Chinese translation and validation of the Oxford Knee Scale for patients with knee osteoarthritis.

BACKGROUND: Oxford Knee Scale (OKS) is a commonly used instrument to assess the symptoms and functional status in people with knee osteoarthritis. However, a Chinese version of this scale is not yet available.
OBJECTIVE: The objective of this study was to translate the OKS into Chinese and validate the Chinese version of OKS.
METHODS: The Chinese OKS was translated from the original English version following the recommendations of the International Society for Pharmacoeconomics and Outcomes Research. One hundred Chinese reading patients with knee osteoarthritis were recruited from local hospitals and physiotherapy clinics. Psychometric properties were evaluated in terms of test-retest reliability and internal consistency. Convergent validity was examined by Spearman rank correlation coefficient tests by comparing its score with the validated Chinese version of the Western Ontario and McMaster Universities Osteoarthritis Index and Health Outcome Survey Short Form-36.
RESULTS: Chinese OKS demonstrated excellent reliability (intraclass correlation coefficient = 0.88). Cronbach α of individual questions was > 0.7. Strong correlation was found between the Chinese OKS and the Western Ontario and McMaster Universities Osteoarthritis Index (ρ > 0.553, p < 0.001). Fairly strong negative correlation was also found between Chinese OKS and Health Outcome Survey Short Form-36 (ρ = -0.273 to -0.666, p < 0.05).
CONCLUSION: The Chinese translated version of OKS is a reliable and valid instrument for clinical evaluation in Chinese reading patients with knee osteoarthritis.

Introduction

Knee osteoarthritis is a major healthcare concern. The overall lifetime risk of symptomatic knee osteoarthritis is an astounding 50% [1]. According to the statistics from the World Health Organization [2], the current Chinese population is > 1.4 billion. It has been suggested that up to 10.3% of people in China suffer from symptomatic knee osteoarthritis [3]. Therefore, it is estimated that there are currently > 100 million patients with knee osteoarthritis in China. It is foreseeable that the number of Chinese reading patients with knee osteoarthritis will increase with the aging population, thereby increasing the already significant economic burden.

For the purpose of evidence-based practice, reliable and accurate clinical tools are required to document the progress and evaluate treatment response for clinical decision-making. The Oxford Knee Scale (OKS) was introduced to assess the symptoms and functional status in patients with knee osteoarthritis [4]. OKS has 12 items addressing the extent of knee pain and the level of functional impairments related to daily activities over the previous 4 weeks. This scale has been used worldwide for evaluating patients before and after total knee arthroplasty and has been translated in other languages [5-10].

To date, there is no validated Chinese version of this outcome measurement. Hence, the purpose of this study was to test the reliability, internal consistency, and convergent validity of the Chinese translation of OKS.

Methods

Participants

A total of 100 patients (35 men and 65 women) with a diagnosis of knee osteoarthritis were recruited from the orthopedic outpatient department and physiotherapy clinics of local hospitals in Hong Kong, China. The diagnosis was confirmed by radiographic findings by an orthopedic surgeon and they were able to read and comprehend Chinese. We excluded patients if they had corticosteroid injection or serotonin treatment within the previous 8 weeks, or another site of osteoarthritis other than the tibiofemoral joint. We also excluded patients who were illiterate. The demographical data (age, height, weight, and body mass index) and information about knee osteoarthritis (distribution of affected leg and duration of knee osteoarthritis) of the patients are presented in Table 1. The study protocol was reviewed and approved by the ethical committees of the involved university and hospitals. All the patients provided their written informed consent before being tested.

Table 1

Demographics of participants

Demographics		Values (SD)
Age (y)		65.6 (8.9)
Height (m)		1.59 (0.09)
Weight (kg)		69.1 (16.6)
Body mass index (kg/m2)		27.2 (4.2)
Involved knee	Left	21
	Right	10
	Both	69
Duration of knee osteoarthritis (y)		7.9 (1.0)

SD = standard deviation.

Development of the Chinese questionnaire

The translation process followed the procedures recommended by the International Society for Pharmacoeconomics and Outcomes Research [11] and other crosscultural adaptation and translation studies [12]. In brief, two Chinese translations of the original English version of OKS were performed by two independent English–Chinese translators. A panel comprising a translator and two bilingual authors compared the two translations and formulated a consensus version. Backward translation of the consensus version questionnaire to English version was performed by two independent translators who were blinded to the original questionnaire and not involved in the previous translation work. The backward translated questionnaire was reviewed for equivalence to the original questionnaire by an expert panel, which consisted of two experienced physiotherapists and two research fellows in the area of musculoskeletal physical therapy and orthopedics. The questionnaire was finalized after a pilot test for crosscultural adaptation, which involved 20 patients with knee osteoarthritis.

