Osteoporosis can be defined literally as “porous bones”. It is a slowly progressive disorder of the skeletal system, that is, the system of bones and joints. Porous bones are a result of demineralization of bones. The bone-mass decreases over time. The resultant loss of strength of bones can result in fractures and broken bones.
Facts and Figures about Osteoporosis
Osteoporosis is a very common occurrence, more so in women than in men. Each year it is estimated to cause 8.9 million fractures around the globe.  Every one in three women, and one in five men above 50 years of age are at risk of osteoporosis. The risk of osteoporosis in women exceeds the risk of heart disease, stroke and breast cancer combined.
The most common sites of fractures include the hip, the leg, the vertebra, or the wrist.
Bone Structural Changes In Osteoporosis
Structurally bone comprises of two parts:
- The cortical bone, which makes the outer hard shell of the bone. It is highly organized, also called compact bone.
- The spongy bone, which makes up the inner trabecular network of the bone. The presence of spongy bone effectively reduces the weight of bones and allows smooth, easy limb mobility.
The bone mass comprises of two essential components, collagen and calcium salts. Proportionally, it is one-third of collagen for two-thirds of calcium salts that make up the bones. Collagen protein provides a scaffold for binding of calcium salts, which may combine with other minerals like magnesium, sulfates, and fluorides. The collagen permits limb flexibility, while the minerals contribute to bone strength. An imbalance in either component can compromise bone function or structure.
With osteoporosis, the bone density decreases, which means that the spaces in the lattice network of spongy bone grow wider. It is also accompanied by the thinning of trabecular network branches, and also of the compact bone. The minerals crystallized on the trabecular network are slowly lost, the collagen framework can then give way to the slightest pressure.
1Underlying Pathology Of Osteoporosis
The bone structural equilibrium is maintained by the activity of active bone cells; osteoblasts and osteoclasts, and relatively dormant mature cells; osteocytes. Osteoblasts function to lay down new bone cells in the bone matrix. In doing so, they progress through stages developing themselves into fully mature osteocytes. Osteoclasts on the other hand, cause bone resorption. They dissolve the bone matrix for the continuation of the cycle of regeneration. Increased osteoclastic activity results in bone loss. This loss, when is unaccompanied by bone formation by osteoblastic activity, results in an overall decrease in bone density and osteoporosis. 
Osteoporosis or Paget’s disease?
These two diseases of the skeletal system are often times confused due to the similarity in causing skeletal deformity. Paget’s disease is characterized by abnormal bone architecture due to an imbalance in the activity of bone cells. It targets only a few bones like skull, leg or forearm, or pelvic bones. The bones in Paget’s disease become weak and prone to disfigurement like curving of long bones and expansion of the skull size.