Clinical library · Modalities
Shortwave Diathermy
Deep heating by radiofrequency. It relieves knee osteoarthritis pain when the dose is high enough to produce a genuine thermal sensation, does not improve function, and is applied at protocols so variable that the literature cannot say what dose you should use.
In one line. High-frequency electromagnetic energy applied through capacitive plates or inductive coils, heating tissue at depth. Delivered continuously for a thermal effect, or pulsed, which may or may not raise tissue temperature depending on the dose.
Two findings organise everything else on this page: the effect appears only when there is real heating, and the effect is on pain rather than on function.
If the patient does not feel warmth, expect nothing. A meta-analysis of seven studies in knee osteoarthritis found that studies with low mean power did not favour shortwave diathermy for pain, while studies employing some thermal effect showed significant results. Its conclusion is that small significant effects on pain and muscle performance appear only when the treatment evoked a local thermal sensation — and that extensive variability in treatment protocols makes it difficult to draw definitive conclusions about what determines effectiveness. [2]
What the evidence shows
| Question | Finding | Source and quality |
|---|---|---|
| Knee osteoarthritis, pain | SMD -0.53 (95% CI -0.84 to -0.21) against sham or no intervention | 8 trials, 542 patients [1] |
| Pulsed versus continuous | Pulsed modality SMD -0.83 (95% CI -1.14 to -0.52); described as superior to continuous | Subgroup analysis within the same review [1] |
| Knee osteoarthritis, function | No significant difference (SMD -0.16, 95% CI -0.36 to 0.05) | The review states plainly that function is not improved [1]. A second review found no treatment effect on functional performance measures either [2] |
| Knee extensor strength | Superior to control (p < 0.05, I-squared 0%) | Combined with isokinetic strength work [1] |
| Does heating matter? | Yes. Low mean power did not favour treatment; thermal-effect studies were significant | 7 studies; protocols varied extensively in dosage, duration and number of treatments [2] |
| Actual temperature change | Skin up to 7.9°C (continuous, coplanar capacitive); muscle up to 4.58°C (inductive pulsed); as little as 0.34°C with low-dose pulsed | 11 studies, 240 healthy subjects. Efficacy depends on setting choices [3] |
| Chronic low back pain | Immediate analgesic effect | Continuous mode differed significantly from placebo on the numeric rating scale [4]. A separate trial found continuous diathermy with exercise more effective for pain than the other modalities compared, with no between-group difference in disability [5] |
| Versus ultrasound, trigger points | No significant differences between the two | Both considered effective for latent trigger points in upper trapezius [6] |
Where it misleads
1. The pulsed-versus-continuous story is not what it looks like
One review found the pulsed modality superior for pain (SMD -0.83 against -0.53 overall). [1] Another found that effects appeared only where there was a thermal effect and that low mean power did not favour treatment. [2] These reconcile only if the pulsed protocols in question were delivering enough average power to heat — and the temperature review shows pulsed application can produce anything from 0.34°C to 4.58°C depending on technique. [3] "Pulsed" describes the waveform, not the dose.
2. Pain improves and function does not
Both reviews agree: no significant difference in physical function [1] and no treatment effect on functional performance measures. [2] For a condition where function is the clinical goal, an analgesic effect that does not translate is a limited result. It may still be useful as a window in which to load the joint — that is a hypothesis, not a finding.
3. Nobody can tell you the dose
Treatment protocols varied extensively between studies in dosage, duration and number of treatments, and the reviewers say this makes it difficult to draw definitive conclusions about the factors determining effectiveness. [2] The temperature review's contribution is to quantify what different techniques actually do — and it concludes that efficacy depends on setting choices. [3] Compare this with laser, where the reviews specify joules per spot.
4. The low back pain evidence is immediate-effect only
The trial reporting an analgesic effect in chronic low back pain measured immediate effects. [4] A second trial found improvements in all groups including exercise alone, with no between-group difference in functional deficiency. [5] Neither supports diathermy as a treatment for the condition rather than a short-term analgesic.
What the evidence supports — and what it does not
Supported
- Pain relief in knee osteoarthritis when the dose produces a thermal effect. [1][2]
- Knee extensor strength when combined with isokinetic training. [1]
- Immediate analgesia in chronic low back pain. [4][5]
- Comparable to ultrasound for latent trigger points. [6]
- Safety. No significant difference in adverse effects against control. [1]
Not supported
- Improving physical function. Null in both reviews. [1][2]
- Sub-thermal or low-power application. Did not favour treatment. [2]
- Any specific protocol. Dosage, duration and number of treatments varied extensively. [2][3]
- Lasting benefit in low back pain. The evidence is immediate-effect. [4]
- Superiority over ultrasound. No significant difference. [6]
How certain is this?
Evidence grade: Low.
