Supplements Management of Early Osteoarthritis: The Role of Acetaminophen
Early Management of Osteoarthritis
Osteoarthritis (OA) is highly prevalent and increasing in frequency; the number of patients with OA has increased by nearly 30% over the past 10 years. The primary symptom of OA is pain. Pain and other symptoms of OA may have a profound effect on quality of life (QOL), affecting both physical function and psychological parameters. The economic costs of OA are high, and include those related to treatment, those for individuals and their families who must adapt their lives and homes to the disease, and those due to lost work productivity. These considerable humanistic and economic burdens of OA provide motivation for early identification and treatment. Early diagnosis is assisted by knowledge of risk factors. Classification criteria for OA of the hand, hip, and knee developed by the American College of Rheumatology assist in diagnosis. The European League Against Rheumatism has developed an elaborate system for diagnosis of OA of the hand. Several societies have developed therapeutic guidelines, with general overall agreement between publications. Therapy of OA is multimodal and requires a combination of pharmacologic and nonpharmacologic treatments.
(Am J Manag Care. 2010;16:S41-S47)
The National Arthritis Data Workgroup estimates the prevalence of osteoarthritis (OA) in the United States as 26.9 million in 2005; this indicates a rise of nearly 30% over the course of the previous 10 years.1,2 This remarkable increase in the prevalence of OA cannot be fully explained by the aging of the US population alone. However, this trend could be better understood by also considering the high and rising prevalence of obesity, an established risk factor.3,4
OA is associated with impaired quality of life (QOL) as well as high economic costs. Direct treatment costs include physician visits, medications, hospitalizations, surgery, and transportation costs. Indirect costs relate to comorbid conditions and lost productivity at home and work.5-8
Thus, for both humanistic and financial reasons, there is strong motivation to identify and treat OA as early as possible. The present article will address disease and economic burden, disease development and progression, risk factors, early identification, and early treatment of OA.
Quality of Life
Patients with symptomatic OA commonly suffer reduced QOL.9 In an Italian study in older patients (mean age, 64.6 years), individuals with OA were compared with healthy matched controls. QOL in patients experiencing recent-onset hip and knee OA symptoms was assessed by the Medical Outcomes Study Short Form-36 (SF-36) questionnaire. The authors found significant differences across all 8 QOL SF-36 domains (P <.0001 for all 8 domains).7 The most dramatic losses in QOL were in physical function, role limitations because of physical problems, and pain; mental health and social function were also reduced in patients with OA.
The effects of OA on QOL are particularly pronounced in patients with more advanced disease. Greater pain and loss of physical function were common, particularly among those with a greater number of comorbidities. Greater pain and loss of physical function were also more common among women than men.10
Disability in OA is more than functional impairment. Emotions, such as feelings of helplessness and depression, influence function.11 Pain itself is associated with reduced function among patients with OA.11 Outcome is influenced by emotions, as patients with OA and psychological distress prior to knee arthroplasty have been shown to experience greater pain and functional impairment postoperatively compared with patients not experiencing such distress in the preoperative period.12
Data from focus groups in patients with OA shed further light on the pain experience. Patients with hip and knee OA describe their pain as intermittent, at times disappearing and reappearing on a daily or weekly basis, or coming and going for months at a time.13 Pain can also be highly variable, for example, manifesting only in the morning, or consistently over the course of a week before dissipating. Patients with OA also describe experiencing pain elsewhere in the body, which they regard as integrated with, and not separable from, their joint pain-a perception that may be partly related to referred pain.13 Pain among patients with OA is furthermore seen as entirely linked with function, with physical movements triggering pain, while pain, in turn, causes limitations in physical function.13 To cope, patients will avoid certain movements and activities that they know will cause pain, and will engage in adaptive behavior to moderate the pain experience, such as organizing their homes to limit the need for movements or positions that are more likely to be painful.13
The economic burden of OA is divided into direct and indirect costs, the latter much more difficult to measure. Direct costs include those related to physician visits, transportation to and from the physician's office, medication, hospitalizations, and surgery. Indirect costs result from comorbid disease and productivity loss at home and at work.5 Moreover, financial costs are related to the degree of disease severity and symptoms. In a study of patients with hip and knee OA of varying levels of disability (based on Western Ontario and McMaster Universities osteoarthritis index [WOMAC]), a strong correlation was found between measure of self-rated disability and total costs (direct and indirect).14 Patients with WOMAC scores of 35 to 44 had costs approximately 76% higher than those with WOMAC scores less than 15 (the reference group), whereas patients with WOMAC scores of 55 or greater had costs 342% higher than the reference group.
Estimating OA-related costs is difficult because of several variables, including differences in study populations, patient age, disease status, and insurance provider. That said, in a review of large groups of patients with OA and varying degrees of disability, the total annual costs of OA were estimated to be between $1750 and $2800. This number excluded costs for other medical expenditures that a given patient might incur.6,8 The costs associated with more severe disease are much greater. The cost of end-stage knee and hip OA was explored using data from a national cohort of Medicare beneficiaries (ie, patients who were at least 65 years of age). Annual costs were determined to be $3800, almost double the cost in the general OA population.15
Direct costs include the costs of total knee arthroplasty (TKA), an increasingly common surgical procedure. The Agency for Healthcare Research and Quality calculates that more than 550,000 TKAs were performed in 2007.16 The average cost associated with TKA, including rehabilitation, was estimated at $20,700. This increases to approximately $24,500 if revision is necessary.15 An additional $12,600 in expenditures can be expected if perioperative complications occur. Early intervention in OA has the potential to delay surgery, and even a small reduction in the number of patients who need TKA could provide large cost savings.
Disease Development and Progression
Prior to age 40, most OA is secondary, such as OA due to trauma.1 The incidence and prevalence of OA increases dramatically between ages 40 and 50 years, particularly among women.1 There is a linear increase in the prevalence of OA up to age 70. The Framingham Osteoarthritis Study examined elderly patients (mean age, 70.8 years; range, 63-91 years), with a mean follow-up of approximately 8 years. After age 70, the prevalence of knee OA plateaued, as new-onset OA and the progression of disease was no more likely than in those younger than 70 years of age.17
The progression of disease severity in OA, although not occurring "overnight," does not require a great deal of time to manifest. A study published in 2004 followed a group of 32 patients with symptomatic knee OA to evaluate disease progression using magnetic resonance imaging procedures. These patients were followed over a 2-year period and overall reflected a significant (P <.0001) loss in global cartilage volume of 6.1% at the end of the study. Of particular interest was that movement to this figure was demonstrated statistically as early as 6 months after the start of the study, increasing at 18 and 24 months, reflecting a progression in the loss of cartilage volume over time.18
Anatomically, although OA invariably involves articular cartilage, it is now considered a disease of the entire joint. In addition to disruption and loss of articular cartilage, there is osteophyte formation at the joint margins, subchondral bony remodeling with cysts and sclerosis, ligamentous contractures and relaxation, muscle atrophy and spasm, and synovial inflammation.19 Cartilage repair is inadequate because an imbalance develops between the normal anabolic and catabolic processes within the cartilage. Inflammatory cytokines seem to drive this destructive imbalance, accentuated by synovial inflammation. Loss of the biomechanical properties of the articular cartilage accentuates abnormal pressures on both cartilage and subchondral bone.
Other factors that contribute to OA provide clues as to preventive therapy. For example, obesity is strongly related to OA of the knee in women, and less correlated to OA of the knee in men or OA of the hip in both sexes. Cooper et al suggest that obesity is related to both the prevalence of OA and the progression of OA.20 Some data suggest prevalence but not progression of knee OA.17