Study design and subjects
This site-based, multicenter, observational, cross-sectionalstudy in China enrolled 601 outpatientswith knee OA from 2 orthopedics, 2 rheumatology, and 1 pain department in 5 tertiary hospitals from March to October 2018.Written informed consent was obtained from each patient beforethey participated in any study-related procedures.
Chinese adult patients (aged ≥40 years) with diagnosed knee OA experiencing chronic pain for at least 3 months and receiving oral medications during the past 12 months were eligible for the study. Patients with rheumatoid arthritisor other inflammatory arthritis; knee pain caused by other diseases (eg, traumatic fracture history or tumor); mental illness, including cognitive disorders such as Alzheimer's disease, schizophrenia; and bedridden patients who were undergoing knee replacement surgery were excluded. Patients with pain level higher than knee pain due to cancer or other reasonssuch, as gout and chondrocalcinosis,were also excluded. Socio-demographics, disease characteristics, Brief Pain Inventory (BPI), treatment information, and patient responses to HRQoL (5-level of Chinese Quality of Life-5 Dimensions version [EQ-5D-5L]and self-assessed health) and Treatment Satisfaction Questionnaire for Medication (TSQM-1.4) interviews were also assessed.
The characteristics measured wereage, sex, body mass index, ethnicity, employment status, education status, insurance status, and comorbidity (detailed patientcomorbidities are presented in Table 1). The following OA characteristics were measured for each enrolled patient: age and location at first diagnosis, current department of visits, number and location of painful sites, and severity of pain. The average number of weekly days of paid work or housework lost due to OA was also recorded. In addition, information related to the current treatment for OA pain management (including non-pharmacotherapy) was collected from each enrolled patient.
The BPI is a validated self-reported questionnaire that assesses pain severity using the Numerical Rating Scale for Pain Intensity (NRS-PI, 0 to 10 scale, where 0 = no pain and 10 = worst possible pain) for the conditions of worst, least, and average pain, as well as “pain right now”. The 5-level Chinese Quality of Life-5 Dimensions version (EQ-5D-5L) comprises 5 dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Each dimension has 5 levels: no problems, slight problems, moderate problems, severe problems, and extreme problems. Self-health care assessment was performed using the EuroQol (EQ) visual analogue scale (EQVAS). The EQ VAS self-rating records the respondent’s own assessment of their health status on a 20-cm vertical VAS with endpoints labelled ‘the best health you can imagine’ and ‘the worst health you can imagine.’ The TSQM was designed to assess treatment satisfaction for patients with chronic diseases. The TSQM 1.4 is a 14-item psychometrically robust and validated instrument consisting of 4 scales: effectiveness, side effects, convenience, and global satisfaction, eachon a scale of 0–100 with higher scores indicatinga higher level of satisfaction.
Demographic and clinical characteristics were assessed using frequencies and percentages for categorical variables and mean values and SDsfor continuous variables (descriptive analysis) in the whole patient population. Impact on QoL (EQ-5D-5L) and treatment satisfaction (TSQM-1.4) by BPI-Severity score (<4 and ≥4) were presented using mean (SD) and were comparedusing a t-test. For each of self-assessed health, EQ-5D-5L, and TSQM, a linear regression model was used to estimate the regression coefficient along with corresponding 95% confidence interval (CI)for BPI-Severity, adjusting for age (continuous),sex, body mass index (BMI), number of pain sites (continuous),and comorbidity (yes or no). We assessed the effect modification of comorbidityon a multiplicative scale by including interaction termbetween BPI-Severity and comorbidity in linear regression models. Additionally, we conducted the same analysis for the association between BPI-Pain interference and self-assessed health, EQ-5D-5L, and TSQM. Missing data were not analyzed. Statistical analyses were conducted using SAS 9.4 (SAS Institute, Cary, NC), and a 2-sided P value of 0.05 was considered statistically significant.