Effects of osteoarthritis grades on pain,function and quality of life

Abstract

BACKGROUND:

Osteoarthritis (OA) is a pathology that frequently affects the geriatric population.

OBJECTIVE:

To investigate the extent to which pain, functionality, and quality of life change over the progression of OA grades.

METHOD:

The study included 161 patients with bilateral OA, whose disease stages ranged from 1 to 4 according to the Kellgren-Lawrence radiographic classification system. Pain was assessed using the Visual Analog Scale (VAS), functionality using the two-minute walk test and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire, and quality of life using the Nottingham Health Profile (NHP).

RESULTS:

There were significant differences between the groups in terms of age, weight, and body mass index. The VAS, two-minute walk test, and WOMAC scores also significantly differed between the groups ( $p<$ 0.05). There was a significant difference between the groups in all domains of the NHP, except for energy ( $p<$ 0.05). The two-minute walk test score was negatively correlated with all the remaining evaluation parameters ( $p<$ 0.05). No correlation was found between the energy domain of the NHP and body mass index, the VAS score, the two-minute walk test distance, or the total WOMAC score ( $p>$ 0.05).

CONCLUSION:

After grade 1, the functional impacts of OA on patients increased by an average of four times. Pain was one of the most basic symptoms, the severity of which started to increase in grade 2. With the added effect of diminishing walking capacity over time, the reduction in the quality of life of the patients accelerated as the OA grade progressed.

Keywords

Osteoarthritis grade function pain quality of life

1. Introduction

Osteoarthritis (OA) is a pathology that frequently affects the geriatric population and is characterized by the degeneration of the articular cartilage, morphological changes in the subchondral bone, and damage and functional changes in soft tissues around the joint where degeneration occurs [1]. The most common symptoms of OA are articular pain, crepitation, osteophytic changes around the affected joint, and morning stiffness. Pain has an insidious onset and can be perceived at different intensities according to the grade of OA [2]. Complaints such as deformations and osteophytic changes in cartilage tissue over time, soft tissue damage, swelling, and crepitation may also differ according to the grade of the disease and prevent the patient from using the affected joint within physiological limits [3]. Increasing body mass index (BMI) exacerbates disease severity by increasing axial loads on the joint. The increased load on the joint is manifested by difficulties performing activities that place a greater load on the joint, such as climbing and descending stairs and squatting. The hormonal changes brought about by the increase in body weight contribute to the degenerative process of joint cartilage [4]. Pain, limitation of movement, and other accompanying changes negatively affect the functions of patients in daily life, causing a decrease in their quality of life [5]. Several methods are used to clearly define the stages of the disease for early diagnosis of the disease and treatment development process, and one of them is the Kellgren-Lawrence (KL) classification system [6].

Studies have generally focused on the intermediate and advanced stages of OA, when the patient’s symptoms increase significantly. However, the insidious onset of pain in patients with knee OA may be among the factors that make it difficult to diagnose the disease. This study focused on the effects of knee OA stages on the patient. In this way, we aimed to explain the anatomical and physiological changes of the disease with predisposing factors such as age and weight. Our hypothesis is that OA at different stages will have a progressive effect on the patient’s pain, function and quality of life.

2. Method

2.1 Study protocol and participant

Before starting the study, necessary permissions were obtained from the Local Ethics Committee of Kutahya Health Sciences University (decision number 2022/08-02). The study was conducted in accordance with the principles of the Declaration of Helsinki. Informed consent was obtained from all participants prior to the study. The study included 161 patients who presented to the physical therapy outpatient clinic of the hospital with the complaint of knee pain between November 2022 and July 2023 and were diagnosed with the same grade of knee OA in both knees by the responsible physician. Radiographic classification was made according to the Kellgren–Lawrence system. In this classification system, there are different classes that define disease stages, such as KL-0 (no OA), KL-1 (suspicious OA), KL-2 (mild OA), KL-3 (moderate OA), and KL4 (severe OA). KL-1; suspected joint space narrowing, possible osteophyte, KL-2; possible joint space narrowing, definite osteophyte, KL-3; definite joint space narrowing, moderate osteophyte, sclerosis, KL-4; significant narrowing of the joint space, large osteophytes, severe sclerosis, bone end deformity [6].

