Increasing level of FDG uptake in shoulder, hip, and knee joints with aging: age related inflammation in the joints.

Objectives: The goal of this study was to evaluate the effects of age-related inflammation on three important joints of the human body: the shoulder, hip, knee, and their surrounding capsules and soft tissues in healthy subjects using global assessment of FDG-PET images.

Methods: This is a retrospective analysis of data from a prospective study (NCT01724749) comprising 49 healthy subjects (25 male, 24 female, mean age: 45 years, range: 21-71) who underwent FDG-PET/CT scans which included the shoulder, hip, and knee joints in the field of view. The cases were divided into five groups according to age decade: 20-29, 30-39, 40-49, 50-59, and 60-70. The 30-39 age group had 9 cases (5 male, 4 female) and the other groups had 10 cases (5 male, 5 female). An adaptive contrast-oriented thresholding algorithm was used to segment the region in each joint and then mean standardized uptake value (SUVmean) of the segmented region was calculated (ROVER software, ABX GmbH, Radeberg, Germany). Association of SUV mean with age was assessed with Pearson's correlation and linear regression methods, and the SUVmean was compared between cases at different age groups.

Results: The Pearson correlation between the mean standardized uptake value and advancing age was 0.488 (P = 0.01). There was an upward trend of global FDG uptake with increasing age (R²=0.238). In the regression analysis, considering SUVmean as the dependent variable and age and gender as the independent covariates, the standardized β coefficient of age was 0.488 (P=0.001). There was a significant difference between different age decades (P=0.004). For patients younger than 45 compared to those older than 45 years, the SUVmean was 4.3659 and 5.5640, respectively (P = 0.01). The difference in SUVmean between males and females was not significant.

Conclusion: The novel quantitative technique was used to demonstrate a significant increase in FDG uptake represented by the global SUVmean with advancing age. This finding demonstrates that FDG-PET imaging is useful for early detection of inflammatory changes that happen in joints with aging, a possibility which may be critical to monitoring of interventions aiming to prevent irreversible joint failure.