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Pathology During the surgical procedure, these two
parts of the hip joint are removed and replaced with smooth
artificial surfaces. The artificial socket is made of high-density
plastic, while the artificial ball with its stem is made of a strong
stainless metal.
These artificial pieces are implanted into healthy portions of
the pelvis and thigh bones and affixed with a bone cement (methyl
methacrylate).
Cementless total hip replacement
An alternative hip prosthesis has been developed that does not
require cement. This hip has the potential to allow bone to grow
into it, and therefore may last longer than the cemented hip. This
is an important consideration for the younger patient. In some
cases, only one of the two components (socket or stem) may be fixed
with cement and the other is cementless. This would be called a
"Hybrid" hip prosthesis.
When do we consider total hip replacements?
Total hip replacements are usually performed for severe arthritic
conditions. The operation is sometimes performed for other problems
such as hip fractures or aseptic necrosis (a condition in which the
bone of the hip ball dies). Most patients who have artificial hips
are over 55 years of age, but the operation is occasionally
performed on younger persons. Circumstances vary, but generally
patients are considered for total hip replacements if:
- pain is severe enough to restrict not only work and
recreation, but also the ordinary activities of daily living
- pain is not relieved by arthritis (anti-inflammatory)
medicine, the use of a cane, and restricting activities
- significant stiffness of the hip
- x-rays show advanced arthritis, or other problems
What can be expected of a total hip replacement?
A total hip replacement will provide pain relief in 90 to 95
percent of patients. It will allow patients to carry out many normal
activities of daily living. The artificial hip may allow you to
return to active sports or heavy labor under your physician's
instructions. Most patients with stiff hips before surgery will
regain near-normal motion, and nearly all have improved motion.
What are the risks of total hip replacement?
Total hip replacement is a major operation. The effect of most
complications is simply that the patient stays in the hospital
longer. The most common complications are not directly related to
the hip and do not usually affect the result of the operation. These
include:
- blood clots in the leg
- urinary infections or difficulty urinating
- blood clots in the lung
Complications that affect the hip are less common, but in these
cases, the operation may not be as successful:
- difference in leg length
- stiffness
- dislocation of hip (ball pops out of socket)
- infection in hip
A few of the complications, such as infection or dislocation, may
require reoperation. Infected artificial hips sometimes have to be
removed, leaving a short (by one to three inches), somewhat weak
leg, but one that is usually reasonably comfortable and one on which
you can walk with the aid of a cane or crutches.
How do artificial hips stand up over time?
As we noted earlier, 90 to 95 percent of hip replacements are
successful up to 10 years. The major long-term problem is loosening
of the prosthesis. This occurs either because the cement crumbles
(as old mortar in brick building) or because the bone melts away (resorbs)
from the cement. By 10 years, 25 percent of all artificial hips will
look loose on x-ray. Somewhat less than half of these (about 5% to
10% of all artificial hips) will be painful and require revision.
Loosening is in part related to how heavy and how active you are.
It is for this reason we do not operate on very obese patients or
young, active patients. Loose, painful artificial hips can usually,
but not always, be replaced. The results of a second operation are
not as good as the first, and the risks of complications are higher.
Dislocation of THR
- occurs in 1-4% of primary THA and upto 16% in revision cases;
- about 74% of THR dislocations are posterior, 16% anterior, and 8%
lateral; (from T.K. Cobb et al, 1996);
- most commonly caused by looseness of hip (improper neck length),
and component malposition (combined
retroversion --> posterior dislocation, vs combined anteroversion
--> anterior dislocation);
- dislocation is much more common in revision THA;
- careful testing w/ trial components w/ correction of neck lengths
w/ correction of neck length, impingement, &
repair of trochanter may avoid this complication;
- dislocation may be more common in radiation therapy osteonecrosis,
and acetabular components should be
placed more horizontally in these patients;
- acetabular liner:
- as noted by Cobb et al 1996, the presence of a high wall liner can
reduce the incidence of dislocation in primary THR from about 3.8%
to 2.2%
- the beneficial effect is probably higher w/ revision surgery;
- paradoxically, the high wall liner may actually increase the
incidence of anterior dislocation (due to impingement between
femoral neck and the elevated lip of the liner);
- liners may also contribute to increased polyethylene wear;
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