The inclusion criteria were having the same OA grade in both knees, being aged between 18 and 65 years, volunteering to participate in the study, not having undergone previous lower extremity surgery. Excluded from the study were patients with neurological disorders; those with a history of surgery related to the lower extremities; those with orthopedic problems in the lower extremities, such as tendinopathy and bursitis; those who had neurological, orthopedic, or cognitive disorders that would prevent walking; those with a diagnosis of diabetes, obesity, or rheumatological disorders; those who had received intra-articular injection therapy within the last three months; and those with malignancy or perception problems. The participants’ age, body mass index (BMI), and disease grade were recorded.

2.2 Assessment methods

2.2.1 Pain

Pain was questioned using the Visual Analog Scale (VAS), which consists of a 10-cm straight line with 0 on one end indicating no pain and 10 on the other end signifying unbearable pain. The participants were asked to mark the intensity of their current pain on the line.

Functional assessment was performed using the two-minute walk test (2MWT) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire.

2.2.2 2MWT

A 45-meter corridor was used for the 2MWT. The start and end points were marked, and the participants were asked to walk at a normal pace within these boundaries. The distance covered in two minutes was recorded [7].

Table 1
Comparison of demographic data according to osteoarthritis grade

			Grade 1 ( $n=$ 40)	Grade 2 ( $n=$ 40)	Grade 3 ( $n=$ 40)	Grade 4 ( $n=$ 41)	$p^{*}$
Age (years)		Median (IQR)	50 (6.0)	48 (15.0)	45 (7.0)	65 (9.0)	0.000 ( $\chi$ 2 $=$ 27.393) [1,2,3–4] [1–3]
Height (cm)		Median (IQR)	162 (5.0)	164 (8.0)	160 (11.0)	160 (15.0)	0.951 ( $\chi$ 2 $=$ 0.347)
Weight (kg)		Mean $\pm$ SD	64.87 $\pm$ 12.32	75.46 $\pm$ 13.37	75.53 $\pm$ 13.24	87.47 $\pm$ 18.51	0.001 ( $F=$ 6.028) [1–4]
BMI (kg/m²)		Mean $\pm$ SD	25.09 $\pm$ 5.25	28.93 $\pm$ 4.76	28.63 $\pm$ 4.94	34.20 $\pm$ 5.23	0.000 ( $F=$ 8.302) [1–4]
Gender	Male	$n$ (%)	6 (40%)	5 (33.30%)	8 (53.30%)	7 (46.70%)	0.716 ( $\chi$ 2 $=$ 1.357)
	Female	$n$ (%)	9 (60%)	10 (33.30%)	7 (46.70%)	8 (53.30%)

^*Mann-Whitney $U$ test (Z-table value) was used to compare the measurement values of two independent groups for non-normally distributed data. F: ANOVA test; $\chi$ 2: Kruskal-Wallis test. IQR: interquartile range, SD: standard deviation, BMI: body mass index.

2.2.3 WOMAC

WOMAC is used to evaluate functionality in hip and knee OA. The validity analysis of the Turkish version was undertaken by Tüzün et al. The questionnaire consists of 24 items, each scored from 0 to 4. The total score is obtained by summing the point equivalents of the responses given to all items. A higher score indicates poorer functionality [8].

2.2.4 Nottingham health profile (NHP)

The quality of life was evaluated using the validated Turkish version of the NHP [9]. This tool comprises 38 questions in six domains, namely energy, pain, social isolation, physical mobility, emotional reactions, and sleep. Each domain is scored from 0 to 100. The total score is obtained by summing the scores obtained from the six domains. High scores indicate a good quality of life.

2.2.5 Statistical analysis

Statistical analyses were performed using a software package called SPSS (IBM SPSS Statistics v. 24). Frequency tables and descriptive statistics were used to interpret the findings. Parametric methods were used for measurement values that complied with the normal distribution. As a parametric method, the analysis of variance test (F-table value) was used to compare the measurement values of three or more independent groups. For pairwise comparisons of variables showing significant differences between three or more groups, the Tukey or Tamhane test was applied according to the homogeneity of variances. Non-parametric methods were utilized for the measurement values that did not conform to the normal distribution. As a non-parametric method, the Kruskal-Wallis $H$ test ( $\chi$ 2-table value) was used to compare the measurement values of three or more independent groups. The Bonferroni correction was applied for pairwise comparisons of variables showing significant differences between three or more groups. The relationship between evaluation parameters was evaluated using the Spearman correlation test for non-parametric values and the Pearson correlation test for parametric values.

