Arthritis and the process of disablement.

Key Words: Arthritis, Osteoarthritis, Physical disability, Rheumatoid arthritis 

Perhaps because it is so common, arthritis is not always regarded as the serious ailment that it is. Arthritis takes its toll on the individual in multiple dimensions, from the organic level to the social level of human existence. Arthritis and related musculoskeletal conditions are found throughout the world and typically present health care practitioners with a cluster of chief complaints (most often, pain), muscle and joint impairments, and functional limitations in activities of daily living ADL).[1-4] Individuals disabled by arthritis confront their inability to fulfill social roles successfully in interpersonal relationships, as members of a family, or as contributors to economic society, often as the result of an environment of physical and sociocultural barriers.[5-12]

The process of disablement due to arthritis that will be discussed in this article is based on the three interconnected hypotheses regarding disease, impairment, and functional limitations and disability originally articulated by Nagi[13] (Fig. 1). The first hypothesis is that disablement begins with a specific disease or active pathology. When confronted by disease, insult, or injury, the organism mobilizes its resources and defense mechanisms against the abnormal state and attempts to return to its normal, prepathological state. Joint inflammation, one of the key characteristics of arthritis, is interesting in that it is part of the body's normal response to injury, yet can evolve into a pathological process itself if left unchecked for the long-term.

Application of the Nagi model of the process of disablement to arthritis requires some recognition that the term "disease" is actually too limited to refer to the numerous musculoskeletal conditions that represent more than a single active pathology. Specifically, rheumatoid arthritis (RA) is a medical syndrome (ie, a recognized cluster of signs and symptoms).[14] Osteoarthritis (OA) is also a cluster of pathological processes, not a single pathological state, and is neither active nor progressive in all cases.[15]

The effects of disease are found in the primary impairments of the particular body system(s) in which the organism's pathological state is manifested. The primary impairments associated with arthritis are found chiefly in the alterations of the normal structures and functions of bones, muscles, and joints of the musculoskeletal system. During the initial assessment of the patient, physical therapy practitioners generally anticipate finding these impairments clinically as losses of range of motion (ROM) or strength in the individual with RA or OA. Impairments of the neuromuscular system (eg, poor balance) or cardiopulmonary system (eg, decreased endurance) can also be found in individuals with arthritis, usually as sequelae of the musculoskeletal impairments. Far beyond the "disease," the impairments that are the end product of active arthritis pose the clinical challenge of most importance to physical therapists. For example, fixed lesions such as joint erosions or attenuated tendons following extended periods of inflammation are two arthritis-related impairments of the musculoskeletal system that influence the trajectory of disability in individuals with arthritis.

The second hypothesis about the process of disablement in arthritis is that the magnitude of some primary and secondary impairments is sufficiently great to limit an individual's capability to perform routine functional tasks in a usual way (eg, reaching for a jar on an overhead shelf without difficulty, being able to dress without assistance). Functional limitations are measures of behaviors that deviate from what is normally expected, in contrast to impairments, which indicate aberrant conditions of tissues, organs, and systems. The primary functional limitations for individuals with RA or OA presumably result from changes on the bone surface, loss of joint mobility, muscle weakness, and atrophy, which contribute directly to limitations in ADL and the ability to work. Pain, secondary to changes in normal joint structure and function, often limits function as well.[16,17]

Individuals with arthritis experience most of their limitations in physical functional activities, but the concept of function has psychological and social dimensions as well. Psychological function encompasses mental tasks such as money calculations and affective states such as anxiety and depression. Social functioning includes social interaction, social activity, and social role. Although each of these dimensions is distinct, the physical function of the individual with arthritis may influence psychological and social function, and in turn be influenced by them.

Although the process of disablement is depicted heuristically as a linear progression, one cannot assume that an individual will be unable to perform the usual tasks and roles of daily living merely by virtue of having an impairment. For example, minor losses of shoulder ROM might barely affect the ability to comb one's hair, or they might have no effect whatsoever. Although more substantial losses of ROM can mean that a person will have great difficulty in performing this activity, special adaptive equipment may be all that is required to complete the task, Another person may learn to compensate for lost shoulder ROM by using the available ROM in other joints to finish the activity. Sometimes, patients will even overcome multiple and severe impairments by the shear force of their motivation.

