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Prevalence of Patello- and Tibiofemoral Osteoarthritis in Elva, Southern Estonia To the Editor: In a recent study in North Carolina, USA, 16% of the population over 45 years of age had symptomatic knee osteoarthritis (OA)1. Depending on the population studied and the epidemiological technique used, the prevalence figures for radiographic knee OA (rKOA; with or without symptoms) vary over a wide range2,3. There are limited data about the prevalence of rKOA in subjects younger than 50 years. In a Dutch study, rKOA was found in 7.7%–14.3% of persons aged 45–49 years4. In Swedish data, rKOA was detected in slightly more than 1% of individuals aged 35–545. The prevalence must be even higher, as the 3 studies addressed only the tibiofemoral (TF) and not the patellofemoral (PF) compartment, where knee OA occurs more frequently2. We investigated the prevalence of PF and TF rKOA among a middle-aged population and associations with the main risk factors. We studied all 559 persons aged 34–55 years included in the register of a selected family doctor in Elva, a small town in Southern Estonia. Of the 348 persons who responded to the postal questionnaire, 220 admitted either knee pain (60%) or other knee symptoms (40%). In 160 of them (79% of those with knee problems; 101 women, 59 men), radiographs of the TF joint and axial radiographs of the PF joint were taken. Two independent radiologists read the radiographs. Joint space narrowing (JSN) of the TF and PF compartments and osteophytes were assessed (grades 0–3) according to Nagaosa, et al6. For classification purposes, the findings of the TF and PF joints of both knees were included. Body mass index (BMI) was > 26 in 64% of the women and 58% of men. Unilateral rKOA was found in 20% and bilateral rKOA in 44% of cases. Grade 1 OA was found in 55.6% and grade 2 or 3 OA in 8.1% of the subjects. Both early and advanced OA occurred more frequently in the PF joint. More precisely, grade 2 OA was detected in 12 persons, among whom the PF area was affected in 9. Grade 3 OA was found in 1 case in the TF area, combined with PF grade 2 OA. Thus in 10 cases out of 13, advanced PF OA would have remained undetected if an axial radiograph of the PF joint had not been taken (Table 1).
The prevalence rate of advanced (grade 2+) TF OA in the age group proved to be 1.7% (6 out of the 348 studied cases). The prevalence rate of PF OA was slightly higher: 3 isolated and 7 cases combined with TF OA (10 cases out of 348), i.e., 2.9%. The actual prevalence of rKOA 2+ (13 cases out of 348) was 3.7%. The majority of the studied cases had grade 1 KOA, usually regarded as clinically innocent. However, current evidence supports revision of this standpoint with respect to progression of rKOA7 and functional impairment8. In the group of women under 45 years of age, the number of both TF OA and PF OA cases was smaller than in those over 45 years of age (p = 0.02, p = 0.06, respectively). Such a difference was not observed in the men. All 7 subjects with TF OA grade 2+ were found in the group aged 45–55 years. Considering the different radiographic findings, on average the youngest subjects were without OA in either TF or PF compartment (TF 0 and PF 0). The subjects with various combinations of OA were older, on average 45–50.5 years versus 43 years (p = 0.04, p = 0.004). The subgroups with PF OA tended to be younger in comparison with the subgroups with TF OA (p = 0.078; Figure 1).
The women who had other knee complaints but were free of pain were younger than the women with knee pain (median ages 44 and 48 years, respectively; p = 0.012). Thus we have some reason to claim that the first symptoms of knee OA may be crepitus, restricted movement, and morning stiffness, while knee pain may follow later. The process of knee OA may begin in the PF compartment, or the latter may form a separate entity. PF OA is thought to be associated with the development of disability1,8. Correlation analysis demonstrated that (1) TF OA was associated with age in both men and women, while PF OA showed this association only in women; (2) increased BMI showed a positive correlation with TF OA for both sexes, but not with PF OA; (3) earlier knee trauma, unlike BMI, was associated in particular with PF OA. In summary, radiographic knee OA is common among the Estonian middle-aged population, with several differences between men and women, occurring more frequently in the PF joint. ANN TAMM, MD, PhD, Senior Lecturer, Department of Sports Medicine and Rehabilitation, University of Tartu, Tartu; MARE LINTROP, MD, MSci, Senior Lecturer; KARIN VESKE, MD, Radiologist, Department of Radiology, Tartu University Clinics; ÜLLE HANSEN, MD, Ü. Hansen Family Practice, Elva; AGU TAMM, MD, PhD, DMSci, Professor of Laboratory Medicine, Clinic of Internal Medicine, University of Tartu, Tartu, Estonia. Address reprint requests to Dr. A. Tamm, Department of Sports Medicine and Rehabilitation, University of Tartu, Puusepa Street 1A, 2070, Tartu 50406, Estonia. E-mail: ann.tamm@kliinikum.ee Supported by Estonian Science Foundation grant no. 5308. 2. McAlindon TE, Snow S, Cooper C, Dieppe PA. Radiographic patterns of osteoarthritis of the knee joint in the community: importance of the patellofemoral joint. Ann Rheum Dis 1992;51:844-9. 3. Lawrence RC, Helmick CG, Arnett FC, et al. Estimates of the prevalence of arthritis and selected musculoskeletal disorders in the United States. Arthritis Rheum 1998;41:778-99. 4. van Saase JL, van Romunde LK, Cats A, Vandenbroucke JP, Valkenburg HA. Epidemiology of osteoarthritis: Zoetermeer survey. Comparison of radiological osteoarthritis in a Dutch population with that in 10 other populations. Ann Rheum Dis 1989;48:271-80. 5. Petersson IF, Boegard T, Saxne T, Silman AJ, Svensson B. Radiographic osteoarthritis of the knee classified by the Ahlback and Kellgren & Lawrence systems for the tibiofemoral joint in people aged 35-54 years with chronic knee pain. Ann Rheum Dis 1997;56:493-6. 6. Nagaosa Y, Mateus M, Hassan B, Lanyon P, Doherty M. Development of a logically devised line drawing atlas for grading of knee osteoarthritis. Ann Rheum Dis 2000;59:587-95. 7. Wolfe F, Lane NE. The longterm outcome of osteoarthritis: rates and predictors of joint space narrowing in symptomatic patients with knee osteoarthritis. J Rheumatol 2002;29:139-46. 8. Tamm AE, Hansen Ü, Veske K, Vija M, Tamm AO. Activity limitations in early knee osteoarthritis in 34-54 year old population in Estonia. In: Marincek C, Burger H, editors. Rehabilitation sciences in the new millennium. Bologna: Medimond International Proceedings; 2004:69-73.
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