331 (M=199, F=132) sequential knee radiographs of patients between the ages of 2-8 were reviewed. This involved a time period from Jan 2014-April 2016. Cases were obtained through a search on the integrated picture archiving and communication system encompassing the three different emergency departments within Barts Health NHS trust.

Patients with features of skeletal dysplasia, developmental disorder and metabolic bone disease were not included in the study. Outpatient and GP requests were also not included to reduce the chance of occult chronic disease influencing the results.

For each radiograph, the presence and craniocaudal length of the patella ossification centre were recorded. Data collection was performed by both authors.