The largest joint in the body, 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 bones, where they touch, are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily. Between the femur and tibia are C-shaped wedges, called menisci, that act as shock absorbers to cushion the joint. Large ligaments holding the femur and tibia together provide stability and long thigh muscles give the knee strength. All remaining surfaces of the knee are covered by a thin lining, or synovial membrane, that releases fluid to lubricate the cartilage, reducing friction to nearly zero in a healthy knee. Normally, these components work together in harmony, but when disrupted by disease or injury the result can be pain, muscle weakness and reduced function.
A knee replacement (or knee arthroplasty) might also be considered a knee resurfacing because only the surface of the bones is actually replaced. There are four basic steps to this procedure, as follows. First, to prepare the bone, damaged cartilage surfaces at the ends of the femur and tibia are removed along with a small amount of underlying bone. Next, the metal implants that will replace the removed cartilage and bone to recreate the surface of the joint are positioned before being cemented or press-fit into place. Depending on your individual situation, your surgeon may choose to cut and resurface the undersurface of the patella, or kneecap, with a plastic button. Finally, a medical-grade plastic spacer is inserted between metal components to create a smooth gliding surface during movement.
People who benefit from total knee replacement surgery often experience one or more of the following: severe knee pain or stiffness that limits everyday activities, such as walking, climbing stairs, and getting in and out of chairs; difficulty walking more than a few blocks without pain or without support of a cane or walker; moderate or severe pain while resting, day or night; chronic knee inflammation and swelling that does not improve with rest or medication; knee deformity, or a knee that bows in or out; failure to substantially improve with treatments such as anti-inflammatory medications, cortisone or lubricating injections, physical therapy, or other surgeries.
Recommendations for this surgery are based on your level of pain and disability. There are no absolute age or weight restrictions for total knee replacement surgery, and although total knee replacements are most common for patients between 50 and 80 years of age, they are performed on patients of all ages, from young adults to the elderly. Before recommending total knee replacement, your orthopaedic surgeon will provide an evaluation based on multiple factors, including: your medical history; a discussion of your level of pain and ability to perform daily activities; a physical examination to assess the mobility, strength and overall leg alignment; and X-rays to determine the extent of damage or deformity in the knee. Occasionally, additional testing such as blood tests or an MRI scan may be needed to determine the condition of the bone and soft tissues of your knee. Once the evaluation is complete, your doctor will review the results with you and discuss whether total knee replacement is the best method to relieve your pain and improve your function. Options such as medications, physical therapy or other types of surgery may also be considered.
The decision to undergo knee replacement surgery should be a cooperative one made by you and your family along with your primary care doctor and orthopaedic surgeon. Your doctor will explain the benefits along with any potential risks and complications, both relating to the surgery and that could occur over time.
Most people experience a dramatic reduction in pain and a significantly improved ability to perform normal activities, however total knee replacement will not allow you to do more than you could before you developed arthritis. An important factor in deciding whether to have total knee replacement surgery is understanding what the procedure can and cannot accomplish. With normal use and activity, the plastic spacer in every knee replacement implant will begin to wear. Excessive activity or being overweight may hasten this normal wear, causing the replacement joint to become loose and painful. Most orthopaedic surgeons advise against running, jogging, jumping or other high-impact activities for the rest of your life after this surgery. More realistic activities include unlimited walking, swimming, golf, driving, light hiking, biking, ballroom dancing, and other low-impact activities. By appropriately modifying your activities, your knee replacement can last for many years.
Once the decision to have surgery is made, your orthopaedic surgeon will require some preparations, such as: having a complete physical, including evaluation by your primary care physician or specialist for any chronic medical conditions; making sure any skin infections or irritations are treated; medication review and management; weight loss if needed to lessen stress on the new joint; dental evaluation; urinary evaluation; and a variety of tests, such as blood and urine samples, electrocardiogram (EKG), and chest X-ray, as needed.