Statistical analysis

Test–retest reliability of the Chinese OKS was determined by comparing the scores obtained from two subsequent treatment sessions (within 7 days apart) by the intraclass correlation coefficient. Internal consistency of the questionnaire was examined by the Cronbach α. Based on previous validation studies [12,13], convergent validity was assessed by comparing the scores with the validated Chinese versions of the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index [14] and Health Outcome Survey Short Form-36 (SF-36) [15] by the Spearman’s rank correlation coefficients (ρ). The correlation value was considered to be very strong if it was between 0.9 and 1.0, strong if it was between 0.7 and 0.9, moderate if it was within 0.5–0.7, and weak if it was < 0.5 [16].

Results

Crosscultural adaptation and psychometric properties

We did not receive any critique about the Chinese OKS in the pilot test involving 20 patients with knee osteoarthritis. All the participants expressed that they understood the wordings used in the instrument. Therefore, the questionnaire was used in the subsequent validation study without any further adaptation. Thirty individuals were asked to fill in the Chinese OKS twice on subsequent two clinical visits (within 7 days apart). The test–retest reliability was excellent (intraclass correlation coefficient = 0.88, p < 0.001). The Cronbach α of the total score in the Chinese OKS was 0.802. Cronbach α when each question was deleted ranged from 0.712 to 0.855 (Table 2).

Table 2

Cronbach α if each question was deleted

Question no.	Cronbach α if item deleted
1	0.813
2	0.830
3	0.816
4	0.855
5	0.818
6	0.812
7	0.826
8	0.824
9	0.712
10	0.833
11	0.818
12	0.809

Convergent validity

Strong correlation was found between the Chinese OKS and the total score of WOMAC Osteoarthritis Index (ρ = 0.832, p < 0.001). The score in Chinese OKS was also associated with the subcategories in the WOMAC Osteoarthritis Index (Table 3). The strength of correlation was highest in the pain domain (ρ = 0.846, p < 0.001), followed by physical function (ρ = 0.793, p < 0.001). The weakest association was found between the joint stiffness domain (ρ = 0.553, p < 0.001) but the strength of the correlation was not weak.

Table 3

Spearman rank correlation coefficients between OKS and WOMAC Osteoarthritis Index

WOMAC Osteoarthritis Index	OKS
Total score	0.832*
Subcategory – pain	0.846*
Subcategory – stiffness	0.553*
Subcategory – physical function	0.793*

OKS = Oxford Knee Scale; WOMAC = Western Ontario and McMaster Universities.

Significant correlation with p < 0.001.

The correlations between Chinese OKS and SF-36 were diverse (Table 4). The strongest correlations were between bodily pain (ρ = −0.666, p < 0.001), physical functioning (ρ = −0.530, p < 0.001), and role-physical (ρ = −0.483, p < 0.001). A weaker correlation was also noticed between the Chinese OKS and nonphysical domains, such as social functioning (ρ = −0.456, p < 0.001) and mental health (ρ = −0.412, p < 0.001). The relationship between the Chinese OKS and the general health was the weakest (ρ = −0.273, p < 0.05).

Table 4

Spearman rank correlation coefficients of the total score of OKS and SF-36

SF-36	OKS
Physical functioning	−0.530**
Role-physical	−0.483**
Bodily pain	−0.666**
General health	−0.273*
Energy vitality	−0.428**
Social functioning	−0.456**
Role-emotional	−0.358**
Mental health	−0.412**

OKS = Oxford Knee Scale; SF-36 = Health Outcome Survey Short Form-36.

Significant correlation with p < 0.05.

Significant correlation with p < 0.001.

Discussion

The Chinese OKS demonstrated acceptable psychometric properties in the patients with knee osteoarthritis. The findings of the current study suggested that this instrument is a reliable and valid outcome measurement for the selected patient group in the Chinese reading population.

Excellent test–retest reliability and internal consistency of the Chinese OKS was demonstrated in the patients with knee osteoarthritis. Such a finding was in accordance with other validation studies in similar patient cohorts [12,14], which could be explained by the disease chronicity of our sample. In addition, the OKS addresses some common scenarios in everyday life and therefore no cultural modification of terms and wordings was required.

The WOMAC Osteoarthritis Index and SF-36 were chosen to test the convergent validity as these two instruments were shown to be valid and highly reliable [14,15]. The strong correlations of between the WOMAC Osteoarthritis Index suggested strong agreement between the two different scales and indicated convergent validity of the Chinese OKS. Since SF-36 assesses generic health instead of disease/pathology-specific parameters, a weaker correlation (ρ range from −0.273 to −666) between the Chinese OKS and SF-36 was expected. When comparing the OKS (with only 12 questions,) patients are required to spend more time to administer WOMAC Osteoarthritis Index (with 24 questions) or SF-36 (with 36 questions). Therefore, the application of OKS should be more clinically friendly.

Two major limitations should be considered in the present study. First, since OKS was not only used to evaluate patients with knee osteoarthritis but also patients who received total knee arthroplasty. Testing of the Chinese OKS in other patient cohorts in the future is warranted. Second, previous validation studies usually had two to 20 samples per item [17]; while we had 100 patients for the 12-item OKS, which may not be convincingly adequate.

Conclusion

The Chinese translated version of OKS is a reliable and valid instrument for patients with knee osteoarthritis. Local research and multinational studies can be facilitated by the current study.