Quantifying the ossification and fusion of the calcaneal apophysis using computed tomography

Knowledge of the anatomical development of the calcaneal apophysis is essential in clinical assessment and management of both paediatric and sub-adult patients presenting with heel pain. Despite this, the current understanding of calcaneal apophyseal development is constrained by the limitations of the imaging modalities used to examine the apophysis, with no current literature reporting the development of the medial and lateral processes. This study aimed to overcome these limitations by investigating the ossification and fusion of the calcaneal apophysis using three-dimensional computed tomography analysis, and statistically predicting the apophyseal developmental stage in contemporary Australian children. The development and fusion status of the apophysis was scored using a novel 11-stage scoring system on 568 multi-slice computed tomography scans (295 females; 274 males) and 266 lateral radiographic scans (119 females; 147 males) from the Queensland Children's Hospital. Multinomial logistic regression along with classification tables and predictive probabilities were then utilised to assess developmental stage likelihood from known age and sex. The apophysis commenced ossification at a mean age of 5.2 years for females and 7.2 years for males, and then elongated to form the apophyseal cap around 10 years for females and 12.4 years for males. Fusion of the apophysis commenced at a mean age of 11.18 years for females and 13.3 years for males, with the earliest age of complete fusion observed at 10 years for females and 14 years for males. The results demonstrate significant sexual dimorphism in ossification and fusion with females developing and fusing significantly earlier. Furthermore, the use of computed tomography in this study allowed for the first time evaluation of the ossification and fusion of the medial and lateral processes of the calcaneus. The medial process formed at a mean age of 9.5 years for females and 10.9 years for males while the lateral process formed at around 9.8 years for females and 11.7 years for males. The medial process demonstrated slower rates of fusion compared to the lateral process. The present study provides Queensland specific standards for assessing the calcaneal apophyseal developmental stage as well as novel predictive regression models for apophyseal stage estimation using known age and sex to aid in the diagnosis of heel pain conditions such as apophysitis or screen for developmental delays in children and subadults.