Effects of serial thermal brine hand baths on hand osteoarthritis: a randomized, double-blind, sham-controlled trial.

The short version

This randomized, double-blind, sham-controlled trial of 38 analyzed adults in Bad Nauheim, Germany, explored whether mineral water baths for the hands ease pain from hand osteoarthritis (HOA). HOA is wear-and-tear damage in the finger and thumb joints that causes pain, stiffness and reduced grip. Balneotherapy, the treatment of conditions with natural mineral waters, is well known for knee osteoarthritis, but evidence for hand osteoarthritis was thin. The tested water was natural thermal brine, a salty spring water (sodium chloride and hydrogen carbonate, rich in carbon dioxide), used at its natural 25 degrees C. Participants averaged 72 years, 86% were women, and all had painful, X-ray-confirmed HOA. One group soaked both hands in thermal brine and the other in ordinary tap water at the same temperature, in identical covered bowls so neither participants nor staff knew which was which. Each bath lasted 15 minutes, with six baths over three weeks. Pain was rated on a 100 mm visual analog scale (VAS, 0 meaning no pain), alongside hand function questionnaires, grip strength, skin blood flow and a blood marker (VEGF). After six baths, pain averaged 7 mm with thermal brine versus 33 mm with tap water, a 26.4 mm gap (P < 0.0001) larger than the 20 mm threshold for a clinically meaningful change. The gap was already present after the first bath (5.3 mm, P = 0.0017) and was still about 26 to 27 mm at 4 and 12 weeks. Pain on the hand index (AUSCAN pain subscore) was also lower (5.86 points, P < 0.0001), though that difference was gone at follow-up. Stiffness, function, grip strength, skin blood flow and VEGF did not differ between groups. Satisfaction favored thermal brine: 72% (13 of 18) rated pain relief good or very good versus 32% (6 of 19) with tap water. No adverse events occurred. The trial was small, ran at one center during the COVID-19 pandemic, and lost 12 of 50 participants, so only 38 were analyzed. Tap water may also have effects of its own. Because blood flow and VEGF showed no change, how the baths relieve pain remains unexplained; the authors note that 25 degrees C is below the 32 to 35 degrees C range where carbon dioxide baths are expected to widen blood vessels. They propose thermal brine baths as a non-pharmacological adjunct and call for larger multicenter trials with longer treatment and optimized temperatures.

Key findings

• In this sham-controlled trial of 38 analyzed adults with painful hand osteoarthritis (wear-and-tear arthritis of the finger and thumb joints), six 15-minute hand baths in natural thermal brine over three weeks lowered resting pain by 26.4 mm more on a 100 mm scale than tap water baths at the same temperature (P < 0.0001).
• The pain difference exceeded the 20 mm change the authors consider clinically meaningful, appeared after the first bath (5.26 mm, P = 0.0017) and was still about 26 to 27 mm at 4 and 12 weeks after treatment ended.
• A hand symptom questionnaire (AUSCAN) pain score also improved (difference 5.86 points, P < 0.0001), but stiffness, hand function, grip strength, skin blood flow and VEGF (a blood-vessel growth marker) did not differ between groups.
• No adverse events were reported, and 72% of the thermal brine group (13 of 18) rated pain relief good or very good versus 32% (6 of 19) of the tap water group.
• The trial was small and single-center, 12 of 50 enrolled participants were lost before analysis (mostly from COVID-19 infection), and tap water may itself have effects, so the size of the true benefit and how it arises remain uncertain.

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