All participants were asked to complete daily diaries to record their average knee pain during the past 24 hours on each day of a 7-day period using an 11-point numerical rating scale where 0 represents "No Pain" and 10 represents "Pain as bad as you can imagine." The average pain scores were calculated across the 7-day diary(s) at baseline and across weeks 5 to 8 post-start of treatment. Percent reduction was then calculated for each participant. To be considered a success, participants must have experienced ≥ 50% reduction in average knee pain. The number of successes is presented.

Full Analysis Set presented. To account for missing data due to missed visits and early terminations, data were also imputed using a mixed-effects model.

At each study visit following the baseline assessment at Visit 1, participants were questioned if any changes in their medical status or condition have occurred since their previous visit. If the participant experienced a change that was a study-related adverse event, an Adverse Event Form was completed by the site. The number of participants that experienced at least one study-related adverse event is reported here. Adverse Events are reported by the trial phase in which they occurred: Group 1 Treatment (active stimulation), Group 2 Control (sham stimulation), and Group 2 Crossover Safety Set (active stimulation).

Safety Analysis Set presented.

All participants were asked to complete daily diaries to record their average knee pain intensity during the past 24 hours on each day of a 7-day period using an 11-point numerical rating scale where 0 represents "No Pain" and 10 represents "Pain as bad as you can imagine." The average pain score was calculated across the 7-day diary(s) at baseline and across weeks 1 to 4 post-start of treatment. Percent reduction was then calculated for each participant. To be considered a success, participants must have experienced ≥ 50% reduction in average knee pain. The number of successes is presented.

Full Analysis Set presented.

All participants were asked to complete daily diaries to record their average knee pain intensity during the past 24 hours on each day of a 7-day period using an 11-point numerical rating scale where 0 represents "No Pain" and 10 represents "Pain as bad as you can imagine." The average pain score was calculated across the 7-day diary for each participant at baseline and at 3-, 6-, 9-, and 12-months post-start of treatment. Percent reduction was then calculated for each participant. To be considered a success, participants must have experienced ≥ 50% reduction in average knee pain. The number of successes is presented.

Full Analysis Set presented. According to the planned study protocol, Group 2 was not assessed for this outcome at 6, 9, and 12-months due to crossover to receive active stimulation. To account for missing data due to missed visits and early terminations, data were also imputed using a mixed-effects model for Group 2 at 3-months post-SOT and for Group 1 at 6, 9, and 12-months post-SOT.

All participants were asked to complete daily diaries to record their average knee pain intensity during the past 24 hours on each day of a 7-day period using an 11-point numerical rating scale where 0 represents "No Pain" and 10 represents "Pain as bad as you can imagine." The mean pain score was calculated across the 7-day diary(s) for each participant at baseline, 1-4 weeks post-start of treatment (SOT), 5-8 weeks post-SOT, and at 3-, 6-, 9-, and 12-months post-SOT. The mean pain score is presented.

Full Analysis Set presented. According to the planned study protocol, Group 2 was not assessed for this outcome at 6, 9, and 12-months due to crossover to receive active stimulation. To account for missing data due to missed visits and early terminations, data were also imputed using a mixed-effects model for Group 2 at 3-months post-SOT and for Group 1 at 6, 9, and 12-months post-SOT.

Participants recorded the amount/type of analgesics used in daily diaries. A blinded, third-party medication committee reviewed participants' diary medications for each time period to determine if each participant's analgesic usage changed. The committee determined whether there was No change (no change in dosage or change is not clinically meaningful to impact pain outcomes), an Increase (clinically meaningful increase in medication that would impact pain outcomes), or a Decrease (clinically meaningful decrease in medication that would impact pain outcomes) for each time period compared to baseline. The number of participants with a Decrease in analgesic medication usage for pain are reported. Participants that did not report any pain medications during the study were excluded from the analysis.

Full Analysis Set presented. According to the planned study protocol, Group 2 was not assessed for this outcome at 6, 9, and 12-months due to crossover to receive active stimulation. Participants that did not report any pain medications during the study were excluded. Data were not available for one Group 2 participant at 3-months post-SOT, five Group 1 participants at 6-months post-SOT, three Group 1 participants at 9-months post-SOT, and six Group 1 participants at 12-months post-SOT.

