Osteoarthritis (OA) is a condition characterized by focal areas of loss of articular cartilage within the synovial joints, associated with hypertrophy of the bone and thickening of the capsule [
OA is the main cause of limitations in activities; difficulties in walking, carrying objects, and dressing; and the need for human assistance [
Ethical approval was obtained from the Departmental Research Committee of the Department of Rehabilitation Sciences, Hong Kong Polytechnic University, and the Ethical Committee of the Hong Kong Hospital Authority. Informed consent was obtained from the participants prior to the study commencing. Participants with knee OA were recruited from the Department of Occupational Therapy of two public hospitals in Hong Kong from August to November 2015 by convenient sampling.
The inclusion criteria were those patients who (1) had been diagnosed with knee OA by their attending orthopedic surgeon, based on clinical and radiographic features; (2) were 18 years old or above; (3) were able to understand Cantonese; and (4) were able to read and understand simple questions. The exclusion criteria were those patients who (1) were unable to give written consent; (2) suffered from other physical disabilities, which may cause functional limitations when performing any task involving the lower limbs; and (3) suffered from psychiatric problems.
A total of 125 participants were recruited to complete the questionnaire. Of those, 35 were randomly selected for test-retest reliability. Sample size was calculated based on previous similar reliable and valid KOOS studies and medium effect size indexes, which represented an average size of observed effects from calculated sample sizes [
It is a self-administered health-related quality of life (HRQoL) outcome measure for patients with knee OA. It was developed based on the WOMAC Osteoarthritis Index Likert version 3.0 [
Cross-cultural adaptation explored cultural adaptation and language issues that arise when developing an instrument in different settings [
Content validity was used to examine if the instrument can be cross-culturally adapted for application in Hong Kong [
To achieve excellent content validity, the Item-level Content Validity Index (I-CVI) should be ≥0.78 and the Scale-level Content Validity Index (S-CVI) should be ≥0.90 [
Test-retest reliability is the degree to which a person provides similar answers to repeated measures over time [
Exploratory factor analysis (EFA), using a maximum likelihood (ML) extraction method with Promax (oblique) rotation was performed to determine the factor structure of each domain. The following criteria were used to determine the factor and item reduction: (1) the Kaiser-Meyer-Olkin Test (KMO) of a factor must be greater than .05, (2) the Bartlett’s Test of Sphericity result for a factor must be below .05, (3) each factor must have an eigenvalue of 1 or above, and (4) items must have a factor loading of 0.3 or above [
Convergent validity and divergent validity were assessed using the Pearson correlation coefficient, with ≤0.25 indicating low correlation, 0.25-0.50 showing fair to moderate correlation, 0.50-0.75 demonstrating moderate to good correlation, and ≥0.75 showing good to excellent correlation [
Internal consistency assesses the extent to which items in a scale are correlated and measure the same concept [
Floor or ceiling effects appear when more than 15% of the participants reach the highest or lowest score [
The demographics of participants are shown in Table
Characteristics of the participants.
| ||
---|---|---|
Total |
Test-retest reliability participants |
|
Age (years) | ||
