After twisting the foot
The most common ankle injury is a twisting of the foot inward with damage to the external ligaments, primarily the anterior talofibular ligament. The x-ray is usually normal, because the bone is intact, and the patient receives a diagnosis of “sprain” without further specification. Ultrasound shows the specific ligament, the degree of its damage - from swelling to complete rupture with divergence of the ends - and the presence of a hematoma, and functional tests help assess joint instability. This directly affects treatment: the period of immobilization and the amount of rehabilitation for a partial and complete rupture are fundamentally different.
The second major section is the Achilles tendon. Ultrasound detects tendonitis, degenerative changes, partial tears and complete ruptures, accurately measures the diastasis between the ends of the rupture and allows you to observe the tendon over time during treatment. This is one of the areas where the method provides information almost equivalent to MRI.
Additionally, the plantar fascia is examined for heel spurs and plantar fasciitis, the tendons of the posterior tibial and peroneal muscles, and in the intermetatarsal spaces - Morton's neuroma, which ultrasound visualizes well with transverse compression of the foot.
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.