The effects of carbonic acid springs have long been known to include flushing of the skin at the site of immersion, increased blood flow in the skin and muscle, decreased blood pressure, and bradycardia [2]. The efficacy of high-concentration carbon dioxide foot bathing on ischemic limbs and skin ulcers in the clinical setting has already been reported [3, 4]. In Japan, tablets for generating artificial carbonated water are commercially available (AS care; Asahi Kasei Medical Co., Ltd.) and are frequently added to foot baths to improve blood flow in the legs of dialysis patients. AS care contains carbonate, sodium dichloroisocyanurate, and sodium dichloroisocyanurate hydrolyzes to produce hypochlorous acid (HOCl) simultaneously with carbon dioxide generation. Transdermally absorbed carbon dioxide is converted to bicarbonate ions, which act directly on endothelial cells to increase nitric oxide (NO) production through phosphorylation of endothelial nitric oxide synthase (eNOS), a process that is considered to improve blood flow [5]. Hypochlorous acid (HOCl) has both antimicrobial and deodorizing effects on wounds [6]. The optimal conditions for improving skin blood flow are as follows: carbon dioxide gas concentration, 1000–1300 ppm; water temperature, 37 °C; bathing time, 15 minutes; and application interval, once a day [7]. However, the osteogenic effect that suggests the improvement of bone metabolism has only been reported in animal experiments [8, 9].
It has been suggested that povidone–iodine sugar ointment (U-PASTA; Kowa Company, Ltd. Japan), which is widely used for incurable ulcers, activates keratinocytes and fibroblasts and promotes wound healing [10], and its effectiveness in improving wound healing has been proven in clinical surgical wounds [11]. Povidone–iodine sugar ointment, which consists of 70% sugar and 3% povidone–iodine, also called Knutson’s formula, has been proposed to improve wound healing due to a reduction in bacterial contamination, rapid debridement of eschar, probable nourishment of surface cells, filling of defects with granulation tissue, and covering of granulation tissue with epithelium [12].
In this study, we applied the combination of these treatments in a case of metatarsal osteomyelitis caused by diabetic foot ulcer, and were able to regenerate the destroyed metatarsophalangeal joint of the second toe, which showed osteolytic changes. There have been no clinical reports on the stimulation of bone and joint regeneration by carbon dioxide foot bathing and povidone–iodine sugar ointment. The synergistic effects of carbon dioxide foot bathing on increased muscle blood flow and the epithelializing interaction of povidone–iodine sugar ointment may be the mechanism underlying this breakthrough result. It is speculated that bone cortex may have regenerated around the remaining bone marrow in areas that were difficult to visualize on X-ray. However, there is no evidence that this is the case. This result also suggests that aggressive debridement or curettage of the lesion may not always be necessary, even if osteolytic changes are seen in osteomyelitis.
As the number of patients for whom surgical intervention is difficult (for example patients on dialysis) is increasing, this therapy is considered to be extremely useful because of its minimal invasiveness and low cost, which allows simple home treatment by the patient or their caregiver. There have been no previous clinical reports on bone and joint regeneration stimulation by artificial carbon dioxide foot bathing and povidone–iodine sugar ointment. This therapy may lead to a reduction in healthcare costs for a huge number of diabetic patients.