Quirk 1985.

Methods	Randomised controlled trial 3‐arm parallel group design* Trial duration: 26 weeks No power calculation reported
Participants	38 patients randomised 38 patients with knee OA reported at baseline Study joints: 38 knees Number of females: 29 of 38 (76%) Average age: 63 years
Interventions	Experimental intervention: interferential current + exercise, interferential current stimulation: 3 times per week, exercise twice daily Control intervention: exercise twice daily Duration of treatment period: 4 weeks Analgesics allowed, unclear whether intake was similar between groups Device: Endomed 433 and Vacutron 423 (unclear whether 2 or 4 pole) Self‐administered: no Waveform: interferential Pulse width: not applicable Pulse frequency: 0 to 100 Hz 10 minutes, 130 Hz last 5 minutes Amplitude: not reported Duration of stimulation per session: 15 minutes Electrodes: suction electrodes Placement: not reported
Outcomes	Extracted pain outcome: other after 26 weeks, described as "Pain composite score with items rest, post‐exercise and night pain (approach unclear; either VAS or verbal scoring technique modified after Newland)"** Extracted function outcome: other algofunctional scale after 26 weeks, described as "Overall clinical condition scale developed by authors, which was based on 3 items for pain; rest‐, post‐exercise‐, night pain and 3 for function; gait, method of climbing stairs and using walking aids (most likely Likert)". No primary outcome reported
Notes	*1 trial arm, in which shortwave diathermy was given, was excluded, **only baseline values with standard error and P values for change from baseline per group reported. No contact could be established with the investigators.
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Unclear risk	No information provided
Allocation concealment?	Unclear risk	No information provided
Free of selective reporting?	High risk	No results reported for some outcomes mentioned in the methods section, including maximum knee girth
Adequate blinding of patients?	High risk	No sham intervention
Incomplete outcome reporting: intention‐to‐treat analysis performed? Pain	Low risk	Quote: "All patients completed their therapy and the first two assessments (baseline and end of treatment), while 92% completed the final assessment (3‐6 months after treatment)"
Incomplete outcome reporting: intention‐to‐treat analysis performed? Function	Low risk	See above
Funding by commercial organisation avoided?	Unclear risk	No information provided
Funding by non‐profit organisation?	Unclear risk	No information provided