After a fall, a twisted ankle or a sore wrist that will not settle, the first scan you are offered is very often an X-ray. Sometimes you are then sent for another scan, which can feel like a setback. It usually reflects something simple: different scans show different tissues. This page explains in general terms what X-ray, ultrasound, CT and MRI are each used for in bones, joints and hands. It is not a guide to any particular injury, and the choice for you is one your doctor makes. For how the main methods compare, see X-ray, CT and MRI compared.
Why an X-ray usually comes first
RadiologyInfo.org says bone X-rays are the fastest and easiest way for a physician to view and assess bone injuries, including fractures, and joint abnormalities such as arthritis. A bone X-ray can image any bone, from the hand, wrist and elbow to the spine, hip, knee and foot. It is used to diagnose fractured bones or joint dislocation, to check the alignment of bone fragments after treatment, to guide orthopaedic surgery, and to look for injury, infection, arthritis or abnormal bone growths.
The practical side is simple. The source says most bone X-rays need no special preparation beyond removing jewellery and metal objects that could interfere with the images, and that the exam is usually completed within five to 10 minutes, with typically two or three images from different angles. Sometimes the unaffected limb is imaged for comparison, and in a child the growth plate, where new bone is forming, may be X-rayed for the same reason. The exam itself is painless, though holding still in a position can be uncomfortable when you are injured, and the technologist will help you find the most comfortable position that still gives a good image. X-rays work because dense bone absorbs most of the radiation and appears white, while soft tissue appears as shades of gray.
On dose, the RadiologyInfo.org table lists an extremity X-ray, such as of the hand or foot, as less than 0.001 mSv, comparable to less than 3 hours of natural background radiation. The page on radiation, contrast and imaging safety explains what such figures mean and their limits.
What an X-ray does not show well
The same source is candid about limits: while X-ray images are among the clearest and most detailed views of bone, they provide little information about muscles, tendons or joints. A normal X-ray therefore does not mean everything in a joint is normal. It means the bone looked normal on that picture.
That is why a second scan may be suggested. According to RadiologyInfo.org, MRI may be more useful in identifying bone and joint injuries, giving examples such as meniscal and ligament tears in the knee and rotator cuff and labrum tears in the shoulder. It can also detect subtle or occult fractures and bone bruises not visible on X-ray. The National Institute of Biomedical Imaging and Bioengineering (NIBIB) agrees that muscles, ligaments and tendons are seen much more clearly with MRI than with regular X-rays and CT, which is why MRI is often used to image knee and shoulder injuries.
CT for complex fractures
CT builds a three-dimensional view from X-rays. RadiologyInfo.org says CT is being used widely to assess trauma patients in emergency departments, and that it can image complicated fractures, subtle fractures or dislocations. In older people or people with osteoporosis, it notes, a hip fracture may be clearly seen on a CT scan while barely seen, if at all, on a hip X-ray. For suspected spine injury or other complicated injuries, three-dimensional reconstructed CT images can be made without additional radiation exposure. NIBIB likewise calls CT particularly useful for imaging complex bone fractures, severely eroded joints or bone tumours, since it usually produces more detail than a conventional X-ray.
Ultrasound for tendons, muscles and nerves
For soft tissue around bones, ultrasound is a common choice. RadiologyInfo.org's page on musculoskeletal ultrasound says it produces pictures of muscles, tendons, ligaments, nerves and joints, and helps diagnose sprains, strains, tears, trapped nerves and arthritis. Its list of uses includes tendon tears and tendinitis of the shoulder rotator cuff and the Achilles tendon, muscle tears, ligament sprains, fluid in joints and bursae, early changes of rheumatoid arthritis, nerve entrapments such as carpal tunnel syndrome in the wrist, and ganglion cysts. For a hand or wrist problem, several items on that list are the ones people ask about.
Because ultrasound captures images in real time, the source says it can show the movement of a tendon, joint or limb. It adds that ultrasound is faster than MRI and does not require the patient to stay completely still, which lets infants be imaged without sedation, and that it is an excellent alternative to MRI for claustrophobic patients and for people with pacemakers or certain metallic implants who often cannot be exposed to the strong magnetic field. It says that compared with MRI, ultrasound may provide greater internal detail when assessing soft tissue structures such as tendons and nerves. Its limit is bone: ultrasound has difficulty penetrating bone and can only see the outer surface, so doctors typically use MRI to see inside bones or certain joints. Infants are the exception, because their hips and skeletons contain more cartilage, and ultrasound can be used to check an infant's hips. More on this method is on the page about ultrasound.
Questions worth asking
If you have been sent for a second scan after an X-ray, it is reasonable to ask what the new scan is meant to answer that the first could not. You can also ask whether an ultrasound could work as well as an MRI, whether you need to avoid metal or have an implant that affects the choice, and how long you will wait for the result. A list of such prompts is on the page about questions to ask before a scan. The answer depends on the body part and the question, so it belongs with your own doctor.
Frequently asked questions
Why did my doctor order an X-ray before an MRI?
RadiologyInfo.org describes X-ray as the fastest and easiest way to assess bone injuries and joint abnormalities. If the X-ray does not answer the question, MRI or another scan may follow, since X-rays provide little information about muscles, tendons or joints.
Can an X-ray miss a fracture?
Yes in some cases. RadiologyInfo.org says MRI can detect subtle or occult fractures and bone bruises not visible on X-ray, and that a hip fracture in someone with osteoporosis may be barely visible on X-ray but clear on CT.
Can ultrasound replace MRI for a tendon problem?
Sometimes. RadiologyInfo.org says ultrasound may show greater internal detail than MRI for soft tissue structures such as tendons and nerves, and suits people who cannot have MRI, but it cannot see inside bone. Your doctor decides which suits the question.
Is a hand X-ray a high dose?
RadiologyInfo.org lists an extremity X-ray at less than 0.001 mSv, comparable to less than 3 hours of natural background radiation, with the caveat that actual doses vary.
The short version
An X-ray is fast and shows bone well, but it says little about tendons, ligaments and joint surfaces, which is why ultrasound, CT or MRI is sometimes added. Each method has a niche, and the sources agree that the right choice depends on the specific question. If a second scan is suggested, ask what it is meant to add.