Instrumentation

The DAP [2] is a simple performance test with an integrated pain score, designed to provide useful information for monitoring treatment progress and evaluating treatment effects in knee OA. The patient is asked to perform as many standing knee-bends as possible within 30 s. For each knee bend, the knees should reach close to 90° of flexion and full extension. This movement is supervised by the rater. The test score is self-reported pain intensity during knee bends on a 0–10 NRS reported immediately after the 30 s of knee-bends as the worst pain during the test. Thus, the pain intensity score is an assessment of pain during performance of a specific weight-bearing activity. The DAP takes 1–2 min to perform, including verbal instructions. Administering the test does not require any equipment beside a stopwatch/watch. The DAP was applied at baseline and at the end-of-treatment visit.

The KOOS [8] is a questionnaire for assessing patient-reported symptoms. KOOS consists of 5 subscales assessing different constructs: Symptoms (7 items), Pain (9 items), Function in daily living (16 items), Function in sports and recreation (5 items), and knee-related Quality of Life (QoL) (4 items). Responses are given using Likert boxes, and each question is assigned a score from 0–4. A normalized score is calculated for each subscale ranging from 0 (extreme symptoms) to 100 (no symptoms). Reliability of KOOS in an OA population has been reported as acceptable [9]. The KOOS questionnaire was applied at baseline and at the end-of-treatment visit.

The 6MWT [10] is a walking test measuring the total distance walked in 6 min. The distance is a surrogate measure of functional capacity and cardiovascular function, originally used for patients with heart and lung diseases. The 6MWT has shown acceptable test-retest reliability and responsiveness in knee OA populations [11, 12]; it was applied at baseline and at the end-of-treatment visit.

Pain rating on a 0–10 NRS immediately after the 6MWT (6MWTpain) is not a standardized test. However, similar ratings of pain subsequent to a performance test have been applied in other studies [5, 6]. The 6MWTpain was included to compare the DAP with this other assessment of pain during a performance test. The 6MWTpain was applied at baseline and at the end-of-treatment visit.

Transition ratings, or Global Perceived Effect scales, are recommended as a core outcome measure in chronic pain trials [13] and have been used as an external criterion to determine responsiveness [14] or Minimal Important Change (MIC) [3] of other measurement instruments. A transition questionnaire (TRANS-Q), modified from Jaschke et al. [15], was used for asking the participants about their experienced change in pain after the intervention with the question: “Did your knee pain change since you entered this project?” Response options were: “It is unchanged,” “It is better,” and “It is worse.” The ‘unchanged’ response is given a score of 0, and no further questions are asked. The responses “It is better” and “It is worse” bring up a seven-point scale, with scores spanning from −7 (worst) to +7 (best), respectively. For the purpose of this study, a clinically important change in pain was defined as a TRANS-Q score of at least 2 (+2: a little better; −2: a little worse). No change was defined as a TRANS-Q score of 0 (no change) or +1/-1 (Almost the same, hardly any better/worse at all). The transition questionnaire was implemented in the hosting trial after the trial commenced and therefore applicable to only a subset of the trial participants. The transition questionnaire was administered only at the end-of-treatment visit.

The Kellgren & Lawrence grading scale is used to assess radiographic severity of knee OA based on radiographic features; osteophytes, periarticular ossicles, narrowing of joint cartilage, sclerotic tissue, altered shape of bone ends. The scores are: 0 (no x-ray changes of OA), 1 (doubtful presence of OA), 2 (minimal presence of OA), 3 (moderate presence of OA), and 4 (severe presence of OA) [16]. X-rays were taken at baseline and at the end-of-treatment visit.

The Ahlbäck classification of radiographic knee OA of the tibiofemoral joint also assesses radiographic severity of OA and has five grades: 1 (joint space narrowing, <3 mm), 2 (joint space obliteration), 3 (minor bone attrition, 0-5 mm), 4 (moderate bone attrition, 5-10 mm), 5 (severe bone attrition, >10 mm) [17]. X-rays were taken at baseline and at the end-of-treatment visit.