Interferential therapy (IFT) has been applied in a quadripolar way so that the two currents intersect in the painful area. Clinically, no clear reduction effect of pain has been confirmed with this application method of IFT. Experimentally, the highest voltage of IFT is being induced outside the intersection area of the two used currents. Thus, it is probably true that placing the painful area outside the intersection spot of the two currents would reveal a significant pain reduction.

A double-blind placebo-controlled clinical investigation. setting: a public hospital physiotherapy department. Participants: 168 subjects with subacute low back pain. Interventions: participants were randomly assigned to: 1 - external IFT (painful spot was at 2cm outside of the outer borders of the electrodes); 2 - placebo external IFT; 3 - traditional IFT (painful spot was at the crossing area of the two currents); 4 - placebo traditional IFT. Groups 1 and 3 received 20min of IFT at 100Hz and comfortable stimulation intensity. Groups 2 and 4 received sham IFT for 20min. Main outcome measures: Before and immediately after IFT session, pain severity, pressure threshold (PPT) and distribution were assessed using visual analogue scale (VAS), algometer, and distance from pain source, respectively. Distance from the tip of middle finger to the ground during forward trunk flexion determined range of motion (ROM).

Only VAS and ROM improved with all groups, P˂0.03 with no statistical differences between them, P>0.1. Active IFTs changed all outcomes to same extent. There was a trend of better VAS reduction with active IFTs compared to placebos.

No therapeutic difference between external and traditional applications. The effect IFT in pain and ROM is not more than placebo. However, a trend of better pain reduction with active IFTs compared to placebos was noticed.