Two meta-analyses agree on the direction and on the two things that matter — heat is necessary, function does not improve — which is the strongest signal available here. They rest on 8 and 7 trials respectively, [1][2] and both are more than five years old, which reflects a literature that has largely stopped growing rather than a choice to cite old work.
The temperature review is the most practically useful item and is not an efficacy study: 11 studies in 240 healthy subjects, measuring what different techniques do to tissue temperature. [3] Applying those figures to injured or oedematous tissue is an extrapolation.
The three clinical trials are single studies with immediate or short follow-up. [4][5][6] The crossover trial against ultrasound reports a non-significant p value (0.27) alongside a confidence interval that excludes zero for one of its outcomes, which is an internal inconsistency worth noticing before relying on that comparison. [6]
What would change the grade: trials using a defined thermal dose, reporting function as well as pain, with follow-up beyond the treatment period.
Common questions
Should the patient feel warmth?
On this evidence, yes. The meta-analysis that separated studies by power found that low mean power did not favour treatment, while studies employing some thermal effect were significant, and concluded that effects appeared only when the treatment evoked a local thermal sensation. [2] If your setting produces no sensation, you are unlikely to be delivering the intervention that was studied.
Pulsed or continuous?
One review found the pulsed modality superior for pain (SMD -0.83 versus -0.53 overall). [1] But "pulsed" spans a wide range of delivered power: measured muscle temperature rise ranged from 4.58°C with inductive pulsed application down to 0.34°C with a low-dose pulsed application. [3] Choose by the thermal effect you intend, not by the waveform label.
Will it improve my patient's function?
The evidence says no. One review found no significant difference in physical function (SMD -0.16, 95% CI -0.36 to 0.05) and states that function is not improved; [1] the other found no treatment effect on functional performance measures. [2] Pain relief and functional gain are separate claims here, and only the first is supported. See knee osteoarthritis for what does improve function.
Is it better than ultrasound?
Not demonstrably. In a randomised crossover trial in latent upper trapezius trigger points there were no significant differences between digital capacitive diathermy and ultrasound on any outcome, and the authors considered both effective. [6] See electrotherapy and passive modalities for the ultrasound evidence.
What dose should I set?
The literature cannot tell you, and this page will not invent a figure. Protocols varied extensively in dosage, duration and number of treatments across the trials, and the reviewers state this prevents definitive conclusions about what determines effectiveness. [2] What is known is what different techniques do to temperature in healthy tissue, [3] and that some thermal effect is necessary. [2]
References
- Wang H, Zhang C, Gao C, et al. Effects of short-wave therapy in patients with knee osteoarthritis: a systematic review and meta-analysis. Clinical Rehabilitation. 2017 May;31(5):660–671. doi:10.1177/0269215516683000 PMID 28118736 Systematic review and meta-analysis
- Laufer Y, Dar G. Effectiveness of thermal and athermal short-wave diathermy for the management of knee osteoarthritis: a systematic review and meta-analysis. Osteoarthritis and Cartilage. 2012 Sep;20(9):957–66. doi:10.1016/j.joca.2012.05.005 PMID 22659070 Systematic review and meta-analysis
- Benincá IL, de Estéfani D, Pereira de Souza S, et al. Tissue heating in different short wave diathermy methods: A systematic review and narrative synthesis. Journal of Bodywork and Movement Therapies. 2021 Oct;28:298–310. doi:10.1016/j.jbmt.2021.07.031 PMID 34776156 Systematic review and narrative synthesis
- Espinoza ANC, Moreira PM, Yamada FT, et al. Immediate effects of two modes of shortwave diathermy in chronic low back pain: randomized controlled clinical trial. Pain Management. 2025 Dec;15(12):931–940. doi:10.1080/17581869.2025.2570117 PMID 41045454 Randomised controlled trial
- Karasel S, Oncel S, Sonmez I. The Effect of Short-Wave Diathermy and Exercise on Depressive Affect in Chronic Low Back Pain Patients. Medical Archives. 2021 Jun;75(3):216–220. doi:10.5455/medarh.2021.75.216-220 PMID 34483453 Randomised controlled trial
- Jiménez-Sánchez C, Cordova-Alegre P, Carpallo-Porcar B, et al. Effects of transcutaneous radiofrequency diathermy versus ultrasound on latent myofascial trigger points in the upper trapezius: A randomized crossover trial. Journal of Back and Musculoskeletal Rehabilitation. 2024;37(4):1049–1058. doi:10.3233/BMR-230296 PMID 38427466 Randomised crossover trial
About this resource
Using this in clinic
Every figure here is traceable to its source.
This page reports the measured temperature change for each application technique, because the reviews find that whether the tissue is actually heated is what separates the positive trials from the negative ones. Where a value could not be verified against the paper it came from, it is not on this page, and the omission is stated rather than filled with a number from a secondary source.