Knees

Investigations

Are they necessary? :: Blood tests :: X-Rays :: CAT scans
:: MRI scans :: Nuclear medicine

Why are they ordered?

A small number of disease processes can be diagnosed by your doctor after an adequate history has been taken and the doctor has examined you. However, many more diseases are not discreetly identifiable with merely your doctor's history and examination and you must rely on extra information that he can obtain. This extra information is either obtained through pictures of the inside of your body (radiological investigations) or blood tests which give information on how your body may be reacting to any disease processes.

Armed with the history and physical examination and the results of further investigations, the doctor has a better chance of accurately diagnosing your condition and therefore treating you appropriately.

Blood Tests; Why do I need them?

Blood tests are divided into three main groups

1. Haematological investigations (looking at your blood count)
2. Electrolyte investigations (looking at the elements and irons in your blood)
3. Specific tests

1. Haematological Investigations

Your blood count is routinely performed before any major surgical operation to ensure that your body is optimally fit for the surgery. A low blood count or red cell count may mean that your body is unable to get adequate oxygen to the cells at the time of surgery. There are a number of different types of blood cells that circulate in your body that react in different ways to different diseases. Your white blood cells increase in response to infection. Thus, if your doctor sees a raised white blood cell level, this will increase the suspicion of infection in the clinical setting of the pain and suffering that you may be encountering.

2. Electrolyte Levels

Electrolyte levels are again routinely performed prior to major operations as abnormal electrolyte levels are associated with increased risk of cardiac arrhythmias and other muscle dysfunctions. These abnormalities are often correctable prior to any major operative procedure. Also different electrolytes and chemicals within your body may again reflect disease specific to different organs of the body. Some chemicals may suggest raised levels of some chemicals may suggest a problem with the bones, while other suggest problems in the liver, kidney, prostate, bladder or heart. Again the doctor uses the results of these investigations in conjunction with the history and clinical examination that have been performed to aide in more accurately diagnosing the disease process.

3.Specific Tests

Over the last decade, with advances in modern technology, a large number of disease specific tests have been identified and are now routinely performed as part of baseline screen and specific marker tests. Tests such as a raised ESR or (erthyrocyte sedimentation rate) or CRP may indicate general markers of infection somewhere in the body. Other tests such as a PSA or prostate specific antigen, may indicate abnormality within the prostate gland. Other specific marker tests are available for heart and liver function problems as well as others for bone disease. Any specific tests are now commonly used for any specific tests now being developed as diagnostic tests for different types of malignancies.

X-rays

X-rays or radiographs are the oldest available non-invasive method of obtaining pictures of the inside of a body. They are still commonly used today and provide excellent valuable information with regard to the bony or skeletal structure. X-rays provide us with a two dimensional picture much like a shadow of the bones with a faint outline of the soft tissues. They involve the use of ionising radiation which is transmitted in a beam form and impacts on a silver impregnated film. Once this film is developed, it gives excellent pictures of the bony or skeletal structure.

X-rays are usually used in the identification of fractures. Many fractures are able to be treated without operations in plasters and your doctor may bring you back at weekly intervals for check x-rays. In the early stages of fracture healing, there is a possibility that even though the bone or limb is encased in plaster that the fracture may move to an unsatisfactory position. It is common practice in many fractures for the doctor to perform weekly x-rays for the first two to four weeks, depending on the fracture. At the end of this stage, the fracture is usually sticky and unlikely to move and will not require such frequent x-rays. Further films are then usually performed to ensure that the fracture has united prior to or just after removal of the plaster.

X-rays are also commonly used to examine pain in major body joints in both the arms and legs. The x-rays only provide a good picture of the bones but from the reaction to the bones around the joint, the doctor can often determine useful information with regard to the status of that joint. The gap between the two bones at the hip joint or the knee joint is normally filled with articular cartilage (a very smooth low friction pain free joint surface). If this articular cartilage is not able to be visualised on the x-ray and thus appears as a transparent gap. If this cartilage has been lost in an arthritic condition, this gap in either the hip or knee joint may be lost or decreased in height. Further to this, with arthritis in the hip or knee there are often particular changes in the bone around the joint that the doctor is looking for to identify wear and tear arthritis (or osteoarthritis) as distinct from the inflammatory arthritis (or a rheumatoid arthritis). Your doctor has been specifically trained to interpret these films and in light of your clinical findings and history will be able to elicit valuable information for your ongoing treatment.