The third hypothesis about the disablement proposes that functional limitations generally underlie disability. Anyone may alter the way in which a few activities are done to compensate for musculoskeletal impairments, or may need special assistance or devices to complete a task. Persistent limitations in the broad spectrum of functional tasks and activities expected of independent adults in specific social roles, however, qualify an individual as disabled. Some approaches to the process of disablement, notably the World Health Organization's International Classification of Impairments, Disabilities, and Handicaps, use "disability" rather than "functional limitations" to describe deviations in the expected manner in which activities are performed. This categorization ignores the difference between the inability to perform functional activities that are essential to a specific social role (eg, student, spouse, parent, worker) and the particular manner in which those activities may be done.[13] For example, a person with arthritis may need adaptive clothing and assistive devices to offset the impact of impaired ROM and strength on function. Yet, this same individual may also be able to live independently, have a family, raise children, and work. Thus, this person would not be accurately labeled as "disabled," despite functional limitations that indicate the manner in which the routine tasks and activities of a social role are done deviates substantially from the norm.

The pathway from disease to disability is not inexorable (Fig. 2). At each junction, the speed of progression, its severity, and its duration shape the clinical presentation. Proper medical care and timely rehabilitation can eliminate or blunt the impact of disease on impairment, of impairment on function limitations, and of functional limitations on disability. Prevention is a critical component of all therapeutic interventions at each step. Furthermore, each of the steps in the process of disablement can be modified by a host of factors such as age, gender, education, income, comorbidity, personal and health habits, motivation, social support, and physical environment. Several factors that modify the trajectory of disability in RA have been identified: education,[18] age, gender, disease severity, duration of illness and treatment,[19,20] and comorbidity.[21] Anxiety, depression, and coping style have been related to functional limitations in individuals with hip or knee OA.[22]

A practitioner's understanding of the process of disablement and the factors that affect its development is useful to achieving the goal of restoring or improving the functional status of individuals with arthritis. The amount of data that can be amassed during an initial evaluation of patients with RA or OA, as with any chronic disease, is enormous, and more than occasionally overwhelming. The model presented allows the physical therapist to categorize the patient's history, prior treatment, and risk factors and to delineate where the impact of these variables on disablement occurs. Most importantly, the clinical presentation can be classified in a way that identifies those particular musculoskeletal impairments impeding the performance of certain functional tasks and activities and that accounts for other limiting or modifying factors. With this analysis, the practitioner can propose goals that are relevant to the individual's everyday life, hypothesize about the impediments to their achievement, estimate the likelihood of success, and plan appropriate intervention.[23]

Clinical Epidemiology

Among individuals with musculoskeletal conditions, RA and OA account for a greater proportion of physician visits, restricted activity and bed rest, and lost workdays than any other rheumatic disorder, including low back pain.[24,25] Rheumatoid arthritis is a systemic inflammatory disease characterized by chronic synovitis and synovial proliferation, which ultimately may result in joint destruction. Long-term inflammation will also weaken the joint capsule and surrounding tendons and ligaments. A bilateral and symmetrical pattern of joint involvement is a strong clinical marker for RA.[26] Each of these disease factors has implications for the kinds of musculoskeletal impairments seen in these patients as well as their effects on everyday functional activities.

In 1988, there were an estimated 4 to 6 million persons with RA, with an incidence of 100,000 to 200,000 new cases of RA that year.[14] Rheumatoid arthritis affects women two to three times more often than men in the typical years of onset (ie, 20-60 years of age), although men and women over the age of 65 years appear to be affected at the same rate. There is a general increase in prevalence for both sexes as age increases.

Due to variations in the racial and worldwide distribution of RA, there have been some suggestions that there are environmental and genetic influences on RA. Black Americans tend to have fewer cases of RA than their Caucasian counterparts, whereas prevalence among some Native American groups is greater.

