osteo

Osteoporosis - A Primer

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Description

Osteoporosis is a disease characterized by decreased bone mass and strength along with micro-architectural deterioration or very small internal structural deterioration of bone tissue which leads to fragile or brittle bones.
Osteoporosis affects the entire skeleton. These changes in bone mass and strength ultimately lead to an increased risk of fractures.
There are two categories: primary and secondary.
Primary osteoporosis is the most common form of the disease and includes
- Type I post-menopausal osteoporosis or "vertebral crush".
- Type II age-associated osteoporosis, which affects a majority of individuals age 70 and older.
- Idiopathic osteoporosis affecting pre-menopausal women and middle-aged men.
Secondary osteoporosis is a disease in which an identifiable agent or disease process causes loss of bone tissue and includes:
- inflammatory disorders
- disorders of bone marrow cellularity
- endocrine disorders of bone remodeling.

Background

Bones provide structural support for the muscles and internal organs.
Bones act as a reservoir for important minerals and elements such as calcium, magnesium, phosphorus, fluoride and sodium. Calcium is probably the most important for providing the essential bone infrastructure
Bones play an integral role in the overall homeostatic control of calcium in the body. Approximately 97% to 99% of the body's calcium stores are found in bone.
Bone has three components:

A collagenous fiber component that is organic and comprises about 40% of the bone
A ground substance component, which is an inorganic mineral component mostly made up of calcium-phosphate (Ca++-P)
A cell component, which is made up of osteoblasts and osteoclasts. Osteoblasts form new bone and osteoclasts remove or re-absorb bone.

There are two major types of bone:

Compact or cortical bone which forms the outer shell and is 5% to 30% porous.
Cancellous or trabecular bone that forms the inner part of the bone and is 30% to 90% porous.

Some bones have the inner trabecular bone replaced by a medullary cavity or an air space.
When an individual grows and matures, their bone mass increases. Maximum bone mass is attained between age 25 and 30. Beyond age 30, especially in women, bones can weaken and become more susceptible to fractures. Drugs and diseases can cause weakening and susceptibility to fractures. By age 40, most individuals will start to lose bone mass.
Bone de-mineralization increases with age causing a decrease in cortical bone density and an increase in average bone porosity. This relates to an overall decrease in bone material strength after age 30.
Bone remodeling occurs throughout life. The average bone turnover rate is 10% per year. The entire skeleton is regenerated every 10 years.
It is estimated that from age 70 on, up to 25% of the bone's entire surface and volume may be occupied by re-absorption. The decline in bone mass that is associated with aging is a remodeling imbalance that results in excess re-absorption.
The mechanical properties of bone also decrease with age. The strain characteristics of the elderly decreases to approximately one half the amount of strain tolerated in the bones of younger adults.
The basic bone renewal process has osteoclasts re-absorbing bone in microscopic cavities and osteoblasts then reforming the bone surfaces to fill in the cavities.
The process of bone remodeling is dependent on several factors including: androgens, calcitonin, corticosteroids, estrogen, exercise, insulin, insulinlike growth factor, interleukins, parathyroid hormone, prostaglandins, thyroid hormone and vitamin D.
Bone loss is classified into three categories: osteopenia, osteoporosis, severe osteoporosis.
Two products of bone re-absorption - hydroxyproline and N-telopeptide - are found in the urine. Checking those levels with a urine test can be used estimate the extent of bone destruction.

BMD Measurement and Values

The accepted and more reliable test to determine the amount of bone re-absorbtion is the Bone Mineral Density (BMD) test. The hip or spine or thighbone or forearm is x-rayed using the DEXA technique. A baseline is established with the first test. Follow-up tests are done very two years after.
The theoretical peak BMD standard is the baseline and is measured as a T-score. A T-score is the number of standard deviations above or below the average BMD for a young person of the same sex and race. The T-score is considered along with A BMD between 2.5 std. deviations inclusive above the average and -1.0 std. deviations inclusive below the average is classed as normal.
A BMD between 1 and 2.5 std. deviations inclusive below peak value is classed as osteopenia. People with bones that appear to have decreased mineral content on an ordinary x-ray have osteopenia.
A BMD at or below 2.5 std. deviations below the peak value is classed as osteoporosis.
A clinical fracture is the major indication of severe osteoporosis.
Doctors can identify osteoporosis 10 to 20 years before clinically identifiable fractures occur. This has given the primary care doctor a potentially leading role in the prevention and treatment of osteoporosis. The primary care doctor can encourage the person to make lifestyle changes and can provide other medical interventions early on, before there is irreversible bone loss or before clinically identifiable fractures occur.

