Carpal tunnel syndrome and hygromas
Carpal tunnel syndrome is the most common tunnel neuropathy and one of the main indications for ultrasound of the wrist. The median nerve becomes compressed under the transverse carpal ligament, causing nighttime numbness and tingling in the first three fingers. Ultrasound measures the cross-sectional area of the nerve at the entrance to the canal: its increase is an objective sign of compression. The method also shows the cause of the compression - thickening of the flexor synovial sheaths, hygroma, accessory muscle or the consequences of injury, which directly affects the choice between conservative treatment and surgery.
Hygroma (ganglion cyst) of the wrist is the second most common finding. Ultrasound distinguishes it from a solid formation and from a vascular aneurysm, shows the connection with the joint or tendon sheath, the exact size and depth of the location, and also allows for puncture under control.
In addition, the first extensor canal is assessed for de Quervain's disease, a tenosynovitis of the tendons at the base of the thumb, common in young mothers and people who type a lot. In rheumatoid arthritis, ultrasound detects synovitis and erosions at an early stage, often before x-rays.
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.