Relationship of calcaneal and iliac apophyseal ossification to peak height velocity timing in children.

BACKGROUND: Ossification of the calcaneal apophysis has never been fully characterized. We examined the ossification sequence of the calcaneus in relation to ossification of the iliac apophysis and the timing of the peak height velocity (PHV).

METHODS: Ninety-four healthy children (forty-nine girls and forty-five boys), from three to eighteen years old, were followed longitudinally through growth with annual serial radiographs and physical examinations. These were done at least annually from ten to fifteen years of age. The PHV was calculated using the height measurements of each child. We measured and compared calcaneal and iliac crest apophyseal ossification using foot and pelvic radiographs made on the same day. We correlated the PHV with the degree of calcaneal and iliac ossification.

RESULTS: Ossification of the calcaneal apophysis occurred in an orderly fashion, with the ossification center first appearing a mean of 4.7 years (95% confidence interval [CI], 5.2 to 4.2 years) before the PHV. The apophysis spread across the plantar surface more quickly than the dorsal surface. The apophysis extended completely over the plantar surface a mean of 0.86 year (95% CI, 1.0 to 0.7 year) before the PHV. Fusion of the apophysis followed complete plantar extension over the next two years and was typically complete a mean of 2.1 years (95% CI, 2.0 to 2.2 years) after the PHV. Fusion began in the middle of the apophysis and proceeded outward. Iliac apophyseal ossification did not appear prior to the PHV in any subject.

CONCLUSIONS: The calcaneal apophysis ossifies in a consistent fashion characterized by six different stages. The calcaneal stages occur during narrow intervals in relation to the PHV, allowing the calcaneal system to be used for assessment of skeletal maturity. The PHV occurs prior to iliac ossification, whereas the calcaneal apophysis has four stages of ossification before and two stages after the PHV.