A HEALTH MAINTENANCE ORGANIZATION

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1 1134 ARTHRITIS & RHEUMATISM Vol. 38, No. 8, August 1995, pp , American College of Rheumatology INCIDENCE OF SYMPTOMATIC HAND, HIP, AND KNEE OSTEOARTHRITIS AMONG PATIENTS IN A HEALTH MAINTENANCE ORGANIZATION SUSAN A. OLIVERIA, DAVID T. FELSON, JOHN I. REED, PRISCILLA A. CIRILLO, and ALEXANDER M. WALKER Objective. To quantify the incidence of symptomatic hand, hip, and knee osteoarthritis (OA) among members of the Fallon Community Health Plan, a health maintenance organization located in central Massachusetts. Methods. Incident OA was defined as the first evidence of OA by radiography (grade on the KellgrenLawrence scale of 4) plus joint symptoms at the time the radiograph was obtained or up to 1 year before the radiograph was obtained. Results. The age and sexstandardized incidence rate for hand OA was 1/1, personyears (95% confidence interval [95% CII 86, 115), for hip OA 8811, personyears (95% CI 75,11), and for knee OA 4/1, personyears (95% CI 18, 6). The incidence of hand, hip, and knee OA increased with age, Presented at the 58th National Meeting of the American College of Rheumatology, Minneapolis, MN, October Supported by WyethAyerst Laboratories, Boston University Multipurpose Arthritis and Musculoskeletal Disease Center (grant AR613), and by the Harvard Pharmacoepidemiology Teaching and Research Fund (Fund donors include Berlex Laboratories, Inc., Boehringer Ingelheim Pharmaceuticals, Inc., The Burroughs Wellcome Fund, CibaGeigy Corporation, HoffmannLa Roche, Inc., ICI Pharmaceuticals Group, Eli Lilly and Company, Merck and Company, and Pfizer, Inc.). Dr. Oliveria s work was supported by the National Institute of Environmental Health Sciences National Research Service Award (1T3ES769) through the Harvard School of Public Health. Susan A. Oliveria, ScD, MPH: Strang Cancer Prevention Center, New York, New York; David T. Felson, MD, MPH: Boston University School of Medicine, Boston City Hospital, and University Hospital, Boston, Massachusetts; John I. Reed, MD, Priscilla A. Cirillo, RN: The Fallon Clinic, Inc., Worcester, Massachusetts; Alexander M. Walker, MD, DrPH: Harvard School of Public Health, Boston, Massachusetts. Address reprint requests to Susan A. Oliveria, ScD, MPH, Strang Cancer Prevention Center, 48 East 7nd Street, Suite 7, New York, NY, 11. Submitted for publication October, 1994; accepted in revised form March 9, and women had higher rates than men, especially after age 5. A leveling off or decline occurred for both groups around the age of 8. Conclusion. In a large study of symptomatic OA we observed incidence rates that increased with age. In women ages 789, the incidence of knee OA approached 1% per year. Most people over the age of 65 have some radiographic evidence of osteoarthritis (OA), which is the most common joint disorder (13). The prevalence of OA increases with age and is higher in women than in men, especially among the elderly (11). OA has a major impact on disability in the elderly as well as on the cost of care in that population (1,1315). Studies describing the frequency of OA have, almost without exception, been prevalence surveys (1,3). These are useful for quantifying the disease burden in a population, but may give an erroneous picture of the incidence, if there are different mortality rates in diseased and nondiseased groups. Monson and Hall (16) and Cerhan et a1 (17) have suggested that individuals with OA have higher rates of mortality than do those without OA, making incidence studies a crucial part of the epidemiologic description of OA. Prevalence surveys (,4,7,1,18,19) have focused on the prevalence of radiographic disease, in large part because it is more common and easier to define than symptomatic OA. Many patients with radiographic evidence of OA do not have symptoms, but it is symptomatic OA that causes pain, suffering, disability, and utilization of health care resources. The purpose of the present study was to quantify the incidence of clinically symptomatic OA of the hand, hip, and knee. We identified incident cases among members of a health maintenance organization (HMO), the Fallon Community Health Plan (FCHP).

