Cortical microstructure and estimated bone strength in young amenorrheic athletes, eumenorrheic athletes and non-athletes

Abstract

Context: Lower bone density in young amenorrheic athletes (AA) compared to eumenorrheic athletes (EA) and non-athletes may increase fracture risk during a critical time of bone accrual. Finite element analysis (FEA) is a unique tool to estimate bone strength in vivo, and the contribution of cortical microstructure to bone strength in young athletes is not well understood.

Objective: We hypothesized that FEA-estimated stiffness and failure load are impaired in AA at the distal radius and tibia compared to EA and non-athletes despite weight-bearing exercise.

Design and setting: Cross-sectional study; Clinical Research Center

Subjects: 34 female endurance athletes involved in weight-bearing sports (17 AA, 17 EA) and 16 non-athletes (14-21 years) of comparable age, maturity and BMI OUTCOME MEASURES: We used HR-pQCT images to assess cortical microarchitecture and FEA to estimate bone stiffness and failure load.

Results: Cortical perimeter, porosity and trabecular area at the weight-bearing tibia were greater in both groups of athletes than non-athletes, whereas the ratio (%) of cortical to total area was lowest in AA. Despite greater cortical porosity in EA, estimated tibial stiffness and failure load was higher than in non-athletes. However, this advantage was lost in AA. At the non-weight-bearing radius, failure load and stiffness were lower in AA than non-athletes. After controlling for lean mass and menarchal age, athletic status accounted for 5-9% of the variability in stiffness and failure load, menarchal age for 8-23%, and lean mass for 12-37%.

Conclusion: AA have lower FEA-estimated bone strength at the distal radius than non-athletes, and lose the advantage of weight-bearing exercise seen in EA at the distal tibia.

Figure 1

Stiffness (left) and failure load (right) in amenorrheic athletes (AA) (black bars), eumenorrheic athletes (EA) (gray bars) and non-athletic controls (white bars) at the distal tibia and distal radius. Stiffness and failure load at the distal tihia were higher in EA (but not AA) compared with controls. Stiffness and failure load at the distal radius were lower in AA (but not EA) compared with controls. * p<0.05

Figure 2

3D rendering of von Mises stress from representative μFEA analysis of the distal radius (left) and distal tibia (right) from an amenorrheic athlete, eumenorrheic athlete and non-athletic control. Each bone was subjected to a uniform axial compression of 1000 N for the distal radius and 2000 N for the distal tibia.