ObjectiveTo compare the effect of intravenous 20% mannitol or dexamethasone (DM) on low back and leg pain after minimally invasive transforaminal lumbar interbody fusion (MI-TLIF). MethodsBetween October 2012 and September 2013, 100 patients with degenerative lumbar diseases underwent MI-TLIF and percutaneous pedicle screw fixation. All patients were randomly divided into 3 groups:34 patients received intravenous 20% mannitol after operation (mannitol group); 32 patients received intravenous DM after operation (DM group); and 34 patients received neither dehydrating agent nor steroid after operation (control group). There was no significant difference in gender, age, disease duration, clinical symptoms, lesion types, and lesion segments between groups (P>0.05). The serum levels of inflammatory factors[tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6] were measured by ELISA at pre-operation and 3, 24, 48, 72, and 96 hours after operation. Low back and leg pain was determined by using visual analogue scale (VAS) score after operation. ResultsAll procedures were smoothly performed without major complications of nerve root injury, hematoma, or infection. There was no significant difference in operation time and intraoperative blood loss between groups (P>0.05). The VAS score of low back pain showed no significant difference between groups at all time points after operation (P>0.05); the VAS score of leg pain in the DM group was significantly lower than that in the control group at all time points (P<0.05), and than those in the mannitol group at 3, 24, 48, and 96 hours after operation (P<0.05). The serum level of TNF-α in the DM group was significantly lower than that in the control group at all time points (P<0.05), and than that in the mannitol group at 3, 48, 72, and 96 hours after operation (P<0.05). The serum level of IL-1β in the DM group was significantly lower than that in the control group at 3, 24, 48, and 72 hours after operation (P<0.05), and than that in the mannitol group at all time points after operation (P<0.05). The serum level of IL-6 in the DM group was significantly lower than that in the control group at 3 and 24 hours after operation (P<0.05), and than that in the mannitol group at 3, 24, and 48 hours after operation (P<0.05). ConclusionIntravenous 20% mannitol may has no effect on postoperative low back and leg pain, while DM can markedly relieve leg pain after MI-TLIF.