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Your Knee

Anatomy of the Knee

The bones of the knee, the femur and the tibia, meet to form a hinge joint. The joint is protected in front by the patella (kneecap). The joint is cushioned by articular cartilage that covers the ends of the tibia and femur, as well as the underside of the patella. The lateral meniscus and medial meniscus are pads of cartilage that further cushion the joint, acting as shock absorbers between the bones.

Ligaments help to stabilize the knee. The collateral ligaments run along the sides of the knee and limit sideways motion. The anterior cruciate ligament, or ACL, connects the tibia to the femur at the center of the knee. Its function is to limit rotation and forward motion of the tibia. A damaged ACL is replaced in a procedure known as an ACL Reconstruction. The posterior cruciate ligament, or PCL (located just behind the ACL) limits backward motion of the tibia.

These components of your knee, along with the muscles of your leg, work together to manage the stress your knee receives as you walk, run and jump.

ACL Reconstruction

The ACL (Anterior Cruciate Ligament) is a ligament in the center of your knee that becomes damaged when twisted too far, such as in a skiing injury. ACL reconstruction is performed using a combination of open surgery and arthroscopic surgery.

This arthroscopic view shows a healthy ACL that is firmly attached to the femur and tibia.

Before the ACL reconstruction process begins, your surgeon will examine your knee arthroscopically, and repair any additional damage to the knee, such as a torn meniscus, or worn articular cartilage.
Reconstruction of the ACL begins with a small incision in your leg where small tunnels are drilled in the bone.

Next your new ACL is brought through these tunnels, and then secured with a staple and buckle system.

As healing occurs, the bone tunnels fill in to secure the tendon.

Total Knee Replacement

Arthritis of the knees can be mechanical (osteoarthritis) in which the surfaces of the knee gradually "wear out." This may be due to age, angular deformity or old fractures. Systemic arthritis such as rheumatoid arthritis or gout affects the synovium (the membrane tissue in the joint that normally lubricates the joint), becomes pathologic and the surface of the joint is destroyed.

In either case when the surface of the joint is worn away, at a certain point in time walking and activities of daily living become very difficult. Standardized treatment such as weight loss, anti-inflammatory medication, braces, orthotics, steroid injections, physical therapy, etc. are all tried and if effective that is fine.

In many cases, however, despite the above non-surgical treatments, functional limitations persist. Most people who are considering knee replacement are limited to walking less than three to six blocks, or less than 15 to 20 minutes. They have difficult time getting up out of a chair. They have rest pain. They are taking antiinflammatory medication and/or pain medicine on a regular basis and the pain is generally progressive.

It is important to realize that a knee "replacement" is actually just a "resurfacing" of the knee joint. The femur or thigh bone is covered with a metal covering and plastic is placed on the tibia so that instead of irregular arthritic surfaces, one has metal and plastic articulating which produces a smooth non-patent surface. In most cases the undersurface of the kneecap is also replaced with a plastic surface so that this articulates with the femoral surface.

Knee replacements have been done since the early 1970s and our most recent designs appear to have 85% to 90% survival at twenty years.

The actual procedure involving knee replacement involves either general or epidural anesthesia with a four to six day hospitalization. The surgery itself takes between 1-1/2 and 2-1/2 hours. In most cases patients donate two units of autologous blood to be used in the postoperative period. Weight-bearing begins immediately the first postoperative day. Patients usually use a walker for a period of one to two weeks, going to crutches and then a cane. People are off all walking aids anywhere from three weeks to two months.

Success rates in knee replacements are approximately 90% with 10% not doing as well. This can be due to either stiffness or ache or swelling in and about the knee. The most significant complications, aside from general medical complications (heart and lung) involve infection of the prosthesis. If this occurs, in some cases the prosthesis can be saved and the patient taken back to the operating room, the knee irrigated with antibiotic irrigation and then be on antibiotics. In some cases if this does not respond, then the entire prosthesis must be taken out and antibodies given for six weeks and then another attempt at re-implantation of the of the prosthesis must occur. In an extremely small percentage of cases, conceivably if the infection could not be controlled, then one is left a knee fusion in which the femur and tibia are fused in one bone.

Activities after knee replacement that should produce no difficulty are simple walking, bicycling, golfing, and swimming. The prosthesis is not designed form impact loading sports such as skiing, basketball, or racquetball. People have been known to play doubles tennis with bilateral knee replacements.