2 INCIDENCE OF OA IN AN HMO POPULATION 1135 Previous incidence data have been limited to a smaller study of hip and knee OA in Rochester, Minnesota (), which excluded posttraumatic OA and included grade 1 (questionable) OA, and to a single study of radiographic OA of the hand (1). We present a largescale incidence study using a comprehensive case definition that includes radiographic and clinical features in a population with a large number of subjects over age 65. PATIENTS AND METHODS Study population and sources of data. FCHP, an HMO located in Massachusetts, has been in operation since As of January 1, 1991, the total membership was approximately 13,. The members are primarily (>95%) Caucasian, bluecollar workers (and their families) or retired bluecollar workers. This reflects the population of Worcester County, where most FCHP members live. A multispecialty group practice, the Fallon Clinic, Inc., provides services to health plan members. The Fallon plan offers the following services: ambulatory visits to primary care physicians, inpatient and outpatient hospital services, services provided by Fallon specialists, approved referrals, radiographs, laboratory tests, radiographic procedures, radiation and respiratory therapy, mental health services, skilled home health care, nursing care, ambulance services, most prescription drugs, and eye examinations. For members age 65 and older, a capitated Medicarefunded plan offers full benefits. The medical care billing and administrative information has been incorporated into a computerized research database, which contains data on all services provided to FCHP members since For each member, information on pharmacy claims, hospitalizations, outpatient diagnoses, outpatient services, laboratory procedures, membership dates, sex, date of birth, and a unique medical record number is included in this research file. Written medical record information can be abstracted and linked through the medical record number. Methods. We used a definition of OA that is similar to the radiographbased definition suggested by the American College of Rheumatology (ACR) (4). It also corresponds to a definition of symptomatic OA used by the Framingham Osteoarthritis Study (), by Lawrence et a1 (7) in their study in the United Kingdom, and by the National Arthritis Data Workgroup in the United States (1). We defined an incident case as follows: I) the first radiograph with evidence of OA, and ) the presence of symptoms in the joint at the same time, or up to 1 year before, the radiograph was obtained. Radiographic evidence of OA was defined as grade on the KellgrenLawrence scale ( 4 scale, where = normal; 1 = doubtful narrowing of joint space, possible osteophytes; = definite osteophytes, absent or questionable narrowing of joint space; 3 = moderate osteophytes, definite narrowing of joint space, some sclerosis, possible deformity; and 4 = large osteophytes, marked narrowing of joint space, severe sclerosis, definite deformity [5]). OA symptoms were defined as pain, stiffness, soreness, aching, discomfort, swelling, andlor tenderness. Standard radiography protocols were utilized for patients at FCHP during this period. Knee radiographs were standard anteroposterior and lateral views without weightbearing; hip radiographs were a view of the pelvis with the feet internally rotated (or of the hemipelvis if only one hip was radiographed) and a frogleg view. Hand radiographs were posteroanterior, oblique, and lateral views. Clinical and laboratory criteria based on physical examination (ACR criteria) were not used. There was no standard protocol for reporting of OA symptoms. Physician query and patient selfreport were the methods of acquiring information about OA symptoms. This information was recorded in the medical record. To be eligible as incident cases, subjects were required to be continuous members of the FCHP from 1988 through 1991 (for cases with radiographs in 1991) or from 1988 through 199 (for cases with radiographs in 199) and had to be ages 89 on July 1 of the year the radiograph was obtained (1991 or 199). Continuous membership was defined as enrollment in the health plan without discontinuance of membership for > weeks. All potential incident cases were those who had at least 1 radiograph of the hand, hip, or knee during (called the index radiograph) and a diagnosis of OA (on computerized records) in any year from 1988 through the year the radiograph was obtained. Subjects who had a radiograph of the joint and had a subsequent diagnosis of OA in the computerized record, all before the index radiograph, were classified as having prevalent OA in that joint at the time of the index radiograph and were therefore not eligible to be incident cases for that joint. To validate this exclusion, we reviewed the medical and radiography records