Prevalence of hip osteoarthritis in Iceland

Abstract

Objective: To assess the prevalence of primary hip osteoarthritis (OA) in Iceland. To compare the prevalence of primary hip OA in Iceland with published rates of primary hip OA for related Scandinavian populations.

Methods: Roentgenographs were examined of 1530 Icelandic people 35 years or older (653 males, 877 females) subjected to colon radiography during the years 1990-1996. The radiographs examined represent approximately 40% of all colon radiographs taken in Iceland during this period. After exclusion of non-primary hip OA cases, the minimum hip joint space was measured with a mm ruler. Presence of hip OA was defined as a minimum joint space of 2.5 mm or less on an anteroposterior radiograph. Intraclass correlation coefficients for inter and intraobserver variability of assessment of mm joint space were 0.91 and 0.95, respectively.

Results: Of the 1517 people included, 227 hips in 165 patients (77 men, 88 women) were diagnosed as having radiological primary hip OA. The mean age at colon examination for these patients was 68 (35-89) years. The overall prevalence of coxarthrosis among all examined patients 35 years and older was 10.8% (12% for men, 10% for women), rising from 2% at 35-39 years to 35.4% for those 85 years or older. If the population structure (age and sex distribution) for those older than 35 years in Iceland was used to standardise prevalence for both Iceland and south Sweden (using previously published data for south Sweden), the age and sex standardised prevalence of hip OA for those older than 35 years in Iceland was 8%, compared with 1.2% for south Sweden.

Conclusions: The prevalence of radiological primary hip OA is very high in Iceland, and in excess of fivefold higher than the prevalence found by using similar techniques in studies on related populations in southern Scandinavia. The rate difference is particularly notable for those younger than 70 years.

Figure 1

Histogram of hip joint space distribution measured on 1517 colon radiographs from Iceland. The vertical axis denotes the proportion of hips. The size class of 0.0 mm includes 49 hips with arthroplasty resulting from primary hip OA. The number of hips for each size class is 0 mm (81), 0.5 mm (1), 1.0 mm (22), 1.5 mm (14), 2.0 mm (53), 2.5 mm (60), 3.0 mm (471), 3.5 mm (278), 4.0 mm (1383), 4.5 mm (145), 5.0 mm (500), 5.5 mm (3), 6.0 mm (19), 6.5 mm (0), 7.0 mm (4). The vertical line indicates the joint space cut off for hip OA.

Figure 2

Hip joint space (mm) by age groups for men and women. Bars denote 95% confidence intervals.

Figure 3

Hip OA prevalence in relation to age in Iceland and Malmö, Sweden, assessed from colon radiographs. Data points represent observed values, lines represent predicted curve fits with r² greater than 0.9, broken lines represent 95% confidence intervals for predicted curves. Data for Malmö, Sweden from Felson.¹²

Figure 4

Predicted age related ratios of prevalence of hip OA between Iceland and Malmö, Sweden. The prevalence data used for calculation of age related ratios are the values predicted from the curve fits in figure 3. A cubic spline fit was made to the predicted ratio values.