What are the different types of scans used to assess for knee pain?
The main types of scans used to assess knee pain are x-rays (radiographs), ultrasound and Magnetic resonance imaging (MRI). All of these are useful to assess knee problems and often used in combination to provide complete assessment and diagnosis.
What is a knee x-ray?
A knee x-ray (or knee radiograph) is the black and white image produced by sending an x-ray beam through the area of interest and getting the images on a film. It is usually the first type of imaging done when a knee problem is suspected. The bones absorb the x-ray beam more than the other surrounding soft tissues and therefore they are usually well seen on x-rays. Therefore, x-rays are usually used to assess bone problems.
Normal Knee X-ray
What does a knee x-ray show?
Knee x-rays are readily available and provide the doctor with valuable information about the condition of the knee joint. The main indications for a knee x-ray are:
Knee arthritis: A knee x-ray will assess if there is any wear and tear (arthritis) and the degree of changes. An x-ray will also help to assess for presence of any extra fluid within the knee joint (called joint effusion). This can be seen in knee arthritis and may require drainage under ultrasound guidance.
Suspected knee fracture.
Suspicion of other bone problems (like bone infection, mass coming from the bone or bone thinning).
Knee arthritis. Note the loss of the joint space (the space between the bones) at the inside of both knee joints. This is because there is complete loss of the cartilage here.
To find out more, please see our article about knee x-rays.
What is a knee ultrasound scan?
Ultrasound is high frequency sound waves produced by a special machine. They provide very useful images of the tissues within the body. Ultrasound is extremely useful in assessing various musculoskeletal conditions that can involve tendons, muscles, joints and the adjacent soft tissues. Unlike x-rays, ultrasound does not involve exposure to radiation or any harmful side effects. To find out more, please see our article about knee ultrasound.
Do I need a knee ultrasound scan?
Knee ultrasound scan is very useful in assessing certain knee conditions. These include:
Knee joint effusion
This refers to the accumulation of excess fluid within the knee joint, which can happen due to a variety of reasons (knee injury, knee arthritis, meniscal injury, etc...). Ultrasound can be also used to guide knee aspiration if indicated. This is a special procedure where the excess fluid within the knee is taken out by inserting a small needle under ultrasound guidance.
Patellar tendinosis can be accurately diagnosed using ultrasound. The ultrasound can be also used to guide any intervention to the inflamed patellar tendon (like PRP injection or high-volume injection around the tendon).
Baker's cyst
Ultrasound is excellent for assessment of Baker’s cyst. The scan will confirm the diagnosis, assess the size of the cyst and suitability for ultrasound guided aspiration.
Soft tissue lumps
Assessing soft tissue lumps around the knee joint. Ultrasound is usually the first choice of imaging to assess for swelling around the knee.
Ultrasound-guided injections
There is a significant evidence that ultrasound guided injections provide better levels of pain relief and longer effects compared with injections done without imaging guidance. Performing the injection under ultrasound guidance allows for visualisation of the adjacent structures and reduces the risk of tissues injury at the injection site. Ultrasound guided injection treatment is used to manage many knee conditions including:
The different treatment options/injections that can be done under ultrasound guidance to help in knee pain management include:
To find out more, please see our article about knee ultrasound.
What is a knee MRI scan?
An MRI examination uses strong magnetic fields and radio waves to produce detailed images of a certain body part. MRI requires going inside a special machine (small tunnel) and staying still for the duration of the scan (approx. 20-30 minutes).
Do I need a knee MRI scan?
A knee MRI examination is an excellent modality to assess most of knee problems. It is the scan of choice when there is significant knee injury as it will allow for assessment of all the ligaments, menisci and internal structures. To find out more, please see our article about knee MRI scan.
Knee ultrasound vs. x-ray vs. MRI
Often a combination of scans is required to assess the knee joint and diagnose the problem. You should always discuss your knee problem with your doctor, to advice you about the most suitable scan for you. We have put a table below to summarise the most common knee conditions we see in our practice, and the role of imaging.
Condition | Ultrasound | X-ray | MRI |
Knee osteoarthritis | Treat | Diagnose | Diagnose |
Meniscal tear | Treat | x | Diagnose |
Baker’s cyst | Diagnose & treat | x | Diagnose |
IT band friction syndrome | Treat | x | Diagnose |
Pes anserine tendinosis | Diagnose & treat | x | Diagnose |
Hoffa’s fat pad impingement | Treat | x | Diagnose |
Patellar tendinopathy | Diagnose & treat | x | Diagnose |
Prepatellar bursitis | Diagnose & treat | x | Diagnose |
Collateral ligaments injury | Diagnose | x | Diagnose |
Cruciate ligaments injury | X | x | Diagnose |
Joint effusion | Diagnose & treat | Diagnose | Diagnose |
Knee conditions and treatment