of 5 patients who had been classified by this method as having prevalent OA. To eliminate additional cases of prevalent OA and to identify and characterize the site of incident OA, we reviewed the radiologists reports, radiographs, and medical records of the remaining potential incident cases of OA. The radiology report is a detailed description of the radiologist s interpretation of the actual films and does not contain KellgrenLawrence scores. The research nurse (PAC) compared descriptors of OA in the radiology report with the descriptors of KellgrenLawrence grades 4. Subjects whose radiology reports included any of the following featuresjoint space narrowing, hypertrophic changes, OA, degenerative changes in either joint, degenerative joint disease, or joint space narrowing and osteophytes or spurswere classified as having prevalent OA and were not eligible to be incident cases. Subjects whose index radiology reports contained descriptions that indicated OA grade or greater were classified as having radiographic OA, and the site (hand, hip, or knee) and laterality were noted. Subjects with hand OA were subclassified according to thumb radiographic OA and fingers 5 radiographic OA. For subjects whose written reports indicated probable (grade 1) radiographic OA (presence of spurs, points, osteophytes or hypertrophic changes, joint space narrowing, or questionable or possible OA), the original films were read by rheuma

3 1136 OLIVERIA ET AL tologists (DTF and JIR) working independently, each using a reference atlas of radiographs (,5). For each subject classified as having radiographic OA of the hand, hip, or knee, a team of 3 research nurses who were experienced with the medical record system at FCHP abstracted and reviewed the medical records for symptoms characteristic of OA. If symptoms were recorded within the year prior to the index radiograph and symptoms were ipsilateral to the radiographic OA, then the case was classified as incident OA and the date of the index radiograph was used as the index date. All subjects were classified with respect to hand, hip, and knee OA, and thus, it was possible to have incident OA in any of the 3 joint areas. In some instances, the medical record provided evidence of OA prior to the index date. These subjects were reclassified as prevalent cases and were excluded from study. To assess the accuracy of using radiology reports for OA classification by radiograph, a rheumatologist (JIR) who was unaware of case status used the reference atlas to read a random sample of the actual radiographs of 96 subjects with and without OA. We compared the agreement between the rheumatologist s classification of OA (positive grades 4 versus negative) and the nurse s classification using the radiology reports only. To evaluate the possibility that subjects with other diagnoses might meet the criteria for OA, we identified a random sample of 5% (n = 13) of the patients who had had a radiograph of the hand, hip, or knee and had been diagnosed at FCHP as having another musculoskeletal disease, and their radiology reports and medical records were reviewed. The diagnoses and ICD9 (International Classification of Diseases9) codes reviewed were as follows: arthropathy (716.9), bursitis anserinus (76.61), internal derangement of the joint (718.9), internal derangement of the knee (717.9), joint effusion (719.1, joint pain in leg (719.46), joint pain in pelvis (719.45), joint pain unspecified (719.4), pain in limb (79.5), synovitis/tenosynovitis (77.), and trochanteric bursitis (76.5). Age and sexspecific incidence rates were calculated for each joint by first eliminating subjects with prevalent disease in the index joint. Second, for the eligible subjects, the total membershipdays at risk during the study period by 1year age groups and by sex were calculated. Third, the number of newly diagnosed cases of OA by 1year age groups and by sex were tabulated. And last, the number of incident cases of OA for each age and sexspecific group was divided by the corresponding membershipdays. The resulting rates were converted to cases per 1,OOO personyears. Ninetyfive percent confidence intervals were calculated on the assumption that case counts were distributed as Poisson variables, using an exact method for case counts below 3 and an approximate method for those above 3 (6,7). The results were standardized to the age and sex distribution of the 199 white population in the US. RESULTS There were 696 FCHP members who had at least 1 radiograph of the hand during , plus a diagnosis of OA prior to or during the year in which the radiograph was obtained. Previous diagnoses and radiographs indicated prevalent hand OA in 89 subjects. For the subjects not ascertained as having prevalent hand OA (n = 67), a further 45 were excluded because radiography records indicated