Symmetrical lesions of the hands
The wrists are the area where bilateral examination is most often justified. Carpal tunnel syndrome in most cases is a bilateral process: complaints appear first on the dominant hand, but when measuring the area of the median nerve, an increase is often detected on the second, still asymptomatic side. This changes tactics - from load correction and orthotics to planning staged surgical treatment.
The second most important indication is early diagnosis of rheumatoid arthritis. The disease begins with symmetrical damage to the small joints of the hands and wrist joints, and Doppler ultrasound reveals active synovitis and marginal erosions long before changes become visible on x-rays. The number of joints with active inflammation, assessed on both sides, is included in the criteria for disease activity and is used to control therapy.
Bilateral assessment is also necessary in a controversial situation where it is unclear whether thickening of the nerve or synovium is an individual feature. Comparison with the opposite side of the same person gives an answer more reliable than any average standards.
What can be seen on an ultrasound of the joint
Ultrasound, better than any other method, shows the soft tissues surrounding the joint: tendons and their sheaths, ligaments, muscles, synovium, joint capsules and peripheral nerves. It reliably detects free fluid in the joint cavity and bursae, tendon ruptures and tears, cysts, bursitis and tendinitis.
There are also fundamental limitations. Ultrasound does not pass through the bone, so the internal structures - menisci along the entire length, cruciate ligaments, articular cartilage deep in the joint, bone marrow - remain inaccessible. They use magnetic resonance imaging, and X-rays are used to evaluate the bone itself.
The main advantage is exploration in motion
Unlike MRI, which takes a picture of a motionless joint, ultrasound allows you to look at the joint in dynamics. The doctor asks you to bend, straighten or rotate the limb straight during the scan and sees how the tendons and ligaments behave under load.
Many conditions manifest themselves only during movement: tendon subluxation from the groove, impingement, trigger finger, ligament instability. At rest, the picture looks normal, and without functional tests the diagnosis cannot be made.
When to start with ultrasound
Ultrasound is reasonable as the first method for pain and swelling of the joint without injury, for suspected bursitis, tendinitis and cysts, for monitoring the treatment of inflammatory diseases and, if necessary, to induce a puncture or blockade.
If there was a serious injury with a suspected fracture, you need to start with an x-ray. If a torn meniscus or cruciate ligament is suspected, MRI remains the method of choice.