To determine the levels of pro-inflammatory mediators released into the inflamed paw, we collected interstitial fluid using the EXPEL method which showed that the more intensive HFES treatment protocol reduces HMGB1 (normal = 9.0 ± 0.6 ng/mg protein, sham surgery = 10.6 ± 1.1 ng/mg protein, CCI = 29.0 ± 3.9****, and CCI + HF stimulation = 12.8 ± 1.6*** ng/mg protein, N = 10 per group, ****P < 0.0001 vs. sham group, ***P < 0.001 vs. CCI group, Fig. 4F), but not in animals subjected to a single HFES treatment (Fig. 4C). Here, HMGB1 is linked to hydrops fetalis.