prevalent disease or because the index radiograph showed no OA. Two hundred two subjects were classified as having radiographic OA of the hand for the first time based on review of the radiography records alone. Medical record review for subjects with radiographic OA of the hand identified symptoms within the year of the index radiograph in 195 of the patients. There were 1,3 FCHP members who had at least 1 radiograph of the hip during , plus a diagnosis of OA prior to or during the year the radiograph was obtained. Previous diagnoses and radiographs indicated prevalent hip OA in 59 subjects. Among the subjects with hip OA not ascertained as prevalent (n = 744), 178 were classified as having radiographic OA of the hip for the first time based on the radiography record review alone. The other patients were excluded because of a previous radiograph showing OA or because the index radiograph did not show OA. Medical record review for subjects with radiographic OA of the hip identified symptoms within the year of the index radiograph in 173 of the hipjoints. There were 1,553 members who had at least 1 radiograph of the knee during , plus a diagnosis of OA prior to or during the year the radiograph was obtained. Prevalent knee OA was ascertained in 398 subjects, and radiography record review was conducted on 1,155 subjects. Subjects were excluded if there was previous evidence of OA or if the index radiograph did not show OA. First radiographic OA of the knee was ascertained in 47 subjects, and subsequent medical record review identified symptoms within the year of the index radiograph in 461 of these joints. Overall, only 17 subjects had missing radiographic information. That is, the medical billing records showed that radiography had been performed, but the actual radiographs and radiology reports were not in the medical record. These 17 patients could not be evaluated for OA. The incidence rates for hand OA are presented in Table 1. Among women, the incidence rates ranged from a low of /1, personyears among those ages 39 to a high of 59/1, personyears among those ages 779. For men, the incidence rates ranged from a low of /1,OOO personyears among those ages 9 to a high of 319/1, personyears among those ages 779. The age and sexstandardized inci

4 INCIDENCE OF OA IN AN HMO POPULATION 1137 Table 1. Incidence of hand osteoarthritis among members of the Fallon Community Health Plan, , by age and sex* No. of Person Incidence Sex, age cases years rate 95% CI Women Men w Standardized incidence I ,886 4,95 18,88 1,91 1 1,339 1,1 3,19,669 5,461 19,45 1,916 1,158 8,15, loo, 17, 15 9, , 94 43, , , 571, 18 1, 8 1, 38 6, 8 18, 316 8, , , 115 ~ ~~ * Incidence rate is per 1, personyears; standardized incidence is per 1, personyears age and sexstandardized to the 199 white population of the US. 95% CI = 95% confidence interval. dence rate for hand OA was 1/1, personyears (95% confidence interval [95% CI] 86, 115). Table shows the incidence rates for OA of the thumb and fingers 5. Although the number of cases within each age and sex category is small, the distribution of rates of OA in the thumb and fingers is similar to the distribution of rates of OA in the hand. The age and sexstandardized incidence rates for OA of the thumb and OA of fingers 5 were 5/1, personyears (95% CI 36, 65) and 71/1, personyears (95% CI 57, 86), respectively. Table 3 shows the incidence of hip OA by age group. The incidence rates for women ranged from a low of O/lOO,OOO personyears among those ages 9 and 449 to a high of 583/1, personyears among those ages 779. For men, the incidence rates ranged from a low of O/lOO,OOO personyears among those ages 9 to a high of 445/1, personyears among those ages 779. The overall age and sexstandardized incidence rate for hip OA was 88/1, personyears (95% CI 75, 11). The incidence rates for knee OA are presented in Table 4. Among women, the incidence rates for knee OA ranged from a low of /1, personyears among those ages 9 to a high of 1,8/1, personyears for those ages 779. The overall ageand sexstandardized incidence rate for knee OA was 4/1, personyears (95% CI 18, 6). The ageand sexspecific incidence rates are presented graphically in Figure 1. In a random sample of FCHP radiographs from this study (n = 96), the rheumatologist s interpretation Table. Incidence of thumb and finger osteoarthritis among members of the Fallon Community Health Plan, , by age and sex* Thumb Finger No. of Incidence No. of Incidence Sex, age cases rate 95% CI cases rate 95% CI Women 9, 17, , I5, , , , , , , , , 51 I , , 489 Men 9, 18, , I5 8 1, 8 449, , , , , , , , Standardized incidence , , , 51 57, 86 * Incidence rate is per 1,OOO personyears; standardized incidence is per 1, personyears ageand sexstandardized to the 199 white population of the US. 95% CI = 95% confidence interval.