Cartilage Repair

About Cartilage

Normal knee function requires a smooth gliding articular cartilage surface on the ends of the bones. This surface is composed of a thin layer of slippery, tough tissue called hyaline cartilage. This cartilage also acts to distribute force during repetitive pounding-like movements such as jumping or running.

Injured Cartilage

A severe knee cartilage injury can radically change an active adult's lifestyle. Symptoms such as locking, catching localized pain and swelling often affect your ability to work, play, and even perform normal activities.

A cartilage lesion appears as a hole or divot in the cartilage surface. Since cartilage has minimal ability to repair itself, even shat may seem like a small lesion (ranging from the size of a dime to a quarter), if left untreated, can hinder your ability to move free from pain, and cause deterioration to the joint surface.

Treatment with Autologous Chondrocyte Implantation (ACI)

Although cartilage in unable to repair itself on its own, advanced FDA-approved technology allows cartilage cells, know as chondrocytes to be harvested from your knee and cultured and multiplied. The fresh chondrocytes are then reimplanted in your knee and cause hyaline cartilage to regenerate. This biological repair is known as ACI. When you successfully complete ACI and rehabilitation, you should be able to resume all normal activities, including sports.

ACI, also known as carticel treatment, restores the articular surface and regenerates hyaline cartilage without compromising the integrity of healthy tissue or the subchondral bone. Carticel has demonstrated important benefits in patients with a type of lesion called a femoral focal lesion. If your orthopedic surgeon has determined that you have this type of lesion, then carticel may be an appropriate treatment option.

The procedure consists of two steps. The first is the harvesting of some healthy cartilage from you knee through and arthroscope. This sample of cartilage is used to create new chondrocytes, which take 3-4 weeks that are then reimplanted in your knee.

The second step is the reimplantation of the cultured chondrocytes, or Carticel. This procedure is done through an arthrotomy, and is depicted below.

Implantation of Carticel

Step 1: An arthroscopic biopsy – First, the surgeon examines your knee through an arthroscope – a small device that allows the doctor to see into your knee joint. If a lesion is detected, a tiny biopsy of healthy cartilage tissue will be removed.

Step 2: Cell culture processing – The cartilage sample is then sent to Genzyme Tissue Repair (GTR), where it is cultured. Cell culturing takes about 4-5 weeks, during which time your cells multiply significantly. About 12 million cells will be supplied to your surgeon at the time of your operation.

Step 3: A surgical procedure is performed, and the damaged cartilage is removed.

Step 4: Periosteum, skin that covers the bone, is sutured over the prepared defect.

Step 5 Surgical implantation – The cultured cells are then implanted into the lesion. Here, the cells may continue to multiply and intergrate with surrounding cartilage. With time, the cells will mature and fill-in the lesion with hyaline cartilage.

Post-Operative rehabilitation

To derive maximum benefit from ACI, you should adhere strictly to the personalized rehabilitation plan recommended by your physician. This will include progressive weight bearing, range of motion, and muscle strengthening exercises, which may begin as early as the day after surgery.

Chondromalacia is a diagnosis referring to damage, and subsequent pain, to the cartilage under your kneecap. It can be caused by several factors, and produces discomfort with such activities as walking up and down stairs, kneeling, squatting, or getting up from a seated position. It can occasionally produce swelling in the knee and a sensation of giving way or "catching" ("locking").

Chondromalacia is a very common problem and is directly related to the amount of pressure between the kneecap and the femur bone beneath it. This pressure is normally 2-3 times your body weight when simply descending stairs - one can imagine the magnitude of the pressure when running! All the following suggestions and treatments are directed at decreasing the pressure between the kneecap and the underlying femur.

The usual precipitating cause of pain in the patient with chondromalacia is either trauma (an injury such as a fall on the knee or a car accident) or a developmental abnormality (malalignment) of the knee, which may predispose a patient to kneecap pain. Some patients suffer from a kneecap that repeatedly dislocates (usually towards the outside of the knee), which not only causes pain, but buckling of the leg and damage to the undersurface of the kneecap.

There is a "normal" relationship between the thigh muscle, the patella, and the point of attachment of the patellar tendon. This is described by the quadriceps angle (q-angle). In those people in whom the q-angle is larger than normal, there is a greater tendency for the kneecap to track abnormally in the groove on the front of the femur with knee bending, leading to increased pressure in certain parts of the kneecap-femur joint.

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