A large effect for laser over ultrasound in knee osteoarthritis

Design

single-centre, assessor-blinded randomised controlled trial, 1:1 allocation, intention-to-treat

Population

66 adults with knee osteoarthritis, treated twice weekly for six weeks as an adjunct to exercise

Primary outcome

change in total WOMAC score from baseline to 12 weeks after the end of treatment

Effect

WOMAC reduction 40.0 vs 8.2 points; adjusted difference −27.7 (95% CI −39.0 to −16.5), P < 0.001, partial η² 0.277

Therapeutic ultrasound and high-intensity laser are both routine adjuncts in physiotherapy departments and neither has much comparative evidence behind it. A single-centre, assessor-blinded randomised trial gave 66 adults with knee osteoarthritis either high-intensity laser or ultrasound twice weekly for six weeks, both on top of exercise, and measured the change in total WOMAC score at 12 weeks after treatment finished.

The difference was large. Mean WOMAC reduction was 40.0 points with laser against 8.2 with ultrasound, an adjusted between-group difference of −27.7 points (95% confidence interval −39.0 to −16.5, P < 0.001). The minimum important change was taken as 10 points, so the difference is nearly three times the threshold at which a patient would notice. Secondary measures — visual analogue pain, Oxford Knee Score, KOOS and EQ-5D-5L — all favoured laser in exploratory analysis, and the laser group held its gains to 12 weeks while the ultrasound group lost theirs gradually.

An effect this size in a 66-patient single-centre trial should make you cautious rather than enthusiastic. Large treatment effects in small trials are the ones that most often shrink on replication, the comparator here is a modality whose own efficacy is uncertain, and assessor blinding does not blind the patient to whether they received laser or ultrasound. The reasonable position is that laser looks the better adjunct of the two and that neither is a substitute for the exercise programme both groups received.

• Keep exercise as the core intervention; both arms received it and it is the part with established evidence.
• Where a department offers both, high-intensity laser is the better-supported adjunct on this trial.
• Do not present the effect size to patients as established — 66 patients at one centre is a starting point.
• Reassess at 12 weeks rather than at the end of the treatment course; the between-group gap widened afterwards.
• Weigh cost and session count: twice weekly for six weeks is twelve visits, which many patients will not complete.

Why it matters

Two modalities used interchangeably in the same department did not perform interchangeably.

Don't overread it

Patients knew which modality they received and WOMAC is self-reported — some of this gap is expectation rather than tissue effect.

The statistics, in plain English

A between-group difference of 27.7 WOMAC points against a minimum important change of about 10 is an unusually large result, and the confidence interval (−39.0 to −16.5) stays well clear of the threshold at its weakest end. The caution is not statistical but structural: in a trial of 66 people, the estimate is precise only relative to itself, and the comparator was not placebo. Patients could tell which treatment they were getting, and WOMAC is a self-reported score, so expectation contributes to the gap in a way assessor blinding does not remove.

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