Hip & Knee Replacement

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Artificial Joint Replacement of the Hip

Introduction

A hip that is painful as a result of osteoarthritis (OA) can severely affect your ability to lead a full, active life. Over the last 25 years, major advancements in hip replacement have improved the outcome of the surgery greatly. Hip replacement surgery (also called hip arthroplasty) is becoming more and more common as the population of the world begins to age.

Rationale

The main reason for replacing any arthritic joint with an artificial joint is to stop the bones from rubbing against each other. This rubbing causes pain. Replacing the painful and arthritic joint with an artificial joint gives the joint a new surface, which moves smoothly without causing pain. The goal is to help people return to many of their activities with less pain and greater freedom of movement.

The Artificial Hip

There are two major types of artificial hip replacements:

cemented prosthesis
uncemented prosthesis

A cemented prosthesis is held in place by a type of epoxy cement that attaches the metal to the bone. An uncemented prosthesis bears a fine mesh of holes on the surface that allows bone to grow into the mesh and attach the prosthesis to the bone.

Both are still widely used. In some cases a combination of the two types is used in which the ball portion of the prosthesis is cemented into place, and the socket not cemented. The decision about whether to use a cemented or uncemented artificial hip is usually made by the surgeon based on your age and lifestyle, and the surgeon's experience.

Each Prosthesis is Made of Two Main Parts:

The acetabular component (socket) replaces the acetabulum. The acetabular component is made of a metal shell with a plastic inner liner that provides the bearing surface.

The femoral component (stem and ball) replaces the femoral head. The femoral component is made of metal. Sometimes, the metal stem is attached to a ceramic ball.

Artificial Joint Replacement of The Knee

Introduction

A painful knee can severely affect your ability to lead a full, active life. Over the last 25 years, major advancements in artificial knee replacement have improved the outcome of the surgery greatly. Artificial knee replacement surgery (also called knee arthroplasty) is becoming increasingly common as the population of the world begins to age.

Rationale

The main reason for replacing any arthritic joint with an artificial joint is to stop the bones from rubbing against each other. This rubbing causes pain. Replacing the painful and arthritic joint with an artificial joint gives the joint a new surface, which moves smoothly and without causing pain. The goal is to help people return to many of their activities with less pain and with greater freedom of movement.

The Artificial Knee

There are two major types of artificial knee replacements:

cemented prosthesis
uncemented prosthesis

Both are still widely used. In many cases a combination of the two types is used. The patellar (kneecap) portion of the prosthesis is commonly cemented into place. The decision to use a cemented or uncemented artificial knee is usually made by the surgeon based on your age, your lifestyle, and the surgeon's experience. The tibial component (bottom portion) replaces the top surface of the lower bone, the tibia.

This component is usually made of two parts - a metal tray that is attached directly to the bone and a plastic spacer that provides the slick surface. The femoral component (top portion) replaces the bottom surface of the upper bone (the femur) and the groove where the patella fits. This component is made of metal.

The patellar component (kneecap portion) replaces the surface of the patella where it glides in the groove on the femur. The patellar component is usually made of plastic as well. In some types of knee implants, the patellar component is made of a combination of metal and plastic.

In the uncemented prosthesis, the metal piece is held snugly onto the femur because the femur is tapered to accurately match the shape of the prosthesis. In the cemented variety, an epoxy cement is used to attach the metal prosthesis to the bone.

Submitted By
Dr. Jeffrey Chew Tech Hock, MBBS. Med, FRCS, FICS.

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