Purpose or Case Report: It is estimated that the ratio between the femoral and tibial growths is 0.94/0.67 (1.4), but the accuracy of the data used to obtain it is limited. We aim to find a correlation between the rate of new bone growth in between each zebra line in the patients with Osteogenesis Imperfects (OI) who have received cyclic bisphosphonate (BP) therapy with each treatment cycle between the distal tibia and proximal femur. This will allow us to quantify the growth of the distal femur and proximal tibia with accuracy.
Methods & Materials: In this retrospective study approved by IRB, we identified on the EMR system, 4 children aged 2 to16 years of age diagnosed with OI who received cyclic BP treatment every 2-6 months between 1/2015 and 6/2022. We reviewed x-rays of both lower extremities to estimate physeal growth rates with each treatment cycle by measuring the distance between zebra lines. We measured 5 lines in the juxta-physeal metaphysis of the distal femurs and proximal tibias and compared the growth between lines to establish trends of growth in both physes.
Results: We measured the growth rate in both distal femurs and proximal tibias of all four children. Children’s age and sex were 9F, 9F, 2M, and 5F. There was a high correlation between the growth of both bones, with coefficients (r2) for zebra line distances of 0.96 for both femurs, 0.89 for both tibias, 0.61 for the right femur and tibia, and 0.83 for the left femur and tibia (all p<0.01). The average growth ratio between the right femur and right tibia in all four patients was 1.39, 2.35,1.89, and 1.97 respectively. Wilcoxon Signed-Rank Test showed differences between femoral and tibial growth rates on both sides (both p <0.001) but no differences between right and left femurs (p=0.9) and tibias (p=0.6). The average growth ratio between the left femur and left tibia in all four patients was 1.55, 2.09,1.81, and 1.93 respectively
Conclusions: In all children, evaluation of growth using the zebra line distances showed that there was a high correlation between the right and left bones and a slightly smaller correlation between the femur and tibia. Femoro-tibial ratios for all patients ranged between 1.4 and 2.1. The estimation of the ratio between zebra lines in children with BP treatment validates the current concepts of growth in children. The ratio may serve to identify local abnormality of the physis in patients with abnormal growth.