Bone fracture risk can increase through bone microstructural changes observed in bone pathologies, such as glucocorticoid-induced osteoporosis. Resorption cavities present one of these microstructural aspects. We recently found that glucocorticoids (GCs) affect the shape of the resorption cavities. Specifically, we found that in the presence of GC osteoclasts (OCs) cultured on bone slices make more trenchlike cavities, compared to rather round cavities in the absence of GCs, while the total eroded surface remained constant. For this study, we hypothesized that trenchlike cavities affect bone strength differently compared to round cavities. To test this hypothesis, we cultured OCs on bone slices in the presence and absence of GC and quantified their dimensions. These data were used to model the effects of OC resorption cavities on bone mechanical properties using a validated beam-shell finite element model of trabecular bone. We demonstrated that a change in the geometry of resorption cavities is sufficient to affect bone competence. After correcting for the increased EV/BV with GCs, the difference to the control condition was no longer significant, indicating that the GC-induced increase in EV/BV, which is closely related to the shape of the cavities, highly determines the stiffness effect. The lumbar spine was the anatomic site most affected by the GC-induced changes on the shape of the cavities. These findings might explain the clinical observation that the prevalence of vertebral fractures during GC treatment increases more than hip, forearm and other nonvertebral fractures.