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St. Mary's Center for Orthopaedics

Implants for the Knee

What are Knee Replacement Implants?

Knee replacement, or knee arthroplasty, is a surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve pain and disability. It is most commonly performed for osteoarthritis, and also for other knee diseases such as rheumatoid arthritis and psoriatic arthritis. In patients with severe deformity from advanced rheumatoid arthritis, trauma, or long standing osteoarthritis, the surgery may be more complicated and carry higher risk. Osteoporosis does not typically cause knee pain, deformity, or inflammation and is not a reason to perform knee replacement.

Other major causes of debilitating pain include meniscus tears, cartilage defects, and ligament tears. Debilitating pain from osteoarthritis is much more common in the elderly.

Knee replacement surgery can be performed as a partial or a total knee replacement. In general, the surgery consists of replacing the diseased or damaged joint surfaces of the knee with metal and plastic components shaped to allow continued motion of the knee.

The operation typically involves substantial postoperative pain, and includes vigorous physical rehabilitation. The recovery period may be 6 weeks or longer and may involve the use of mobility aids (e.g. walking frames, canes, crutches) to enable the patient’s return to preoperative mobility.

During the surgery, an orthopedic surgeon will replace your damaged knee with an artificial device (implant). Although replacing the total knee joint is the most common procedure, some people can benefit from just a partial knee replacement.

Implants are made of metal alloys, ceramic material, or strong plastic parts, and can be joined to your bone by acrylic cement. There are many different types of implants. Your surgeon will discuss with you the type of implant that best meets your needs.

Normal Knee Anatomy and Function

Your knee is the largest and strongest joint in your body. The knee joint is where the lower end of your femur (thighbone) meets the upper end of your tibia (shinbone). Your patella (kneecap) sits in front of the joint to provide some protection.

A healthy knee lets you move your lower leg forward and backward, and swivel slightly to point your toes in or out. Ligaments and cartilage stabilize and support the joint, preventing your knee from moving too far from side to side.

The knee is considered a hinge joint because of its ability to bend and straighten like a hinged door. In reality, the knee is much more complex because the bone surfaces actually roll and glide as the knee bends.

What is the Right Implant for You?

The brand and design used by your doctor or hospital depends on many factors, including your needs (based on your age, weight, activity level, and health), your doctor’s experience and familiarity with the device, and the cost and performance record of the implant. You should discuss these issues with your doctor.

Implant designs recognize the complexity of the joint and closely mimic the motion of a normal knee. Some designs preserve the patient’s own ligaments, while others substitute for them.

In some cases, just the damaged parts of the knee joint are replaced. This is sometimes called partial joint replacement or unicompartmental replacement.   It replaces just the inner knee surfaces or the outer knee surfaces, depending on where the damage is. Another partial replacement is called a patellofemoral replacement. In this surgery, the end of the thigh bone is replaced, and an artificial surface is used to line the back of the kneecap.

What are the Risks of Knee Implants?

Risks and complications in knee replacement are similar to those associated with all join replacements. Possible complications include:

  • Infection
  • Deep vein thrombosis
  • Nerve injuries
  • Persistent pain and stiffness
  • Prosthesis failure

Doctors often use general anesthesia for joint replacement surgeries. This means you’ll be unconscious during surgery. But sometimes they use regional anesthesia, which means you can’t feel the area of the surgery and you are sleepy, but you are awake. The choice of anesthesia depends on your doctor, on your overall health, and, to some degree, on what you prefer.

Your doctor may recommend that you take antibiotics before and after the surgery to reduce the risk of infection. If you need any major dental work, your doctor may recommend that you have it done before the surgery. Infections can spread from other parts of the body, such as the mouth, to the artificial joint and cause a serious problem.

What Happens After Knee Replacement Surgery?

  • The average hospital stay after knee joint replacement is usually three to five days.
  • The vast majority of people who undergo knee joint replacement surgery have dramatic improvement. This improvement is most notable one month or more after surgery. The pain caused by the damaged joint is relieved when the new gliding surface is constructed during surgery.
  • After knee joint replacement, people are standing and moving the joint the day after surgery. At first, you may walk with the help of parallel bars, and then a walking device such as crutches, walker, or cane will be used until your knee is able to support your full body weight.
  • After about six weeks, most people are walking comfortably with minimal assistance. Once muscle strength is restored with physical therapy, people who have had knee joint replacement surgery can enjoy most activities (except running and jumping).

How Long Will I Need Physical Therapy After Knee Replacement?

After knee replacement surgery, you are usually sent home or to a rehabilitation facility, depending on your condition at that time. If you are sent to a facility, the average rehabilitation stay is approximately seven to ten days. If you are sent directly home from the hospital, your doctor will usually have a physical therapist come to treat you at home. Your doctor also may have you go to an outpatient physical therapy facility as the final stage of the rehabilitation process. Outpatient therapy may last from one to two months, depending on your progress.

Remember, every person is different and the course of rehabilitation will be determined on an individual basis with the assistance of your doctor and physical therapist.

What Precautions Should I Take After Knee Replacement Surgery?
After knee replacement surgery, you should not pivot or twist on the involved leg for at least six weeks. Also during this time, when lying in bed, you should keep the involved knee as straight as possible. Kneeling and squatting also should be avoided soon after knee joint replacement surgery.

Your physical therapist will provide you with techniques and adaptive equipment that will help you follow guidelines and precautions while performing daily activities. Not following the given precautions could result in the dislocation of your newly replaced joint.

The following tips should make your recovery at home easier.

  • Stair climbing should be kept to a minimum. Make the necessary arrangements so that you will only have to go up and down the steps once or twice a day.
  • A firm, straight-back chair is extremely helpful in adhering to these joint precautions. Recliners should not be used.
  • To help avoid falls, all throw rugs should be removed from the floor and rooms should be kept free of unnecessary debris.
  • Enthusiastic pets should be kept far away until you have healed.