Ultrasound musculoskeletal / soft tissue
Region of clinical concern, with dynamic assessment and contralateral comparison
When to use it
- Superficial soft-tissue lump characterisation.
- Tendon pathology, where dynamic assessment adds information MRI cannot.
- Joint effusion, and guidance for aspiration or injection.
Technique
- High-frequency linear transducer, typically 7-15 MHz and up to 18-24 MHz for superficial structures such as digital tendons and peripheral nerves; a curvilinear probe is substituted where the lesion is deep or the patient large, at the cost of resolution.
- The patient is positioned so the structure of interest is superficial and accessible and the joint can be moved through range — shoulder examined seated with the arm in modified Crass position for the supraspinatus, Achilles prone with the feet over the end of the couch, elbow and wrist supported on a table with the sonographer seated.
- A generous standoff of gel, or a standoff pad, for the most superficial lesions; excessive transducer pressure obliterates a small collection, empties a vein and abolishes flow in a lesion being assessed for vascularity.
- Every lesion is imaged in two orthogonal planes and measured in three dimensions, with depth and the relation to fascia, tendon and neurovascular structures recorded — for a lump the deliverable is not just what it is but which compartment it sits in.
- Anisotropy is controlled deliberately by keeping the beam perpendicular to the fibre bundle and by heel-toeing the probe; a hypoechoic area that fills in when the angle is corrected is anisotropy, not a tear.
- Dynamic assessment is what this study offers over MRI: tendon subluxation, impingement, hernia with Valsalva, snapping structures and dynamic instability are all seen in movement and are invisible on a static image.
- Colour or power Doppler with a low wall filter and low pulse repetition frequency for lesion vascularity and for hyperaemia in tenosynovitis or an inflamed joint; contralateral comparison is used wherever normality is in question.
Where it goes wrong
- Depth limits assessment — a deep or large lesion needs MRI, and an indeterminate lump on ultrasound should escalate rather than be called benign.
Contrast
None