In contrast to RA, OA is a localized process marked by joint-space narrowing due to progressive destruction of articular cartilage and the formation of osteophytes at the joint margin.[15] Pain and disease severity in individuals with OA are potentially related to functional loss, although not in the same way as in individuals with RA. Unlike individuals with RA, who report pain on motion and at rest, the pain associated with OA is likely to occur or worsen only with motion, except in the later stages of the disease. Pain in individuals with OA is not well correlated with the severity of the disease on radiographs. Guccione and co-workers have shown that functional deficits in elders are more likely in asymptomatic individuals with severe radiographic OA than in individuals with milder, but more symptomatic, disease.[27] It is likely that some individuals with severe OA remain relatively asymptomatic precisely by avoiding those activities that elicit pain.

Some radiographic evidence of OA is an extremely common condition after 40 years of age, although symptoms may not be present.[16] Osteoarthritis is widespread in adults over 60 years of age, and OA is found in women more often than in men, a sex difference that widens with age decade. More than 60 million adults in the United States are thought to have OA.[28] No single factor that predisposes an individual to OA has been identified. Studies that have questioned a racial predisposition of OA have generated conflicting data, depending on which joint was chosen to be studied.

Although aging is indeed strongly associated with OA, aging in itself does not cause OA, nor should OA be considered a "normal" aging process.[29,30] Several factors related to aging may, however, contribute to the development of OA. One possibility is that trauma as an adolescent or in early adulthood may initiate a remodeling of bone, which alters joint mechanics and nutrition in a way that becomes problematic only later in life.

The etiology of OA is most likely specific to the particular joint affected.[28] For example, routine physical activity without injury apparently does not lead to symptomatic knee OA,[31] but may contribute to hip OA.[3] The etiology of knee OA, however, may be influenced by repetitive "microctrauma."[29] Specifically, occupational tasks such as carpet laying and roof repair with intense repetitive knee-bending have been linked to the development of OA.[32] Obesity, which might be considered a variation of "repetitive microtrauma," has also been shown to be a risk factor for the development of OA in later life[33] and may, as Verbrugge et al[34] found, propel disability when a person has arthritis.

Functional Consequences of Arthritis

Several investigations have established both a cross-sectional and a longitudinal relationship between arthritis and functional limitations. Rheumatoid arthritis and OA are not equivalent, however, in their impact on function. Yelin et al[35] found that individuals with RA experienced reductions across a broad spectrum of activities in comparison with age- and gender-matched controls. In contrast, individuals with OA were restricted only in their ability to engage in household chores, shopping and errands, and leisure activities in comparison with a non-OA control group. When OA affects the knee, the joint most frequently studied in epidemiological investigations, the impact of the disease on a person's performance of an array of basic and instrumental ADL involving the lower extremity has been found to be joint-specific.[17,21] Guccione and co-workers[36] found that the association of knee OA with functional limitations accounted for a substantial proportion of disability in 1,769 community-dwelling elders of the Framingham study, even when controlling for comorbidity. Furthermore, this association was stronger than the association of heart disease and functional limitations in this same cohort of individuals, whose mean age was 73.7 years. Davis and colleagues37 have also provided evidence that the impact of knee OA on the physical functioning of older women is greater than its impact on all other age and gender subgroups. Because of both its functional impact and its prevalence, chronic arthritis represents a major threat to the health of female elders, of equal concern as any other medical condition with respect to quality of life.

Beyond limiting ADL, arthritis also has substantial effects on labor force participation of working-age Americans.[38] Men with arthritis have a labor-force participation rate that is approximately 20% less than that of men without arthritis. The work participation rate of women with arthritis is even lower. When a working-age individual with arthritis of either gender also has another medical condition and experiences limitations in ADL, labor-force participation rates for both genders plummet, but the impact is greater for women than for men. In a series of studies,[5-7] Yelin and colleagues demonstrated that work-related disability in arthritis is often a function of the job itself; a job with fewer physical requirements and a higher degree of worker autonomy in how the job is performed allows the person with arthritis to remain in the work force longer.

