Reinforcement of Placebo Response in Knee Osteoarthritis: A Randomised Trial

Knee pain defined as "the average level of pain in your knee today" will be assessed with a 100 mm visual analogue scale (VAS) with anchors 0 = "no pain" and 100 = "Worst imaginable pain".

The key secondary objective is to assess if pain variability in the week before treatment is a determinant of the effect of the subsequent treatment.

The Brief illness perception questionnaire (BIPQ) is a generic questionnaire developed to measure illness perception in a variety of illnesses. The questionnaire is patient-reported and assesses perceptions on the following five dimensions: Identity, Cause, Timeline, Consequences and Cure-Control. It contains eight numerical rating scales questions (0-10) and a memo field based on the patients' own beliefs about their condition. In some circumstances it may be possible to compute an overall score which represents the degree to which the illness is perceived as threatening or benign. To compute the score, reverse score items 3, 4, and 7 and add these to items 1, 2, 5, 6, and 8. A higher score reflects a more threatening view of the illness.

The Knee injury and Osteoarthritis Outcome Score (KOOS) is used to assess patient-reported knee-related symptoms. The KOOS is a patient-reported outcome measurement instrument developed to assess the patient's opinion about their knee and associated problems.KOOS comprises of 42 items in 5 separately scored subdomains: KOOS Pain (9 items), KOOS Symptoms (7 items), Function in daily living (KOOS Function; 17 items), Function in Sport and Recreation (5 items), and Knee-related Quality of Life (4 items). The previous week is the time period considered when answering the questions, and the questions relate to one knee (the target knee in this trial).

The 30 seconds chair stand test (30sCST) is a physical performance test that quantifies how many sit-to-stand movements an individual can perform within 30 seconds. The 30sCST is a measure of balance 500 during functional activities and lower extremity function and strength. It is recommended as a 501 performance-based test to assess physical function in people diagnosed with hip or knee OA. From the sitting position in the middle of seat with feet shoulder width apart, flat on the floor, arms crossed at chest, the participant is asked to stand completely up, then sit completely back down, repeatedly for 30 seconds. The total number of complete chair stands (up and down represents one stand) is counted. There is given only one trial. If a full stand is completed at 30 seconds, then this is counted in the total. The same chair is used at all assessments.

The 4x10 meter fast walk test (40mFWT) is a physical performance test that quantifies short distance walking performance. The 40mFWT is a measure of walking speed over short distances and changing direction during walking. It is recommended as a performance-based test to assess physical function in people diagnosed with hip or knee OA (26).

The participant is asked to walk as quickly but as safely as possible to a mark 10 m away, return, and repeat for a total distance of 40 m. Regular walking aid is allowed and recorded. Time of one trial, with turn time excluded, is recorded and expressed as speed m/s by dividing distance (40 m) by time (s).

A stair climbing test (SCT) is a physical performance test that quantifies how fast an individual can ascend and descend a flight of stairs in a usual manner. The SCT is a measure of balance during functional activities and lower extremity function and strength. It is recommended as a performance-based test to assess physical function in people diagnosed with hip or knee OA.

The participant is asked to ascend and descend a flight of stairs in a usual manner, and at a safe and comfortable pace. Use of any walking aid and handrail is permitted and recorded. Total time to ascend and descend steps for one trial is recorded in seconds. The same flight of stairs is used at all assessments.

The expectation for treatment scale (ETS) is a 5-item questionnaire concerning the patients' expectations of a given treatment. (E.g: 1) "I expect the treatment will help me to cope with my complaints", 2) "I expect the treatment will make my complaints disappear", 3) I expect the treatment will improve my energy", 4) "I expect the treatment will improve my physical performance" and 5) "I expect that after the treatment, my complaints will be considerably better".

Each question has four response options on a likert scale: "partially disagree", "partially agree","agree", "definitely agree".

We will replace the word "treatment" with "saline injection" and "complaint" with "knee pain". The questionnaire has been translated into Danish for this study.

Via ultrasound, the amount of synovial hypertrophy will be measured in mm in position using specific landmarks. The following positions will be examined: 1) The medial joint space and recess (medial longitudinal scan) 2) The lateral joint space and recess (lateral longitudinal scan)

Via ultrasound, the Doppler activity will be measured on a semi-quantitative score from 0-3.

Participants will register their daily use of paracetamol and ibuprofen for knee pain

As a safety outcome, the presence of knee joint effusion will be recorded for each knee as a dichotomous score (present/absent) using ultrasound.