Risk Factors

The following factors can increase the risk of developing osteoporosis:

Advanced age
Female sex
Being white or of Asian origin
Thin build
Premature menopause
Family history of osteoporosis
Low dietary intake of calcium
Smoking
Heavy alcohol intake
Endocrine problems which can include gonad failure, hyperthyroidism and hyperparathyroidism
Corticosteroid use.

Exercise Health Benefits

Osteoporosis can be prevented or slowed down or even reversed through a program that combines nutrition, medication and exercise. However, the exercise portion of the program must be done continuously. The body will lose the exercise benefits. BMD will start dropping when the exercise is stopped.
Weight-bearing activity can reduce bone loss and improve bone strength. People who exercise regularly or who are physically active have greater muscle bulk, strength and balance. They are less likely to fall, resulting in a decreased number of fractures of the hip, the proximal femur and the arms and the wrists.
Systemic study analyses have found a benefit of physical activity, particularly impact exercise, for the spine. BMD at the hip may also benefit from impact exercise but the effect of non-impact exercises on hip BMD remains unproven.
Exercise affects different parts of the skeleton differently, according to the pattern of stress produced.
Non weight-bearing activities can be useful in improving cardiopulmonary fitness and strength but are less helpful in maximizing the benefit to bone.
People with osteoporosis with established fractures who take physiotherapy and do strengthening exercises will improve their muscle strength and reduce the pain associated with fractures.

Types of Exercise

Impact exercises or activities are most effective in maintaining or increasing BMD.
Aerobic activities - Weight-bearing exercises include brisk walking, dancing, climbing stairs and performing a low-impact exercise program. Using small ankle or wrist weights can further improve BMD in weight bearing exercise programs. The activities should be done for about 1 hour, 3 to 5 times a week. Intensity should fall within 40% to 70% of the HR max adjusted for age. Walking can be done with weighted vests or weight belts.
Balancing exercises - Tai Chi can be used to maintain and improve balance. Heel-to-toe walking and balancing can help to maintain and improve balance.
Strength exercises - weight training or strength conditioning exercises can improve strength, which can improve the body's ability to maintain balance. Intensity should be high relative to the person's capacity with an ideal intensity of at least75% of 1 repetition maximum. Strength training should be done twice a week for 20 to 40 minutes.
Spinal BMD is correlated with spine extensor strength. Exercise for the spine muscles is important. High impact activities such as walking with weight belts, jogging and climbing stairs can increase spinal BMD. See Safety Issues section for limits.
Daily Activity - Maintaining and increasing daily activities is encouraged.
Bone adaptation is site specific to the limbs used. Exercises should target both the upper and the lower body - especially the extensor muscles.
The pectoral muscles should be targeted for range of motion activities.
People with severe osteopenia, multiple vertebral fractures or back pain may not be able to do impact exercise. Swimming, walking in water, water aerobics programs or chair exercises can improve muscular strength and balance.

Safety Issues

Fear of falling often leads to long-term inactivity. This inactivity can increase the risk of coronary heart disease. ECG monitoring for ischemic or damaged heart muscle response to exercise is recommended.
Exercises and activities have to be modified to accommodate orthopedic limitations due to fractures or spinal kyphosis.
Exercise facilities should have handrails for exercises done while standing. Facility staff should closely monitor balancing exercises to prevent falling and unintended injuries.
People with severe osteoporosis must be cautioned to avoid active forward flexion of the thoraco-lumbar spine or bending forward from the waist up. Forward bending can result in anterior wedging or crushing the front parts of the of the spine's vertebrae.
People with severe osteoporosis are advised to bend or flex at the hips and knees rather than bending forward to pick up objects from the floor.
Extreme over-activity, by affecting hormone levels, especially in pre-menopausal women, and perhaps because of associated under-nutrition, can be detrimental to the skeleton.

