Background

Central sensitization has recently been documented in patients with knee osteoarthritis. So far, the presence of central sensitization has not been considered as a confounding factor in studies assessing the pain inhibitory effect of TENS on osteoarthritis of the knee.

Purpose

First, to explore the pain inhibitory effect of burst TENS in OAk patients. Second, to 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. Temporal summation, before and after a heterotopic noxious conditioning stimulation, will be measured. 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 a period of 6 and 12 weeks.

Discussion/ 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, ie. non-sensitized patients, who are likely to benefit from burst TENS.

Inclusion Criteria:

• To be included, patients need to be over 50 years old.
• All should have osteoarthritis in at least one knee fulfilling the American College of Rheumatology classification criteria and report peak knee pain over the last 24 h of more than 3 on a Numeric Rating Score (0-10 scale).

Exclusion Criteria:

• Patients are excluded if they have had a knee surgery or intra-articular corticosteroid injection within 6 months
• Current or past (within 4 weeks) oral corticosteroid use
• A history of knee joint replacement or tibial osteotomy
• Contraindications to burst TENS (pacemakers, epilepsy, dermatological conditions, abnormal sensation in the knees, pregnancy) or if they are unable to apply TENS independently