3. Results

A total of 161 patients with OA, including 40 patients in each grade from 1 to 3 and including 41 grade 4 patients, were included in the study. Age and BMI were calculated respectively in the groups; 50 and 25.09 $\pm$ 5.25 for grade 1; 48 and 28.93 $\pm$ 4.76 for grade 2; 45 and 28.63 $\pm$ 4.94 for grade 3; 60 and 34.20 $\pm$ 5.23 for grade 4. Patient genders in the groups are similar ( $p=$ 0.716). There was a statistically significant difference between OA grades in terms of age ( $\chi$ 2 $=$ 27.393; $p=$ 0.000). The mean age of the patients in the grade 4 group was significantly higher than that of those in the first three grade groups. Similarly, a significant difference was found between the patients in the grade 1 and grade 3 groups. The weight values of the patients also statistically significantly differed according to OA grade ( $F=$ 6.028; $p=$ 0.001). The mean weight of the patients in the grade 4 group was significantly higher when compared to the grade 1 group. A statistically significant difference was also observed in BMI ( $F=$ 8,302; $p=$ 0.000), with the mean BMI value of the patients in the grade 4 group being significantly higher than that of the patients in the grade 1 group (Table 1).

Table 2
Comparison of pain and functionality according to osteoarthritis grade

		Grade 1 ( $n=$ 40)	Grade 2 ( $n=$ 40)	Grade 3 ( $n=$ 40)	Grade 4 ( $n=$ 41)	$p^{*}$
VAS score	Median (IQR)	0.7 (2.1)	4.1 (2.0)	6.6 (3.1)	10 (0.0)	0.000 ( $\chi$ 2 $=$ 47.068)[1–2.3.4] [2 vs. 3 and 4] [3–4]
2MWT distance	Mean $\pm$ SD	154.09 $\pm$ 15.60	132.71 $\pm$ 15.83	144.20 $\pm$ 15.64	47.97 $\pm$ 23.28	0.000 ( $F=$ 110.792)[1 vs. 2, 3, and 4] [1 vs. 2]
WOMAC total score	Mean $\pm$ SD	8.67 $\pm$ 4.94	32.20 $\pm$ 10.10	35.60 $\pm$ 11.19	73.60 $\pm$ 12.43	0.000 ( $F=$ 106.620)[1 vs. 2, 3, and 4] [2 and 3 vs. 4]

^*Mann-Whitney $U$ test (Z-table value) was used to compare the measurement values of two independent groups for non-normally distributed data. F: ANOVA test; $\chi$ 2: Kruskal-Wallis test. VAS: Visual Analog Scale, IQR: interquartile range, SD: standard deviation, 2MWT: two-minute walk test, WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index.

There were statistically significant differences in the VAS scores according to OA grade ( $\chi$ 2 $=$ 47.068; $p=$ 0.000), with these differences being observed in the comparison of all groups ( $p<$ 0.05). A statistically significant difference was also found in the 2MWT value according to OA grade ( $F=$ 110,792; $p=$ 0.000). The 2MWT value of the patients in the grade 4 group was significantly lower when compared to the first three grade groups. There was also a significant difference between the grade 1 and grade 2 groups. Concerning the total WOMAC score, a statistically significant difference was found according to OA grade ( $F=$ 106,620; $p=$ 0.000). The WOMAC total scores of the grade 2, 3, and 4 groups were significantly higher compared to the grade 1 group. Another significant difference was detected when the grade 2 and 3 groups were compared to the grade 4 group (Table 2).