Related News or Promising New Research

Strontium Drug Reduces Fractures

Women suffering with osteoporosis have a potential new tool to combat this insidious disease.

A drug, strontium ranelate, appears to stimulate bone renewal and it appears to slow the natural process of bone destruction that is associated with osteoporosis. In osteoporosis,bone destruction occurs faster than bone renewal. Ultimately that weakens bones which then fracture under everyday activity.

"The Effects of Strontium Ranelate on the Risk of Vertebral Fracture in Women with Postmenopausal Osteoporosis" published in the January 29, 2004 issue of The New England Journal of Medicine studied 1649 postmenopausal women with osteoporosis and at least one vertebral fracture for three years. All of the women were given Calcium and vitamin D supplements before and during the study. Some of the women were given strontium ranelate and some of the women were given a placebo.

Lead researcher, Pierre Meunier, M.D. observed that the women who took strontium ralelate had a 49% lower risk of fractures in year one and a 41% lower risk of fraqctures in year two of the study. Bone density in the lumbar spine increased by 14.4%, by 8.3% at the femoral neck, and by 9.8% at the total hip area at the end of the third year.

This study was sponsored by the privately owned drug company Servier Laboratories Ltd.

The entire article is found at
New England Journal of Medicine

Hibernating Bears do not Lose Bone Density

Researchers analyzed blood samples from black bears hibernating in Virginia and found that the bears did not experience profound bone loss while they were hibernating. In humans, bone regeneration slows or stops during prolonged periods of inactivity brought on by disease or osteoporosis or injury. The researchers want to determine why bears continue to regenerate bone and they want to look for ways to stimulate that process in humans.

This study appears in the March 2003 issue of the journal Clinical Orthopedics and Related Research and was done by Henry J. Donahue, a professor of orthopedics and rehabilitation at Penn State University College of Medicine in Hershey, and Seth Donahue, assistant professor of biomedical engineering at Michigan Technological University. Seth Donahue said the study did not determine exactly why bears continue to regenerate bone. But he suspects a hormone or other chemical might be responsible and they hope to do follow-up studies to test that hypothesis.

"If we can identify what that molecule is in bears that makes them resistant to osteoporosis, then perhaps that could somehow be used to prevent the onset of osteoporosis in humans," Seth Donahue said.

Osteoporosis affects around 10 million Americans, 80% of them women. Brittle bones can lead to fractures and hunched backs.

Calcium and Vitamin D Help Reduce Hip Fractures

A 1992 European study published in the New England Journal of Medicine Vol. 327 No. 3 that considered levels of calcium and vitamin D in elderly nursing-home patients found that providing calcium citrate as 1200 mg of calcium and 800 IUs of vitamin D daily resulted in a reduction in hip fractures of up to 50%.

References

http://www.tpta.org/Osteo/definition.htm texas physiotherapist association website.

Dr. Jacques P. Brown, Dr. Robert G. Josse. 2002. "Clinical Practice Guidelines for the Diagnosis and Management of Osteoporosis in Canada". Canadian Medical Association Journal. November 12, 2002; 167 (10 supplement).

Durstin, J. Larry. editor. ASCM's Exercise Management for Persons with Chronic Diseases and Disabilities. Champaign, Illinois: Human Kinetics. 1997.

Timothy J. Maher, Ph.D. Sawyer Professor of Pharmaceutical Sciences Professor of Pharmacology Osteoporosis and Calcium. Massachusetts College of Pharmacy and Health Sciences. December 2000.

Shankar, Kamala. Exercise Prescription. Philadelphia, PA: Hanley & Belfus Inc. 1998.

Dr. John Wade, "Clinical basics Rheumatology: 15. Osteoporosis". Canadian Medical Association Journal. 2001. 165-1 pp. 45-50. Series Editor - Dr. John M. Esdaile, Professor and Head, Division of Rheumatology, University of British Columbia, and Scientific Director, Arthritis Research Centre of Canada, Vancouver BC.