One of the most common causes of knee pain and loss of mobility is the wearing away of the joint’s cartilage lining. When this happens, the bones rub against each other, causing significant pain and swelling. The most common cause is a condition known as osteoarthritis. Trauma or direct injury to the knee can also cause osteoarthritis. Without cartilage there is no shock absorption between the bones in the joint, which allows stress to build up in the bones and contributes to pain.

Your Treatment Options for Knee Pain

You may be able to get pain relief from treatments like steroidal and nonsteroidal anti-inflammatory drugs, physical therapy, bracing, and cortisone injections. But, if you’ve tried these methods and haven’t experienced adequate relief, you don’t have to live with severe knee pain and the limitations it puts on your activities.

Knee replacement surgery may provide the pain relief you long for and enable you to return to the things you enjoy doing. Remember, even if your doctor recommends knee replacement for you, it is still up to you to make the final decision. The ultimate goal is for you to be as comfortable as possible with your choice — and that always means making the best decision based on your own individual needs.

If you do choose surgery, you’ll be in good company: More than a quarter-million Americans have knee replacement surgery every year.1 First performed in 1968, the procedure typically relieves pain and restores joint function.

Knee Replacement

 

Knee replacement is a surgical procedure — performed in the U.S. since the 1960s — in which a diseased or damaged joint is replaced with an artificial joint called a prosthesis.Made of metal alloys and high-grade plastics (to better match the function of bone and cartilage, respectively), the prosthesis is designed to move just like a healthy human joint. Over the years, knee replacement techniques and instrumentation have undergone countless improvements. Today, knee replacement is one of the safest and most successful types of major surgery; in about 90% of cases it is complication-free and results in significant pain relief and restoration of mobility.1

Knee Implants That Promote Easier Motion

Stryker knee replacements are different than traditional knee replacements because they are designed to work with the body to promote easier motion,1,2,3 and a study has shown a more rapid return to functional activities after surgery.2 This is due to the single radius design of the knee implant. Single radius means that as your knee flexes, the radius is the same, similar to a circle, requiring less effort from your quadriceps muscle.1,4,6

Because the thigh muscle (the quadriceps) is attached to your knee, it is unavoidably involved in the surgery. Therefore, the quadriceps muscle can become a source of discomfort or pain during your recovery period. The quadriceps muscle plays an important role in your ability to move your legs so it also has a major impact on your recovery and how quickly you can get back to living your life.2

Knee implants designed to last longer

Several factors influence how long an implant will continue to perform. Stryker knees are designed to resist wear in many ways — they use advanced bearing surfaces; they’re balanced to help avoid excessive stress in any one spot; and, they’re sized to better fit your personal anatomy. X3 Advanced Bearing Technology has demonstrated up to 96% decrease in wear in laboratory testing compared to competitive premium bearing technologies.5

What Typically Happens During the Surgery

To begin the surgery, the surgeon will make an incision on the front of your knee, cutting through the tissue surrounding the muscles and bone. The kneecap, or patella, is rotated to the outside of the knee, to help your doctor see the area where the implant will be placed. The surgeon will use special cutting instruments to measure and make precise cuts of the bone. The end of the femur (thigh bone) is cut into a shape that matches the corresponding surface of the metal femoral component. The femoral component is then placed on the end of the femur.

The tibia (shin bone) is prepared with a flat cut on the top. The exposed end of the bone is sized to fit the metal and plastic tibial components. The metal tibial component is inserted into the bone. Then a plastic insert is snapped into the tibial component. The femoral component will slide on this plastic as you bend your knee.

If needed, the patella (kneecap) is also cut flat, and fitted with a plastic patellar component. Bone cement may be used to help secure the implants onto your bone. Your surgeon will conduct several tests during the surgery to ensure the correct sized components are used to help you regain good balance and motion in your knee. Your surgeon will then close the wound in layers with stitches and/or staples.

Risks Associated with Knee Replacement

But as good as the results can be, knee replacement is major surgery, and as such, there are certain risks and expectations that must be recognized. As with any major surgical procedure, patients who undergo total joint replacement are at risk for certain complications, the vast majority of which can be successfully avoided or treated. In fact, the complication rate following joint replacement surgery is very low. Serious complications, such as joint infection, occur in less than 2% of patients.1 Other possible complications include blood clots and lung congestion, or pneumonia. Talk to your doctor for a complete assessment of the potential risks.

Life After Knee Replacement

The vast majority of individuals who have joint replacement surgery experience a dramatic reduction in joint pain and a significant improvement in their ability to participate in the activities of daily living. However, joint replacement surgery will not allow you to do more than you could before joint problems developed. Your doctor will recommend the most appropriate level of activity following joint replacement surgery.

Don’t Let Knee Pain Slow You Down

Don’t let severe knee pain limit your activities. If you haven’t experienced adequate relief with medication and other conservative treatments, joint replacement may provide the pain relief you long for and enable you to return to your favorite activities. Remember, even if your doctor recommends knee replacement for you, it is still up to you to make the final decision. The ultimate goal is for you to be as comfortable as possible with your choice — and that always means making the best decision based on your own individual needs.

For more information visit AboutStryker.com and contact your doctor.

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