<qa>  How many patients will be enrolled at up to 19 sites?This multi-center study will evaluate Cortoss for the augmentation of one or two vertebrae, fractured as a result of osteoporosis, located between and including the levels of the sixth thoracic and the fifth lumbar vertebrae. A total of 243 patients will be enrolled at up to 19 sites. All subjects must have radiographic evidence of a vertebral body fracture due to osteoporosis. After complying with all eligibility criteria, subjects will sign an informed consent document and will be randomized into vertebroplasty treatment with Cortoss or PMMA 1:1 ratio. Patients will be followed for at least 24 months and recruitment is expected to take between 9 and 12 months. Visits and assessments are planned according to the time and events schedule. 