Use of digital image analysis to improve rigor and efficiency of physeal bone growth measurements

In larger, translational animal models, manual measurements of longitudinal bone growth using fluorochrome labels is tedious and may be prone to less rigor due to variations in reader experience, sampling differences, and photobleaching that limits the repeatability of measurements. This study assesses the reliability of three different digital methods to assist in measurement of distance between pulsed fluorochrome labels. Forty-five tibial physes from skeletally immature New Zealand White rabbits were pulsed with fluorochrome labels and measured using Fully Manual Technique (FMT), Manual Digital Measurement (MDM), Computer Assisted Image Processing (AIP), and Fully Automated Measurement (FAM). Pearson's correlation coefficient and Bland-Altman analysis were used to analyze the different methods. Intraclass correlation coefficient (ICC) assessed inter- and intra-reader reliability. Regardless of the method, all growth rate measurement techniques exhibited excellent agreement and reliability. The computer assisted methods allowed rapid data acquisition without compromising reliability, thereby improving efficiency in bone growth research. Clinical Significance: Distances between fluorochrome bone labels on large samples can be reliably measured using digital imaging and processing techniques.