Table 3

Comparison of NHP domain scores according to osteoarthritis grade

		Grade 1 ( $n=$ 40)	Grade 2 ( $n=$ 40)	Grade 3 ( $n=$ 40)	Grade 4 ( $n=$ 41)	$p^{*}$
Energy	Median (IQR)	60.8 (52.0)	76 (39.2)	76 (39.2)	100 (39.2)	0.007 ( $\chi$ 2 $=$ 12.035) [1 vs. 4]
Pain	Median (IQR)	16.3 (38.4)	66.6 (35.5)	79.8 (38)	100 (19.7)	0.000 ( $\chi$ 2 $=$ 34.323) [1 vs. 2, 3, and 4] [2 and 3 vs. 4]
Social isolation	Median (IQR)	0 (19.4)	22.5 (25.2)	16 (22.5)	41.9 (60.5)	0.021 ( $\chi$ 2 $=$ 9.695) [1 vs. 2 and 4]
Physical mobility	Median (IQR)	10.8 (31.3)	32.6 (10.6)	41.9 (10.6)	67.2 (12.7)	0.000 ( $\chi$ 2 $=$ 38.901) [1 vs. 2, 3, and 4] [2 and 3 vs. 4]
Emotional reactions	Mean $\pm$ SD	43.95 $\pm$ 28.36	54.08 $\pm$ 27.91	55.17 $\pm$ 18.99	55.99 $\pm$ 26.92	0.550 ( $F=$ 0.709)
Sleep	Median (IQR)	28.7 (50.4)	55.9 (72.7)	37.8 (50.4)	77.6 (34.2)	0.018 ( $\chi$ 2 $=$ 10.063) [1 vs. 4]
Total	Mean $\pm$ SD	172.19 $\pm$ 99.43	303.69 $\pm$ 96.42	301.72 $\pm$ 92.67	405.71 $\pm$ 94.04	0.000 ( $F=$ 14.210) [1 vs. 2, 3, and 4]

A statistically significant difference was found in the energy ( $\chi$ 2 $=$ 12.035; $p=$ 0.007) and sleep ( $\chi$ 2 $=$ 10.063; $p=$ 0.018) scores of the patients according to OA grade. The energy scores of the patients in the grade 4 group were significantly higher than those of the patients in the grade 1 group. Pain scores also statistically significantly differed according to OA grade ( $\chi$ 2 $=$ 34,323; $p=$ 0.000). The pain scores of the patients in the grade 2, 3, and 4 groups were significantly higher when compared to the grade 1 group. Another significant difference was observed between the patients in the grade 2 and 3 groups and those in the grade 4 group. The pain scores of the patients in the grade 4 group were significantly higher than those of the patients in the grade 2 and 3 groups. There were statistically significant differences in social isolation scores according to OA grade ( $\chi$ 2 $=$ 9.695; $p=$ 0.021). The social isolation scores of the grade 2 and 4 groups were significantly higher than those of the grade 1 group. Physical mobility scores were determined to statistically significantly differ according to OA grade ( $\chi$ 2 $=$ 38.901; $p=$ 0.000). The social isolation scores of the grade 2, 3, and 4 groups were significantly higher when compared to the grade 1 group. Similarly, a significant difference was found in the comparison of the grade 2 and 3 groups with the grade 4 group. The social isolation scores of the patients in the grade 4 group were significantly higher than those of the patients in the grade 2 and 3 groups. There was no statistically significant difference in emotional reactions scores according to OA grade ( $p>$ 0.05). Lastly, a statistically significant difference was detected in the total quality of life score according to OA ( $F=$ 106,620; $p=$ 0.000). The total quality of life scores of the patients in the grade 2, 3, and 4 groups were significantly higher than those of the patients in the grade 1 group (Table 3).

