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A Theoretical Model for Preventing Osteoarthritis-Related Disability
Osteoarthritis (OA) affects many aspects of life for affected individuals. Effective interventions to prevent and restore function must be based upon an understanding of what contributes to OA and its associated disabilities. A hypothetical OA disability model built upon the previous work of Nagi (1991), Verbrugge and Jette (1994), the International Classification of Functioning of World Health Organization (World Health Organization, 2001), and other scientific findings is proposed. The model includes a main disease pathway, which describes the sequence of events from OA-associated impairments to disabilities. Contextual factors influencing the process include individual characteristics, psychological state, coping style, comorbidities, social support, and physical environment. The model provides a useful conceptual framework for understanding the OA disability process from a biopsychosocial perspective and for guiding rehabilitation nursing interventions in OA care.
Osteoarthritis (OA) is the second most common primary diagnosis among adults receiving Social Security disability payments (Lawrence et al., 1998) and the leading cause for hip and knee replacement in the United States (Felson et al., 2000). As OA progresses, it changes the musculoskeletal system, decreases physical capacity, and affects the ability to perform functional activities independently. The mechanisms of how OA lead to associated disability remain unclear. Several disease or pathological symptoms, such as joint pain, joint deformity, and muscle weakness, have been linked to OA disability outcomes (Davis, Ettinger, Neuhaus, Barclay, & Segal, 1992; Davis, Ettinger, Neuhaus, & Mallon, 1991; Hannan, Felson, & Pincus, 2000; Hurley, 1999; Lethbridge-Cejku et al., 1995; McAlindon, Cooper, Kirwan, & Dieppe, 1993). Factors other than disease itself, such as demographics, psychological state, comorbid conditions, lifestyle, physical environment, and social support, also contribute to function limitations and activity restrictions in people with OA (Badley, Rothman, & Wang, 1998; Brenes, Rapp, Rejeski, & Miller, 2002; Creamer, Lethbridge-Cejku, & Hochberg, 1999; Kee, 2003; Keefe et al., 2000; Rapp, Rejeski, & Miller, 2000; Steultjens, Dekker, & Bijlsma, 2001; van Baar, Dekker, Lemmens, Oostendorp, & Bijlsma, 1998). This evidence suggests the pathway from OA pathological change to disability is multifaceted and influenced by multiple personal and environmental factors.
The purposes of this paper are: (a) to describe the process of how osteoarthritis leads to disability outcomes; and (b) to discuss the implications of this process for nursing practice. First, the previous works of Nagi (1991), Verbrugge and Jette (1994), and the International Classification of Functioning (ICF) of the World Health Organization (WHO; World Health Organization, 2001) are summarized. Second, the hypothetical OA disablement model built upon these previous generic disability models and other scientific findings is presented. Third, the implications of this model are discussed. Finally, the implications for the model’s practice and limitations are given.
Previous disability models
Nagi’s (1991) disability scheme and the ICF (World Health Organization [WHO], 2001) are two widely accepted and applied generic disability models. Nagi posits a disease-disability pathway to describe the sequence of events from pathology to various functional outcomes. Nagi suggests that pathological changes lead to impairment, functional limitation, and, ultimately, to disabilities. Impairments are “anatomical, physiological, mental, or emotional abnormalities or losses” (Nagi, p. 322). Functional limitations are “limitations in performance at the level of the whole organism or person” (Nagi, p. 322). Disabilities are viewed as “limitations in performance of socially defined roles and tasks within a sociocultural and physical environment” (Nagi, p. 322). Verbrugge and Jette (1994) further expand Nagi’s disability scheme by introducing social, psychological, and environmental factors that, while not part of the main disease disability, operate to modify it, either increasing or decreasing its speed and magnitude.
As a natural derivative of Nagi’s and Verbrugge and Jette’s disability models (1994), the World Health Organization published the ICF to describe dimensions of functioning and disability. As a classification scheme, ICF does not intend to model the process of disability. ICF’s definitions of functioning and disability, however, provide unified language for describing these constructs:
Nagi’s disability scheme, Verbrugge and Jette’s (1994) disablement process model, and the ICF are the foundations of the proposed OA disability model. The ICF’s functioning and disability constructs and definitions are the building blocks for modeling the OA disability process from a biopsychosocial approach.
