Implications of local osteoporosis on the efficacy of anti-resorptive drug treatment: a 3-year follow-up finite element study in risedronate-treated women.

UNLABELLED: The existence of local osteoporosis necessitates patient-specific analysis. Lower and higher ranges of local buckling ratio were found at femoral necks for adequate and inadequate drug response groups, respectively (grouped based on fracture loads). Management of hip fracture risk should be targeted at local geometric abnormalities causing instability.

INTRODUCTION

Hip fracture amongst the elderly is a growing concern especially with improvements in living standards and increasing lifespan. Approximately half of the total hip fractures result from those without osteoporosis. This escalates the need to observe local osteoporosis. By observing the local buckling ratio (BR) in the femoral neck in ten risedronate-treated subjects over 3 years, we discovered that subjects with improved fracture loads, as predicted by finite element (FE) analysis, were associated with lower local BR and vice versa.

METHODS

The 3D models of the left proximal femurs were generated, and local BR values at 30° intervals were obtained from femoral neck slices by measuring the respective mean cortical thickness and mean outer radius. Following geometric analysis, structural strength was examined with FE analysis where critical fracture loads (F cr) were acquired from sideways fall load simulations.

RESULTS

We classified subjects in three groups according to the change in F cr: adequate (+20 %), inadequate (-22 %) and indefinite (-2 %) drug response groups. A common striking feature was that lower and higher ranges of local BR values (baseline year) were found for adequate (min = 2.14, max = 8.04) and inadequate (min = 1.72, max = 11.38) drug response groups, respectively.

CONCLUSIONS

Subjects in the inadequate drug response group exhibited high local BR at the supero-anterior and supero-posterior regions. These high local BR values coincided with FE-predicted critical strain regions, whereas subjects from the adequate drug response group showed significantly reduced strain regions. The superiority of coupling geometry (BR) with structure (F cr) over bone mineral density measurements alone by monitoring local osteoporosis has been illustrated.