The lateral clavicular epiphysis: fusion timing and age estimation

This study utilizes a forensic autopsy sample of twentieth century American Whites (the McCormick Clavicle Collection) to describe the morphology, variation, and fusion timing of the lateral clavicle epiphysis. Clavicles from individuals between 11 and 25 years at the time of death were used to document fusion of the lateral epiphysis (n= 133, 38 females and 95 males). The lateral epiphysis was scored as unfused, fusing, or fused. A linear weighted kappa indicates that this scoring method is highly replicable with almost perfect inter-rater agreement (kappa = 0.849), according to a widely used standard for assessing kappa values. Transition analysis, or probit regression, was employed to quantify fusion timing of the lateral epiphysis. The transition from "unfused" to "fusing" is most likely to occur at 16.5 years in females and 17.5 years in males. The transition from "fusing" to "fused" occurs at age 21 in females and age 20 in males. The earliest age at which fusion began was 15 years (n = 1), but the majority began fusing between 17 and 20 years. Most individuals (98.5 % of the sample) aged >24 years had fused lateral epiphyses. The epiphysis assumes one of two forms: (1) a separate bony flake fusing to the diaphysis or (2) a mound of bone glazing/smoothing over the diaphyseal surface. As socioeconomic status has been cited as the most influential variable on skeletal maturation rates, the fusion ages offered here should not be applied to populations with a socioeconomic status different from the greater US population.