Mean (SD) | 67.37 (8.29) | 65.40 (8.99) |
Range | 47-85 | 50-80 |
Sex | ||
Male | 38 (30.4) | 7 (20.0) |
Female | 87 (69.6) | 28 (80.0) |
Education | ||
No education | 7 (5.6) | 2 (5.7) |
Primary education | 82 (65.6) | 24 (68.6) |
Secondary education | 33 (26.4) | 7 (20.0) |
Tertiary education | 3 (2.4) | 2 (5.7) |
Occupation | ||
Retirees | 64 (51.2) | 14 (40.0) |
Homemakers | 30 (24.0) | 13 (37.1) |
Workers | 31 (24.8) | 8 (22.9) |
Onset of knee OA (years) | ||
1-5 | 53 (42.4) | 20 (57.1) |
6-10 | 37 (29.6) | 8 (22.9) |
11-15 | 15 (12.0) | 2 (5.7) |
>15 | 20 (16.0) | 5 (14.3) |
Means, standard deviations, score ranges, and the number of floor and ceiling effects of the HK-KOOS subscales (
Mean | SD | Range | Floor effect |
Ceiling effect |
|
---|---|---|---|---|---|
KOOS pain | 48.42 | 19.90 | 0-97 | 1 (0.8) | 0 (0) |
KOOS symptoms | 48.98 | 21.26 | 0-100 | 1 (0.8) | 2 (1.6) |
KOOS ADL | 54.19 | 20.67 | 0-94 | 1 (0.8) | 0 (0) |
KOOS sport/recreation | 22.44 | 20.33 | 0-95 | 24 (19.2) | 0 (0) |
KOOS QoL | 36.45 | 21.80 | 0-100 | 7 (5.6) | 1 (0.8) |
Simplified Chinese characters were converted into traditional Chinese characters. Discussions were raised for items A16, A17, P2, SP4, and Q4, as the Mandarin and Cantonese expressions of “intensity of housework” and “knee joint” were different. The wordings were replaced with culturally relevant Cantonese translations. Three groups of expert panels (
A total of 35 participants were randomly selected to complete the questionnaire for a second time. The ICC of the five domains ranged from 0.76 to 0.86, which indicated good to excellent test-retest reliability. The MDC ranged from 3.86 to 12.06 (Table
Reliability indices of the HK-KOOS subscales (
KOOS subscale | The 1st attempt | The 2nd attempt | Difference | ICCa (95% CI) | SEMb | MDC95c |
---|---|---|---|---|---|---|
Mean (SD) | Mean (SD) | Mean (SD) | ||||
Pain | 17.69 (6.11) | 16.97 (6.25) | -0.71 (4.32) | 0.86 (0.72, 0.93) | 2.34 | 6.48 |
Symptoms | 14.00 (5.25) | 12.89 (4.90) | -1.11 (3.45) | 0.86 (0.72, 0.93) | 1.83 | 5.09 |
ADL | 27.00 (11.85) | 25.89 (12.56) | -1.11 (8.31) | 0.88 (0.77, 0.94) | 4.34 | 12.06 |
Sport/recreation | 13.94 (4.15) | 13.43 (4.20) | -0.51 (3.63) | 0.78 (0.55, 0.89) | 3.33 | 6.45 |
QoL | 9.49 (2.84) | 9.26 (2.84) | -0.23 (2.46) | 0.76 (0.52, 0.88) | 1.39 | 3.86 |
aIntraclass correlation coefficient. bStandard error measurement. cMinimal detectable change with 95% confidence.
Exploratory factor analysis (EFA) was examined for the whole sample (
Factor loadings of each item for HK-KOOS (
HK-KOOS items | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
---|---|---|---|---|---|---|---|
A9 | 1.134 | ||||||
A11 | 1.102 | ||||||
A12 | 0.688 | ||||||
A14 | 0.619 | ||||||
A10 | 0.609 | ||||||
A15 | 0.488 | ||||||
SP4 | 0.413 | ||||||
S7 | 0.758 | ||||||
S6 | 0.758 | ||||||
S3 | 0.691 | ||||||
S1 | 0.552 | ||||||
S2 | 0.49 | ||||||
Q3 | 0.447 | ||||||
SP3 | 0.923 | ||||||
SP2 | 0.888 | ||||||
SP5 | 0.694 | ||||||
SP1 | 0.674 | ||||||
A5 | 0.349 | ||||||
A16 | 0.707 | ||||||
A17 | 0.539 | ||||||
Q4 | 0.518 | ||||||
S5 | 0.442 | ||||||
A8 | 0.431 | ||||||
Q2 | 0.31 | ||||||
P9 | 0.837 | ||||||
A4 | 0.811 | ||||||
P5 | 0.609 | ||||||
A6 | 0.52 | ||||||
A1 | 0.878 | ||||||
A2 | 0.741 | ||||||
P6 | 0.723 | ||||||
P4 | 0.464 | ||||||
A7 | 0.419 | ||||||
P3 | 0.651 | ||||||
S4 | 0.569 | ||||||
A3 | 0.502 | ||||||
P8 | 0.429 | ||||||
P7 | 0.385 | ||||||
A13 | 0.359 | ||||||
Q1 | 0.345 |
Items with factor loadings under .03 were suppressed (items P1 and P2). P=pain, S=symptoms, A=activities of daily living, SP=sport and recreation, and Q=knee-related quality of life.
