Trabecular Bone Contributes to Strength of the Proximal Femur Under Mediolateral Impact in the Avian

Background: Osteoporosis in long bones involves loss of cortical thickness and of the trabecular microarchitecture. Deterioration and weakening of trabecular bone tissue during osteoporosis imposes greater physiological loads on the cortical shell. However, it is unclear whether trabecular bone significantly contributes to the strength of whole bones under non-physiological impact loads. Method of Approach: We hypothesize that trabecular tissue in epiphyses of long bones contributes to resisting and distributing impact loads. To test this hypothesis, we caused artificial trabecular bone loss in proximal femora of adult hens but did not alter the bone cortex. Subsequently, we compared the energy required to fracture the proximal part of femora with missing trabecular tissue with the energy required to fracture control femora, by means of a Charpy test. Results: Extensive loss of trabecular bone in hens (over 0.50 grams or $∼71%$ weight fraction) significantly reduced the energy required to fracture the whole proximal femur in mediolateral impacts (from $∼0.37$ joule in controls to $∼0.20$ joule after extraction of core trabecular tissue). Conclusions: These findings indicate that trabecular bone in the proximal femur is important for distributing impact loads applied to the cortex, and support the concept that in treating osteoporosis to prevent hip fractures, it is just as important to prevent trabecular bone loss as it is important to prevent loss of cortical thickness.