Hip Implant Basics

Total hip replacement is considered to be an effective treatment option for patients suffering from osteoarthritis of the hip. In the case that the patient decides to go in for a surgery, it is important to have a detailed conversation with the orthopedic surgeon regarding the hip implant to be used to ensure the best fit.

During the procedure, the orthopedic surgeon will replace the damaged cartilage and bone of the hip joint and replace it with an artificial implant. The hip implant will replicate the movements of the ball and socket hip joint, enabling it to function smoothly.

A hip implant has 4 parts:

Stem: The patient’s diseased femoral head is replaced with the stem, which fits into the centre of the thigh bone or the femur. The stem is made out of metal.

Head or Ball: The head fits into the top of the femur bone, which is shaped like a sphere. It is attached or welded to the stem during the surgery.

Shell: The shell or the cup of the implant replaces the acetabulum. There have been many advancements made on the coating of the shell, which can now promote natural bone growth.

Liner: The liner of the implant is used to lock the shell in place. The surface of the liner touches and articulates with the ball.  The liner can be metal, ceramic or polyethylene (high sturdy grade of plastic).

The Implant "Bearing"

The “bearing surface” of the implant refers to the area where the “ball” or head of the femur connects to the “socket” or acetabulum of the hip joint. (Visit the Hip Anatomy section for more information on the femur and the acetabulum). This is a very important component of the implant since the bearing surface provides the “ball” a smooth area where it can slide and rotate easing mobility and range of motion for the patient.  The bearing surface of the implant may impact the outcome of the hip replacement surgery significantly as it directly affects the longevity of the implant and the range of motion and flexibility that the patient can achieve post-surgery.

Today's bearing materials offer excellent performance. Surgeons can choose the materials best suited for each patient. The bearing is where the weight and motion of the body are transferred from the pelvis to the femur. This is similar to the function of ball bearings used in moving parts of machines. The bearing is important because it affects how well the hip replacement will perform. Today, due to innovations in orthopedic technology, doctors can choose from a combination of polyethylene, metal or ceramic materials to create the appropriate bearing surface for the patient. The section on Types of Hip Implants will shed more light on the different kinds of bearing surfaces and their pros and cons.