In addition to the effects both kinds of arthritis have on paid work, RA has a devastating effect on the unpaid work performed by women as homemakers. Women with moderate to severe RA delegate many more hours of household work each week to other family members.8 These women also experience greater limitations in the social and nurturant dimensions of running a household compared with their peers without RA.[9]

Work-related disability has long-term implications on the function of the individual with RA or OA. The financial losses that accrue to an individual during the process of disablement are substantial and can be deleterious to well-being.[10,11] For example, RA leads to the most frequent use of physician services among all individuals with musculoskeletal conditions.[12] Thus, as their disease progresses and the functional consequences of that disease take their toll, individuals with RA may find that they have fewer financial resources for treatment. Diminished medical care, lack of rehabilitation services, and the inability to pay for even simple architectural changes such as handrails may lead to a perilous deterioration of health and function. Although most physical therapy practitioners are aware that the functional consequences of RA are not minor, there is growing evidence that functional decline is a marker for early mortality among persons with RA.[39]

Joint Impairment and Function

We do not know the degree to which limitations in physical functional activities among individuals with arthritis are linked to musculoskeletal impairments. Some functional limitations are likely to be the result of neuromuscular or cardiopulmonary impairments that accompany chronic arthritis, or they may evolve as a result of musculoskeletal impairments. In simple clinical terms, a person with arthritis who does not move will sooner or later have more than just joint problems. Despite the combined prevalence of individuals with either OA or RA, a very small number of studies have attempted to establish the relationships among the medical condition, its impact on the musculoskeletal system, and function. In a simple descriptive study of 95 patients with arthritis, Badley et al[40] sought to determine the association of limited ROM with difficulty in performing basic ADL. They found that their subjects had difficulty walking to a toilet, transferring to a toilet, getting in and out of a bathtub, and walking up and down stairs if they could not flex their knees at least 70 degrees, and these subjects required even greater ROM for some activities.

The degree to which musculoskeletal impairments are associated with limitations in physical functional activities is a central question for physical therapy practice and research, and some notable progress has been made to determine the strength of this relationship. Interestingly, much of what we know about musculoskeletal impairments and their relationship to functional decline has been obtained by research focused on gerontology as much as by a primary interest in arthritis-related disability in adults.

Bergstrom and colleagues[41,42] investigated the connection between joint impairment and function in a group of 79-year-old men and women. They found that lower-extremity joint complaints were more common than upper-extremity complaints. Among those elders who had upper-extremity complaints, ROM was most restricted in the wrists or shoulders. Hip motion was limited in 84% of the individuals who had lower-extremity complaints. When elders with symptoms and joint complaints were compared with elders without such problems, significant differences were found in their ability to use public transportation and climb stairs. Elders with musculoskeletal impairments were also more likely to use ambulation aids. Hughes et al[43] rated joint impairment based on the presence of tenderness, swelling, pain on motion, decreased ROM, crepitus, and deformity in 541 elders. They found that musculoskeletal impairment explained 15% of the variance in scores on an index of functional limitations.

The impact of musculoskeletal impairments is not limited to current level of functional status. Jette and colleagues[44,45] identified a strong predictive relationship among musculoskeletal impairment, its progression, and future functional decline in the elderly. They also noted that the impact of musculoskeletal impairment of the hand was chiefly on basic ADL, whereas lower-extremity impairment affected instrumental ADL such as housekeeping, meal preparation, and shopping more.

The degree of disability among individuals with arthritis has been linked to the severity of the disease, but this relationship may be dependent on both the particular joint studied and the measure of function used. The connection between radiographic grade of OA and function is strong for OA of the knee,[17,27,37] but much weaker for OA of the hand.[46] Functional loss in OA of the hand has been shown to be more associated with strength loss than the OA itself.[46] Muscle weakness has also been related to disability in persons with OA of the knee.[47] Besides the direct effects of arthritis on impairment and function, Verbrugge and colleagues[48,49] have also confirmed that the functional impact of chronic arthritis is enhanced when the individual with arthritis has another comorbid condition. A similar modifying effect of comorbidity on function has been found specifically for individuals with RA as well.[50]

