Knees for You Guide to Knee Replacement

Common Knee Problems by Dr. Bose

Injuries due to sports or accidents while driving a two wheeler causing tear of the ligaments of the knee joint is common. Ligaments are structures which stabilize joints. They are cord like bands of connective tissue and resist abnormal movements between the bones of the joints. When their endurance limit is exceeded, they fail and this leads to instability. In the knee there are four ligaments binding the thigh bone to the shin bone. These are the anterior cruciate, the posterior cruciate, the medial collateral and the lateral collateral.

Two of them run within the knee joint cavity, the ACL (anterior cruciate ligament) being one of the two. It prevents the shin bone from sliding forward from the thigh bone in activities like coming downstairs. A hard twist or excessive pressure on the ACL can tear it, so that the knee gives out and can no longer support the body. Unless an injured ACL is accurately diagnosed and treated, the cushioning cartilage (the menisci) in the knee could be seriously damaged. Without this cushion, the thighbone and the shinbone would rub against each other, leading to further damage. - The majority of ACL injuries occur in females aged 15-25.

The PCL (posterior cruciate ligament) arises from the top of the tibia and is inserted to the inner aside of the lower end of the femur at the front. It prevents the thigh bone from sliding forwards on the leg bone or it prevents the leg bone from sliding too backwards on the thigh bone. An injury to the posterior cruciate ligament is the rarest of all ligament injuries in the knee. This is common in contact sports like football, and Kabaddi in which there is the risk of a blow to the front of the knee or twisting injury.

Post Traumatic Arthritis can follow a serious knee injury. A knee fracture or severe tears of the knee's ligaments may damage the articular cartilage over time, causing knee pain and limiting knee function.

Rheumatoid Arthritis is a autoimmune disease in which the synovial membrane becomes thickened and inflamed, producing too much synovial fluid, which over-fills the joint space. This chronic inflammation damages the cartilage and eventually causes cartilage loss, pain and stiffness. RA strikes 3% of women and 1% of men, usually between the ages of 20 and 55 years. Ankylosing spondylitis affects men between 20 and 30 years.

In the older age group the most common cause of chronic knee pain and disability is osteoarthritis, Osteoarthritis usually occurs after the age of 50 and often in an individual with a family history of arthritis. It is twice as common in women. Osteoarthritis is a degenerative joint disease, characterized by progressive wearing away of the cartilage of the joint. Due to the protective cartilage being worn away by knee arthritis, bare bone is exposed within the joint.

Surgical Treatment of Osteoarthritis of the Knee

Osteotomy Osteotomy of the knee is a method used to realign the angle at which the bones forming the joint meet. It is used as an alternative treatment to knee replacement in younger and active patients with limited arthritis. The goal of the surgery is to shift the body weight onto the better half of the joint where the cartilage is still healthy thereby relieving pain.

Partial knee Replacement This is also called unicompartmental or unicondylar knee replacement, as only one part of the knee which is the affected side is replaced with theartificial knee.

Advantage of this procedure is that the incision is smaller with less blood loss. There is more natural function at the joint as one half of the knee is preserved. Disadvantage of this procedure is that it can be performed in patients with limited arthritis only and in those who are not obese and who do not have inflammatory arthropathy. It can not be done on people who do heavy work.

Unicondylar knee replacement with fixed bearing	unicondylar knee replacement with mobile bearing

Total Knee Replacement In this procedure the diseased knee joint is replaced with an artificial implant. The lower end of the femur bone is removed and replaced with a metal shell. The end of the tibia, is also removed and replaced with a channeled plastic piece with a metal stem. A plastic may also be replaced under the surface of knee-cap.

Revision Knee Replacement The artificial knee implanted lasts for 10 to 15 years depending on the activity level of the patient. After this time the implants may start to loosen and patients complain of pain in the joint. The artificial knee will have to be replaced with new joints. This is surgically more demanding procedure.

Femoral component is made of titanium or cobalt chrome alloy.

Tibial component has a high-density polyethylene piece fixed on top of a metal alloy tray that sits on top of the cut tibial surface.

A high-density polyethylene piece replaces the underside of the kneecap in the center of the knee. Some surgeons leave the patellar surface untouched and this gives the same results to the patients.

Disadvantage: Excessive activity and extra weight can accelerate the process of wear to parts of a fixed-bearing prosthesis, causing it to loosen from the bone and become painful. This prosthesis allows maximum flexion of 110 degree at the knee joint.

High Flex Knee Prosthesis

This prosthesis accommodates greater flexion or more than 125 degree at the knee joint. Flexion of up to 155 degree can be done. For maximum results patients have to undergo intensive physiotherapy.

Advantage: Patients can sit cross legged on the floor, climb stairs with ease as also kneel down on the floor for prayers.

Disadvantage: High flexion will not be achieved in patients whose mobility is very severely restricted before the surgery

Mobile-Bearing Prosthesis

Like fixed-bearing replacements, mobile-bearing knees use three components to provide a relatively natural and even interface. The difference between them is in the bearing surface. In a mobile-bearing knee, the femoral component and tibial tray move across a polyethylene insert to create a dual-surface articulation. This helps reduce the amount of wear to the bearing and helps prevent loosening in places where the prosthesis attaches to bone. Mobile-bearing knees are also designed to allow greater rotation of the knee.

Advantage: The polyethylene bearing plate has a large contact area with the femoral component during the whole range of knee joint movement. Hence the stresses on the polyethylene bearing plate are substantially lower than the stresses on the polyethylene plate in the stabile bearing total knee prosthesis. The risk for loosening of the total knee components is low too Disadvantages. Mobile-bearing knee implants are less stable than fixed bearing. They may increase the chance of dislocation and also cost more. The most frequent cause of failure in these prostheses is the accelerated wear, destruction, or dislocation of the mobile polyethylene plate in knees with ligament and soft tissues instability.

Gender Specific Knee

Zimmer has brought forth this knee which is specifically designed for women. It is different in that it has a thinner profile and better contour to fit naturally in the female knee.

This prosthesis is made of a oxidised Zirconium, a ceramic coated metal. Advantages of this implant are.