Breaking the 50+ barrier: Cortical speed of sound via quantitative ultrasound as a new age-at-death estimator in older adults

Abstract

The increasing number of forensic cases and solitary deaths (“kodokushi”) involving older adults warrants targeted methods to serve this growing and vulnerable group. However, age-at-death estimation past midlife remains challenging due to diminished accuracy of traditional macroscopic age markers, often resulting in a single categorization of older age groups as “50 + .” This study evaluates the utility of cortical bone speed of sound (SoS), measured by quantitative ultrasound (QUS), as an alternative biomarker to quantify age-related changes in cortical bone quality and to estimate age-at-death in older adult skeletons. Using QUS, we collected SoS from three peripheral long bones (the radius, tibia, and third phalanx) of 168 anatomical and reference skeletal samples aged 18–103 years. Bayesian linear and generalized additive models were used to model the shift in cortical bone quality from early to late adulthood. Age-at-death predictive model performance was evaluated using correlation (r), mean absolute error (MAE), and credible intervals (CIs). Skeletal SoS reflected nonlinear, sex-specific age-related changes in cortical bone from accrual to loss beyond 40 years. SoS-based age-at-death estimates showed a strong correlation (r ≈ 0.7) with chronological ages, with the lowest MAEs (7.4–8.8 years) observed in the 40–49 and 70–79 age groups. In males, the lowest MAE was observed in the 60–69 age group (3.8 years), and, in females, in the 30–39 age group (5.6 years), followed by the 70–79 age group (6.24 years). This study demonstrates that skeletal SoS offers a biologically justified, non-destructive, fieldwork-suitable alternative to traditional methods for age estimation in older adults.