If standard x-rays do not indicate hip problems, the following additional tests are available:
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.
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.
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.