Sato Y, Kashiwabara K, Taniguchi Y, et al. - A total of 553 healthy middle-aged individuals who underwent the first and second comprehensive health screening at an interval of 5.9 years were recruited in this study in order to ascertain correlated factors for and the progression rate of the sacroiliac (SI) joint degeneration. Seventy individuals revealed substantial degeneration (type 2 or 3) of the SI joints at the first checkup. Multivariate analysis showed that related factors for SI joint degeneration were female gender; pubic symphysis degeneration, L4/5, and L5/S facet joint degeneration; high BMI; and several blood parameters. The laterality of SI joint degeneration was significantly more common in comparison with L4/5 or L5/S facet joint degeneration. Kaplan–Meier survival analysis unveiled that the progression rates accounted to 3.4% and 35.5% subsequent to 10 years, of SI joint degeneration from type 0 (no degeneration) or type 1 (slight degeneration) to substantial degeneration, respectively. Therefore, substantial SI joint degeneration was discovered in 12.7% of healthy middle-aged individuals and it was acknowledged as a part of the normal aging process. Moreover, there may be individual factors related to its occurrence.