Introduction
Knee osteoarthritis (KOA) is one of the most common chronic diseases [
1,
2]. Pain is the main factor that drives patients to pay attention to medical treatment, and it is also the main factor that leads to functional limitation and quality of life decline [
3]. In addition, pain may be the most important variable in deciding whether to operate [
4]. Therefore, the measurement of pain is important in clinical practice [
5]. However, since pain is a subjective symptom and cannot be reliably measured through external evaluation, effective and reliable measurement tools are needed to evaluate the patients’ subjective perception on pain [
6]. Patient-reported outcome measures scale (PROMs) is now widely accepted as the gold standard for pain evaluation [
7].
The Brief Pain Inventory (BPI) is an validated, reliable, and commonly used instrument that can assess the location and severity of pain and its impact on pain individuals [
6]. BPI was originally invented for cancer patients and has been adapted into multiple languages [
8‐
12]. There is already a Chinese version of BPI for cancer patients [
13]. However, its psychological characteristics for nonmalignant pain have not been verified in China, especially for KOA patients.
Currently, English and Norwegian studies have reported that BPI has favorable psychometric properties in osteoarthritis patients [
4,
14]. As far as we know, there is no study showing the psychometric characteristics of BPI in Chinese KOA patients. Therefore, the purpose of the present study was to translate and adapt the short form of BPI cross-culturally into a simplified Chinese version (BPI-CV) and verify its reliability and validity in KOA patients.
Discussion
The present study translated BPI into a Chinese Version and culturally adapted, and the results showed that BPI-CV had good psychometric properties in patients with KOA.
Epidemiological studies have shown that symptomatic KOA affects 24% of the general population, and the main harms of KOA are pain and functional limitations, which are important factors for patients to decide on surgery when in pain [
26]. The accurate evaluation of pain, which can provide a reference basis for the management of KOA patients and the development of targeted interventions, is of great clinical value [
27].
BPI has been validated and adapted for several languages, including Chinese [
28]. But so far, Chinese version of BPI has only been validated in patients with cancer pain. Although pain is a universal experience, patients with cancer pain versus non-cancer pain may differ in how they perceive pain and how the pain interferes with their lives. Some scholars compared BPI pain ratings of patients with typical nonmalignant pain and cancer pain and found that the former were more likely to rate their pain intensity at the top of the scale, whereas pain ratings of patients with cancer tended to be more evenly distributed across the various levels of the scoring scale [
29]. Therefore, it cannot be assumed that the reliability and validity data of BPI scales in patients with cancer pain also support validity in other chronic pain patient populations. So, it is urgent to verify the reliability and validity of BPI in a large number of patients with nonmalignant pain, such as those with KOA.
There were no ceiling or floor effects in BPI-CV in the KOA patients, which is consistent with the results of the Norwegian version [
4] and Spanish version of BPI [
22], and indicates that the BPI-CV is a questionnaire with good discriminatory ability.
Internal consistency for all versions of the BPI was expressed using the Cronbach α coefficient. The Cronbach α coefficient for the BPI-CV in the present study was 0.894, which is generally consistent with the English version (0.86–0.96) [
14], the Norwegian version (0.87–0.88) [
4], the Spanish version (0.834–0.850) [
22], the Turkish version (0.84–0.89) [
5,
30], and the Persian version of BPI (0.88–0.91) [
31]. All alpha values above indicated good internal consistency. The ICC of the present study was 0.852, which was basically consistent with the Turkish version (
r = 0.77–0.88) [
5,
30] and the Persian version of BPI (
r = 0.87–0.91) [
31].
In terms of construct validity, the results of the present study showed that the BPI-CV was moderately to highly correlated with the pain dimension (
r = 0.496–0.860) and the functional interference dimension (
r = 0.517–0.712) of the WOMAC and weakly correlated with the WOMAC stiffness dimension (
r = 0.152–0.367), probably because the BPI mainly assesses pain and functional interference and does not assess stiffness with specific items. This observation result is basically consistent with the trend of the results observed in the Norwegian version [
4], which confirms the rationality of the dimension classification used in the present study. There was a strong correlation between the total BPI-CV and EQ-5D (
r = 0.768). All these results indicate that BPI-CV has qualified construct validity.
The structural validity of the BPI-CV was verified using exploratory factor analysis. The results of the Turkish version [
5,
30] and Persian version [
31] were consistent with the original version and contained two factors, four pain severity items and seven pain interference items. However, the interference items “sleep” and “enjoyment of life” in the English version did not load steadily on either factor [
14]. Compared to the results of the English version, all factors in the present study were loaded stably with factor loadings greater than 0.6. However, the results of the present study revealed three factors, rather than two. There were studies that also reported a three-factor model in which the “sleep” item loaded on the emotional dimension, and in the present study, the “sleep” loaded on the pain dimension [
32,
33]. It has been shown that osteoarthritis is associated with short sleep duration due to disease-related pain leading to disruption of sleep patterns [
34]. This may be the reason why the “sleep” item loaded into the pain dimension.
Since BPI was originally developed to assess the pain severity and impact of cancer patients and evaluate the analgesic effectiveness for these patients, we have adapted the original BPI to better evaluate the pain status of KOA patients. First, the first item of the original BPI is to ensure that the scale is only used for cancer pain patients, while the present study is mainly used for KOA patients, so we decided to delete this item [
35]. Secondly, the second item of the original BPI is to identify the specific site of cancer pain, while the present study focuses on KOA patients. Therefore, we use the partial picture of the knee joint instead of the whole-body picture. Thirdly, when using BPI, the setting of reference period is directly related to the purpose of the investigation, which may limit the collection of information and is the premise of pain assessment [
35]. The reference period of the original version of BPI is only 24 h, but the pain of KOA patients is a chronic pain [
36], and the reference period should be extended accordingly, so that the patient's pain status can be assessed more comprehensively [
35]. Some studies have increased the reference period to 1 week and achieved satisfactory results [
30]. Therefore, we decided to use “1 week” as the reference period of BPI.
Moreover, it is important to acknowledge that our research has certain limitations. Firstly, the lack of longitudinal data poses a challenge in accurately measuring responsiveness, such as determining the smallest clinically significant difference or impact size. Secondly, the patient sample primarily consists of individuals from central and western regions of China, which may not be fully representative of the entire Chinese population. To address these limitations, we aim to conduct a multi-center study in the future investigations.
In conclusion, we have successfully translated and adapted the BPI-CV instrument. The translated and adapted version has demonstrated good feasibility, reliability, and validity. The BPI-CV serves as a simple, valid, and reliable tool for assessing subjective experiences of pain severity, activity interference, and emotional interference in patients with KOA.
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