The OA Disability Model
An OA disability model describes the process by which OA affects functioning over time. The model links the sequence of events resulting from joint damage, pain, activity avoidance, and muscle weakness to activity limitations and participation restrictions (Figure 2). Research conducted with OA populations supports relationships between each concept. Factors other than OA or its primary consequences that affect functioning are included in the model as contextual factors. These factors include individual characteristics, psychosocial attributes, coping, lifestyle, comorbidities, social support, and physical environment.
Joint damage: Increased joint damage evidenced by radiographic joint change is positively associated with pain and functional limitations (Davis et al., 1991). However, radiographic joint changes alone are insufficient to explain the severity and impact of the disease. In population-based studies, about 37% of adults showed a certain degree of radiological OA, but only 50% of these adults presented with OA symptoms, and about 25% had moderate or severe disease (Felson, Lawrence, Hochberg et al., 2000; Hannan et al., 2000).
Pain, activity avoidance, and muscle weakness: These factors also play important roles in the downward spiral of the OA disablement process. Studies show that knee pain and knee strength mediate the effects of joint damage on functional performance, self-reported physical functioning, and self-reported role and social functioning (Bennett, Stewart, Kayser-Jones, & Glaser, 2002; Bookwala, Harralson, & Parmelee, 2003; Miller, Rejeski, Messier, & Loeser, 2001). OA patients often restrict their activities to avoid movement-associated pain. Prolonged physical inactivity leads to muscle weakness, and weak muscles lose their ability to support and protect joints (i.e., shock absorption, proprioceptive acuity), resulting in excessive joint laxity. An unstable joint is less capable of carrying weight and is more difficult to move. Joint damage caused by activity avoidance leads to muscle weakness, further damaging the joint. Minor joint damage can result in significant disability through this vicious cycle. Muscle weakness was once considered strictly the result of joint damage. Subsequent evidence suggests muscle weakness may indeed precede joint damage (Hurley, 1999). Over time, accumulated trauma due to unstable joints and inappropriate gait can result in joint degeneration (Slemenda et al., 1997). In the proposed model, a feedback loop among joint damage, pain, activity avoidance, and muscle weakness represents OA’s cycle.
Activity limitations and participation restrictions: Without appropriate management, OA-associated joint damage, muscle weakness, and pain may eventually lead to activity limitation and participation restriction. Musculoskeletal impairments as measured by joint pain, range of motion (ROM), deformity, and crepitus explained 15% of the variance in functional limitation in one study (Hughes, Edelman, Singer, & Chang, 1993). Jette (1999) also found that musculoskeletal impairment strongly predicts OA progression and functional decline in older adults. Although it is reasonable to assume that activity limitations should precede participation restrictions, evidence suggests otherwise. A hierarchical relationship between activities of daily living (ADLs, activities related to self-care) and instrumental activities of daily living (IADLs, activities necessary to adapt independently to the environment such as shopping, transportation, and housekeeping) has been suggested (Kempen & Suurmeijer, 1990, p. 498). Impaired ADL functions (individual level) are found to represent more severe dysfunction than impaired IADL functions (involved in life situations; Kempen & Suurmeijer, 1990). A person who experiences difficulty performing social activities (such as holding a job) due to pain and joint deformity may still perform their ADLs quite independently. Most likely, OA-associated impairments affect both domains (individual and social) simultaneously.
Personal factors: Demographics, psychological state, coping style, personality, and comorbid conditions are personal factors linked to OA disability outcomes. OA’s prevalence and severity is influenced by characteristics, such as age, female gender, education, and marital status (Caspi et al., 2001; Jordan et al., 1996). People with OA-associated disability tend to be age 65 and older; have less education and income; and be widowed, separated, or divorced. Women report significantly higher levels of pain and physical disability than men (Keefe et al., 2000).
