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Health-related quality of life in Egyptian patients with knee osteoarthritis: correlation with performance-related measures

Objective The aim of this work was to study the correlation between health-related quality of life and performance-related measures in Egyptian patients with primary knee osteoarthritis (OA). Patients and methods One hundred patients with primary knee OA who were attending the outpatient clinic of the hospital were included in the study. All patients had bilateral medial tibiofemoral knee OA. Radiological severity of the disease was evaluated with the Kellgren–Lawrence scale. All patients completed Knee Injury and Osteoarthritis Outcome Score (KOOS); that is a knee-related disorder-specific questionnaire for the assessment of quality of life. The Timed Up and Go test was used for the evaluation of performance-based functional status. Results Eighty-eight (88%) patients were female. The mean age was 57.30±6.37 (50–75) years, and the mean BMI was 36.83±5.37% kg/m2. The mean symptom duration was 8.76±4.71 years. The mean radiological stage was 2.88±0.82. There was a statistically significant negative correlation between all of the KOOS domains and Timed Up and Go (P≤0.01). Conclusion KOOS is not only a good indicator of physical performance in patients with knee OA but also provides information about the impact of knee-related disability on the quality of life and recreational activities.


Introduction
Osteoarthritis (OA) is an age-related disorder and the primary cause of pain, disability, and shortening of adult working life. The incidence of OA increases with age, with 25% of the population older than 50 years of age having OA of the knee [1].
OA is characterized by cartilage erosion, development of osteophytes, and changes in the subchondral bone and synovial fluid. The exact pathogenesis has yet to be clarified. OA is generally considered to have a complicated agenda that includes genetic, hormonal, metabolic, and biomechanical factors, and specific risk factors such as age, sex, obesity, and past injury have been identified [2].
Pain and physical dysfunction are main criteria for patients with knee OA. Both self-report questionnaires and performance-based tests are often used to assess knee-related pain and physical function. Self-assessment questionnaires provide information about the experience of a person during activities.
Self-report tests can easily be performed without investigator's intervention in a relatively short time [3].
Performance-based tests measure functional limitation, whereas self-report tests can show disability, which is the social side of the functional limitation [4]. Performancebased tests are considered to assess the functional loss earlier than the self-report tests [5].
Knee Injury and Osteoarthritis Outcome Score (KOOS) is an easy self-administered test based on Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Short Form-36 (SF-36) tests that contain activities of daily living (ADL), sport, and quality-of-life domains besides pain-related and symptom-related questions in knee OA. KOOS can be completed in ∼10 min [6]. The Timed Up and Go (TUG) test shows the lower extremity performance and measures the time that is required for standing up from the chair, walking 3 m, returning, and sitting back again in a clinical setting. The TUG test is also an easy test to perform and needs a physician for supervision. The TUG test can give information about the inadequate activity of a person; however, KOOS provides more comprehensive information about the indoor and outdoor activities of an individual [7].
As the progression of the disease can sometimes be slow and gradual, many patients are not aware of the impact their OA has had upon important dimensions of their lives. Examining the impact of their OA on these dimensions will allow clinicians to personalize treatment and better outline the potential benefits [8]. A key reason for serial measurement of healthrelated quality of life is to reflect the changes that occur in an individual's health state in response to disease progression, various therapies, and recovery [9].
Aim of the work The aim of this work was to study the correlation between KOOS (as a quality-of-life assessment questionnaire) and TUG (as a performance-related measure) in Egyptian patients with primary knee OA.

Patients
One hundred patients with primary knee OA (12 male and 88 female) were included in this study. Their ages ranged from 50 to 75 years. They were recruited from the outpatient clinic of the Rheumatology and Rehabilitation Department, Beni-Suef University Hospital, Egypt. All knee OA patients fulfilled the criteria of American College of Rheumatology for the diagnosis of OA [10].
Inclusion criteria were as follows: age at least 50 years, knee pain, radiological stage of 2 or more; and medial tibiofemoral joint OA according to the Kellgren-Lawrence (KL) scale [11]. Exclusion criteria were as follows: presence of inflammatory joint disease or other secondary OA causes (e.g. acromegaly), a history of hip or knee surgery, severe back or hip pain, or presence of any neurological disease affecting their mobility.
The study was approved by the local ethical committee.
Consent was obtained from all patients involved in this study.

Methods
All patients were subjected to the following: full clinical history, thorough clinical examination, and evaluation of BMI. Plain radiograph of both knees anteroposterior and lateral views in standing position was obtained and scored using the KL radiological scale (for tibiofemoral joint only). Kellgren and Lawrence [11] classified the severity of OA as follows: grade 1, doubtful narrowing of joint space and possible osteophytic lipping; grade 2, definite osteophytes and definite narrowing of joint space; grade 3, moderate multiple osteophytes, definite narrowing of joints space, some sclerosis, and possible deformity of bone contour; and grade 4, large osteophytes, marked narrowing of joint space, severe sclerosis, and definite deformity of bone contour.

Specific tests: Timed up and Go test
The TUG test measures the functional mobility. The time required for standing up from the chair, walking 3 m on the floor, turning around, returning, and sitting down again is recorded [12].

Knee Injury and Osteoarthritis Outcome Score
KOOS consisted of 42 items in total addressing five patient-related domains, including pain, ADL, sport and recreation function, and knee-related quality of life. All items were evaluated using a five-point Likert scale. Total score ranges between 0 and 100 [13].

Statistical analysis
Statistical package for scientific studies for Windows package program, version 19 was used for statistical analysis. Data were statistically described in terms of mean±SD, frequencies (number of cases), and relative frequencies (%) when appropriate. Correlations were made using the χ 2 -test whenever needed. Spearman's correlation coefficients were calculated to evaluate the relationship between performance-based tests and selfreported tests in patients with OA.

