The hip is a ball and socket joint. The ball portion of the joint is called the femoral head, and is part of the upper leg bone (femur). The socket portion is called the acetabulum, and is part of the pelvic bone. The femoral head (ball) fits into the acetabulum (socket) and moves within its natural fluid, called synovial fluid, which helps to lubricate the joint during motion.
In a healthy hip joint, the surfaces of these bones where the ball and socket rub together are very smooth and covered with a tough protective tissue called cartilage. Arthritis causes damage to the bone surfaces and cartilage. These damaged surfaces eventually become painful as they wear.
There are many ways to treat the pain caused by arthritis. One way is total hip replacement surgery. The decision to have total hip replacement surgery should be made very carefully after consulting your doctor and learning as much as you can about the hip joint, arthritis, and the surgery.
In total hip replacement surgery, the ball and socket that have been damaged by arthritis are removed and replaced with artificial parts made of metal and a durable plastic material. We call these artificial parts "implants," or "prostheses."
The patient is first taken into the operating room and given anesthesia. After the anesthesia has taken effect, the skin around the upper thigh is thoroughly scrubbed with an antiseptic liquid.
An incision about six inches long is then made over the hip joint. The incision is gradually made deeper through muscle and other tissue until the bones of the hip joint are exposed.
One type of implant that replaces the socket consists of a metal shell that is lined with a strong plastic liner.
The leg is maneuvered until the femoral head is dislocated from the socket.
A special reamer is then used to remove the damaged cartilage and bone surface from the acetabulum, and to shape the socket so it will match the shape of the implant that will be inserted.
The shell portion of the socket implant may be attached either by using a special kind of epoxy cement for bones, or by pressing the implant into the socket so that it fits very tightly and is held in place by friction. Some implants may have special surfaces with pores that allow bone to grow into them to help hold the implant in place. Depending on the condition of the patient bone, the surgeon may also decide to use screws to help hold the implant in place.
When the shell portion of the socket implant is in place, the plastic liner is locked into place inside the shell.
The implant that replaces the ball consists of a long metal stem that fits down into the femur. The metal ball is mounted on top of this stem.
A special power saw is used to remove the damaged femoral head.
The upper leg bone has relatively soft, porous bone tissue around the center. This part of the bone is called cancellous bone. It surrounds the canal, which mainly contains blood vessels and fatty tissue.
Special instruments are used to clear some of the cancellous bone from the canal, and then to mold the inside walls of the canal to fit the shape of the implant stem.
The stem implant may be held in place by either using the special cement for bones, or by making it fit very tightly in the canal. If cement is used, it is injected into the canal first, and then the implant is inserted into the canal. If cement is not used, the implant is simply inserted into the canal. Like the socket implant, the stem implant may have a special surface with pores that allow bone to grow into them.
On some implants, the stem and ball are one piece. On others, they may be two separate pieces. If the ball is a separate piece, it is usually secured to the top of the stem after the stem has been inserted.
When all the implants are in place, the surgeon places the new ball that is now part of the upper leg bone into the new socket that is secure within the pelvic bone. If necessary, the surgeon may adjust the ligaments that surround the hip to achieve the best possible hip function.
When the ligaments are properly adjusted, the surgeon sews the layers of tissue back into their proper position. A plastic tube may be inserted into the wound to allow liquids to drain from the site during the first few hours after surgery. After the tube is inserted, the edges of the skin are sewn together, and a sterile bandage is applied to the hip. Finally, the patient is taken to the recovery room.
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