Psychological states, such as depression, self-efficacy, coping style, and personality also modify the disease-disability relationship in people with OA. Significant correlations between depression and both pain and physical disability have been reported in older OA patients (Dekker, Tola, Aufdemkampe, & Winckers, 1993; van Baar et al., 1998; Zautra & Smith, 2001). Among individuals with arthritis, poorer function, more physical limitation, and greater joint pain were found in those with depressive symptoms than in those without these symptoms (Katz & Yelin, 1993). Depression predicts pain and disability even after controlling for disease severity (van Baar et al., 1998).
Individual hardiness and self-efficacy also modify the OA disablement process. One study reported that along with pain and social support, hardiness explained 54% of the variance in physical function of people with OA (Kee, 2003). Rejeski et al. (2001) reported a significant interaction effect between self-efficacy and baseline knee strength in predicting both self-reported disability and stair climb performance in older adults with knee pain. Adults who had low self-efficacy and low strength at baseline showed the largest decline in function after 30 months.
Passive coping styles (rest, pain transformation) predict pain and disability in patients with knee OA, even after controlling for the severity of disease and clinical and demographic variables (Steultjens et al., 2001). Self-regulatory and active pain coping strategies buffer the effects of OA on functioning (Keefe et al., 2000; Rapp et al., 2000). In contrast, catastrophizing reactions to pain enforce a patient’s tendency to avoid pain-related activities, resulting in muscle weakness, unstable joints, pain, and, ultimately, disability (Keefe et al., 2000; Rapp et al., 2000; Steultjens et al., 2001). Personality traits also contribute to the understanding of physical disability. In studying 480 adults with knee pain, Brenes, Rapp, Rejeski, and Miller (2002) found that pessimism was significantly associated with difficulty walking, lifting objects, climbing stairs, and getting into and out of cars, after controlling for demographic and health variables.
Comorbid conditions, such as obesity and cardiopulmonary disease, have been shown to increase the amount of disability in knee OA (Ettinger, Davis, Neuhaus, & Mallon, 1994; Verbrugge, Gates, & Ike, 1991). Obesity is one of the major modifiable risk factors for development of hip and knee OA (Al-Arfaj, 2002; Lievense et al., 2002). It can accelerate the underlying disease process, aggravate pain, and increase OA-associated disability (Creamer, Lethbridge-Cejku, & Hochberg, 2000; Messier, 1994). Decreased aerobic capacity due to cardiopulmonary disease also has been linked to the development of disability in knee OA (Ettinger et al., 1994). Marks and (2002) also found that when two or more comorbid conditions exist, OA-associated disability is increased.
Environmental factors: Physical environment and social support can modify the strength of relationships in the disease-disability pathway in a complex way. Although environmental barriers (such as stairs) may accelerate pain and hinder ambulation, some level of environmental stress (such as walking, climbing, or carrying) is essential for maintaining musculoskeletal function and physical fitness (Ettinger & Afable, 1994). Environmental adaptations are associated with increased risk of physical dependence (Badley et al., 1998). Having less social support as indicated by the extent of the network, strength of the support, and amount of resources also predict disability in OA (Kee, 2003; Rejeski & Shumaker, 1994; Weinberger, Tierney, Booher, & Hiner, 1990).
Implications for rehabilitation nursing practice
OA influences many aspects of life. The pathway from disease to disability is multifaceted and is influenced by multiple contextual factors. At each stage, the severity, duration, and speed of progression mold the clinical presentation. Information regarding the OA disability process and the factors that affect its development helps healthcare providers deliver proper preventive and restorative care. Although a cure is not yet tangible, OA symptoms can be controlled and disability can be delayed or prevented through appropriate management. The model suggests multiple points for intervention. Rehabilitation nurses should collaborate with other disciplines to provide care in managing pain, promoting exercise, protecting joints, controlling weight, addressing psychosocial issues, enhancing perceived social support, mobilizing resources, modifying physical environments, and educating patients.
Pain management and exercise: As presented in the model, pain, activity avoidance, and muscle weakness play an important role in the downward spiral of the OA disability process. Appropriate pain control and improved muscle strength are key to breaking the vicious cycle and delaying or preventing OA disabilities. Analgesics, corticosteroid injections, cognitive-behavioral methods (relaxation, distraction, and music), and use of heat or cold are current pain management modalities. Because of the chronic and dynamic nature of joint pain, treatments should be individualized, regularly evaluated, and constantly monitored for adverse effects.
