'joint surfaces'

Arthritis is a degenerative condition that occurs due to wear & tear of the articular surfaces of joints. It can be caused by degenerative process (osteoarthritis), inflammatory process (rheumatiod arthritis, ankylosing spondylarthropathy, connective tissue diseases, etc.) or incongruity of joint surfaces (post-traumatic arthritis, avascular necrosis, developmental dysplasia, etc.). The wear & tear process of arthritis is progressive and can be slowed down by modification of activities, weight-reduction, anti-inflammatory medications (in case of inflammatory arthritis) and correction of deformities (like bow-leg deformity). However it cannot be completely stopped and the joint continues to wear out in spite of treatment.

In a total hip replacement, the worn out surfaces are replaced by artificial device (prosthesis). The socket is replaced by a hemispherical cup which has a metallic shell and an inner high-density polyethylene liner. The head is replaced by a metal sphere supported on a tapered stem which fits into the bony canal of the femur. The implants have specially textured surface which allows them to grip the bone. Sometimes acrylic bone cement is also used to fix the implants.

Total knee replacement involves removing the worn-out joint surfaces and implanting prosthetic device in place of the damaged surfaces. Only 8 -10 mm of the damaged bone surface is removed. The shape of the implants (prosthesis) closely matches the amount of bone removed. The femoral component is made of metal and has a bi-condylar shape. The tibial component consists of an oval shaped metal tray with a highly cross-linked polyethylene inset. The patellar component is a circular polyethylene disc with convex surface. Resurfacing of the knee cap is optional. The implants are fixed using acrylic bone cement.