Hip Anatomy
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."
Getting to the
Joint
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.
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Replacing the Socket
Portion of the Joint
One type of implant that replaces the socket consists of a metal
shell that is lined with a strong plastic liner. |
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Removing the Surface of the
Socket
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.
Inserting the
Implant
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.
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Replacing the Ball Portion of the Joint
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. |
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Removing the Ball
A special power saw is used to remove the damaged femoral head.
Clearing and Shaping the
Canal
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.
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Inserting the
Implant
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.
Closing the Wound
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.
