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Effect of heated mittens on physical hand function in people with hand osteoarthritis: randomised controlled trial

PainSci » bibliography » Bartholdy et al 2024
updated
Tags: ice heat, rehab, injury, pain problems, self-treatment, treatment

Two pages on PainSci cite Bartholdy 2024: 1. Heat for Pain and Rehab2. Hot hands: a surprising test of powered mittens for arthritis

PainSci notes on Bartholdy 2024:

The British Medical Journal gave us a weird Christmas gift! This is a study I didn't think I’d ever see in one of the big, general medical journals: not just a study of heat for hand arthritis, but the unusually practical and folksy option of electrically heated mittens. Power mittens.

Mittens with inbuilt battery driven heat elements are now commercially available and offer an easy means of delivering heat therapy to patients with hand osteoarthritis in an accessible manner outside of clinics.

The goal of Bartholdy et al was to give us some evidence on this topic that’s actually good for once, and I think they more or less did it. It’s biggish, rigorous, well-planned. The paper is also open-access and quite readable.

Obviously hand osteoarthritis is just about as common as painful problems get. It makes life harder for hundreds of millions of people. Although heat is a staple treatment, the evidence is of course super lame — as usual for this field, as my first post of 2025 explained. It’s rare but nice to see a study like this in a top-tier journal, because they often immediately become the best evidence available for many years to come, out-ranking a bunch of junkier studies.

And sometimes they don’t.

This one does have a huge flaw: Bartholdy et al compared hot mittens them to cold ones. Which begs a burning question: who did they think they were fooling? How exactly is a unheated mitten an effective sham for a hot one? Wouldn’t people be rather disappointed to get the cool ones? Or perhaps too enthusiastic about the niceness of the hot ones? Isn’t that a glaring confounder?

Yes, and they knew it:

It was not possible to mask the participants throughout the trial, which is a major limitation. This is not surprising as heated mittens would become warmer shortly after switching on the heating element, and the control mittens would not, despite the LED lights being active. Unsuccessful masking and use of patient reported outcomes could have led to an overestimation of effects, which is an inherent weakness and challenge when assessing effects of physical treatments in clinical trials.

But science is messy, flawed data is better than none, and everything else was done quite well. And so let’s crack on…

An infographic showing the design of heated mittens used in an experiment. The mitten has labeled components, including a “Heating element” winding through the mitten, a “Battery pack” attached near the wrist, and a “Heat control and intensity indicator” with three settings: Low (green), Moderate (yellow), and High (red). A box labeled “Control mittens” explains that the heating elements in the control mittens were disconnected, but the heat control and indicator light remained connected. The background is gradient blue and orange, suggesting warmth.

The heated mittens were far from perfect: "more concentrated heat around the joints would have been preferable. … Developing mittens specifically for people with hand osteoarthritis, with a better, possibly customised fit and easier battery recharging system, might help to enhance the effect of heated mittens. Image by Bartholdy et al. & BMJ, CC BY-NC 4.0.

They measured pain and function in a couple hundred older Danish patients with bad hands. Everyone got a pair of mittens, with or without power, and were asked to wear them for at least 15 minutes/day for six weeks, “preferably when symptoms were worst (typically in the morning).” Another study by Kominami et al showed that it takes about that long to fully heat up. Actual wear times were somewhat longer.

But of course everyone knew what they got! The researchers made a diligent effort to conceal allocation up until the start of the trial, but the jig was up as soon as anyone put them on.

The results

Hot mittens didn’t help. Boooo.

There was no important difference between the groups in pain or function, and what little difference there is probably attributable to the frustrebo effect, more negative reporting from the “frustrated” cold-mitten group … and a more standard enthusiasm-powered placebo for the hot-mitten group.

Many participants expressed a positive experience from use of heat. It is therefore reasonable to assume that participants allocated to the intervention group were more enthusiastic about the mittens, which also could have contributed to an overestimation of the true effect.


P.S. Just one adverse effect reported: itching. 😜


Common issues and characteristics relevant to this paper: ?Scientific papers have many common characteristics, flaws, and limitations, and many of these are rarely or never acknowledged in the paper itself, or even by other reviewers. I have reviewed thousands of papers, and described many of these issues literally hundreds of times. Eventually I got sick of repeating myself, and so now I just refer to a list common characteristics, especially flaws. Not every single one of them applies perfectly to every paper, but if something is listed here, it is relevant in some way. Note that in the case of reviews, the issue may apply to the science being reviewed, and not the review itself.

  1. Major limitation or flaw related to poor masking.

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

OBJECTIVE: To assess the effect of electrically heated mittens on physical hand function in people with osteoarthritis of the hands compared with control mittens.

DESIGN: Randomised controlled trial.

SETTING: Osteoarthritis outpatient clinic, Copenhagen, Denmark.

PARTICIPANTS: 200 people with hand osteoarthritis aged 42-90 years. 100 participants were assigned to the intervention group and 100 to the control group.

INTERVENTIONS: Electrically heated mittens or control mittens (heating elements disconnected) worn for at least 15 minutes daily for six weeks.

MAIN OUTCOME MEASURES: The primary outcome was change in hand function measured on the function subscale of the Australian/Canadian hand osteoarthritis index (AUSCAN; score 0-100 points) at six weeks. Key secondary outcomes included changes in the AUSCAN hand pain subscale (score 0-100 points), global rating of hand osteoarthritis related problems (0-100 visual analogue scale), and grip strength (newtons) at six weeks. Analysis of secondary outcomes was performed using a hierarchical gatekeeping approach.

RESULTS: 91 participants in the intervention group and 95 in the control group completed the trial. The mean age of participants was 71 years, 87% (n=173) were women, and mean body mass index was 24.9 (SD 4.4). Median disease duration was 10 years (interquartile range 5-15 years). The between group difference for change in AUSCAN function at week 6 was 3.0 points (95% confidence interval (CI) -0.4 to 6.3; P=0.09) in favour of heated mittens. For the key secondary outcome, change in AUSCAN hand pain score from baseline, a group difference was observed of 5.9 points (95% CI 2.2 to 9.5) in favour of heated mittens. Changes in global rating of hand osteoarthritis related problems and grip strength did not differ between the groups with an observed difference between groups of 2.8 points (95% CI -3.7 to 9.2) and 2.3 newtons (95% CI -16.3 to 21.0) in favour of heated mittens, respectively.

CONCLUSION: Use of electrically heated mittens for six weeks was not related to a positive change in physical hand function compared with control mittens. Heated mittens provided no additional benefits on global rating of hand osteoarthritis related problems and grip strength. A small benefit was detected for hand pain, but this could have been overestimated.

TRIAL REGISTRATION: ClinicalTrials.gov NCT04576403.

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