The Pearson product-moment correlation was conducted to measure the linear correlation between the KOOS subscale and the selected measures. KOOS pain, ADL, Sports/Rec, and QoL scores demonstrated fair to good correlation with the VAS-Pain, the C-MBI, the SF-12 Physical Component Summary (PCS) scale score, and the SF-12 Mental Component Summary (MCS) scale score. The KOOS symptoms only had correlations with the VAS-Pain, SF-12 PCS, and SF-12 MCS scores (
Convergent and divergent validity of select scales (
VAS pain | MBI | SF-12 PCS | SF-12 MCS | |
---|---|---|---|---|
KOOS pain |
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KOOS symptoms |
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.095 |
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KOOS ADL |
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KOOS sport/recreation |
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KOOS QOL |
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Cronbach’s alpha was used to assess the internal consistency of the KOOS. Two models were performed, one for the original factor structure and one for the seven-factor structure. The Cronbach’s alpha of the original version of the KOOS subscales ranged from 0.80 to 0.96, which indicated good internal consistency. The Cronbach’s alpha of the seven-factor structure ranged from 0.80 to 0.94 (Table
Comparison of internal consistency of the original KOOS and HK-KOOS (
Original KOOS | Cronbach’s alpha | HK-KOOS | Cronbach’s alpha |
---|---|---|---|
Symptoms | 0.82 | Factor 1 (A9-A12, A14-A15, SP4) | 0.93 |
Pain | 0.92 | Factor 2 (S1-S3, S6-S7, Q3) | 0.84 |
ADL | 0.96 | Factor 3 (SP1-SP3, SP5, A5) | 0.88 |
Sport and recreation | 0.85 | Factor 4 (A8, A16-A17, Q2, Q4, S5) | 0.80 |
QoL | 0.80 | Factor 5 (P5, P9, A4, A6) | 0.90 |
Factor 6 (A1-A2, A7, P6, P4) | 0.91 | ||
Factor 7 (P3, P7-P8, A3, A13, S4, Q1) | 0.86 |
A ceiling effect (indicating the best possible score) was not present in the HK-KOOS, as none of the participants scored the highest score in any of the subscales. A floor effect (indicating the worst possible score) was not present in the subscales of pain, symptoms, and ADL and QoL. However, it was found in the Sports/Rec subscale, with 20% of participants scoring the lowest score in this subscale (Table
An occupational therapist, as one of the members in a multidisciplinary team, plays an important role in the management of knee OA and rehabilitation following surgery, e.g., total knee replacement (TKR). The rehabilitation goal is to promote functional recovery and facilitate safe and early discharge through reliable and valid preoperative assessments and postoperative education, functional training, provision of assistive devices, and/or home modification. The occupational therapist would conduct various functional assessments to evaluate the rehabilitation outcomes and monitor the treatment program. The health status and health outcome perceived by a patient were widely considered as an essential component in outcome evaluation. Preoperative pain and functional status, as measured by patient-reported outcome measures, have been shown to predict pain and functional ability after TKR [
The results of the present study indicated that the HK-KOOS was a reliable and valid measure of HRQoL for patients with knee OA. The HK-KOOS was successfully cross-culturally adapted in HK, as shown by the satisfactory results of the reliability and validity tests. For content validity, I-CVI and S-CVI ranged from 0.80-1 to 0.90-1, respectively. This revealed that the HK-KOOS had excellent content validity in the areas of relevance, representativeness, and understandability. In terms of test-retest reliability, acceptable ICC was found in all subscales. The overall results were consistent with those of other validation studies, including Singapore-Chinese (
In terms of internal consistency, Cronbach’s alpha ranged from 0.80 to 0.96 for the five subscales. This result was consistent with the original Swedish (0.78-0.91), Arabic (0.80-0.96), and French versions of KOOS (0.76-0.91) [
In terms of dimensionality, the Hong Kong version of the KOOS was loaded on seven factors, which is different from previous validation studies [
Finally, in terms of floor and ceiling effects, 20% of participants scored the lowest score in the Sports/Rec subscale, which was comparable to the Dutch version [
This study has a major limitation since the average age of the participants is 67.37 years old, which may make the study results not generalizable to young patients with knee OA and other knee problems. Previous studies have proven that the KOOS can be applicable to young people and patients with different knee problems, such as Anterior Cruciate Ligament and those who have undergone total knee replacement. Further validation studies of the HK-KOOS, administered to younger populations, are recommended.
Developing the HK-KOOS is of great clinical significance. First, the HK-KOOS can help occupational therapists to measure multiple dimensions of HRQoL, other than the functional outcomes of patients with knee OA. Occupational therapists could use the KOOS to conduct early screening on patients prior to performing any kind of knee treatment and intervention.
The HK-KOOS is a validated and reliable outcome measure for patients with knee OA. The HK-KOOS could be used as a self-reported, disease-specific instrument for those with primary knee OA in Hong Kong to evaluate both short-term and long-term consequences of knee OA. It can help occupational therapists to quantify knee-related disabilities and provide useful directions for future interventions.
This survey asks for your view about your knee. This information will help us keep track of how you feel about your knee and how well you are able to do your usual activities. Answer every question by ticking the appropriate box, only one box for each question. If you are unsure about how to answer a question, please give the best answer you can.
These questions should be answered thinking of your knee symptoms during the
S1. Do you have swelling in your knee?
□ Never □ Rarely □ Sometimes □ Often □ Always
S2. Do you feel grinding/friction, hear clicking/cracking, or any other type of noise when your knee moves?
□ Never □ Rarely □ Sometimes □ Often □ Always
S3. Does your knee jam or lock when moving?
□ Never □ Rarely □ Sometimes □ Often □ Always
S4. Can you straighten your knee fully?
