To understand THR, you should be familiar with the structure of the hip joint, a ball-and-socket joint. The ball component is attached to the top of the femur (long bone of the thigh). The acetabulum (socket) is part of the pelvis. The ball rotating in the socket permits you to move your leg forward, backward and sideways, i.e., in all planes of motion.
With a healthy hip, smooth cartilage covering the ends of the thigh bone and pelvis allows the ball to glide easily inside the socket.
With a problem hip, the worn cartilage no longer serves as a cushion. As the diseased or damaged bones rub together, they become rough, and the resulting pain causes difficulty in walking.
THR consists of replacing the worn out socket with a durable plastic or polyethylene cup with or without a metal titanium shell. The femoral head is replaced with a chromium-cobalt alloy metal ball that is attached to a metal stem of titanium or chromium cobalt metal alloy.
There are several ways to fasten the components (implant to the bone) during the hip replacement procedure. With a cemented THR, the prosthesis is held in place by bone cement. In a non-cemented THR, fixation occurs as the bone grows on and into the implant surface.
Bearing surfaces include metal-on-polyethylene (plastic), ceramic-on-ceramic, and metal-on-metal. The most commonly used FDA approved bearing surface is metal with highly cross-linked polyethylene. The best bearing surface for you will be decided in consultation with your surgeon.
Clinical and biomechanical research has steadily improved the methods and materials available for THR. Prosthesis durability varies with the usage demands of each patient.