Primary Total Hip Replacement
Primary Total Hip Replacement is a surgical procedure in which the worn-out joint is replaced with artificial components. The hip joint is one of the body's largest weight-bearing joints, located between the thigh bone (femur) and the pelvis (acetabulum). It is a ball and socket joint in which the head of the femur is the ball, and the acetabulum forms the socket. The femoral head and the acetabulum are covered by a smooth connective tissue layer called articular cartilage. The hip joined is also lined up by a thicker connective tissue layer called the labrum. Together, the labrum and the articular cartilage provide shock-absorbing effects and facilitate movements of the joint. Repetitive wear and tear, injury, inflammatory disorders, developmental deformities, and other diseases of the joint can damage the hip joint, resulting in pain and difficulty performing daily activities. Total hip replacement surgery is an option to relieve severe pain due to degenerative hip disease.
During the procedure, an incision is made over the hip to expose the hip joint, the femoral head is dislocated from the acetabulum and then resected. The surface of the socket is prepared with a hemispherical reamer. The acetabular component is then inserted into the prepared surface and sometimes augmented with screws to hold the fixation. A plastic, ceramic or metal liner is placed inside the acetabular component. The femur is then instrumented and subsequently fitted with a prosthetic femoral component. The femoral component is secured into the femoral canal either by a press fit (cementless) technique or using bone cement. Finally, a femoral head component is secured onto the femoral stem and the hip joint is reduced. The muscles and tendons around the new joint are repaired and the incision is closed.
Components of a Hip Implant
The components of a hip replacement replicate the natural shape and structure of the ball-and-socket joint. The components used may depend on the size of the body and vary from patient to patient. A total hip replacement usually has four parts:
- Stem: The stem fits into the femur.
- Ball: The ball replaces the spherical head of the femur.
- Cup: The cup replaces the worn-out hip socket.
- Liner: The liner acts as a bearing interface between the cup and the ball.
Any of the following types of articulations may be used during total hip replacement:
- Metal-on-polyethylene articulation involves the use of a metal ball and a polyethylene liner.
- Ceramic-on-polyethylene articulation involves the use of a ceramic ball and a polyethylene liner.
- Metal-on-metal articulation involves the use of a metal ball and a metal liner.
- Ceramic-on-ceramic articulation involves the use of a ceramic ball and a ceramic liner.
Types of Implant Fixation
Depending on certain patient factors, such as the quality of bone, any of the following three types of fixation can be used:
- Cemented Fixation: The femoral and acetabular components are held together with special bone cement. The bone cement is made from a polymer called polymethylmethacrylate. Cemented fixation is an option for patients with weak bones.
- Cementless Fixation: Cementless implants are coated with a porous material that allows new bone to grow on the surface of the implant. Cementless fixation is an option for patients with good bone quality.
- Hybrid Fixation: Hybrid fixation uses a combination of cemented and cementless fixation, usually the acetabular socket is inserted without cement and the femoral stem is inserted with cement.
Below are before (left) and after (right) X-rays of a sixty-two-year-old woman showing severe arthritis of the right hip (left side on image) that was treated with a total hip replacement using press-fit (cementless) fixation. Two screws were used to augment the fixation of the socket. This patient had a ceramic head on a polyethylene liner.
Below are the before (left) and after (right) X-rays of a 56-year-old female who presented with advanced posttraumatic left hip osteoarthritis. Total hip replacement with removal of hardware was performed.
Below are the before (left) and after (right) X-rays of a 44-year-old male who presented with advanced posttraumatic left hip osteoarthritis. Total hip replacement with limited removal of hardware was performed.
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