Osteoporosis pathophysiology – What is the pathophysiology of Osteoporosis ?
Osteoporosis pathophysiology – Introduction
Osteoporosis is characterized by loss of bone mineral density (BMD). It mostly affects people aged over 50 years, specifically one in four women and one in eight men. There are approximately two million Canadians currently suffer from osteoporosis.
Complications associated with osteoporosis are due to a weakening of the skeleton. First there are fractures, mainly vertebrae, wrist and hip. Chronic pain and postural deformities resulting from these fractures progressive.
Patients experience a reduction in their mobility. Osteoporosis leads therefore a significant reduction in their quality of life. Mortality can be as high as 20% in the year following a hip fracture.
Finally, the costs associated with hip fractures are estimated at $ 26,000.
Pathophysiology of Osteoporosis
Two types of bones composing the skeleton: cortical bone (compact) and trabecular (spongy). The cortical bone forms the exterior and constitutes 80% of the total bone mass. It is primarily found at the ends of long bones. Only 2-3% of its mass is renewed each year. Trabecular bone forms the network inside the bones. It is primarily found in the vertebrae and wrist. Annual renewal can reach more than 25%.
Bone remodeling (resorption and formation) is an ongoing process. In osteoporosis, bone mass is reduced, which shows that the rate of bone resorption exceeds that of formation. Speeds of remodeling differ not only between cortical and trabecular tissue, but also between different bone sites. Surfaces of active resorption are lined of osteoclasts, and the forming surfaces are characterized by the presence of osteoid covered edges of active osteoblasts. Resorption precedes formation and is probably more intense but shorter than the formation. If formation does not compensate exactly resorption, bone mass decreases.
Bone mineral density peaked at the age of 35 years. Subsequently, there was a gradual decrease. In men and premenopausal women, the annual decrease is approximately 1%. It is the slow phase. Accelerated phase occurs only during the 10 years following menopause. Bone loss can be as high as 3 to 5%. Thereafter, bone loss returns to the slow phase.
There are two types of osteoporosis: primary osteoporosis (postmenopausal and senile) and secondary osteoporosis. Primary osteoporosis postmenopausal (type I) occurs in women within 5 to 15 years after the onset of menopause. Estrogen deficiency causes a rapid loss of trabecular bone. Primary osteoporosis senile (type II) occurs in men and women aged over 70 years as a result of a decrease in bone formation, calcium deficiency or chronic secondary hyperparathyroidism. Finally, secondary osteoporosis (type III) is caused by a disease or other drugs.