In the simplest sense Osteoporosis is defined as a condition that results in an inherent increase in the risk of fracture. A fracture occurs when the integrity of a bone is disrupted, which in everyday parlance is referred to as a broken bone.
In any discussion of Osteoporosis it is important to note that any bone is at risk of fracture if subjected to a sufficient force, as occurs with major trauma, such as in a significant motor vehicle accident or following high impact in body contact sports. In these situations the injured person does not necessarily have osteoporosis. Instead, osteoporotic fractures are suggested when the injured is subjected to a force that is not normally expected to break a bone, such as falling from a standing height. These sorts of fractures are termed minimal trauma fractures, which constitute the typical fractures that occur in those with Osteoporosis. Examples include fractures of the distal radius (forearm bone adjacent to the wrist), neck of femur (thigh bone adjacent to the hip joint), and the vertebrae (spinal bones).
Bone Densities: Normal and Osteoporotic
The reason for which bone becomes fragile, predisposing to minimal trauma fracture, has become increasingly known. The major factors that occur leading to the development of Osteoporosis is the loss of bone mass and a deterioration in the architecture of the bone at a microscopic level. It has long been considered that the loss of bone mass is a part of the aging process, whereby peak bone mass is achieved in early adulthood. However, the current concept of bone biology suggests that the process instead is pathological. The ability to measure bone mass with bone densitometry has revolutionized the diagnosis of the condition, whereby the World Health Organisation (in 1994) defined Osteoporosis as present when the bone mass is more than 2.5 standard deviations below that expected for a young adult of the same gender. This will be discussed in greater detail in ‘How is Osteoporosis diagnosed’.
The importance of micro-architecture has only more recently been appreciated to be a major contributing factor to bone strength, explaining the situation in which those with preserved bone mass have osteoporotic fractures. Micro-architecture relates to the microscopic structure of bone. This includes the size, shape, and width of the bone in addition to the density that relates to bone mass. Furthermore, it relates to the lattice pattern of bone that is similar to the appearance of scaffolding seen on a construction site. Against popular conception, bone is in fact a living structure constantly undergoing remodeling, whereby these struts that make up the lattice are shaved back and rebuilt. In osteoporosis, the shaving seems to outdo the rebuilding causing these important struts to become thin or simply break apart, which ultimately leads to collapse.
