Aspiration and Arthrograms
Aspiration is performed if there is suspicion of infection in
a hip replacement. A needle is inserted into the joint under
x-ray control, using local anesthetic. It is not particularly
uncomfortable. Fluid obtained from the hip joint is sent to the
laboratory for culture. At the same time, an arthrogram is
performed: dye is inserted into the joint to see if it spreads
to the space between the implant and bone. These tests are
helpful in ruling out the presence of infection and, in some
cases, outlining areas of loosening of an implant.
Bone Scans
There are several types of bone scans:
1. The most routine type is done utilizing Technetium
Diphosphonaten (TDP). The radioactive material is injected and
the whole body is scanned a few hours later. This test is most
useful in identifying hairline bone fractures which do not show
up on x-ray, and bone tumors. It may be helpful in diagnosing
loosening of a hip or knee implant.
2. Another scan is the Sulfur Colloid Scan. This test
evaluates the status of the bone marrow in and around the hip
joint, and can be helpful in diagnosing osteonecrosis.
3. A Gallium Scan is ordered if there is concern about
infection.
4. Another test that may be performed if infection is
suspected is an Indium-111 Radioisotope Scan. This requires
removing some of your own blood, labeling it with an isotopic
material (Indium-111) and re-injecting it. You return a day
later, and the joint is scanned. This is a relatively new
procedure, sometimes used in combination with other, more
routine types of scans. The isotopic agents are relatively
innocuous. The amount of radiation is generally not much more
than that in a single x-ray.
Magnetic Resonance Imaging (MRI)
MRI has been a diagnostic revolution. It is done using giant
magnets. No radiation is involved. It is useful in diagnosing
the early stages of osteonecrosis or in searching for bone
tumors.
CAT Scan (Computerized Axial Tomography)
This is used to search for hairline fractures, and also to
obtain additional information about the anatomy of the pelvis or
thigh bone. This technique is used to identify the amount of
bone available for performing a total hip replacement if there
is any doubt that the bone is not adequate. It is frequently
used in such conditions as congenital hip dysplasia or when a
custom type of hip prosthesis may be needed.
Epidural Injection
An Epidural Injection of dilute anesthetic agent is helpful
in determining whether a patient’s pain is coming from the hip
joint or from a pinched nerve in the back. This is a fairly
common diagnostic dilemma.
