Tibial flexural wave propagation in vivo: Potential for bone stress injury risk assessment

Objective. To determine the reliability of tibial flexural wave propagation velocity (FWPV) and the effect of overlying soft-tissues on the result. Design. The velocity of tibial flexural wave propagation was repeatedly measured in healthy subjects. Background. The tibia is the most frequently stress-fractured bone of runners and in military training populations. Developing techniques to measure tibial bone strength and, thereby, fracture resistance may be useful in pre-participation examinations in order to identify at-risk individuals. One such method, tibial flexural wave propagation velocity (FWPV) has been reported to be a measure of tibial stiffness. Methods. The tibial FWPV was measured 80 times per subject (10 trials X 2 setups/day X 4 days) in a sample of 25 young women. Two methods of calculating FWPV were used (Peak method time domain and Phase method frequency domain). Intraclass correlations (ICCs) were calculated. Results. The results demonstrated that the peak method was more reliable then the phase method. The ICCs ranged from 0.81-0.96 for the peak method and from 0.59-0.89 for the phase method. The 95% confidence intervals demonstrated that the FWPV could discriminate between subjects with low, medium, or high velocity values with reasonable accuracy and confidence. The soft-tissue overlying the tibia was not significantly (p = 0.63) correlated with FWPV. Conclusion. In summary, it is possible to discriminate between varying levels of tibial FWPV. Furthermore, if FWPV is related to bone stress fracture resistance, then this method may be useful in determining stress fracture risk prior to intensive physical activity. Relevance. The tibia is the most frequently stress-fractured bone of runners and in military training populations. This study explores the feasibility of tibial FWPV as a potential method to assess tibial stress fracture resistance.