5 1138 OLIVERIA ET AL of the radiograph (as OA or no OA) agreed with the nurse s classification of the radiology report 76% of the time. Of those subjects classified by the nurse reviewer as having radiographic OA based on the radiology report, 5 of 54 (9.3%) were read by the rheumatologist as not showing OA. These included knee radiographs with osteophytes only at the tibia1 spines and hip radiographs with lateral acetabular osteophytes, features that our criteria excluded as OA, but which some readers might characterize as evidence of OA. The rheumatologist interpreted many reportedly negative films from persons with joint symptoms as showing OA (18 of 4, or 4.9%), but in almost all cases, the radiographic OA was mild (small osteophytes only), suggesting that the radiologists were often conservative in diagnosing OA, at least on the films we studied. Of 37 subjects with probable radiographic OA of the hand, hip, or knee, the readers interpretation of the films led to the classification of 19 subjects as having radiographic OA and 18 as not having OA. There was 1% agreement between the two readers independent classifications. Of the 13 subjects selected because they had diagnoses that might have led to their being misclassified as not having OA (see Patients and Methods), 83 had an index radiograph and a computerbased diagnosis of OA (in addition to the nonoa diagnosis) and had already been evaluated for Table 3. Incidence of hip osteoarthritis among members of the Fallon Community Health Plan, , by age and sex* No. of Person Incidence Sex, age cases years rate 95% CI Women 9 1,888, ,949 4, ,81, ,913 55, , , , , , , 74 Men 9,669, ,463 8 I, ,43 1 6, 54 5s9 3 1, , , , , , , , 574 Standardized 88 75, 11 incidence * Incidence rate is per 1,OOO personyears; standardized incidence is per 1,OOO personyears age and sexstandardized to the 199 white population of the US. 95% CI = 95% confidence interval. Table 4. Incidence of knee osteoarthritis among members of the Fallon Community Health Plan, , by age and sex* No. of Person Incidence Sex, age cases years rate 95% CI Women 9 3cL Men Standardized incidence ,881 4,945 18,793 1,875 11,46 9,796 3,138,668 5,444 19,13 1,881 1,64 7,985, ,8 1, , 17 6, 47 73, , , , 1,88 693, 1,411, 7 19, 7 77, , , , 1,4 338, 1,39 18, 6 * Incidence rate is per 1, personyears; standardized incidence is per 1,OOO personyears age and sexstandardized to the 199 white population of the US. 95% CI = 95% confidence interval. incident OA. Twentyfour subjects had rheumatoid arthritis or acute injuries (fractures, acute meniscus/ cruciate tears). Among the remaining 3 subjects there were 3 cases of radiographic OA. Review of the radiology records and medical records of 5 patients who had been classified as having prevalent OA (based on our algorithm of a joint radiograph prior to the index radiograph and subsequent computerbased diagnosis of OA) confirmed that all 5 patients had prevalent OA. DISCUSSION In the first largescale and comprehensive incidence study of symptomatic hand, hip, and knee OA, we found that OA incidence increased with age and that women had higher rates than did men, especially after age 5. The incidence of knee OA was twice that of hand or hip OA. The annual incidence of clinical knee OA was >l%/year in women ages 789. The rates of OA in fingers 5 were higher than the rates of thumb OA across most age groups, with women having higher rates of both thumb and finger OA compared with men. The fema1e:male sex ratio for hand, hip, and knee OA was approximately :1, suggesting similar sex and age predilection for disease in these joints. The trend of increasing incidence of OA with age continued until the age of 8, after which there was

