Law 2004.

Methods	Randomised controlled trial 4‐arm parallel group design Trial duration: 4 weeks No power calculation reported
Participants	36 patients randomised 36 patients with knee OA reported at baseline Study joints: 48 knees* Number of females: 35 of 36 (97%) Average age: 82 years
Interventions	Experimental intervention: 2 Hz TENS in group 1, 100 Hz TENS in group 2, modulation TENS with alternations between 2 to 100 Hz in group 3, 5 times per week in all groups 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: Han Acupoint Nerve Stimulation LH204H Self‐administered: no Waveform: unclear Pulse width and frequency: 576 µsec and 2 Hz in group 1, 200 µsec and 100 Hz in group 2, 576/200 µsec and 2/100 Hz alternation in group 3 Amplitude: above sensory threshold, up to comfortable level, range 25 to 35 mA Duration of stimulation per session: 40 minutes Electrodes: 4 rubber electrodes of 4.5 x 3.8 cm Placement: 4 acupuncture points: ST35, LE4, SP9, GB34
Outcomes	Extracted pain outcome: pain on walking after 4 weeks, described as "intensity of pain felt while walking (VAS)" No function outcome reported No primary outcome reported
Notes	Outcome data were reported on knee level.
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Low risk	Quote: "Randomization was carried out by drawing lots from the randomization envelope."
Allocation concealment?	Unclear risk	No information provided
Free of selective reporting?	Unclear risk	Insufficient information provided; no access to study protocol
Adequate blinding of patients?	Low risk	Use of sham device: identical in appearance, internal circuit disconnected, no current passed, indicator light on, digital display of intensity control functioned normally. Quote: "Only therapists who administered treatment to the subjects knew the group allocation, while the subjects and the assessor were not given this information."
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	Unclear risk	Not applicable
Funding by commercial organisation avoided?	Unclear risk	No information provided
Funding by non‐profit organisation?	Unclear risk	No information provided