Knee Anatomy and Function

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.

References:

1. Arthritis Foundation – February 2006

Knee FAQs

What is knee replacement?

Knee joint replacement is a surgical procedure in which certain parts of an arthritic or damaged 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 and allows you to get back to enjoying normal, everyday activities without pain.

How “bad” does my joint pain have to get before I should consider having joint replacement?

This is a very personal decision that only you can make with the help of an orthopaedic specialist’s evaluation of your pain and its effects on your daily life. For example, experiencing knee pain day after day without relief can lead to “staying off” the joint — which often weakens the muscles around it, so it becomes even more difficult to move.

When other more conservative treatment options — including medication and physical therapy — no longer provide pain relief, joint replacement may be recommended.

What is minimally invasive (MIS) knee joint replacement?

With a minimally invasive knee surgery, specialized techniques and instrumentation enable the physician to perform major surgery without as large an incision. In this respect, it is indeed “minimally invasive,” requiring a smaller incision and causing less trauma to the soft tissues. MIS knee replacement is considered a step forward in total knee replacement for a number of reasons, which include the following: potential for a shorter hospital stay, faster recovery, and less scarring. However, MIS surgery is not the right procedure for everyone. Only your orthopaedic specialist can determine its benefits for you.

Are there risks associated with MIS surgery?

The MIS knee replacement technique is significantly less invasive than conventional knee replacement surgery, but it is still a major surgery.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.

What will I need to know about postoperative recovery in the hospital?

Following joint replacement surgery, hospital stays vary depending on insurance coverage and individual medical status. A total of four days (including the day of the surgery) is typical. On the first day after your surgery, you will likely get out of bed and begin physical and occupational therapy, typically several brief sessions a day.

Usually a case manager is assigned to work with you as you move through your rehabilitation routines. When you’re ready for discharge, the decision will be made concerning whether you can best continue to recover at home (the usual procedure) or in another facility where you may receive specialized rehabilitative help. If you do go to another facility, the goal will be to return you to your home, able to move about with a safe level of independence, within three to five days.

What can I expect in the first days after I’m discharged?

You shouldn’t be surprised if you feel a little shaky and uncertain for the first day or two after you’re discharged. But soon you may get a routine going and gain confidence in your new joint — the start of a new life with less pain. (As with any surgery, you’ll probably take pain medication for a few days while you are healing.) Be aware that you’ll probably need a walker and/or crutches for about six weeks, then use a cane for another six weeks or so. You’ll be in touch with your doctor or orthopaedic specialist as well as your case manager, so you’ll have plenty of opportunities to ask questions or discuss concerns as well as to report your progress.

When will I be able to go back to a normal daily routine, such as going to work or driving a car?

This is a decision that only you and your doctor or orthopaedic specialist can make. Be sure to follow your doctor’s or orthopaedic surgeon’s advice and recommendations. Individual results may vary.

How long does a knee replacement last?

As successful as most of these procedures are, over the years the artificial joint can become loose or wear out, requiring a revision (repeat) surgery. How long it will last depends not only on a person’s age, but also on a patient’s activity level. These issues — together with the fact that increasing numbers of younger and more active people are receiving total joint replacement — have challenged the orthopaedic industry to try to extend the life cycle of total joint replacements.

What happens during knee replacement surgery?

In surgery, the knee is flexed and the leg suspended. One muscle is separated to expose the femur (thighbone); later, the tibia (shinbone) is exposed. The damaged surfaces at the end of the thighbone are trimmed to shape it to fit inside the total knee prosthesis. The shinbone is cut flat across the top and a hole is created in the center to hold the stem of the tibial component. If needed, the knee cap is trimmed and the patellar component attached.

At various points during surgery, the alignment, function, and stability of the knee joint are evaluated and required adjustments are made. The prosthesis components are cemented into place, any contracted ligaments are released, the midvastus muscle is reconstructed, and the incision is closed.

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