Prevalence of Hip Osteoarthritis
Osteoarthritis (OA) is a pathologic disease process affecting the synovial joints that is characterized by focal areas of articular cartilage loss associated with hypertrophy of the bone and thickening of the capsule.1,2 Historically, a precise definition of OA has been difficult to determine because of a discrepancy between the clinical presentation and the radiographic evidence of OA. The symptomatic definition considers patients with both radiographic and jointrelated symptoms (ie, pain, stiffness, loss of function) as meeting the criteria for OA.3 The most commonly used radiographic scoring system is the Kellgren-Lawrence (KL) scale4 (Table 1). KL scores of 2 to 4 are diagnostic for radiographic OA. Additionally, several studies have used as the criteria patient self-reporting about a prior diagnosis of OA.5
Pereira et al6 performed a systematic review of the literature on the incidence and prevalence of knee, hip, and hand OA based on symptomatic, radiographic, and self-reported criteria. A higher prevalence of OA was found when radiographic criteria were used to define OA. The overall prevalence of OA was 43.3% in the hand (95% confidence interval [CI], 42.7 to 42.9), 23.9% in the knee (95% CI, 23.6 to 24.2), and 10.9% in the hip (95% CI, 10.6 to 11.2).
Using the radiographic criteria, 19 studies reported hip OA prevalence ranging from 1% in Japan7 and China8 to 45% in Tasmania.9 Four studies used self-reported criteria, with prevalence ranging from 5.5% in Norway10 to 9.7% in the Netherlands.11 Using symptomatic criteria that required both hip symptoms and radiologic OA, four studies reported estimates of 0.9% in Greece,12 1.6% in Italy,13 5% in France,14 and 7.4% in Spain15 (Figure 1). The prevalence of symptomatic hip OA in the United States is approximately 3% in adults aged ≥30 years.34,35
Oliveria et al36 reported the ageand sex-adjusted incidence of symptomatic hip OA in the United States to be 0.09 person-year (95% CI, 0.75 to 1). Using the radiographic criteria, the cumulative incidence was found to be 9.3% in the Netherlands.37 A Norwegian study reported that the cumulative incidence of patient self-reported hip OA was 5.8% in women and 3.8% in men.10
Musculoskeletal disease affects quality of life and function. Because of the improved treatment of chronic diseases and lower mortality from infectious diseases, the US population is aging, and older Americans are living with disabling conditions such as arthritis and chronic joint symptoms. The prevalence of OA increases with age, and some studies have reported a 2- to 10-fold increase in the incidence and prevalence of OA between the ages of 30 and 65 years.36 The Centers for Disease Control and Prevention applied data from the 2001 Behavioral Risk Factor Surveillance System to projected national population data for the years 2005 to 2030 and surmised that, if the prevalence of OA remains stable, the number of affected persons aged ≥65 years will nearly double by 2030.38 Between 2005 and 2030, the percentage of the US population aged ≥65 years is expected to increase from 12.9% to 20.0%.38 The number of older adults with arthritis or other chronic musculoskeletal joint symptoms is projected to nearly double from 21.4 million in 2005 to 41.1 million by 2030.39
The US Census Bureau has predicted that the population will grow 18% between 2000 and 2020.40 The US population was 300 million in 2006 and is projected to reach 400 million by 2043. It is projected that, of the estimated 78 million baby boomers expected by 2030, >33% will be obese, 50% will have OA, and 60% will have more than one chronic condition.
Obesity is a risk factor for OA of the knee and hip, and any increase in obesity would be expected to lead to a commensurate increase in OA rates. The prevalence rate of obesity in the United States has more than doubled in the past 25 years and shows no signs of slowing down.41 Since 1985, the Centers for Disease Control and Prevention has collected data on obesity prevalence in the United States.41 In 1985, for states with data, no state had an obesity rate >15%. By contrast, in 2011, no state had an obesity rate <20%, and the regions of the South and Midwest had obesity rates of 29.5% and 29%, respectively.42
There also appears to be a genetic role in the development of hip OA, and genetic factors may account for ≥50% of cases of hip and hand OA.43 The authors of a recent study that characterized differences in hip morphology in white and Chinese women reported significant differences in the center edge angle (CEA).44 The Chinese women had a higher percentage of hips with a CEA <20°, whereas the white women had a higher percentage of hips with a CEA >35°. Shi et al45 also reported a high association between the D-repeat polymorphism of asporin and developmental dysplasia of the hip in a Han Chinese population. The asporin (ie, ASPN) gene has been linked to the risk of OA of the knee and hip in Asian populations.44
Activity-related risk factors also have been associated with hip OA. Clohisy et al46 conducted a multicenter study to determine which radiographic structural abnormalities were associated with the early onset of end-stage hip OA. Those authors determined that 73% of patients who underwent a total hip arthroplasty (THA) in one hip for femoroacetabular impingement (FAI) would require a contralateral THA. Several studies have reported a significant association between occupational demands and the risk of hip OA. Athletic activities, particularly highintensity activities, have been shown to confer a high risk for the development of hip OA.47
The Economic Burden of Hip Osteoarthritis in Developed Nations
The societal burden of any medical condition typically is defined as having two elements: direct and indirect (ie, personal) medical costs.48 Many investigators, especially those whose work addresses chronic disease, consider a third element—the impact on quality of life (ie, well being).49
Several studies have examined the burden of the direct medical cost of managing OA in the United States. Bitton50 summarized these studies in a review published in 2009. Included in this report was a study by MacLean et al51 reporting that attributable direct medical cost, that is, the cost of medical care due to arthritis and associated comorbidity, was $2,827 per year for patients aged <65 years and $1,963 per year for patients aged ≥65 years in 1991 to 1993. Given a hip OA prevalence of 51 million, this expense would lead to direct medical costs >$100 billion per year. Bitton50 also reported that other investigators have found that costs increase exponentially with disease severity.
