When to look at both feet
When ankle ligaments are damaged, comparison with the healthy side has direct practical significance. The thickness of the ligaments is individual, and you can understand whether a particular ligament is thickened only by comparing it with the ligament of the same name on the other leg. The same goes for the Achilles tendon: its normal thickness varies depending on height, weight and level of physical activity, so the assessment of “thick” is always relative.
Bilateral examination is necessary for gout, which classically begins at the first metatarsophalangeal joint, but often affects the ankles, for seronegative spondyloarthritis with characteristic bilateral enthesitis at the insertion of the Achilles tendon and plantar fascia, as well as for rheumatoid arthritis.
A separate group stands out for runners and people with heavy loads on their feet. Overuse Achilles tendinopathy and plantar fasciitis occur on both sides, but the pain is usually in one leg. Examination of the second foot often reveals the same changes at the preclinical stage, which makes it possible to change the load in time, select shoes and insoles and not lead to rupture.
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.