The knee joint is one of the largest and most complex joints of the body. It is a hinge type of joint that allows movement to occur between the lower end of the thigh bone (femur) and upper end of the leg bone (tibia). It has the knee cap (patella) in the front which improves the mechanical efficiency of the quadriceps apparatus. The movements occur mainly in one plane (flexion – extension) but a few degrees of rotation are also possible. The knee has a set of strong ligaments which control these movements and give it stability. Between the femur and the tibia are two semicircular pieces of special cartilage called as menisci which act as shock absorbing cushions. This complex mechanism allows a wide range of activities like walking, running, jumping, sitting and squatting.

The lower end of the femur, upper end of tibia and the undersurface of the patella are covered with articular cartilage. This special cartilage allows the normal painless movements that occur in our joints. With age, injury or disease, this smooth articular cartilage begins to wear off and the bone ends become roughened. When two rough bone surfaces rub against each other it produces pain, swelling and limitation of movements. This is known as Arthritis.

Knee joint replacement surgery involves replacing the lower end of the femur and the upper end of the tibia with an artificial joint made of metal and plastic. This artificial joint has smooth surfaces which results in reduction of pain and improvement in the range of motion. Sometimes the patella also needs to be resurfaced with a plastic button.

A Total Knee prosthesis is made up of the following components:

• Femoral component made up of a metal alloy which resurfaces the lower end of the femur.
• Tibial component: This can be of different types
  • A single piece component made of plastic – all polyethylene component.
  • A two piece component consisting of a metal alloy base plate and a plastic insert. The plastic insert may either be fixed to the metal base plate (fixed bearing TKR) or it may rotate on the tibial base plate (mobile bearing TKR).
• Patellar component made up of plastic which resurfaces the undersurface of the patella.

In majority of the cases these components are fixed to bone using bone cement.

There are many different designs of knee prosthesis available and your surgeon will choose the one considered most suitable for you.  However, the final decision may need to be made during the time of your operation.

There are a number of conditions that can result in a patient having to undergo knee replacement surgery.

PRIMARY OA: commonly referred to as 'wear and tear arthritis'. Osteoarthritis can occur with no previous history of injury to the knee joint. The knee simply 'wears out'. There may be a genetic tendency in some people that increases their chances of developing osteoarthritis. 90% knee replacements are for this type of arthritis.

SECONDARY OA: arthritis develops secondary to an underlying disorder or following a significant injury of the knee joint

INFLAMMATORY ARTHRITIS:

• Rheumatoid Arthritis
• Seronegativespondyloarthropathy (ankylosing spondylitis, psoriasis)

Surgery to replace the knee joint is usually recommended when:

• Pain becomes:
  
  • Severe, unremitting
  • Not responding to conservatives means
  • Night pain which disturbs sleep
  • Affects activities of daily living
• Restriction of motion
• Deformities of the joint develop affecting function

The aim of knee replacement surgery is to:

• Relieve your pain.
• Correct any deformity.
• Provide stability to your joint.
• Restore loss of movement & function in your knee.
• Increased leg strength (if you exercise)
• Improve your quality of life.

• Infection
• Persistent pain
• Instability / Dislocation
• Stiffness
• Leg length inequality