Table 4

Correlations between evaluation parameters

		VAS	2MWT	WOMAC total	Energy	Pain	Social isolation	Physical mobility	Energy	Sleep	Total
BMI	$r$	0.455^**	$-$ 0.623^**	0.488^**	0.229	0.451^**	0.269*	0.505^**	0.074	0.262*	0.417^**
	$p$	0.000	0.000	0.000	0.078	0.000	0.038	0.000	0.573	0.043	0.001
VAS	$r$	1	$-$ 0.635^**	0.862^**	0.345^**	0.714^**	0.286*	0.717^**	0.223	0.395^**	0.597^**
	$p$	.	0.000	0.000	0.007	0.000	0.027	0.000	0.087	0.002	0.000
2MWT distance	$r$	$-$ 0.635^**	1	$-$ 0.726^**	$-$ 0.343^**	$-$ 0.590^**	$-$ 0.286^*	$-$ 0.670^**	$-$ 0.123	$-$ 0.401^**	$-$ 0.536^**
	$p$	0.000	.	0.000	0.007	0.000	0.027	0.000	0.348	0.002	0.000
WOMAC total	$r$	0.862^**	$-$ 0.726^**	1	0.503^**	0.768^**	0.328^*	0.866^**	0.287^*	0.524^**	0.736^**
	$p$	0.000	0.000	.	0.000	0.000	0.011	0.000	0.026	0.000	0.000
Energy	$r$	0.345^**	$-$ 0.343^**	0.503^**	1	0.472^**	0.440^**	0.527^**	0.596^**	0.454^**	0.783^**
	$p$	0.007	0.007	0.000	.	0.000	0.000	0.000	0.000	0.000	0.000
Pain	$r$	0.714^**	$-$ 0.590^**	0.768^**	0.472^**	1	0.335^**	0.690^**	0.369^**	0.600^**	0.779^**
	$p$	0.000	0.000	0.000	0.000	.	0.009	0.000	0.004	0.000	0.000
Social isolation	$r$	0.286^*	$-$ 0.286^*	0.328^*	0.440^**	0.335^**	1	0.309^*	0.291^*	0.264^*	0.593^**
	$p$	0.027	0.027	0.011	0.000	0.009	.	0.016	0.024	0.041	0.000
Physical mobility	$r$	0.717^**	$-$ 0.670^**	0.866^**	0.527^**	0.690^**	0.309^*	1	0.282^*	0.530^**	0.752^**
	$p$	0.000	0.000	0.000	0.000	0.000	0.016	.	0.029	0.000	0.000
Energy	$r$	0.223	$-$ 0.123	0.287^*	0.596^**	0.369^**	0.291^*	0.282^*	1	0.273^*	0.658^**
	$p$	0.087	0.348	0.026	0.000	0.004	0.024	0.029	.	0.035	0.000
Sleep	$r$	0.395^**	$-$ 0.401^**	0.524^**	0.454^**	0.600^**	0.264^*	0.530^**	0.273^*	1	0.704^**
	$p$	0.002	0.002	0.000	0.000	0.000	0.041	0.000	0.035	.	0.000
Total	$r$	0.597^**	$-$ 0.536^**	0.736^**	0.783^**	0.779^**	0.593^**	0.752^**	0.658^**	0.704^**	1
	$p$	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	.

VAS: Visual analog scale, 2MWT: two-minute walk test, WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index, r: correlation coefficient, ^*p < 0.05; ^**p< 0.01.

The correlation analysis revealed that the 2MWT distance had a negative correlation with all the remaining evaluation parameters ( $p<$ 0.05). The energy domain of the NHP was not correlated with BMI, the VAS score, 2MWT distance, or the total WOMAC score ( $p>$ 0.05), but it was found to be positively correlated with the remaining parameters ( $p<$ 0.05) (Table 4).

4. Discussion

The results of the study show that the oldest group is at grade 4. While pain increases with grade, functionality decreases. While the highest walking distance is at grade 1, the lowest is at grade 4. Quality of life parameters worsen with the degree of OA. This study indirectly showed how well the diagnosis and initiation of treatment for knee OA could keep the patient at a clinically optimal level. Identifying, staging, and appropriately treating degenerative processes clinically, radiologically, and histologically can delay the progression of such a common disease to advanced stages [10].

Patients should be guided toward losing weight, increasing quadriceps strength, and performing exercises suitable for OA in order to alleviate symptoms in the early period. For pain relief, researchers recommend non-invasive conservative treatments [11]. Our results showed that BMI was significantly higher in patients with grade 4 OA compared to those with grade 1 OA. This is an important indicator of keeping body weight under control as the disease progresses. The patients with grade 4 OA also had an older age than those in the earlier stages of the disease. Physical processes, such as menopause and andropause, and osteoporosis-related bone tissue losses increase bone and joint degeneration in middle and advanced ages. OA can progress rapidly, especially in load-bearing joints, such as the knee [12].

