The medial clavicular epiphysis: evidence for secular change in skeletal maturation

This study documents fusion of the medial clavicular epiphysis in the American population over 100 years (1880s –1920s birth cohorts). The sample consists of 1,289 Americans from 3 skeletal samples: the William McCormick Clavicle Collection (n=594), the Hamann‐Todd Osteological Collection (n=354), and McKern and Stewart's Korean War data (n=341). The McCormick Collection is a documented autopsy sample of clavicles from 1986–1998 autopsies in East Tennessee. The Hamann‐Todd Collection consists of skeletal remains from ~3,000 cadavers autopsied between 1912 and 1938 in Cleveland. The McKern and Stewart data is from the 1957 government report Skeletal Age Changes in Young American Males . The epiphysis was scored as unfused, fusing, or fused. A statistical treatment referred to as transition analysis was used to evaluate differences in fusion timing between the samples. Transition analysis returns a probability density function with a maximum likelihood estimate representing the most probable age at which an individual transitions from one phase to the next (i.e. from unfused to fusing). T‐tests were performed on the maximum likelihood estimates to evaluate significance in transition timing (α=0.05). The results indicate that modern females transition to fusion at approximately 15 years of age and males transition at 16 years. These transitions are 4 years earlier than early 20 th century individuals from the Hamann‐Todd Collection and 3.5 years earlier than individuals from the mid‐20 th century (McKern and Stewart's Korean War data). These results have important implications for our understanding of skeletal maturation in modern populations.