6 INCIDENCE OF OA IN AN HMO POPULATION u) 3 I 5 w P z 3 6 w 5 4 s z AGE GROUP (YEARS) Figure 1. Incidence of osteoarthritis of the hand, hip, and knee, in members of the Fallon Community Health Plan, , by age and sex. a leveling off or decline in the rates for all joints. This change may be related to sedentary activity levels in the older age groups, resulting in less joint injury and/or decreased joint pain. The elderly may have increased pain thresholds, which would reduce the number of reported joint symptoms (8). The presence of more serious concurrent disease in the elderly could also lead physicians to be less diligent in making or recording diagnoses of nonlifethreatening conditions. Some radiographbased prevalence studies suggest that hip OA is more common in men than in women (7,18,19). In our study, men had a slightly higher incidence rate of hip OA only up to age 5, after which women had a higher rate, which persisted into the elderly years. Sex differences in reporting of symptoms may account for the difference, since most prevalence studies have used only radiographs to define disease. While it has been suggested that hip and knee OA should be treated as separate disorders in epidemiologic investigations (l), our findings suggest hand, hip, and knee OA have similar epidemiologic profiles: both increase with age up to age 79 and are more common in women after about age 5. There may be more similarity in hand, hip, and knee OA epidemiology than has previously been thought. Because of the uncertain onset of OA and because we studied subjects presenting at the HMO for radiography and diagnosis, the incidence rates we obtained relate to symptomatic OA. The estimates of OA incidence might have been higher if our study involved active surveillance with radiographs of all FCHP members. Routine radiologic surveillance would be ethically unacceptable since there is no anticipated benefit to offset even the minimal risks of radiation; it would also be costly and difficult to administer for such a large number of study subjects. Wilson et a1 () conducted a populationbased incidence study of OA of the hip and knee using the medical record linkage system of the Mayo Clinic (Rochester, MN). The age and sexadjusted rates for OA of the hip and knee were found to be 47.3/1, personyears (95% CI 7.8, 66.8) and 163.8/1, personyears (95% CI 17.1,.6), respectively. The ageadjusted rates for OA of the hip and of the knee were similar for men and women. In men, the results showed a steadily increasing rate with age. In women, a sharp increase followed by a plateau was noticed after menopause. Based on a larger number of subjects, our data suggest a higher incidence of OA (). We observed an age and sexstandardized incidence rate of 88/1, personyears (95% CI 75, 11) for

7 114 OLIVERIA ET AL hip OA and 4/1, personyears (95% CI 18, 6) for knee OA. Unlike Wilson et a1 (), we found that incidence rates increased with age up to ages 889, when a plateau occurred, and that beginning about the age of 5, women had higher rates of both hip and knee OA than did men. Like ours, Wilson s study was restricted to patients who were specifically seeking medical care for symptomatic joint disease. In that study, cases of OA were included only if they were of idiopathic origin, and an unknown number of cases related to structural abnormalities, trauma, or infections were excluded. Subjects with radiographic grade 1 or higher, according to the KellgrenLawrence criteria, were also included. In our study, all subjects with radiology reports suggesting grade 1 disease were reviewed and reclassified as definite OA or no OA. Our criteria were therefore different from those of Wilson and coworkers (), and the higher rates we found suggest that there might have been more serious underascertainment, perhaps because of exclusion of a large number of cases of secondary OA, in Wilson s study. Another plausible explanation for the observed differences between the studies may be the dissimilarity of the two populations from which the study subjects were drawn. Kallman et a1 (1), in the Baltimore Longitudinal Study of Aging, examined the prevalence, incidence, and progression of radiographic features of hand OA over 149 years in a group of 177 welleducated men. The prevalence and incidence of radiographic evidence of hand OA increased with age, with an incidence of over IOO/l,OOO personyears (>I%) in men ages 6 and older. Our rates of clinical symptomatic OA of the hand in men were onefifth to onethird this rate. Kallman s study was restricted to a small group of male volunteers. Our study included a large number