Unanswered Questions in Practice and Research

The cited studies indicate that there are relationships among arthritis, impairments, and functional status that are clinically important to physical therapists. Yet, few of these studies have been reported in the physical therapy literature. Thus, the first question to be addressed is: What is the reason for this apparent lack of interest in arthritis-related disablement, which is somewhat startling in light of its prevalence and the magnitude of its impact? Although many of the barriers to monitoring clinical outcomes have been eliminated by recent developments in the measurement of medical status, joint involvement, and function, particularly by patient self-report, these technological advances have barely filtered into physical therapy clinics or been adopted for research purposes by physical therapist scientists.[51-54]

A second concern is that clinical practice and research in physical therapy have rarely ventured outside of the dimension of physical function in order to explicate the process of disablement for the individual with a musculoskeletal disorder, Although most physical therapy interventions are directed toward outcomes in the dimension of physical functional activities, limitations in psychological or social function are also relevant to the evaluation and treatment of the patient with a musculoskeletal disorder. Successful performance of complex physical functional activities, such as personal hygiene and housekeeping, typically require integration of cognitive and affective abilities as well as physical abilities.

Social function encompasses three domains: social interaction, social activity, and social role. Each of these domains requires a certain degree of physical functional ability. Physical functional limitations in manipulating a phone can decrease social interaction and shrink the size of a person's social network. A person who is physically limited to household ambulation also has severely limited options for social activity. Social roles specify expected relationships between people and generally obligate individuals to performing specific physical tasks to fulfill the requirements of the role. A woman in the social role of a mother needs hand strength and dexterity to provide care and comfort to her child. Therefore, improvement in physical functional status may not be the only, or even the most important, measure of the positive effects of physical therapy. Future research should determine which measures of physical, psychological, and social function are most pertinent to documenting the outcomes of physical therapy intervention.

Future investigations must also show some appreciation of the rich and varied context in which the process of disablement unfolds. A person's age, gender, level of anxiety or depression, and other personal characteristics may help to shape the process, and should be taken into account by the researcher in the same way a clinician integrates these data into treatment planning. Similarly, factors extrinsic to the individual such as social support, mediated through a person's marital status, apparently modify the process of disablement in arthritis.[55,56] Although some of these influences are postulated in Figure 2, based on the current literature, conclusions about the importance of these factors to disablement remain tentative. Multivariate analyses exploring these relationships will greatly enrich our understanding of disability in persons with arthritis. Futhermore, disablement research in arthritis need not be confined to quantitative analysis. On the contrary, the fact that "disability" is a socially constructed notion with personal meaning for the individual recommends it for qualitative study as well.

As mentioned previously, an impairment does not always entail functional limitation. Few studies have attempted to correlate functional status with the magnitude of impairment. Patients with arthritis will undoubtedly have musculoskeletal impairments, Clinical practice today, particularly in attempting to prevent functional decline, proceeds without a strong empirical basis for parceling out which impairments should be treated immediately, which should be monitored, and which can be ignored.

Although countless individuals with arthritis have received physical therapy, we still know very little about how to improve functional outcomes consistently. A confluence of two forces, specifically increased accountability for clinical practice under health care reform and the prevalence of arthritis in an aging population, demand that this deficit in our knowledge base be addressed as quickly as possible. Physical therapy intervention may be aimed at remediating the impairment, allowing or teaching the patient to compensate through substituted movements, or adapting the environment or conditions of the activity. Each of these clinical strategies appropriates different resources, presents different costs, and potentially achieves different outcomes. These sorts of clinical differences are rarely discussed in the physical therapy literature from the perspective of either practice or research. The evidence suggests that functional limitations among people with arthritis are not static, and that over a period of years, at least some individuals improve functionally.[57.58] Our challenge is to demonstrate that physical therapy contributes positively to the trajectory of disability among individuals with RA or OA.

References

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AA Guccione, PhD, PT, is Lecturer, Department of Orthopaedics, Harvard Medical School, and Directo of Quality Assurance, Research, and Education, Physical Therapy Services, Massachusetts General Hospital, 15 Parkman St, WAC 128, Boston, MA 02114 (USA).

This work was supported by a National Institutes of Health Special Emphasis Research Career Award from the National Institute on Aging (K01 AG00567).