According to a study by Andriacchi et al. who evaluated patients with knee OA, the load on the knee in the initial phase of OA causes kinematic changes in rarely loaded parts of the cartilage, but the disease accelerates with increased load on the knee in advanced stages. The response to mechanical stimulation is to alter cellular metabolism. This indicates a cellular adaptation to cartilage degeneration. In other words, the abnormal kinematics in the initial phase begin by damaging the collagen on the joint surface, increasing friction in the joint. As the disease progresses, tangential shear forces increase. With increasing load, the shear force value further increases. Degeneration progresses rapidly through this mechanism [13]. Based on this mechanism, it is inevitable that functionality will decrease in the advanced stages of OA. Our results showed a 68% decrease in walking distance from grade 1 to grade 4 OA. Functionality, on the other hand, was two to nine times worse in grade 4 OA compared to other grades. Our results emphasize the absolute importance of an early diagnosis of OA in the initiation phase. After the initial phase, the characteristics of OA grades converge on those of grade 4, reducing the patient’s functionality.

Although it is impossible to deny the significant role of pain in the worsening of functionality in patients with OA, the main cause of pain is not completely connected to the joint. Cartilage loss is an important factor, but it is not the main source of pain, especially in the initial and intermediate phases, since it cannot be innervated. The main factor here is the nociceptors contained in the soft tissues in the joint, including the meniscus and synovium. In grade 4 OA, neurovascular invasions at the osteochondral junction contribute to pain. In addition, the inflammatory process that occurs in response to phagocytosis in OA triggers pain originating from synovitis [14]. As a result of our research, the severity of pain was evaluated as “mild” in grade 1 and 2 OA, “moderate” in grade 3 OA, “severe” in grade 4 [15]. This supports the described pain mechanism and is an indication of the increase in the degenerative process until it reaches the osteochondral stage.

The quality of life is important in diseases such as OA, which have high negative outcomes for society. In particular, as OA progresses, the patient not only has complaints of pain and function but also experiences pathomechanical changes brought about by the process and a feeling of inadequacy, evolving into an individual process, such as depression, increased perceived pain, and dissatisfaction that directly affect the quality of life. Thus, the process extends beyond the mere physiological symptoms that need to be treated. Affected mental health can result in mental pathologies. In working patients, social isolation begins to make the cycle more vicious [16]. As revealed by the results of our study, sleep, which provides mental and physical regeneration [17], is affected by the increase in disease grade. Expectedly, social isolation, pain, and physical mobility showed significant deterioration with increasing OA grades. With the addition of reduced energy to this situation, it is inevitable that the quality of life of patients will also be negatively affected.

This study evaluates the grades of OA from a different perspective. However, it has some limitations. If objective data such as measurement of cartilage thickness and blood biomarkers were examined, the mechanisms of action could be better elucidated. We recommend these evaluation criteria for future studies that will examine the stages of OA in different perspectives.

5. Conclusion

In a disease such as OA that is diagnosed so frequently, clinical and physical differences that occur with increasing grade should not be overlooked. Our results revealed that, after grade 1 OA, the effect of the disease on the functionality of patients increased by an average of four times. The severity of pain, one of the most basic symptoms, started to increase in grade 2 OA. With the added effect of diminishing walking capacity over time, the reduction in the quality of life of patients accelerated. We suggest that the diagnosis of OA made at the initial phase can slow down the disease by taking it under control through pharmacological and conservative treatments. This can optimize the capacity of the patient. For public health, new strategies to be added in the early stages of OA may reduce the negative consequences of the disease.

Author contributions

All authors contributed to the study’s conception and design. Material preparation and data collection were performed by EC, CSP and MAL. Statistical analysis was performed by CSP. The first draft of the manuscript was written by EC and CSP. All authors commented on previous versions of the manuscript and read and approved the final manuscript.

Availability of data and materials

The data can be available from the corresponding author upon reasonable request and with permission of the Local Ethics Committee of Kutahya Health Sciences University.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Ethics statement

Informed consent for this study was obtained from all patients. Ethical approval was granted by the Local Ethics Committee of Kutahya Health Sciences University (protocol number 2022/08-02) before the enrollment of patients.

Footnotes

Acknowledgments

The authors would like to thank the patients who voluntarily participated in this study.

Conflict of interest

The authors have no conflict of interest to declare regarding the authorship and/or publication of this article.

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