Age-related bone loss and fracture risk: A stochastic model☆

Abstract A stochastic model of age-related bone loss capable of predicting age-specific incidence of fractures has been implemented by Monte Carlo simulation. Each simulation involves ageing a large cohort of individuals from 20 to 100 years. Every individual is randomly allocated a particular amount of bone as a young adult, an age of onset of bone loss, and parameter values which determine the subsequent loss. Fracture risk is assumed to be zero when the amount of bone is above a global threshold level, increasing progressively as the amount of bone falls below the threshold. From the individual fracture risks, a fracture subpopulation is identified and age-specific incidence evaluated numerically. By adjusting the model parameters, predicted and observed incidence of femoral neck fractures can be closely matched in both sexes using a linear function to describe age-related bone loss. For the fracture of the distal radius, a close match can be achieved in females using an exponential function to describe the bone loss phase; in males, the incidence is independent of age and trauma, rather than the amount of bone in the forearm, appears to be the main determinant of fracture risk.