Osteoporosis

Topic Highlights

●    Osteoporosis is the thinning of bones that occurs due to an imbalance in bone resorption and bone formation.  

●    Osteoporosis increases the risk of fractures.

●    Hormones and minerals play a vital role in maintaining normal bone density and preventing bone loss.

●    Measuring bone mineral density (BMD) helps diagnose osteoporosis, while treatment aims at preventing bone loss.

●    This visual presentation describes bone structure, bone remodeling, causes of osteoporosis ' including the role of hormones and minerals, risk factors, diagnosis of osteoporosis, treatment, and self help for the disease.

Transcript

Osteoporosis is a silent disease that causes thinning and weakening of the bones. It is typically associated with aging. The word osteoporosis means porous bones. It causes a decrease in bone density, making the bones weak and brittle.

Weak and brittle bones are prone to fractures caused by even mild stress like bending, lifting or coughing. The fractures most commonly occur in the spine, hip or wrist. Although it was previously thought to only affect elderly women, osteoporosis can occur early in life as peak bone density is achieved by the age of 25. Women have a greater risk of fractures than men.

A normal bone is composed of a protein called collagen and the mineral calcium. A bone consists of three types of tissues. The outermost tissue is composed of dense and compact cortical tissue. This surrounds an inner spongy lattice-like trabecular tissue. The bone marrow comprises the innermost tissue. It is soft and spongy and fills the holes and passageways of the bone. Bone marrow is the source for red blood cells, platelets and some white blood cells.

The combination of dense compact cortical bone and the supple trabecular bone makes them both strong and light in weight.

Bone is a living tissue. It is constantly in a state of renewal or repair. Throughout our life the old bone tissue is replaced by new bone tissue by a process called bone remodeling.

The process of remodeling involves three types of cells, namely, osteocytes, osteoclasts and osteoblasts.

Osteocytes are spidery cells that are formed from osteoblasts. They detect stress in the bone and transmit signals to other bone cells. These cells are actively involved in replacing the bony matrix periodically.

Osteoclasts are large, multinucleate cells that are involved in bone resorption, a process by which the bone is broken down and minerals are released. The process of resorption transfers the mineral calcium from the bone to the blood.

Osteoblasts are mononucleate cells that take part in bone formation, particularly the bone framework. They are involved in repairing the damaged bones.

Bone remodeling takes place in two stages with the help of these specialized cells. The first stage of bone breakdown or resorption is carried out by the osteoclasts and the second phase of bone formation is carried out by the osteoblasts. This entire cycle of bone remodeling takes about 3-6 months in children and adolescents and 6-12 months in adults. In older adults the process may take up to 18 months.

The bones pass through three stages during their lifetime. The first stage lasts throughout childhood and adolescence, until young adulthood. These are the prime years of physical growth during which the bone mass increases with bone formation exceeding the breakdown. Thus the bone mass or bone quantity reaches its peak in the third decade and is known as peak bone mass.

The second stage sets in as we age. The balance shifts to a state of equilibrium, at which point bone formation equals bone resorption or bone destruction. The third stage occurs during old age and is characterized by increased bone loss.

Osteoporosis occurs when there is an imbalance in the process of bone resorption and bone formation. The other factors that increase the risk for osteoporosis include:

Gender: The condition is more common among women, although it is known to affect men as well. Women are at a greater risk for developing osteoporosis because they have a lower peak bone mass than men. Menopause is another factor that accelerates bone loss in women.

Age and heredity: Advancing age and heredity are risk factors for both men and women.

Race: Osteoporosis is more common among Caucasians and Asians than it is to the Hispanic and Black population due to the racial differences in bone mass and density.

Lack or deficiency of calcium and vitamin D, excessive weight loss, imbalanced diet, lack of physical activity, smoking and alcohol abuse are the additional factors that can cause osteoporosis.

Vitamin D and calcium are essential for bone health. Both these components are regulated by parathyroid hormone (PTH) and calcitonin.

Vitamin D is important for the build-up and maintenance of healthy bones as it promotes calcium absorption into blood. Low concentrations of vitamin D are associated with reduced intestinal calcium absorption, thus increasing the risk for osteoporosis.