Results
One hundred patients were included in this study with bilateral primary knee OA, 12 (12%) male and 88 (88%) female. Their ages ranged from 50 to 75 years with a mean of 57.30±6.37 years. Their disease durations ranged from 1.00 to 20.00 years with a mean of 8.76±4.71 years. Their BMIs ranged from 25.97 to 49.12% with a mean of 36.83±5.37%.
The KL score ranged from 2.00 to 4.00 with a mean of 2.88±0.82, and the TUG test ranged from 11.00 to 27.00 s with a mean of 17.64±4.64 s.
Correlation between KL score and both BMI and age revealed a nonsignificant positive correlation (P=0.196 and 0.241, respectively).
Results of KOOS questionnaire and its subtypes are presented in Table 1.
Correlations between the TUG test of OA patients with some of the demographic and radiographic parameters of the disease showed different results ( Table 2).
Correlations between KOOS questionnaire of OA patients with some of the demographic and radiographic parameters of the disease are presented in Table 3.
Correlation between KOOS questionnaire and the TUG test of cases showed a significant negative correlation (r=−0.884, P=0.001). Correlations between all subtypes of KOOS questionnaire and the TUG test showed a significant negative correlation (P=0.001) ( Table 4 and Fig. 1).

Discussion
In the present study we found a significant positive correlation between age and the TUG test, wherein the time needed for the test increases as the age      of the patient increases, and there was a negative correlation between age and KOOS, which was not significant.
Similar to the results of our study, Sivachidambaram et al. [14] correlated self-reported questionnaire (KOOS) with some objective measures in primary OA knee patients and found that KOOS has almost no correlation with age.
Paradowski et al. [18] found that women in the age group 55-74 years had poorer physical function and knee-related quality of life. Moreover, Zakaria et al. [19] used SF-36 to assess health-related quality of life in patients with knee OA and found that there were correlations between mental health components and physical functioning with age.
There have been inconsistent results about the correlation of BMI with health status in patients with knee OA. In our study there was no significant correlation between BMI and the score of KOOS and the TUG test. This could be attributed to the fact that all of our patients were overweight with no great variations in their BMI.
Smith et al. [21] studied the associations between physical disability measures [WOMAC and general health status (SF-36) questionnaires] and BMI in knee OA patients and found that increasing BMI was associated with high objective and self-reported measures of physical disability [22].
The relation between BMI and OA is mediated by another local factor such as changed mechanical loading of the joint − for example, malalignment [24]. Moreover, Maly et al. [20] reported mild positive correlation between BMI and sit-to-stand performance (r=0.47, P<0.01).
The association between the radiographic severity of OA and disability was conflicting. In the present study, the radiological finding assessed using KL score was found to be significantly correlated with KOOS and the TUG test. Akune et al. [25] found that women with OA and KL score (grade 4) were strongly associated with the magnitude of quality of life loss in a study investigating the impact of knee OA on the quality of life in Japanese women.
In a study by Sabirli et al. [26], there was a statistically significant positive relationship between KL radiological stages and the TUG test (r=0.628; P<0.01).
Moreover, Muraki et al. [27] found that patients with OA and KL grade 3 or 4 had a significantly lower physical quality of life as measured using the physical component summary score of the SF-8 and pain domains of the WOMAC, whereas mental quality of life, as measured using the mental component summary score of the SF-8, was higher in patients with KL grade 3 or 4 than in those with KL grade 0 or 1.
In contrast, Creamer et al. [28] found that self-reported disability in patients with knee OA has a nonsignificant correlation with radiological severity. This could be due to socioeconomic differences. Barker et al. [29] also found that radiographic score was not found to be closely associated with function, and among patients with the same radiographic score there was a significant variation in function, pain, and power.
Külcü et al. [30] reported that radiological examination of the knee is used for the evaluation of OA, but its use for assessing the severity of the disease is questionable.
In this study, all subgroups of KOOS showed a moderate inverse correlation with the TUG test. This relationship between two measures indicates that KOOS can give useful information about the functional performance of the patient with knee OA. The correlation between the performance-based tests and self-reported questionnaires is important, as they together or alone are frequently used for evaluation and to follow-up the knee OA patients in clinical practice. These tests give information about knee-related pain, symptoms, and functions.
In the study by Terwee et al. [31], there was a modest correlation between WOMAC and various performance-based tests in knee OA. Lin et al. [32] also found a mild correlation between WOMAC and physical performance tests in OA knee patients (r=0. 33 Sabirli et al. [26] reported that all subgroups of KOOS showed a moderate inverse correlation with the TUG test, which is similar to our result. Moreover, Sivachidambaram et al. [14] correlated selfreported questionnaire (KOOS) with some objective measures in primary OA knee patients and found that all KOOS subtypes have a significant correlation with 6-MWT. 6-MWT had a weak correlation with KOOS-ADL (=0.461) and a strong correlation with KOOS symptom, KOOS-pain, and KOOSsports (=0.578, 0.619, and 0.536, respectively) and a very strong correlation with KOOS-quality of life (=0.733) [14].

Conclusion
The significant correlation between KOOS questionnaire and the TUG test in patients with primary knee OA indicates that KOOS is not only a good indicator of physical performance in patients with primary knee OA but also provides information about the impact of kneerelated disability on the quality of life and recreational activities.
Thus, it will be of great benefit for patients with primary knee OA to include KOOS questionnaire and the TUG test as a part of the routine care of OA patients. Further longitudinal studies including larger OA population are needed to assess the efficacy of different lines of treatment in these patients using KOOS questionnaire and the TUG test.

Financial support and sponsorship
Nil.

Conflicts of interest
There are no conflict of interest.