Understanding How the Knee Works

By understanding how a normal, healthy knee works, it will be easier for you to understand the way a knee joint prosthesis, or artificial knee joint, works — and the difference it may make in your life. A joint is formed by 2 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.

Causes of Knee Pain

One of the most common causes of joint pain is arthritis. The most common types of arthritis are:


Normal knee joint, showing healthy articular cartilage


Diseased knee joint, showing worn cartilage


Post-operative knee joint with prosthesis in place

  • Osteoarthritis (OA) - sometimes called degenerative arthritis because it is a "wearing out" condition involving the breakdown of cartilage in the joints. When cartilage wears away, the bones rub against each other, causing pain and stiffness. OA usually occurs in people aged 50 years and older, and frequently in individuals with a family history of osteoarthritis.
  • Rheumatoid Arthritis (RA) - produces chemical changes in the joint space that cause it to become thickened and inflamed. In turn, the synovial fluid destroys cartilage. The end result is cartilage loss, pain, and stiffness. RA affects women about 3 times more often than men, and may affect other organs of the body.
  • Post-traumatic Arthritis - may develop after an injury to the joint in which the bone and cartilage do not heal properly. The joint is no longer smooth, and these irregularities lead to more wear on the joint surfaces.

Other causes of joint pain include avascular necrosis, which can result when bone is deprived of its normal blood supply (for example, after organ transplantation or long-term cortisone treatment), and deformity or direct injury to the joint. In some cases, joint pain is made worse by the fact that a person will avoid using a painful joint, weakening the muscles and making the joint even more difficult to move. What's causing your knee joint pain? Is getting relief through joint replacement an option for you? These are just some of the answers that we can provide you.

Treating Knee Pain

What You Should Know About Knee Joint Replacement

"Joint Replacement" (the term orthopaedic surgeons use) is usually reserved for patients who have severe arthritic conditions. Most patients who have artificial knee joints are over 55 years of age, but the operation is being performed in greater numbers on younger patients thanks to new advances in artificial joint technology. Circumstances vary, but generally patients are considered for total joint replacement if:

  • Functional limitations restrict not only work and recreation, but also the ordinary activities of daily living.
  • Pain is not relieved by more conservative methods of treatment - such as medications, physical therapy, or arthroscopy (cleaning the joint) - by the use of a cane, and/or by restricting activities.
  • Stiffness in the joint is significant.
  • X-rays show advanced arthritis or other problems.

What Is Total Joint Replacement?

Total joint replacement is a surgical procedure in which certain parts of an arthritic or damaged joint, such as a knee joint, are removed and replaced with a prosthesis, or artificial joint. The artificial joint is designed to move just like a normal, healthy joint. In total knee replacement, the artificial joint is composed of metal and polyethylene to replace the diseased joint. The artificial joint is most commonly anchored into place with bone cement. In some applications, it is covered with a porous coating that allows bone tissue to grow into it.

MIS (Minimally Invasive Surgery) Knee Replacement

MIS Knee Joint Replacement is considered a giant step forward in total knee replacement for a number of reasons, which may include the following: a shorter hospital stay, faster recovery, and much less scarring.

Less Is More

Unlike conventional total knee replacement - which requires a large incision (8 to 12 inches) and significant disruption of the muscles and tendons - MIS Knee Joint Replacement is performed through an incision as small as 3 to 4 inches. In some MIS procedures the amount of soft tissue (muscles and tendons, etc.) that are disrupted during surgery may also be reduced. Through that same small incision, the diseased surfaces of the knee joint are exposed and then replaced, one at a time, with the artificial joint components.

Minimally Invasive Surgery

Over the past 25 years, minimally invasive surgery has revolutionized many fields of medicine. Its key characteristic is that it uses specialized techniques and instrumentation that enable the physician to perform major surgery without a large incision. In this respect, MIS Knee Joint Replacement is indeed "minimally invasive", requiring only a small incision and causing minimal trauma to the soft-tissues. Minimally invasive surgical techniques may offer benefits including: less pain, less recovery time, and less scarring.

Listing the Advantages

Because fewer muscles and tendons are disturbed with MIS Knee Joint Replacement, their reconstruction is more natural, wound closure is easier, and recovery may be faster. Clinical studies have shown that the MIS technique results in less pain (at both 8 days and 6 weeks after surgery) and quicker restoration of muscle control and strength. It can take several months to recover from the large incision and muscle disruption with the standard approach.

Risks Associated with Minimally Invasive Surgery

The MIS Knee Joint Replacement technique is significantly less invasive than conventional TKR, but it is still a total knee replacement, not a partial knee replacement. It takes little additional time to complete and may result in advantages for the patient. Joint replacement surgery is a major surgery and significant complications, while rare, can occur.

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 and/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.

Possible Complications of Surgery

Serious complications may occur with any surgical procedure. These include but are not limited to: problems with anesthesia, cardiovascular problems including heart attack, vascular problems including thrombus, bronchopulmonary problems including emboli, genitourinary problems, and gastrointestinal problems. Certain additional complications related to joint replacement surgery in particular may include but are not limited to: bleeding problems, blood clots in the legs and/or lungs, wound healing problems, damage to nerves and blood vessels, limb length discrepancy, bone erosion or abnormal bone formation, dislocation, infection, pain, bone fracture or non-union, component wear or fracture, component loosening. Complications may require medical intervention including additional surgery and, in rare instances, may lead to death.

Will an Artificial Knee Joint Last Forever?

As successful as most of these procedures can be, over the years, the artificial joints can become loose and unstable or wear out, requiring a revision (repeat) surgery.

Orthopaedic Evaluation<

The medical management of arthritis and joint degeneration may be handled by a family doctor, an internist, or a rheumatologist. However, when medical management is not effective, an orthopaedic surgeon should be consulted to determine if surgery is an option. In some cases, we may be the first to see a patient and make the diagnosis of arthritis. If you’re ready to consider having knee joint replacement, the next important step is to set up an appointment with one of our orthopedic surgeons.