Comparison of tibial and femoral physeal diffusion tensor imaging in adolescents.

Background: Distal femoral diffusion tensor imaging (DTI) is a predictor of height gain but it is uncertain whether DTI can demonstrate differences in growth potential between the tibia and femur.

Objective: To explore the differences in structure and growth potential of the proximal tibia physeal-metaphyseal complex compared to those of the distal femur through DTI tractographic characterization and DTI metric comparison.

Materials and methods: Prospective cross-sectional study involved 108 healthy children (59 females) aged 8-14 years (females) and 10-16 years (males) around the growth spurt. We acquired knee DTI once at 3 T with b-values of 0 s/mm² and 600 s/mm². Tract parameters including number, length, volume, and fractional anisotropy were measured. Regression analysis with linear and negative binomial models, incorporating bone age-based quadratic fitting, characterized DTI parameter changes in relation to bone age and sex, as well as variations between physes. Femorotibial ratios were calculated based on paired DTI parameter absolute values during peak height gain. The study was approved by the institutional review board of two tertiary pediatric centers in compliance with the Health Insurance Portability and Accountability Act.

Results: Proximal tibial tracts were more numerous in the central physis, whereas distal femoral tracts predominated peripherally. Tract volume rose and fell during adolescence and peaked earlier in females (140-160 months vs. 160-180 months, P=0.02). At maximal height velocity (160 months), tibial tract volume (5.43 cc) was 37.4% of total knee tract volume (14.53 cc). Tibial fractional anisotropy decreased and then increased, both earlier than the femur.

Conclusion: Proximal tibial and distal femoral tract distributions differ. The tibia accounts for 37.4% of total knee tract volume during maximal height velocity. Tract volumes rise and fall, earlier in females. Tibiofemoral ratios of DTI metrics resemble known ratios of growth rates between tibia and femur.