Law 2004a.

Methods	Randomised controlled trial 2‐arm parallel group design Trial duration: 2 weeks Unstratified randomisation Multicentre trial with 2 centres No power calculation reported
Participants	39 patients randomised 39 patients with knee OA reported at baseline Study joints: 39 knees Number of females: 37 of 39 (95%) Average age: 75 years Average BMI: 27 kg/m2 Average disease duration: 7.6 years
Interventions	Experimental intervention: TENS, 5 times per week Control intervention: sham TENS, 5 times per week Duration of treatment period: 2 weeks Unclear whether analgesics were allowed and whether intake was similar between groups Device: ITO model 120Z (dual channel) Self‐administered: no Waveform: unclear Pulse width: 200 µsec Pulse frequency: 100 Hz Amplitude: above sensory threshold, up to a comfortable level, range 25‐35 mA Duration of stimulation per session: 40 minutes Electrodes: 4 rubber electrodes, 4.5 x 3.8 cm2 Placement: acupuncture points: ST35, LE4, SP9, GB34
Outcomes	Extracted pain outcome: pain on walking after 2 weeks, described as "intensity of pain felt while walking (VAS)"** Extracted function outcome: walking disability after 2 weeks, described as "Timed‐Up‐and‐Go test over 3 meters (seconds)" No primary outcome reported
Notes	**Only baseline values reported in the report. Contact established with investigators Law and Cheing, who provided end of treatment and follow‐up data.
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Low risk	Quote: "'by drawing lots from the randomization envelope without replacement"
Allocation concealment?	Unclear risk	Quote : "(...) carried out by physiotherapists who performed the treatment"
Free of selective reporting?	High risk	No results reported for some outcomes mentioned in the methods section, including pain intensity on VAS
Adequate blinding of patients?	Low risk	Use of sham device: ITO model 120Z, no current delivered but flashing light on. Quote: "The assessors and subjects were blind to the group allocation. All subjects were told that when the indicator light of the TENS was blinking, it meant the machine was working properly. They might or might not feel any tingling sensation during treatment because the intensity of the current was small."
Incomplete outcome reporting: intention‐to‐treat analysis performed? Pain	High risk	In total, 3 patients dropped out and were excluded from analysis, as indicated by Gladys Cheing and Pearl Law in personal communication
Incomplete outcome reporting: intention‐to‐treat analysis performed? Function	High risk	See above
Funding by commercial organisation avoided?	Unclear risk	No information provided
Funding by non‐profit organisation?	Unclear risk	No information provided