Calcium is crucial for bone strength. About 90% of the bone, by weight, is composed of calcium hydroxylapatite made of calcium, phosphate and hydroxyl groups. Adequate dietary intake of calcium is necessary to maintain strong and healthy bones.

Calcitonin, a hormone produced by the thyroid gland, works as a physiologic antagonist to parathyroid hormone. Calcitonin decreases the osteoclastic bone resorption, in turn lowering blood calcium levels. The hormone also prevents reabsorption of calcium in the kidneys, leading to increased excretion of calcium in urine.

Parathyroid hormone is secreted from the parathyroid glands when the blood calcium levels decrease. PTH is found to increase blood calcium levels by three processes. The hormone stimulates the osteoclasts, increasing the calcium levels in blood. PTH also increases absorption of calcium from the small intestine by stimulating the production of vitamin D in kidneys. Increased vitamin D levels increase the intestinal absorption of calcium, elevating blood calcium levels. PTH stimulates tubular reabsorption of calcium, resulting in minimal calcium excretion in urine.

No signs or symptoms are exhibited during the early stages of osteoporosis. It is often detected accidentally when a fracture occurs. Symptoms occurring late in the disease include:

●    fracture of the vertebra, hips or wrist

●    low backache

●    neck pain

●    bone pain or tenderness

●    loss of height over time, and

●    stooped posture

The doctor will take a detailed medical history, perform a thorough physical examination and take special X-rays to measure bone density before arriving at a conclusive diagnosis of osteoporosis.

Measuring the bone mineral density (BMD) helps diagnose osteoporosis or determine if a patient is at risk for the disease. Different types of bone densitometers are available to determine bone density.

Dual-energy X-ray absorptiometry (DEXA), also called the bone scan is the most common method used to measure the bone density. During this procedure the entire body is scanned and BMD is measured, particularly of the hip, spine and wrist to assess the risk for fractures.

Other tests used to evaluate BMD are:

Quantitative computerized tomography (QCT) is used to measure bone density in the hip and spine. The three dimensional quantitative image that is produced from the procedure helps in direct measurement of bone density.

Quantitative ultrasound ' helps predict the overall risk for fractures.

Peripheral DEXA (pDEXA) ' makes use of ultrasound to determine bone loss in localized areas like the hand or heel.

Radiographic absorptiometry ' measures the bone mass from radiographs of peripheral sites.

Bone marker tests ' are used to check the concentration of several enzymes, proteins and other substances in the blood. Bone marker tests help a physician evaluate the progress of disease and the treatment procedure.

The aim of treatment for osteoporosis is prevention of bone loss and fractures. There are many drugs available to treat osteoporosis because of the recent advances in medical research. Medications generally prescribed for osteoporosis include Bisphosphonates, Parathromone, Selective estrogen receptor modulators (SERM's), Calcitonin, Calcium supplements, Vitamin D and hormone replacement therapy (HRT).

Bisphosphonates: this group of drugs inhibit osteoclast mediated bone breakdown, increase bone density and reduce the risk of fractures. Examples are alendronate, risedronate, ibandronate, etidronate and zoledronate.

Teriparatide: An analog of parathyroid hormone, the drug is used to treat men at risk of fractures and postmenopausal women. The drug stimulates new bone growth.

SERMs: This class of drugs works similar to estrogen and slows the thinning of bone, increases bone thickness and reduces the risk of spinal fractures. Raloxifene is an SERM used to prevent and treat osteoporosis in women.

Calcitonin: Slows bone resorption and increases bone density. It has been shown to reduce the risk of spine fractures and provide relief from bone pain.

Hormone replacement therapy or HRT: Reduction in estrogen levels during and after menopause affects bone strength. Replacing the levels of estrogen has been shown to reduce bone loss, increase bone density and prevent fractures. Also known as menopausal hormone therapy, the procedure helps prevent osteoporosis in postmenopausal women. HRT is not routinely used due to the health risks associated with long-term use.

Calcium and vitamin D supplements help maintain bone density and strengthen the bones.

In addition to medications, healthy diet, regular physical activity and healthy lifestyle help control osteoporosis.

Some other preventative measures include taking adequate amounts of calcium, vitamin D and plant estrogens (e.g. Soy), and limiting alcohol, caffeine and nicotine intake.