Appropriately designed exercise programs can improve muscle strength, ROM, endurance, and aerobic and overall fitness, thereby decreasing further joint damage and slowing the progression of disability. Many types of exercise (aquatics, walking, cycling, and resistance training) are beneficial if attention is given to joint protection and if the exercise gradually is increased. Individuals with OA should be encouraged to exercise regularly. In addition, because decreased quadriceps muscle strength may be associated with development of knee OA (Hurley, 1999; Slemenda et al., 1997), it is important to identify people with this weakness. Interventions that strengthen quadriceps may prevent knee OA in this population.
Psychosocial health: Assessing psychosocial distress and adjustment (especially depression, coping, and self-efficacy) will help to identify those at highest risk for disability. Individuals with OA are at higher risk for depression than those who do not have OA, and depression is known to increase physical disability. To prevent disability, nurses should routinely screen OA patients for depression and collaborate with other disciplines to treat depression.
Understanding how individuals manage their OA symptoms also is important. Passive coping strategies, such as activity avoidance, pain transformation, and catastrophizing pain reactions, are associated with increased disability, while active coping strategies (self-regulation, self-control, and acceptance) may buffer OA’s effect on functioning. Nurses should work with each individual to identify effective coping techniques. Coping strategies may be effective for some patients, but not for the others; individualized care is necessary.
Self-efficacy beliefs also are associated with OA disability outcomes and may mediate the effects of treatment on physical functioning. Self-efficacy should be assessed and strengthened through patient education, if needed.
Social support: Social support plays an important role in ameliorating the effects of pain, functional limitation, and physical disability. By identifying support needs and providing support through communication and resource mobilization, nurses can help patients adjust to living with OA and manage their disease more effectively.
Patient education: Effective OA management is a joint effort between patients and their healthcare providers. Use understandable terms to teach patients about the OA’s physiological changes, impairments, and progression, OA’s appropriate therapeutic interventions, preventive actions, and coping strategies.
Limitations and suggestions
This model is based upon previous research and should be tested with empirical data to validate its usefulness and applicability. The roles of each contextual factor in each stage of the disability process require further clarification because these contextual factors may affect the entire process. Depression, for example, may affect pain severity, activity levels, and social participation. Depression is an example of a contextual factor that is modeled outside of the main disease-disability pathway, and it plays a dynamic role in the disablement process. Further clarification of relationships between the main disease disability pathway and contextual factors will advance our knowledge of the disability process.
The model proposed here primarily focuses on OA’s impact on physical functioning. Less attention has been paid to psychological functioning. In this model, psychological states are constructed as contextual factors that modify the main disability pathway. For example, depression may be both a contributor to or a result of OA disability. The model does not present depression as a possible result of OA impairment or disability. Further investigation of the role of psychological functioning is needed.
This OA disability model provides a useful conceptual framework to understand the ways in which OA might progress and how a host of contextual factors modify the trajectory of the disability process. Rehabilitation nurses can use this model to more effectively provide holistic care for patients with OA, and researchers may employ it to develop and test more effective ways to manage this debilitating and costly condition.
The authors thank Professor Basia Belza, PhD RN, Catherine Warms, PhD RN, and Maria Pettinato, MSN RN, for valuable comments, and acknowledges funding support from the Biobehavioral Nursing Research Training Grant funded by NINR (T32 NR 07106-02) and Women Health Research Training Grant funded by NINR (T32 NR 070-17).
About the Authors
Tsae-Jyy Wang is an assistant professor at the Department of Nursing, National Taipei College of Nursing in Taiwan, ROC. Horng-Lin Chern is a physician at the Department of Family Medicine, Cardinal-Tien Hospital in Taiwan, ROC. Yueh-Er Chiou is a lecturer at the Department of Nursing, Fu Jen Catholic University in Taiwan, ROC. Address correspondence to Tsae-Jyy Wang, 13F No. 162, Sec. 3, Zhongxiao E. Rd., Taipei 106, Taiwan, or via e-mail to email@example.com.
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