Investigations are tests that can be performed in order to diagnose a condition. In orthopaedics, investigations are generally very straightforward. The most common investigations we use are x-rays, computer tomography scans (CT scans), magnetic resonance imaging (MRI) and ultrasound scans. In complicated cases, we may also use diagnostic injections and even diagnostic arthroscopic surgery. But the latter two are rather unusual.
X-rays are commonly used to diagnose bone and joint issues. The use of x-rays was first described by German scientist Wilhelm Röntgen in 1895. Since then, they have been, and still are used extensively in orthopaedics! While x-rays are excellent imaging modalities to visualise bones, they are not so useful for soft tissue problems. This is because while bones are well seen on x-rays, soft tissues are either not visible on x-rays or simply appear as vague shadows. I often tell patients that while x-rays can be invaluable in giving me a “bird’s eye view” of the problem, I often require more information in order to give the best treatment recommendation. I usually order x-rays if I would like to know if the patient has a cracked or broken bone, if the patient has arthritis (destruction of a joint), or if I would like to know the severity of a malalignment of a damaged joint so that I know how much correction is required. If more details about a broken bone, for example, is required, a CT scan is usually done. X-rays are generally very safe, quick and painless. Taking one view is as fast as taken a picture on your phone camera. But often at least 2 views of a bone or joint are required. The amount of radiation one is exposed to from x-rays is very minimal. You will receive about the same amount of radiation in a single x-ray as you would if you took a 10 hour flight from Singapore to New Zealand (yes, flying does expose you to radiation!).
CT scans are basically multiple x-rays taken in many different directions. The information is that fed into a computer which then generates images in various cross-sections. They are even capable of producing 3 dimensional images! CT scans give extremely clear views of bones and are the investigation of choice if clear details of bones or fractures are needed. If, for example, a patient fell and requires surgery to fix the bone, I will often order a CT scan. It will show me exactly how the fracture looks which will then allow me to carefully plan how I will go about piecing the bone together and fixing it. Patients are required to lie on a bed and the scanner spins around the patient within the doughnut shaped machine as the bed moves the patient in and out of the machine. The machine does not feel “enclosed” and hence patients tolerate CT scans very well. CT scans are painless and safe as well. But understandably, they expose the patient to greater doses of radiation. A CT scan may be equivalent to 100 to 300 x-rays! Having said that, the chances of getting cancer from radiation received from a CT scan are extremely, extremely remote. Do not be put off by the amount of radiation received. If the scan is required for optimal treatment, it would be most unwise not to do it for fear of radiation!
The attached images show standard x-rays, CT scan and 3D reconstructed CT images in the same patient. You will be able to appreciate the level of clarity provided by CT imaging. An example of a typical CT scan machine is also shown.
Ultrasound scans rely on a probe that a trained sonographer or radiologist applies on the part of the to be scanned. The probe emits ultrasound waves which bounce off different tissues in the body to different extents. The waves are then received by the probe and a computer converts the signals from the waves into moving images that can then be seen and interpreted.Ultrasound scans are relatively quick and can be a great imaging modality. They are used for soft tissue problems such as tendon tears, muscle injuries, nerve problems etc. They are not useful for bony issues such a fractures or arthritis. They are non-invasive and comfortable for the patient. Another advantage of the ultrasound scan is that it is very useful when problems are apparent when moving. For example, some patient may feel a clicking sensation when they bend their knees. With an ultrasound, the patient can bend the knee to demonstrate the clicking sensation while the sonographer images the knee. It is possible to sometimes see a mass moving in the knee while the patient moves the knee!The biggest drawback of the ultrasound scan is that the results of the scan are only as accurate as the experience and skill of the sonographer. It is a lot harder to simply look at the still images or films and decipher the problem (Fig 3). In addition, ultrasound scans cannot penetrate bones so details within a joint will be obscured. Deeper structures are also not well seen. As such, ultrasound scans are some of my most infrequently ordered scans.
The attached images show a typical ultrasound image seen in a patient with tennis elbow and a small bone spur. It also shows how an ultrasound examination of a knee is performed.
