Study Protocol: Effect of tens in relation to central sensitization in patients with osteoarthritis of the knee

Background Central sensitization has recently been documented in patients with knee osteoarthritis (OAk). So far, the presence of central sensitization has not been considered as a confounding factor in studies assessing the pain inhibitory effect of transcutaneous electrical nerve stimulation (TENS) on osteoarthritis of the knee. Aims This study will explore the prognostic value of central sensitization on the pain inhibitory effect of TENS in Oak patients. Methods Patients with knee pain due to OAk will be recruited through advertisements in local media. Central sensitization will be measured by temporal summation (TS), before and after a heterotopic noxious conditioning stimulation (HNCS). In addition, pain on a numeric rating score and WOMAC subscores for pain and function will be assessed. Patients will be randomly allocated to one of two treatment groups (TENS, sham TENS). Follow-up measurements will be scheduled after 6 and 12 weeks. The prognostic value of TS and HNCS on the pain inhibitory effect of TENS will be statistically analyzed. Conclusion TENS influences pain through the electrical stimulation of low-threshold A-beta cutaneous fibers. The responsiveness of central pain-signaling neurons of OAk patients who are centrally sensitized may be augmented to the input of these electrical stimuli. This would encompass an adverse therapy effect of TENS. Therefore it might be interesting to identify a subgroup of symptomatic OAk patients, i.e. non-sensitized patients, who are likely to benefit from TENS.