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Rainer Brenke, an internist and specialist in physical medicine and naturopathy, published this review in the Zeitschrift für Komplementärmedizin in 2017. It summarises the evidence on sauna use for complaints of the musculoskeletal system and derives indications and practical recommendations from it. It is written in German.
The review covers osteoarthritis, fibromyalgia and rheumatic diseases. Among other work, it refers to studies of infrared A hyperthermia in rheumatic disease and of infrared saunas in rheumatoid arthritis and ankylosing spondylitis. Those studies concern infrared applications, not the Finnish sauna, and their results cannot simply be transferred. As a review, it has no comparison group of its own.
The review also cites an earlier survey by the German Sauna Association on complaints and perceived improvement among sauna guests. Those figures come from an industry association survey without a comparison group, not from a controlled study, and are therefore not reported here as a result. Several of the primary studies cited date from the 1960s to the 1990s and appeared in the International Sauna Archive, which makes them hard to check.
The paper gives an overview of the conditions for which sauna use has been studied or discussed. It does not show that sauna use relieves musculoskeletal complaints in an individual, and its practical recommendations rest partly on old or uncontrolled data.