Indirect medical costs are those incurred as a result of illness but that are not associated directly with treatment. They include the cost of productivity loss, care seeking, and care by nonprofessionals and family members. Bitton50 reported on one study52 that indicated that indirect costs amount to approximately one third of total costs.
A different study reported on by Bitton50 indicated that indirect costs might be 1.5 times the direct cost of medical care. Bieleman et al,53 reporting the results of a Netherlandsbased cohort, found that the workforce participation of people with early OA was similar to that of persons without arthritis but that among those with less education, an impact on employment was seen. They speculated that this might imply that people with less education disproportionately suffer disability due to OA.
Bozic et al54 studied the societal impact of hip OA and THA using the health state utility (HSU) assessment. The HSU refers to the desirability that individuals or societies have for a given health outcome55 and ranges from perfect health (weighted 1) to death (weighted 0). The authors enrolled 231 patients from two institutions, and the subjects completed an electronic time trade-off (TTO) survey asking how many years of life a patient would be willing to give up for her or his hip problems to be resolved completely.56,57 The HSU for chronic hip OA was 0.6, but the HSU for successful primary THA was 0.96.54 Laupacis et al58 studied 188 Canadian patients and found, using TTO, that the mean baseline utility score of 0.29 improved to 0.87 at 2 years postoperatively. Katz et al,59 using TTO, found that in 54 patients, the preoperative utility score of 0.69 improved to 0.90 after THA.
An alternative method of examining the impact of disease on quality of life is the so-called willingness to pay. Based in consumer theory, this metric provides a direct estimation of the value a patient or community member places on a health state.60 Two studies have examined the value placed on the management of hip OA. In a study of patients treated with THA in Australia, Cross et al61 found that only 25% of patients would be willing to pay in excess of the cost of the procedure for their hip replacement. Of note, those authors also found that only 18% of patients undergoing a knee replacement were willing to pay the actual current average cost of the operation. Among the predictors of patients who placed a higher value on the procedure were less postoperative pain and higher income. In the United States, Bozic et al62 conducted a study of willingness to pay in patients who had undergone either THA or hip resurfacing. On average, patients who chose THA were willing to pay $69,419 and those who chose resurfacing were willing to pay $83,195. No correlation was found between income and reported willingness to pay. The authors did find, however, that if they excluded responses from lowerincome persons who exceeded their ability to pay, the correlation with income increased.
The trend in the United States indicates that the number and rate of primary and revision THA will increase steadily. Data from the National Hospital Discharge Survey and the US Census report a 46% increase per 100,000 persons, from 119,000 in 1990 to 193,000 in 2002.63 The rate of revision THA increased by only 17.5% over the same period, but the revision THA burden is higher in the United States than in any other country with a registry database.63
In 2003, 202,500 primary THAs and 36,000 revision THAs were performed in the United States.64 Kurtz et al65 made projections of primary and revision THA in the United States from 2005 to 2030 based on data collected from the Nationwide Inpatient Sample (NIS) and US Census data between 1990 and 2003. The authors projected that there would be 209,000 primary THAs and 40,800 revision THAs in 2005, and 384,000 primary THAs and 67,600 revision THAs in 2020. The authors reported that the demand for primary THA is estimated to grow by 174% to 572,000 by 2030; revision THA is projected to double by 2026.
In a report on the epidemiology of revision THA in the United States, Bozic et al62 reported that there were a total of 51,345 revision THAs performed between October 1, 2005, and December 31, 2006. These data were obtained from the National Hospital Discharge Survey, which is the same source that was used to calculate the projected increase in primary and revision THA in the study by Kurtz et al.65 The actual number of revision THAs in 2006 exceeded the projected number of revision THA by >10,000 cases.65 The disease burden of revision THA has not decreased over time; in fact, it appears to be increasing at a higher rate than previously predicted.
The demand for THA in patients younger than 65 years also is increasing, further worsening the disease burden of revision THA. According to the NIS, in the year 2006, 229,900 patients younger than 65 years underwent primary THA and 37,200 underwent revision THA.65 The percentage of young patients who underwent primary THA was 25% in 1993 and 46% in 2006. This percentage is projected to increase to 52% by 2030. Kurtz et al65 reported that the initial projected demand for total joint arthroplasty based on the 1993 to 2003 NIS data underestimated the actual demand that was observed in 2006.
Hip OA is a common and disabling musculoskeletal condition that affects millions of people worldwide. The burden of hip OA has been growing over the past two decades and is projected to grow 174% by 2030; however, the actual number of primary and revision THAs has been exceeding the prior estimates. Additionally, the percentage of patients aged <65 years undergoing primary THA continues to increase. Further research is needed on the percentage of patients who develop end-stage hip OA, at least one component of whose disease is due to FAI morphology. When intermediate- and long-term outcomes of surgery for FAI become available, the potential reduction in the burden of hip OA disease that can be achieved with these interventions must be studied, along with the improvement in the patients’ quality of life.
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