Unfortunately x-rays do not show good pictures of soft tissue structures such as ligaments, menisci or muscles and significant pathology within the soft tissue structures is often not found on plain radiographs. Thus, there is a need for further specific investigations depending on the pathology that the doctor is looking for.

CAT Scans (Computerised Axial Tomography Scans)

CAT scans are a computerised form of x-ray and involves the patient lying on a table where a very fine x-ray beam travels inside a gantry and provides very good fine slice pictures through the body. With modern computerised technology these pictures can then be reassembled in the computer to give an excellent three dimensional image. CT scans are very useful in providing further information on bony detail and do give accurate information on some soft tissue problems. CT scans also involve ionising radiation but are relatively quick and easy to perform. CT scans are often used to provide information on the spine such as spinal stenosis or disc protrusion.

MRI

What is it?

MRI stands for 'magnetic resonance image'. It is a special type of scan. In the spine it is used to look at the nerves and discs, which don't show up on normal x-rays. It shows these structures better than a CT scan, and can also look at the spine in more directions than a CT scan can.

How is it done?

It is performed in a very specialised scanning machine. The test is done by a radiographer (an x-ray technician). A radiologist (a doctor who is an x-ray specialist) supervises the test and then reads the scans. The MRI machine is like a CT scanner as you lie on a table that slides in and out of a narrow tunnel. The machine uses a very strong magnetic field and radio waves rather than normal x-rays. This means there is no radiation and the test is very safe.

What are the risks?

Because it uses a magnet, there are some people that cannot have an MRI. These include people with pacemakers, metal aneurysm clips in their brain, and particles of metal in their eye. People who have worked with metal such as with welding or grinding may need to have an x-ray of their eyes to make sure there are no metal fragments there. Precautions sometimes need to be taken if people have had heart, brain or eye surgery. Hearing aids and dentures may need to be removed.

The tunnel in the machine is quite small. This is a problem for large people and those who are claustrophobic. If you suffer from severe claustrophobia you can be given sedation to calm you before the test. This can be either tablets or an injection. If any of the above problems apply to you, you need to contact the Radiology Department before the scan, as well as tell the radiographer when you arrive.

What will happen during the test?

You will be asked to change into a gown. You must leave your watch, jewellery, keys, purse or wallet and credit cards outside the scan room, as the magnet may affect your watch and erase your credit cards! You will then lie on the scan table and move into the tunnel. You will need to lie as still as possible. While the machine is scanning it makes a loud humming and knocking noise. You can choose to wear headphones and listen to music during the scan. Sometimes a special magnetic dye (not iodine like for other scans) is injected into a vein through a needle in the back of your hand for the scan. The scan usually takes about half an hour. When they are finished, the scans will be reported and then sent to your doctor.

How much does it cost?

This depends on who orders the test and where you have it done. If the test is ordered at this practice and done either at the Holy Spirit or St Andrews hospitals, there is usually a gap to pay on the day of $75. In some circumstances, you will have to pay the whole amount (about $500). In most cases you will be able to claim most of this amount back on Medicare. If the scan is for a work-related injury, approval must be obtained by your doctor from WorkCover before they will pay for it. There are special arrangements for scans for a medico-legal report and for Veteran's Affairs. Please ask your doctor if there is any doubt.

Nuclear Medicine Scans

Valuable information of skeletal or bony problems can often be obtained with the use of nuclear medicine bone scans. A bone scan of Technician bone scan or white cell labelled scan involves the injection of a minute amount of radioactive chemical into the blood stream. This is similar to a normal needle. This radioactivity is specially marked so it is taken up by cells in the bone that are active. A number of hours after having the injection, the patient is called back and placed in front of a gamma camera that measures radioactivity and then produces a picture of radioactivity in the body. This does not produce a sharp accurate picture as do radiographs, CT scans or MRI scans but shows a more dynamic picture of bony activity and turnover. There are a number of conditions that cause increased bony turnover in the body. Your doctor would be the best person able to discuss these conditions with you. Specific white cell labelled scans are thus more complex to perform and will require the radiology laboratory to take a small amount of blood which is then treated with radioactivity before being re-injected. These white cell labelled scans are more specific and active for bony infection and give good indicators in this light.

There is no need to worry about being injected with a small amount of radioactive isotope as this is rapidly broken down and there is no trace within the body within 24 hours. There is no documented side effects to this small amount of radioactivity that is introduced to the body.