There are also modifications to your home that can be made to make navigation easier during your recovery, such as: removal of loose carpets and electrical cords from areas where you walk; handrails along stairways; raised toilet seat; stable chair and firm pillows for chairs, sofas and car; safety bars or handrails in shower or bath; stable shower bench or chair for bathing; long-handled sponge and shower hose; a reacher to grab objects; dressing stick, sock aid and long-handled shoe horn for putting on socks and shoes without excessively bending your new joint. You may also find it convenient to set up a recovery center equipped with phone, remote control, reading materials, medications and other items in the area where you spend most of your time.
After admission into the hospital, you will be evaluated by a member of the anesthesia team. The most common types of anesthesia are general anesthesia (you are put to sleep) or spinal, epidural, or regional nerve block anesthesia (you are awake but your body is numb from the waist down). The anesthesia team, with your input, will determine the best option for you. Your surgeon will see you before the surgery and sign your knee to verify the surgical site. The surgical procedure itself takes approximately 1 to 2 hours. Your orthopaedic surgeon will remove the damaged cartilage and bone, and then position the new metal and plastic implants to restore the alignment and function of your knee.
Following surgery, you will be moved to the recovery room where your recovery from the anesthesia will be monitored for several hours. Once you are awake, you will be taken to your hospital room. You can expect to be in the hospital for 2-3 days. You will feel some pain after surgery, but your surgeon and nurses will provide medication to make you as comfortable as possible. Pain management is an important part of your recovery because feeling less pain will allow you to start moving and get your strength back more quickly. If postoperative pain becomes a problem, speak with your surgeon.
The success of your surgery will depend in large measure on how well you follow your orthopaedic surgeon's instructions regarding home care during the first few weeks after surgery.
Your activity program should include: a graduated walking program to slowly increase your mobility, initially indoors and later outside; resuming normal household activities, such as sitting, standing and climbing stairs; specific exercises to restore movement and strengthen your knee, performed several times a day. If needed, you may have a physical therapist help you at home or in a therapy center the first few weeks after surgery.
To assure proper recovery, you may be asked to take special precautions—usually for the first six weeks after the surgery. Avoid falls by using a cane, crutches, walker or handrails, or have someone help you until you improve your balance, flexibility, and strength. Your orthopaedic surgeon and physical therapist will help you decide which assistive aides will be required following surgery, and when those aides can safely be discontinued.
The complication rate following knee replacement surgery is low, with serious complications, such as a knee joint infection, occurring in fewer than 1% of patients. Among these are: minor infections; deep infections; blood clots in leg veins or pelvis; limited motion due to scarring in the knee; loosening and wear of implant; risks of anesthesia; and in a very small number of patients, neurovascular injury or continued pain. Occurring even less frequently are major medical complications, such as heart attack or stroke. Chronic illnesses may increase the potential for complications. Although uncommon, these complications can prolong or limit full recovery.
Although improvement of knee motion is a goal of total knee replacement, restoration of full motion is uncommon. The motion of your knee replacement after surgery can be predicted by the range of motion you have before surgery. Most patients can expect to be able to almost fully straighten the replaced knee and bend it sufficiently to climb stairs and get in and out of a car. Kneeling is sometimes uncomfortable, but it is not harmful. You may experience numbness in the skin around your incision, as well as some stiffness, particularly with excessive bending. Most patients feel or hear some clicking of the metal and plastic when bending the knee or walking, which is normal. These often diminish with time, and most patients find them minor compared with the pain and limited function they experienced prior to surgery.
Your new knee may activate metal detectors required for security in airports and some buildings. Tell the security agent about your knee replacement if the alarm is activated.
You can protect your knee replacement and extend the life of the implant by participating in a regular, light exercise program to maintain strength and mobility; take special precautions to avoid falls and injuries; inform your dentist of the implant and that you will need antibiotics before any dental procedure; and of course, be sure to see your orthopaedic surgeon as recommended for periodic routine follow-up examinations and X-rays, even if your knee replacement seems to be doing fine. More than 90% of modern total knee replacements are functioning well 15 years after the surgery. Following your orthopaedic surgeon's instructions after surgery and taking care to protect your knee replacement and your general health are important ways you can contribute to the final success of your surgery.