Investigating the Ossification and Fusion of the Fifth Metatarsal Apophysis Using Computed Tomography and Plain...

An understanding of the anatomical development of the fifth metatarsal apophysis is essential for clinical assessment and management of subadult patients presenting with lateral foot pain or oedema that worsens with activity. Despite the common occurrence of subadult lateral foot pain, current understanding of apophyseal development is constrained because of the reliance on plain radiography in the literature, resulting in simplistic descriptions of development. To overcome these limitations, this study aimed to investigate the development of the fifth metatarsal apophysis using 3-dimensional computed tomography analysis, to provide novel morphologic descriptions and normative sex-specific age tables for each developmental stage in a contemporary Australian subadult population.

Development and fusion status of the apophysis was scored using a novel 5-stage scoring system on 295 multi-slice computed tomography scans (158 females, 137 males; 0-15 years of age) and 258 lateral, anteroposterior, and oblique radiographs (120 females, 138 males; 0-7 years of age) from the Queensland Children's Hospital.

The apophysis commenced ossification as early as 7 years for females and 8 years for males, initially appearing as a thin fleck of bone that elongated to form a crescent shape, with the proximal aspect being wider and extending more medially compared with the distal aspect. Apophyseal fusion demonstrated significant sexual dimorphism with fusion commencing at a mean age of 10.09 years for females and 12 years for males, with the earliest age of complete fusion observed at 9 years for females and 12 years for males.

This cross-sectional study provides contemporary descriptive reference data for staging development of the fifth metatarsal apophysis and an updated account of its morphology. These observations may assist radiographic interpretation in adolescents; however, the study was not designed to evaluate diagnostic accuracy or clinical outcomes. Further clinical validation is needed before using these data to guide diagnosis or to reduce misclassification of fractures versus apophysitis.