of men and women with hand OA, although our study population was mostly current and former bluecollar workers and primarily Caucasian. Kallman and coworkers identified radiographic characteristics of disease; OA as a disease entity was not examined. We studied symptomatic hand OA, defining OA according to clinical and radiographic features, and quantified the distribution of OA in the thumb and fingers. Based on a sample of radiographs (n = 96) reread independently by a rheumatologist (JIR), there was misclassification of radiographic OA in both directions in our study. Some subjects who were characterized as having radiographic OA may not have had it, whereas others who had radiographic evidence of mild OA were not given the clinical diagnosis. It is not surprising that there was disagreement between the initial radiographic interpretations by the clinical radiologists and the subsequent readings by the rheumatologist, who used a KellgrenLawrencebased atlas. The incidence data presented here are clinically based and are necessarily subject to the variability of clinical diagnosis. In a random sample of 5% of patients with other musculoskeletal diseases, we estimated that overall, fewer than 6 subjects with new radiographic OA were missed. Not all of these persons had joint symptoms, and this misclassification would cause our incidence rates to be underestimated by no more than 7%. Although members of the FCHP may not be representative of the entire US population, most rheumatic disease incidence studies, like this one, are from limited geographic areas (e.g., Olmsted County, MN). We believe the FCHP represents the surrounding geographic community, Worcester County. Membership in FCHP is available through employers and a Medicare plan is available to Worcester elders. The study was conducted using a computerized research database in conjunction with abstraction from written medical records. Automated databases based on medical billing or utilization of services present a unique opportunity to study large numbers of subjects at relatively little expense. Such databases may have relatively complete data, with no potential for recall bias or interview bias (9). They can be problematic if covariate information is unavailable or if validity of the diagnosis is questionable (9,3). Shapiro (31) and Gabriel (3) have described the nearimpossibility of reliably identifying disease or the timing of disease events using computerized diagnoses from automated medical databases. We agree, and therefore used the computerized system to point us to a variety of text records that provided the data for case definition. We were able to exclude some cases with prevalent disease, based on computer diagnoses of OA. We suggest that automated databases can be useful epidemiologic tools that give nonspecific identification of subjects who may have a disease. More detailed information from medical records will generally be needed to make case identification both sensitive and specific. The results of this study suggest a high incidence of hand, hip, and knee OA that increases with age. Women have higher rates than men, and a leveling off or decline occurs for both groups around the age of 8.

8 INCIDENCE OF OA IN AN HMO POPULATION 1141 ACKNOWLEDGMENTS Appreciation is expressed to the Research Department at the Fallon Clinic, Inc. for their assistance with the medical records review. We acknowledge Robert Astrella and Management Information Services at the Fallon Clinic, Inc. for their continued assistance with data preparation REFERENCES Felson DT: Epidemiology of hip and knee osteoarthritis. Epidemiol Rev 1: 18, 1988 Felson DT, Naimark A, Anderson J, Kazis L, Castelli W, Meenan RF: The prevalence of knee osteoarthritis in the elderly: the Framingham Osteoarthritis Study. Arthritis Rheum 3:91&918, 1987 Felson DT: Osteoarthritis. Rheum Dis Clin North Am 16:499 51, 199 National Center for Health Statistics: Basic Data on Arthritis of the Knee, Hip, and Sacroiliac Joints, in Adults Ages 574 Years, United States, National Center for Health Statistics series 11, no. 13. DHEW Publication no. 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