The Pain Catastrophizing Scale (PCS) questionnaire has 13 questions that assess rumination, magnification, and helplessness. Participants are asked to think back on painful experiences in the past and reflect on how often they had specific thoughts or feelings. Each of the 13 questions is scored on a 5-point scale where 0 represents "not at all," and 4 represents "all the time." The scores from each question were summed for each participant to provide a total PCS score, with a possible range from 0 to 52 with higher scores indicating a greater tendency to catastrophize pain (i.e. a higher score indicates a worse outcome). The mean score for each time point is presented.

Full Analysis Set presented. Data were not available for one Group 1 participant and two Group 2 participants at 4-weeks post-SOT and for one Group 2 participant at 8-weeks post-SOT.

The Patient Global Impression of Change (PGIC) Survey asks participants to rate their improvement with treatment on a 7-point scale ranging from -3 to 0 to +3, where -3 represents "very much worse," 0 is "no change," and +3 represents "very much improved" as compared to before stimulation treatment. The participants combine all the components of their experience into one overall score. The mean score of each group was calculated for each time frame.

Full Analysis Set presented. According to the planned study protocol, Group 2 was not assessed for this outcome at 6, 9, and 12-months due to crossover to receive active stimulation. Missing data due to missed visits and early terminations were also imputed using a mixed-effects model for outcomes at 6, 9, and 12-months post-SOT. Data were not available for one Group 1 and two Group 2 participants at 4-weeks, one Group 2 participant at 8-weeks, and one Group 2 participant at 3-months post-SOT.

Question 9 of the Brief Pain Inventory-Short Form (BPI-9) is a 7-part question that assesses the level of interference that participants experience in their daily lives due to pain. The 7 categories are general activity, mood, walking ability, normal work, relations with other people, sleep, and enjoyment of life. Participants were asked to rate how much their post-surgical knee pain interferes with each aspect on an 11-point numerical scale where 0 represents "Does Not Interfere" and 10 represents "Completely Interferes." The average of these 7 scores was calculated for each participant at each time point. Percent reduction was then calculated for each participant. To be considered a success, participants must have experienced ≥ 50% reduction in pain interference. The number of successes is presented.

Full Analysis Set presented. According to the planned study protocol, Group 2 was not assessed for this outcome at 6, 9, and 12-months due to crossover to receive active stimulation. For participants that completed treatment, missing data due to missed visits and early terminations were also imputed using a mixed-effects model at 6, 9, and 12-months post-SOT. Data were not available for one Group 2 participant at 8-weeks and 3-months post-SOT.

The Western Ontario and McMaster University Osteoarthritis Index (WOMAC) questionnaire consists of 24 items that evaluate pain, stiffness, and physical functional disability. Each item is scored on an 11-point numerical rating scale from 0 to 10, where higher scores indicate greater pain, stiffness, and disability. For each participant, the scores from each of the 24 items were averaged to calculate the participant's total score, with a minimum score of 0 and a maximum score of 10. The mean total score was then calculated across participants and percent reduction was calculated for each time point. To be considered a success, participants must have experienced ≥ 33% reduction in their score. The number of successes is presented.

Full Analysis Set presented. According to the planned study protocol, Group 2 was not assessed for this outcome at 6, 9, and 12-months due to crossover to receive active stimulation. For participants that completed treatment, missing data due to missed visits and early terminations were also imputed using a mixed-effects model at 6, 9, and 12-months post-SOT. Data were not available for one Group 2 participant at 8-weeks and 3-months post-SOT.

The total distance that a participant could walk in 6 minutes was recorded, and participants unable to walk at all were given a score of 0 meters. The mean distance was then determined across participants. The baseline score was compared to the score at the specified intervals after start of therapy.

Full Analysis set presented. Data were unavailable for two Group 1 participants and one Group 2 participant at 8-weeks post-SOT and for four Group 1 participants and one Group 2 participant at 3-months post-SOT.