Therapeutic Ultrasound in Physiotherapy: What It Is and What the Evidence Shows

What is therapeutic ultrasound?

Therapeutic ultrasound is a long-standing physiotherapy modality that delivers high-frequency sound waves into soft tissue through a hand-held applicator. The clinician applies a coupling gel and moves the probe over the skin so the sound energy passes into the tissue below. It is used mainly for musculoskeletal pain and to support soft-tissue healing.

It is different from diagnostic ultrasound (the kind used for scans). Here the goal is treatment, not imaging.

How it works

The sound waves produce two kinds of effect. Thermal effects warm the tissue, which can increase local blood flow, tissue metabolism, and flexibility. Non-thermal (mechanical) effects come from micro-vibration and cavitation — tiny pressure oscillations in tissue fluid — which are proposed to stimulate cellular activity and healing.

The frequency determines depth: lower frequencies (around 1 MHz) reach deeper tissues, while higher frequencies (around 3 MHz) target more superficial structures. The clinician selects settings and treatment time for the specific area.

What the evidence shows

There is real, high-quality evidence that ultrasound helps in specific situations. In a landmark double-blind trial published in the New England Journal of Medicine, ultrasound helped dissolve calcium deposits in the shoulder (calcific tendinitis): deposits resolved or shrank by half in nearly half of treated shoulders, versus far fewer with sham treatment, and symptoms improved faster in the early weeks.

For knee osteoarthritis, meta-analyses of randomised trials consistently find that ultrasound reduces pain — a moderate effect — and improves physical function, with no adverse events reported. Its tissue-warming (thermal) effect is also well established: it raises local blood flow and makes collagen more extensible, which is why physiotherapists use it to prepare tight tissue before stretching. Low-intensity pulsed ultrasound (LIPUS) can also help heal long-standing fracture non-unions.

It is honest to note that ultrasound is not a cure-all: for some conditions (such as chronic low back pain) the evidence does not support it, and for others the effect is uncertain. That is why a physiotherapist uses it selectively — for the problems where it helps — and always alongside active rehabilitation. Its safety record is excellent, with adverse effects rarely reported.

Using it at home

Compact, portable ultrasound units allow a trained clinician to deliver the same treatment during a home visit, typically over a short session per area. Importantly, effectiveness does not improve simply because the device is portable — the same evidence and cautions apply as in a clinic.

Safety and contraindications

Therapeutic ultrasound is generally well tolerated with few reported adverse effects, but there are important situations where it should not be used.

• Do not apply over or near a tumour or area of suspected malignancy.
• Avoid over the pregnant abdomen, pelvis, or lower back.
• Avoid over the eyes, testes, a pacemaker or implanted device, active infection, or blood clots.
• Avoid over growing bone (growth plates) in children and over fractures.
• Use with caution over areas of reduced sensation.

Sources

• Ebenbichler GR, et al. Ultrasound therapy for calcific tendinitis of the shoulder. N Engl J Med, 1999
• Zhang C, et al. Therapeutic ultrasound for pain and function in knee osteoarthritis: review & meta-analysis, 2016
• Ultrasound Therapy. StatPearls (NCBI Bookshelf)

Other modalities

• TENS (transcutaneous electrical nerve stimulation)
• Muscle stimulation (NMES / EMS)
• Interferential current therapy (IFC)
• Heat and cold therapy
• Low-level laser / red-light therapy (LLLT)
• Resistance bands
• Weights & resistance training
• Pneumatic resistance training
• Cable functional trainer
• Motorised cycling therapy
• Supported treadmill gait training