Musculoskeletal Ultrasound: Imaging Tendons, Muscles and Nerves

Ultrasound of the musculoskeletal system has moved from a niche skill to a first-line investigation for tendons, muscles, ligaments and peripheral nerves. It is inexpensive, radiation-free, quick and — uniquely — can be performed while the patient moves the painful part, and with the probe pressed exactly where it hurts. The 2021 guidelines of the European Federation of Societies for Ultrasound in Medicine and Biology, part one, cover extra-articular pathology: tendons, muscles, entheses, ligaments, nerves and soft-tissue masses.

What it shows

Tendinopathy appears as thickening, loss of the normal fibrillar pattern and hypoechoic change, with increased blood flow on Doppler in active disease. Partial and full-thickness tears are identified directly, and tendon subluxation can be demonstrated dynamically. Enthesitis — inflammation where tendon or ligament meets bone, the hallmark of spondyloarthritis — shows thickening, hypoechogenicity, Doppler signal, erosions and enthesophytes. Muscle injury is graded from strain to tear to haematoma; ligament injuries, ganglion cysts, bursitis, foreign bodies and superficial masses are all well demonstrated. Peripheral nerve assessment can show entrapment — swelling and altered echotexture at a compression site such as the carpal tunnel or the cubital tunnel — and can identify neuromas or nerve sheath tumours.

How it compares with MRI

MRI images deeper structures and the inside of joints better — bone marrow, cartilage, labra and intra-articular ligaments remain its territory. Ultrasound wins on superficial detail (it has higher spatial resolution than MRI for small superficial tendons), on dynamic assessment, on speed, on cost, and on patient acceptability, including in those with implants or claustrophobia. Both are operator-dependent, and ultrasound's dependence is substantial: image quality and interpretation vary considerably with the experience of the operator and the machine. The two are complementary and often used together.

What the examination involves

The patient is positioned so the area is accessible, the probe is moved along and across the structure, and both sides are compared — comparison with the unaffected side is one of the most useful discriminators in ultrasound. Doppler assesses active inflammation. Dynamic manoeuvres — moving the tendon or joint under real-time imaging — demonstrate impingement, subluxation or snapping. The examination usually takes 15–30 minutes, and findings can be discussed with the patient immediately, which is one of its practical advantages.

Interventional use

Ultrasound guidance has improved the accuracy of musculoskeletal injections markedly: corticosteroid, hyaluronic acid and platelet-rich plasma injections, aspirations of bursae and cysts, and, increasingly, procedures such as percutaneous tenotomy or hydrodissection of an entrapped nerve are all performed under direct vision. This means the same appointment can often combine diagnosis and treatment.

Practical advice

Wear loose clothing that allows the painful area to be exposed, and bring previous imaging and any operative notes. Ask whether the scan will be performed by someone who does musculoskeletal ultrasound regularly, whether Doppler will be used, and whether the report distinguishes between active inflammation and chronic damage — a distinction that determines whether an injection or rehabilitation is the right next step. Doppler signal indicates active disease and is the finding that reliably predicts response to anti-inflammatory treatment; degenerative change without Doppler signal responds better to loading exercise than to injection.