MRI scans involve using strong magnetic fields which causes different types of atoms within cells to spin differently. This is then picked up by a radiofrequency coil in the machine and a computer then interprets the changes in signals as images. The exact way that an MRI machine works is very complicated and is not well understood even by most medical professionals, me included! But the images that an MRI scan produces are extremely detailed and can usually pick up problems with a 95-98% accuracy, and orthopaedic doctors are very familiar with interpreting MRI scan images. They are the investigation of choice for me as they give me the information I require to decide the best form of treatment for patients.MRIs do not expose patients to radiation. Hence they are safe even if you should do multiple MRI scans in a short span of time. For most orthopaedic conditions, “plain” MRIs will suffice. This means there is no need to inject patients with any drugs or contrast, so there is no risk to patients. There are some drawbacks to MRI scans though. Patients need to lie very still in a rather cramped tube throughout the duration of the scan. The scan often takes anything from 30 minutes to over an hour, depending on the region or regions to be scanned. In addition, the patient must lie absolutely still, otherwise images produced will be blurred and the MRI technician may have to repeat that part of the scan, further prolonging the duration of the scan. Furthermore, some patients who have metal implants or foreign objects in their bodies may not be suitable to undergo MRI scans due to risk of either the metal implants migrating or heating up. Most modern metal implants used in orthopaedic surgery, however, are MRI safe and patients can still have MRI scans done even if they have such implants put in from previous surgeries.Another common problem that patients encounter is due to the fact that the tube in which patients have to lie for the duration of the scan is rather narrow. Some large patients may not fit in the tubes. Others may have no problems fitting in the tubes comfortably but may experience anxiety in enclosed spaces (claustrophobia) and may not be able to tolerate the scan. The problem of claustrophobia is actually much more common than you might think. Alternatives to such “traditional” MRI scans do exist. Extremity MRIs are smaller MRI machines that are designed for scans of the extremities like the arms and legs. However it is not possible to scan areas such as the neck, back, shoulders and hips in extremity MRI scanners. Open MRIs are MRI machines that do not require patients to lie within a small confined tube. They are great conceptually, but I have found that image quality in such MRI machines tend to be very poor, making accurate diagnosis very difficult. For most patients with claustrophobia, taking medications before the scan is generally very effective in helping patients to cope and tolerate the scan.The attached images show a typical MRI scan image of a patient with a torn rotator cuff tendon. It also shows what a traditional MRI machine looks like versus an extremity MRI scan machine.
Diagnostic injections are not often performed although I do find that they can be very useful. The procedure involves injecting a small amount of local anaesthetic into the area where the patient is experiencing pain. If the pain is either reduced or completely alleviated by the injection, that is a sure sign that that particular site is where the problem lies. This may sound like something completely unnecessary and you might be thinking,” Well, if the scan shows a problem, obviously that is where the pain is!” But it is not unusual for an MRI scan to pick up multiple abnormalities. A patient may have, perhaps, 6 problems identified by an MRI scan. And all these problems may be within a single joint! Usually only one or 2 of the problems may be causing the patient pain, while the others may simply be “wear and tear” issues that are asymptomatic and completely irrelevant to the current issue. Undertaking surgery on all the 6 problems would result in a lot of unnecessary and extensive surgery. In such patients, a diagnostic injection would be most helpful in giving me the confidence that any surgery I perform will be targeted at the correct issue.
A diagnostic arthroscopy is the most uncommon investigation that I undertake. It involves a minor surgery, during which the patient is put under anaesthesia and I perform a keyhole surgery, inserting a small camera into the joint to visually inspect it for problems. (You may find out more about keyhole surgery or minimally invasive surgery by reading the section on it). You might recall that even an MRI scan, being the most sensitive and thorough investigation, is about 95 – 98% sensitive. That still leaves 2 – 5% of patients in whom the scan may not pick up the problem. It is hence possible that some patients may experience pain and problems with a certain joint, seek help from various doctors, try courses of physiotherapy, do various scans including MRI scans and yet have no good diagnosis or explanation as to why they continue to experience pain in that particular joint. In these patients, I have performed diagnostic arthroscopy surgeries to visually inspect and probe the joint in question. The decision to operate on these patients is not taken lightly and I only broach this option when all other investigative options have been performed, to no avail. In almost all of these patients, we would have had a long chat and usually the understanding is that I will perform the keyhole surgery and if a problem is identified, I am given permission (by the patient) to proceed with therapeutic surgery to fix the problem on the spot. I have never, till date, encountered any patient who objected to giving me the discretion to fix the problem because that would mean he/she will need to undergo another surgery later on to fix the problem that I had identified! I always advise patients that a diagnostic-cum-therapeutic arthroscopy is a bit of a “gamble”. In many of such cases, I have identified a problem and I have managed to fix the problem resulting in a favourable outcome. But in a few patients, I have not managed to find any obvious problem. In such patients, unfortunately, they will have to accept that all options have been exhausted and the cause of their pain cannot be identified. Clearly this is not an optimal outcome, but unfortunately medical science is still not (and probably will never be) perfect and there are still many unknowns.
The easy availability, high sensitivity and accuracy of modern day investigations have made precise diagnosis possible in most cases. Before launching into any treatment modalities, your doctor will certainly want to confirm his/ her suspicion. Do have a chat with your doctor about what is the most suitable investigation modality for your problem.
The above information is meant to be used as a guide and for patient education purposes. This article is not meant to be a used for self diagnosis or a substitute for professional medical evaluation or advice. As patients may be differing symptoms, please see your family doctor or orthopaedic specialist if you have any symptoms or worries.
Ask and get some answers!