Glossary
Ultrasound of the knee
Quick answer
A knee ultrasound uses sound waves to show tendons, fluid, bursae and cysts in real time, without radiation. It is useful for tendon problems, Baker's cysts and guiding injections, but cannot see inside the joint well enough to assess the ACL, cartilage or most meniscus tears, explains Doha knee surgeon Dr. Pablo Gelber at Aman Hospital.
What to expect
You lie or sit with the knee exposed. Cool gel is spread on the skin and a small probe is moved over the area. It is painless, quick and needs no preparation. The operator may ask you to bend or tense the knee so tendons can be seen moving, which is an advantage over static scans.
What it shows and what it misses
Ultrasound is good at showing the patellar and quadriceps tendons, the collateral ligaments near the surface, fluid in the joint, swollen bursae, and cysts such as a Baker's cyst behind the knee. Doppler ultrasound adds blood-flow information and is used to check for clots.
Sound waves cannot pass through bone, so structures deep inside the joint, including the cruciate ligaments, most of the meniscus and the joint cartilage, are poorly seen. A normal knee ultrasound therefore does not rule out these injuries; an MRI is used when they are suspected.
Guided injections and aspiration
Ultrasound can guide a needle precisely into the joint, a bursa or a cyst, which can make injections and fluid drainage more accurate, especially in a knee with little swelling.
Frequently asked questions
Can ultrasound diagnose a meniscus tear?
Only partly. It may show the edge of the meniscus or a cyst beside it, but most tears are inside the joint and need MRI for reliable assessment.
Why would my surgeon use ultrasound for an injection?
To see the needle reach the right place. This can improve accuracy, particularly for small effusions, cysts or bursae.
Related
