Background

Knee dysfunction is a complex interaction of multiple factors [1]. Knee dysfunction can be due to a pathological process at the knee joint [1], or changes in body functions, activities, and social participation [2]. Previous injuries or knee structure changes are not always observed [2]. Since knee dysfunction can lead to limitations and disabilities that negatively impact quality of life and functioning during activities of daily living [3], it is important to assess the functioning of patients using an instrument with a comprehensive perspective, as recommended by the International Classification of Functioning, Disability and Health (ICF).

The ICF was developed to broaden the perspective on people’s functioning, including components such as body functions and structures, activities, participation, environmental, and personal factors [4]. To increase the viability and operational use of the ICF, the core sets project was created [5, 6]. The purpose of a core set is to establish a selection of the ICF categories that describe the functioning of a person in a specific health condition or in a specific care context [6]. This selection and subsequent reduction in the number of categories in the core sets, as opposed to the use of the entire ICF for the assessment of a health condition, encourages clinical use [5, 6].

A preliminary core set for knee dysfunction with 24 categories capable of assessing the functioning and health of people with knee dysfunction was created based on the opinion of patients and then using a statistical model by regression analyses [7]. Afterwards, a panel of experts participated in the content validity assessment of this preliminary core set [8]. After a 4-round Delphi, 25 categories showed adequate content validity to compose the comprehensive core set for knee dysfunction [8]. This comprehensive core set indicates the main ICF categories that should be considered when assessing patients with knee dysfunction [8].

The ICF is based on a conceptual model in which functioning is an umbrella term for body functions and structures as well as for activities and participation [4, 9, 10]. A clinical measure of functioning based on the integration of information obtained from an ICF core set can be considered a unidimensional model [9,10,11]. Rasch analysis allows this unidimensional analysis by checking the data variance, which is the sum of the squares of the values predicted by the analysis around their central values [12]. Rasch analysis can also test whether the order of qualifiers in the comprehensive core set for knee dysfunction is adequate to represent the degree of knee dysfunction [13]. In addition, the consistency between factors such as age, sex, educational level, and time of complaint in the core set [14] allows comparing the functioning in different contexts and populations. Therefore, if the categories of the comprehensive core set for knee dysfunction reflect a unidimensional instrument for assessing body functions and structures, activities and participation, and environmental factors and if the categories are consistent in populations, well-directed, and not redundant, this core set can become a clinical instrument to measure the functioning of people with any knee dysfunction.

Thus, the primary objective of this study was to analyze the construct validity of the comprehensive core set for knee dysfunction as a potential instrument for measuring functioning. The secondary objective was to verify whether there is a difference in the construct validity of the comprehensive core set for knee dysfunction when applied during an interview (conducted by a person trained in the use of the ICF) or self-administered.

Methods

Study design

Cross-sectional study to assess construct validity. All methods were carried out in accordance with relevant guidelines and regulations.

Setting

Face-to-face data collection with an interview was carried out at all levels of care. The interview settings were: Primary Health Care Unit of Bonsucesso (Guarapuava, Paraná), Physical Therapy School of Universidade Estadual do Centro-Oeste (Guarapuava, Paraná), Center for Excellence in Clinical Research in Physical Therapy at Universidade Cidade de São Paulo (São Paulo, São Paulo), and São Vicente de Paulo Charity Hospital (Guarapuava, Paraná). Due to the Covid-19 pandemic, which resulted in social distancing, remote assessments were carried out with a self-administered questionnaire in all levels of care and in several cities in Brazil.

Participants

Participants were aged 18 years or older and had subjective complaints of pain, instability, and/or knee movement restriction of any type. Clinical diagnosis of knee pathology and undergoing treatment were not mandatory for inclusion, as well as having prior surgery was not considered for exclusion. Exclusion criteria were lower limb amputation and congenital and/or acquired malformation distal to the knee. Eligibility was assessed by a standardized set of questions.

Two hundred urban participants were recruited and assessed: 100 were recruited by verbal invitation at the study settings for face-to-face interview assessments, and 100 were identified in social networks of associations of physiotherapists and groups of professionals involved with knee rehabilitation, and in the general community for the remote assessments with a self-administered questionnaire. The assessments were conducted from October 2019 to June 2020.

Variables and measurement

Sample characteristics were assessed with a questionnaire including questions on sociodemographic details and clinical conditions. After that, the comprehensive core set for knee dysfunction was applied using the description of each category as a question and the qualifiers as answer options. The comprehensive core set for knee dysfunction had 25 categories, including 11 categories from the component body functions, three representing body structures, 10 activities and participation, and one environmental factor [8]. The qualifiers for the components body functions, body structures, and activities and participation had five possible answers, ranging from 0 to 4, with 0 being no problem and 4 being a major problem. Additional qualifiers for the body structures and activities and participation components were not used. The qualifiers for the environmental factors component had nine possible answers, ranging from facilitators (+ 1 to + 4, mild facilitator to complete facilitator, respectively) to barriers (1 to 4, mild barrier to complete barrier, respectively) or no barriers/no facilitators (qualifier 0). For all components, qualifier 8 meaning “not specific” and qualifier 9 meaning “not applicable” could also be used [4].

The subjective knee assessment form of the International Knee Documentation Committee (IKDC) [15] was also applied. The IKDC had 10 questions that evaluate symptoms, sports activities, and functioning. The total score ranged from 0 to 100, in which 100 indicated that the patient had no limitations with daily living or sports activities, as well as the absence of symptoms [16].

Finally, to assess self-perception of general health and functioning, patient answered two questions: one on general health status and one on functioning, using a numerical scale from 0 to 10 as answers, in which 0 meant poor general health and/or functioning, and 10 meant excellent general health and/or functioning [36]. However, the difficulty in converting the ICF categories into a questionnaire has already been reported in the study investigating the construct validity of the core set for breast cancer [31]. In addition, a cross-cultural adaptation may be necessary to increase the understanding of categories [37]. The results of this study also highlight the importance of a trained professional in using the ICF to conduct the assessment.

As a strength of the present study, a clinical instrument to measure the functioning of people with any knee dysfunction was developed, considering the multiple aspects of functioning recommended by the ICF. As we proposed a measurement tool, a weakness of the study was the failure to evaluate other measurement properties for the instrument to have all the scientifically required parameters. The results of this study demonstrated the potential of the brief core set for knee dysfunction as a scale. Future studies can evaluate other measurement properties of the brief core set for knee dysfunction, such as inter- and intra-rater reliability and responsiveness, in addition to checking for possible ceiling and floor effects.

Regarding the limitations of this study, first, the sample was limited to only two cities in Brazil. Therefore, different results could be found in other countries or regions. Although patients were asked about other comorbidities, we did not assess whether these comorbidities impacted functioning. Furthermore, lifestyle habits and the use of orthoses were not recorded. Regarding educational level, other studies [14, 25] conducted the analysis considering the average schooling time in the country. However, in our study, educational level was assessed as a categorical variable, not allowing analysis by the average schooling time of the Brazilian population, which is 9.4 years [38]. Finally, the face-to-face sample may not represent all people with knee dysfunction, because they are relatively less educated, older, and retired. Although the study identifies which categories can be used as a measurement tool, scores from qualifiers can be considered provisional until repeated evidence in larger samples supports the current interpretation.

Conclusion

From the comprehensive core set for knee dysfunction, 12 categories showed adequate construct validity to compose the brief core set for knee dysfunction to be applied face-to-face via interview by a professional. These 12 categories cover body functions and structures and activities and participation and can be used to measure the functioning of people with any knee dysfunction, aged between 18 and 89 years.