Are knee mechanics during early stance related to tibial stress fracture in runners?

BackgroundTibial stress fractures are a serious overuse injury in runners. Greater vertical loading rates and tibial shock have been found in runners with previous tibial stress fracture compared to controls. The timing of these variables occurs very early in the stance phase and suggests that conditions shortly after footstrike may be important in determining injury risk. The purpose of this study was to further investigate lower extremity mechanics in early stance in runners with a history of tibial stress fracture. In addition, the relationships between these variables were explored.MethodsTwenty-three runners with a history of tibial stress fracture were investigated. They were compared with 23 age and mileage matched control subjects with no previous lower extremity bony injuries. Data were collected as subjects ran at 3.7 m/s. All variables of interest were computed over the period from footstrike to the impact peak of the vertical ground reaction force. Independent t-tests and effect sizes were used to assess the differences between the groups. Pearson Product Moment correlations were used to determine whether initial stance variables were related to tibial shock in the two groups.FindingsSagittal plane knee stiffness was significantly greater in the tibial stress fracture group. Stiffness was also positively correlated with shock. Knee excursion, knee angle at footstrike and shank angle at footstrike were not different between groups.InterpretationThese findings provide further support for the relationship between mechanics during initial loading and tibial stress fractures in runners. This relationship may be important in terms of retraining gait to reduce the risk of stress fracture in runners.