Cortical shell is outher layer of bone (placed also in the middle of long bones. The cancellous the sponge-like bone in the ends of long bones and vertebrae.  Cortical bone is the hard and high density. Because osteoblasts and osteoclasts inhabit the surface of bones, trabecular bone is more active, and is more subject to bone turnover and remodeling. Not only is bone density decreased, but the microarchitecture of bone is also disrupted. The weaker spicules of trabecular bone break and are replaced by weaker bone. Common osteoporotic fracture sites, the wrist, the hip and the spine, have a relatively high trabecular bone to cortical bone ratio. These areas rely on trabecular bone for strength, so the intense remodeling causes these areas to degenerate most when the remodeling is imbalanced. The beginning of process is of 30 -35 ages. Women lose could be higher up to 50% while men is about 30%.