Written consent to participate in this study was obtained from all participants, with no financial incentives. The inclusion criteria were as follows: (1) pain at the inferior pole of the patella that had persisted for ≥ 1 month for patellar tendinopathy, (2) being > 18 years old, and (3) the ability to provide written informed consent. The exclusion criteria were as follows: (1) inability to understand Japanese language, (2) history of knee surgery or surgery during the study period, and (3) other knee injuries that can mask the anterior knee pain. The participants were recruited at only the Athletic training room at the Juntendo University. We examined MRI or US as required by physician to confirm lesions and clinical conditions.
This study was performed at Juntendo University, Chiba, Japan, from February 2021 to February 2022, with ethical approval from the institutional review board of the Research Ethics Committee of Juntendo University (H20-0289). Informed consent to participate in this study was obtained from all participants, with no financial incentives. Evaluations were made at three time points: at the baseline, 1 week, and 12 weeks. The observation items were the VISA-P-J, visual analog scale (VAS) for pain, Roel's classification of symptoms , and Patient Global Impression of Change (PGIC) . The VISA-P-J, VAS, and Roel’s classification were used during the study period. The PGIC was assessed at 12 weeks. The participants neither received any interventions during the study period nor were they advised any activity restrictions. The sample size was determined based on COSMIN’s recommendation.
Translation procedures of the Japanese of version of VISA-P
We developed the VISA-P-J based on a guideline for cross-cultural adaptation of self-report measures . The process was composed of the following six steps: (1) Translation of the original English version into Japanese; (2) Review and modification of the translated items by experienced sports medicine physicians; (3) Back translation into English by an English native speaker; (4) Review of the back-translated version by experienced sports medicine physicians and sports medicine specialists; (5) Testing of the prefinal version on a group of 43 people; and (6) Approval of the final version of the VISA-P-J (Additional file 1).
The participants’ pain was assessed using the VAS. The classification according to symptoms was based on the four categories of symptoms developed by Roels et al. [24, 27]. The PGIC was used to evaluate participants’ subjective judgment about any change (improvement) perceived . It comprised a 7-point scale that indicated the following: 1 = very much worse, 2 = much worse, 3 = minimally worse, 4 = no change, 5 = minimally improved, 6 = much improved, and 7 = very much improved.
We evaluated the reliability, validity, responsiveness, and interpretability of the VISA-P-J according to the COSMIN guidelines [21, 28]. The test–retest reliability measures the stability of a stable construct questionnaire obtained from the same population on two occasions. A retest was performed one week after the primary test to avoid changes in participants’ condition between tests and recall bias . Measurement errors were calculated using standard error of measurement (SEM). Internal consistency, which measures whether subscales measure the same concept, was evaluated using Cronbach's alpha .
Clarifying the aim of measurement, target population, and concepts  was required to evaluate content validity. For the VISA-P-J, we set a measurement aim to assess the pain and disability of patellar tendinopathy subjectively. This instrument was used to assess the symptoms, function, and ability of participants with patellar tendinopathy [7, 30]. To assess criterion validity, which measures whether a scale is related to existing external criteria, we assessed the correlations between the VISA-P-J score and (1) Roel’s classification, (2) VAS–activities of daily living (VAS-ADL), and (3) VAS-Sports as the criterion validity. Construct validity, which indicates whether a scale represents the intended construct, and responsiveness were assessed using hypothesis testing . The construct validity hypotheses were H1–H3, and the hypotheses of responsiveness were H4–H6. The hypothesis testing method was proven when at least 75% of the predetermined hypothesis was achieved .
VISA-P-J scores will have a negative correlation with symptom classification.
VISA-P-J scores will have a negative correlation with the VAS-ADL scores.
VISA-P-J scores will have a negative correlation with the VAS-Sports scores.
Participants who answer 5–7 on the PGIC scale will have a more positive change in VISA-P-J scores than those who answer 1–4 on the PGIC scale.
The amount of change in VISA-P-J scores will negatively correlate with the amount of change in VAS-ADL scores.
The amount of change in VISA-P-J scores will negatively correlate with the amount of change in VAS-Sports scores.
The floor or ceiling effect was defined as > 15% of participants reporting minimum or maximum scores, respectively . The minimal clinically important difference (MCID) was defined as the participant’s perception of whether there was an important change in the patellar tendinopathy status . The within-group MCID was measured according to the mean score changes in the PGIC scale between "minimally improved" and "no change" from baseline to 12 weeks.
The demography of the participants was shown with standard deviation (SD). Test–retest reliability was assessed using two-way random-effects, absolute agreement intraclass correlation coefficient (ICC). ICC values less than 0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability and values greater than 0.90 indicate excellent reliability . Criterion validity, construct validity (H1–H3), and responsiveness (H5–H6) were assessed using Pearson's and Spearman's rank correlation coefficient tests. Responsiveness (H4) was tested using the Mann–Whitney U test. All analyses were performed using SPSS version 22 for Windows (SPSS Inc., Chicago, IL, USA), with statistical significance set at p < 0.05.