□ Always □ Often □ Sometimes □ Rarely □ Never
S5. Can you bend your knee fully?
□ Always □ Often □ Sometimes □ Rarely □ Never
The following questions concern the amount of joint stiffness you have experienced during the
S6. How severe is your knee joint stiffness after first wakening in the morning?
□ None □ Mild □ Moderate □ Severe □ Extreme
S7. How severe is your knee stiffness after sitting, lying, or resting
□ None □ Mild □ Moderate □ Severe □ Extreme
P1. How often do you experience knee pain?
□ Never □ Monthly □ Weekly □ Daily □ Always
What amount of knee pain have you experienced in the
P2. Twisting/pivoting on your knee
□ None □ Mild □ Moderate □ Severe □ Extreme
P3. Straightening knee fully
□ None □ Mild □ Moderate □ Severe □ Extreme
P4. Bending knee fully
□ None □ Mild □ Moderate □ Severe □ Extreme
P5. Walking on flat surface
□ None □ Mild □ Moderate □ Severe □ Extreme
P6. Going up or down stairs
□ None □ Mild □ Moderate □ Severe □ Extreme
P7. At night while in bed
□ None □ Mild □ Moderate □ Severe □ Extreme
P8. Sitting or lying
□ None □ Mild □ Moderate □ Severe □ Extreme
P9. Standing upright
□ None □ Mild □ Moderate □ Severe □ Extreme
The following questions concern your physical function. By this, we mean your ability to move around and to look after yourself. For each of the following activities, please indicate the degree of difficulty you have experienced in the
A1. Descending stairs
□ None □ Mild □ Moderate □ Severe □ Extreme
A2. Ascending stairs
□ None □ Mild □ Moderate □ Severe □ Extreme
A3. Rising from sitting
□ None □ Mild □ Moderate □ Severe □ Extreme
A4. Standing
□ None □ Mild □ Moderate □ Severe □ Extreme
A5. Bending to floor/pick up an object
□ None □ Mild □ Moderate □ Severe □ Extreme
A6. Walking on flat surface
□ None □ Mild □ Moderate □ Severe □ Extreme
A7. Getting in/out of car
□ None □ Mild □ Moderate □ Severe □ Extreme
A8. Going shopping
□ None □ Mild □ Moderate □ Severe □ Extreme
A9. Putting on socks/stockings
□ None □ Mild □ Moderate □ Severe □ Extreme
A10. Rising from bed
□ None □ Mild □ Moderate □ Severe □ Extreme
A11. Taking off socks/stockings
□ None □ Mild □ Moderate □ Severe □ Extreme
A12. Lying in bed (turning over, maintaining knee position)
□ None □ Mild □ Moderate □ Severe □ Extreme
A13. Getting in/out of bath
□ None □ Mild □ Moderate □ Severe □ Extreme
A14. Sitting
□ None □ Mild □ Moderate □ Severe □ Extreme
A15. Getting on/off toilet
□ None □ Mild □ Moderate □ Severe □ Extreme
A16. Heavy domestic duties (moving heavy boxes, scrubbing floors, etc.)
□ None □ Mild □ Moderate □ Severe □ Extreme
A17. Light domestic duties (cooking, dusting, etc.)
□ None □ Mild □ Moderate □ Severe □ Extreme
The following questions concern your physical function when being active on a higher level. The questions should be answered thinking of what degree of difficulty you have experienced during the
SP1. Squatting
□ None □ Mild □ Moderate □ Severe □ Extreme
SP2. Running
□ None □ Mild □ Moderate □ Severe □ Extreme
SP3. Jumping
□ None □ Mild □ Moderate □ Severe □ Extreme
SP4. Twisting/pivoting on your injured knee
□ None □ Mild □ Moderate □ Severe □ Extreme
SP5. Kneeling
□ None □ Mild □ Moderate □ Severe □ Extreme
Q1. How often are you aware of your knee problem?
□ Never □ Monthly □ Weekly □ Daily □ Constantly
Q2. Have you modified your lifestyle to avoid potentially damaging activities to your knee?
□ Not at all □ Mildly □ Moderately □ Severely □ Extremely
Q3. How much are you troubled with lack of confidence in your knee?
□ Not at all □ Mildly □ Moderately □ Severely □ Extremely
Q4. In general, how much difficulty do you have with your knee?
□ None □ Mild □ Moderate □ Severe □ Extreme
The data used to support the findings of this study are available from the corresponding author upon request.
The preliminary results of this study were reported in the 2016 HA convention.
The authors have no conflicts of interest to declare.
The authors would like to thank all participants who had participated in this study. We would also like to offer special thanks to Dr. Alex Hui and Mr. Maurice Wan for their unfailing support in this study.