Summary:​ Periosteal expansion and bone loss have opposite effects on femur strength. Their combined effect has not been fully understood. Our investigation using a recently developed beam model suggested that periosteal expansion may maintain femur bending stiffness among elderly women, but not help preserve femoral strength and reduce hip fracture risk.

Introduction:​ Periosteal expansion and bone loss are two accompanying biological phenomena in old population. Their combined effect on bone stiffness, strength, and fracture risk is still not clear, because previous studies have reported contradictory results.

Methods:​ A recently developed DXA (dual-energy X-ray absorptiometry)-based beam model was applied to study the effect at the femoral neck. We first made a theoretical analysis. Then, a clinical cohort consisting of 961 women (316 hip fractures and 645 controls, age of 75.9 ± 7.1) was used to investigate the associations quantitatively. We investigated (1) correlations of femoral-neck width and bone mineral density with femoral stiffness and strength;​ (2) correlations of femoral stiffness, strength, and hip fracture risk index with age;​ (3) associations of femoral stiffness, strength and fracture risk index with actual fracture status, measured by the area under the curve (AUC) and odds ratio (OR).

Results:​ The investigation results showed that (i) femoral-neck width had stronger correlation with femoral bending stiffness (r = 0.61–0.82, p < 0.001) than with the other stiffness components, while bone mineral density had stronger correlation with axial/shearing stiffness (r = 0.84–0.97, p < 0.001), strength (r = 0.85–0.92, p < 0.001), and fracture risk index (r = −0.61–0.62, p < 0.001) than with bending stiffness. (ii) The association between femoral bending stiffness and age was insignificant (r = − 0.06–0.05, r > 0.05);​ The associations of axial/shearing stiffness (r = − 0.27–−0.20, p < 0.001), strength (r = − 0.28, p < 0.001), and fracture risk index (r = 0.38, p < 0.001) with age were significant. (iii) Fracture risk index had the strongest association with actual fracture status (AUC = 0.75, OR = 3.19), followed by strength (AUC = 0.74, OR = 2.84) and axial/shearing stiffness (AUC = 0.56–0.65, OR = 2.39–2.49). Femoral bending stiffness had the weakest association (AUC = 0.48–0.69, OR = 1.42–2.09).

Conclusion:​ We concluded that periosteal expansion may be adequate to maintain femoral bending stiffness among elderly women, but it may not help preserve strength and reduce hip fracture risk.