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General Joint Surgery Information
Why Are X-Rays Important After Your Total
Joint Replacement — Even If You Feel Fine?
Roger Emerson, Jr., MD
There are several reasons to get regular x-rays of your total
joint prosthesis, even if you are having no symptoms. X-rays
are the best way of following a joint prosthesis since your
orthopedic surgeon can "see" your prosthesis and the
surrounding bone. Unfortunately, the symptoms coming from a
joint prosthesis tell us little about the state of the implant
itself. Minor cases of tendonitis, for example, can mimic a
serious implant problem, and serious implant problems in early
stages produce very few symptoms. The purpose of this article
is to discuss several of these issues.
In the first few months after your joint surgery, the fixation
of the implant needs to be known in order to advise you about
weight bearing, as well as how active to be. The x-rays tell
the doctor how strong the bond to the bone has become.
Implant loosening, a rare event at this time, is best determined
by an x-ray. Early loosening will cause no symptoms. Long standing
looseness will damage the surrounding bone, and other parts
of the implant.
Over time your total joint will wear, just like a car tread
or the sole of your shoe. All of these are bearing surfaces.
The amount of wear of your implant can be measured on the x-ray.
Fortunately, prosthesis wear is very slow and your total joint
should give you pain-free comfort for many years. Minor wear
changes in the implant do not cause pain and do not affect the
function of the prosthesis, so you cannot determine the wear
status of your implant by any means other than a good quality
x-ray. Rapid or abnormal wear will severely damage the Surrounding
bone, and requires surgery for correction.
The bone surrounding your prosthesis is the support for the
prosthesis, much like the foundation of your house supports
the house structure itself. The better the bone foundation,
the more durable your prosthesis is going to be. As you can
see, it is important for you and your doctor to know the status
of the bone surrounding your prosthesis. The situation to avoid
is where sufficient damage from loosening or wear has occurred
that makes corrective surgery difficult or unreliable. Fortunately
newer implant designs and bone grafting techniques are available
for restoring implants that in the past could not be revised.
There are also normal bone changes around an implant that
develop with time. As you can imagine, placement of a total
joint prosthesis constitutes a major alteration of a hip, knee,
shoulder or elbow. You can appreciate these changes because
the new joint is more comfortable, with better motion and stability.
There are also changes in the joint that you cannot feel. These
are changes in the mechanical environment of the joint, which
are the forces coming through the operated joint.
Bone will change in response to the forces across the joint.
Orthopedic surgeons call these changes "bone remodeling."
Basically, these are the adaptive changes in the bone due to
the presence of the prosthesis. The prosthesis alters the normal
weight transfer across the joint, and this is reflected in the
bone itself. The more normal the weight-bearing forces, the
fewer changes in the bone structure. I am sure that you have
heard that prolonged weightlessness in outer space has effects
on the bones of astronauts. This is the same type of response
that we see surrounding a total joint prosthesis. These remodeling
changes occur over several years time. Only rarely do we think
that these remodeling changes can cause symptoms or adversely
affect your implant. The best x-ray schedule for all implants
is yearly for the first few years, during the "break-in
period" to monitor the fixation of the implant to the bone,
and then every two to three years thereafter to assess the bone
remodeling and implant wear.
We recognize though that travel to Dallas is difficult for
some of you. In these cases, we are happy to coordinate with
your local doctor and will gladly check any x-ray that is sent
to us and send you a letter reviewing the status of your implant.
Before going to your local doctor, please call us so we can
make sure that the correct x-ray technique is used.
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