The components of the total hip prosthesis are pushed (press-fitted or blown into) directly in the space made by the surgeon in the skeleton and held there by the elastic forced generated in the bone tissue. The form of the total hip prosthesis must be adapted for the cementless fixation.
First, the polyethylene or ceramic cups of the cementless prostheses must be enshrouded within a metallic encasing before they are pushed into the reamed space in the acetabulum. Bone tissue does not stand direct contact with polyethylene or ceramic materials of the cup and polyethylene or ceramic cup in direct contact with raw bone would loosen. These cementless cups are thus relatively thick; their wall consists of the polyethylene or ceramic inner cup ('lining') plus the metallic encasing.
The hip joint is called a ball-and-socket joint because the spherical head of the thighbone (femur) moves inside the cup-shaped hollow socket (acetabulum) of the pelvis.
To duplicate this action, a total hip replacement implant has three parts: the stem, which fits into the femur; the ball, which replaces the spherical head of the femur; and the cup, which replaces the worn out hip socket. Each part comes in various sizes to accommodate various body sizes and types.
Today, the stem portions of most hip implants are made of titanium- or cobalt/chromium-based alloys. They come in different shapes and some have porous surfaces to allow for bone ingrowth.
Cobalt/chromium-based alloys or ceramic materials (aluminum oxide or zirconium oxide) are used in making the ball portions, which are polished smooth to allow easy rotation within the prosthetic socket.
Cement fixation has a 30-year history in total hip arthroplasty. Cement fixation is a durable and reproducible means of fixation in a variety of hips. A key determinant to a cement mantle's longevity is the technique of cementing. This article reviews what has been learned in the past and outlines the state of the art in cement technique today.
The overall technique of cementing THR has evolved from first- to third-generation techniques (Table). Major improvements between these 'generations' have been stratified in terms of bone preparation, cement preparation, and cement delivery. Improvements in bone preparation include the use of a plug for compression of cement, pulsatile lavage to remove loose cancellous bone, and blood to improve interdigitation of cement to bone and proximal pressurization of the cement mantle.
Cement delivery has also been improved with the use of a cement gun to provide consistent retrograde filling of the canal followed by pressurization of the mantle. The literature supports improved outcomes in cemented THR with these improvements in cement techniques
What is a Total Hip Replacement ?
Total hip replacement surgery has become a common procedure to alleviate pain and debilitation caused by osteoarthritis, rheumatoid arthritis, fractures, dislocations, congenital deformities, and other hip related problems.
What part of the hip is replaced ?
The head (or ball) of the patient's femur and the neck of the femur (the thigh bone) are removed. An acetabular component is placed into the damaged socket. This component is a metal 'cup' lined with a polyethylene shell (a hard plastic-like inner lining). The ball of the femoral implant (or stem) fits into this cup, creating a new, movable joint.
The operation usually takes about 2 hours. The hospitalization time also is relatively short, usually about five or six days. In most cases, full recovery takes about 4 to 6 months.
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