Procedures
After selection through consultation with a doctor, the patients provided their written consent and were given an opportunity to ask any questions regarding the procedure. The patients were examined by an independent physiotherapist, who used a pre-prepared card composed of several instruments: visual analog scale (VAS),22 Brazilian version of the McGill Pain Questionnaire classified according to the number of words chosen (NWC), Pain Rating Index (PRI), Pain Intensity Index (PPI)23-25 and Roland-Morris Disability Questionnaire (RMDQ).26 The examination was done by an independent physiotherapist before and after the protocol of ten treatment sessions. This examiner did not follow the treatment and did not know which group the patients had been included in. After each treatment session, however, the pain intensity was also evaluated using VAS among the patients that received TENS and interferential current.
After evaluation by the physiotherapist, the patients were randomized, through numbers created by a computer, into three groups: 1) TENS (n = 50); 2) interferential current (n = 50); 3) controls (n = 50). The randomized design was balanced in groups of 50. A set of sealed, sequentially numbered opaque envelopes was used for study group assignment. Thus, the study was single-blinded, i.e. the examiner had no contact with the patient during the treatment, and the patient was instructed not to report what assistance had been received during the sessions.