Early Maturity as the New Normal: A Century-long Study of Bone Age

Abstract

Background: Epiphyseal fusion (EF) marks the completion of longitudinal bone growth, a critical milestone monitored during treatment of skeletal growth and/or developmental disorders. Recently, a trend toward accelerated skeletal maturation in children has been documented. Because current methods for assessing skeletal maturation include children in their reference populations born as early as the 1930s, the timing of EF events in contemporary patients may differ substantially from those standards.

Questions/purposes: (1) Do children today initiate the process of EF in the hand and wrist earlier than past generations on which maturity standards are based? (2) Do children today complete EF in the hand and wrist earlier than past generations on which maturity standards are based?

Methods: A total of 1292 children (665 males, 627 females) participating in the Fels Longitudinal Study, born between 1915 and 2006, were included in this retrospective, observational study. Each participant had between one and 39 serial left hand-wrist radiographs during childhood obtained specifically for research purposes. Main outcomes were the chronological age at the first sign of EF initiation (EF-I) and the first chronological age when EF was complete (EF-C) in the radius and ulna, and metacarpals and phalanges of the first, third, and fifth rays according to criteria of the Fels method. EF is a reliable metric with an average κ agreement statistic of 0.91. Penalized B-splines were used to model the changes in EF-I and EF-C ages and to identify changes across continuous birth years with major comparisons between children born in 1935 and 1995.

Results: Approximately half of the epiphyses of the hand and wrist examined exhibited earlier EF-I and/or earlier EF-C in children born in 1995 compared with those born in 1935. The age at each milestone (EF-I and EF-C) decreased by as much as 6.7 and 6.8 months in males and 9.8 and 9.7 months in females, respectively. This change occurred gradually over the past century. The more proximal traits (EF of the distal radius, distal ulna, and metacarpals) were more likely to experience a shift in timing, whereas timing of EF in the phalanges remained relatively stable across birth years.

Conclusions: A trend has occurred over the past century in the timing of EF, in both initiation and completion of the process, for many of the bones of the hand and wrist. Earlier EF reflects modern population advances in both skeletal and sexual maturation. Shifts in the timing of EF have the potential to influence treatment strategies for skeletal growth and/or developmental disorders such as scoliosis or leg length inequality, moving treatment windows to earlier ages. Earlier EF-I and EF-C identified in this study signals a need to reevaluate the timing of maturational milestones and current standards for skeletal assessment.

Level of evidence: Level II, prognostic study.

Fig. 1

This STROBE diagram shows the distribution of participants in the Fels Longitudinal Study and the inclusion in the present study based on inclusion and exclusion criteria as well as the final participant group used in the current analysis.

Fig. 2

These graphs illustrate penalized B-spline curves for EF-I and EF-C traits in the distal ulna and radius as well as the metacarpals and distal phalanges of the first, third, and fifth rays in males born between 1935 and 1995. EF-I is represented by purple-dotted lines and EF-C is represented by green solid lines, each with 95% confidence bands. Models that were statistically significant are denoted by an asterisk.

Fig. 3

These graphs illustrate penalized B-spline curves for EF-I and EF-C traits in the distal ulna and radius as well as the metacarpals and distal phalanges of the first, third, and fifth rays in females born between 1935 and 1995. EF-I is represented by purple-dotted lines and EF-C is represented by green solid lines, each with 95% confidence bands. Models that were statistically significant are denoted by an asterisk.