Grimmer 1992.

Methods	Randomised controlled trial 3‐arm parallel group design Trial duration: 1 day No power calculation reported
Participants	60 patients randomised 60 patients with knee OA reported at baseline Study joints: 60 knees Number of females: 37 of 60 (62%) Average age: 66 years
Interventions	Experimental intervention: high frequency TENS, once only in group 1, burst TENS, once only in group 2 Control intervention: sham TENS, once only Duration of treatment period: 1 day Analgesics not allowed Device: Medtronic Neuromed Selectra (dual channel) Self‐administered: no Waveform: unclear Pulse width: unclear Pulse frequency: 80 Hz in group 1, 3 Hz trains of 7 80 Hz pulses in group 2 Amplitude: above sensory threshold, strong tolerable tingling paraesthesia Duration of stimulation per session: 30 minutes Electrodes: 4 carbon rubber silicone electrodes, 2 x 3 cm Placement: 4 acupuncture points around the knee: medial (SP9), lateral (GB33), posterior (UB40), anterior (SP10)
Outcomes	Extracted pain outcome: global pain immediately after first and only application, described as "Immediate pain relief (VAS)" No function outcome reported No primary outcome reported
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Unclear risk	Quote: "randomly allocated (by dice) into three groups of 20"
Allocation concealment?	Low risk	By a person independent of the study
Free of selective reporting?	Unclear risk	Insufficient information provided; no access to study protocol
Adequate blinding of patients?	Low risk	Sham device: Medtronic Neuromed Selectra, with non‐functioning leads. Patient were told that a very high frequency current was being tested and that no skin sensation would be felt.
Incomplete outcome reporting: intention‐to‐treat analysis performed? Pain	Low risk	Degrees of freedom reported indicate that all randomised patients were included in the analysis
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