Objective. To test the hypothesis that sex-related and joint compartment-related differences in the risk of osteoarthritis (OA) of the knee might be associated with variations in cartilage development, we investigated knee cartilage volume in healthy children. Methods. We studied 92 children who were randomly selected from among students in grades 3-12 of a single school in Hobart, Tasmania (49 boys, 43 girls; age range 9-18 years). Articular cartilage thickness and volume were determined at the patella, medial tibial compartment, and lateral tibial compartment by magnetic resonance imaging (MRI). Sagittal T1-weighted fat-suppressed MRI images were obtained and processed on an independent computer work station. Results. Males had significantly more knee cartilage than females. Sex accounted for 6-36% of the variation in cartilage thickness and volume, which was statistically significant at all sites. Even after adjustment for age, body mass index, bone area, and physical activity, males had 16-31% higher cartilage volume; this was most marked at the medial tibial site. In addition, lateral tibial thickness was greater than medial tibial thickness (5.9 versus 3.6 mm; P < 0.0001) and lateral tibial volume was greater than medial tibial volume (2,823 versus 2,299 l; P < 0.0001). Furthermore, physical activity was a significant explanatory factor for cartilage volume at all sites (R 2 7-14% depending on site; all P < 0.05). The most consistent activity association was with vigorous activity in the previous 2 weeks (difference between any vigorous activity versus none 22-25% greater; all P < 0.05). Conclusion. Sex-and joint compartment-related differences in cartilage development may be one explanation for variations in the pattern of knee OA seen in later life. Furthermore, the physical activity associations suggest that cartilage development is amenable to modification. Osteoarthritis (OA) is the major cause of disability in persons over the age of 65 years (1). Sex-related and joint compartment-related differences in knee OA are well described. Women have a 1.5-4 times higher risk than men (2) while medial compartment disease is 4 times more common than lateral compartment disease (3). The reasons for these variations are unclear at the present time. There is convincing evidence that other diseases of later life, such as ischemic heart disease, diabetes mellitus, and particularly, osteoporosis, are associated with childhood development (4,5). Although there are no data in humans with regard to early life exposures and risk of OA, a study in senescent moose linked a higher incidence of OA with a famine when the moose were weanlings (6). Defects in cartilage are widely considered to be the initial problem in OA (7), although this viewpoint is not shared by all investigators (8). However, cartilage development is poorly understood, and descriptive or etiologic data are few. In part, this is due to the lack of a noninvasive, accurate, in vivo method of assessing cartilage. Recently, magnetic resonance imaging (MRI) ha...

The aim of this study was to describe the effect of sex, growth, Tanner stage, and physical activity on knee articular cartilage volume development. A total of 74 randomly selected male and female children aged 9 -18 y were measured on two occasions at an average interval of 1.6 y (range 1.3-1.9). Articular cartilage volume was determined at the patella, medial tibial, and lateral tibial compartments by processing images acquired in the sagittal plane using T1-weighted fat saturation magnetic resonance. Height, weight, and BMI were measured while Tanner stage and physical activity were assessed by questionnaire. Articular cartilage volume increased at all sites peaking in Tanner stage two. Males gained articular cartilage faster than females at all sites (patella ϩ233 L/y, 95% CI Ϫ7, ϩ473, medial tibial ϩ350 L/y, 95% CI ϩ118, ϩ582, lateral tibial ϩ256 L/y, 95% CI ϩ22, ϩ488). In both sexes, articular cartilage volume accrual at tibial but not patella sites correlated significantly with height change but not weight change. Overweight children did not differ significantly from normal children in articular cartilage volume either cross-sectionally or longitudinally. The most consistent physical activity association was with average intensity of sport with those above the median gaining approximately twice as much as those below the median at tibial (p Ͻ 0.05) but not patella sites. In conclusion, most children gain articular cartilage during growth, but there is wide variation in the amount of articular cartilage accrual. In particular, younger children, males, and those undertaking more vigorous sports have substantially higher accrual rates. These results provide novel data on articular cartilage development in humans. The long-term significance of these results with regard to osteoarthritis of the knee in later life remains hypothetical. Osteoarthritis (OA) is the major cause of disability in those over age 65 y (1). Risk factors such as genetic factors, sex, and body mass index have been identified for knee OA (2-4). However, much remains to be understood about this very common condition. There is convincing evidence that other diseases of later life such as ischemic heart disease, diabetes mellitus, and particularly osteoporosis are associated with childhood development (5, 6). Although there are no data in humans with regard to early life exposures and risk of osteoarthritis in later life, a study in senescent moose linked a higher incidence of osteoarthritis with a famine when the moose were weanlings (7). Defects in articular cartilage are widely considered to be the initial problem in osteoarthritis (8) although this viewpoint is not shared by all authors (9). However, articular cartilage development in humans is poorly understood. In part, this has been due to the lack of a noninvasive, accurate, in vivo assessment of articular cartilage. Recently, magnetic resonance imaging (MRI) has been shown to be a simple, safe, noninvasive, and reproducible technique for measuring knee articular cartilage thickness (...

Men have substantially higher knee cartilage volumes than women. These sex differences appear to be mediated in part by body and bone size but a significant amount remains unexplained. Furthermore, the differences become more marked over the age of 50 yr suggesting that both cartilage development and cartilage loss in later life contribute to sex differences in cartilage volume. Further longitudinal studies in large samples will be required to confirm these findings.

Early medial compartment ROA is associated with substantial reductions in cartilage volume and increases in bone area. These large changes, when combined with similar measurement error for MRI and radiographs, suggest that MRI may be superior at detecting and hence understanding early osteoarthritis of the knee in humans.

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