ILibrary: Osteoporosis

Osteoporosis

02:15 | Posted by Sidharth |

Osteoporosis is where the amount of bone tissue in the body is below what is normal for a person, taking into account their sex and age.

Put simply, osteoporosis causes weaker bones, increasing the likelihood of a fracture.

Osteoporosis on its own does not cause symptoms. Unless it's caused a bone fracture, it’s not a painful condition, nor is it a type of arthritis.

Understanding bone structure

Bone has a complex structure that achieves the maximum amount of strength for the least amount of weight.

It can increase its thickness in areas subjected to repeated heavy loads, repair itself when broken and is the site of manufacture of most of the components of blood (the bone marrow).

If you take a typical bone, such as the femur (upper leg bone), and cut it across – you will see there's an outer shell of hard bone. In the middle space it has a honeycomb structure, through which is mingled the bone marrow.

Bone is made up mostly of collagen fibres, upon which are laid down crystals made from calcium and phosphate that give bone its ability to withstand compression and bending forces.

Cells that repair and dissolve bone

If you looked at bone under a microscope, you'd see two types of specialised cells scattered throughout:

cells that continually make new bone, called osteoblasts
cells that continuously dissolve bone into its component materials, calledosteoclasts.

Bone is therefore not a static tissue, but is always on the go. The actions of bone manufacture and disassembly are usually exactly balanced.

How bone repairs itself

When increased loads are repeatedly put upon a bone, the osteoblasts become more active, laying down more bone and increasing the strength of the region.

When a bone fractures, osteoblasts go into overdrive around the fracture site, laying down more collagen fibres and minerals on top to strengthen them.

How does osteoporosis affect bone?

In osteoporosis, the osteoclasts – usually over years – dissolve a bit more bone than is replaced, resulting in weaker bones.

Fractures in bone affected by osteoporosis are most likely in areas where there is a greater percentage of the honeycomb type of bone, which is less able to take the shock of a fall:

in the wrist
in the femur close to the hip joint (called the ‘neck’ of the femur)
in the vertebrae of the lower spine.

Hip and wrist fractures usually result from falls, whereas fractures of the spine tend to occur spontaneously when a weakened vertebra eventually crumples under the stress of supporting the body's weight.

The scale of the problem

One in three women and 1 in 12 men over the age of 50 will suffer a fracture of the hip, wrist or spine as a result of osteoporosis.

In total, osteoporosis causes 310,000 fractures in the UK every year. The estimated cost of treating these fractures is an enormous £1.7 billion each year.

But the cost to the individual can be higher.

Bone fractures can cause considerable pain and disability.
Fifty per cent of people who suffer a fractured hip lose the ability to live independently.
Around 20 per cent of people who fracture a hip die within a year, as a result of their fracture.

Detecting osteoporosis

The majority of people who suffer a fracture from osteoporosis are not known to have the condition prior to breaking their bone.

Osteoporosis is an under-recognised condition, which is partly because an organised approach to detecting it has not yet been developed in the UK. As a result, people at high risk of getting a fracture are not offered appropriate advice or treatment to reduce their risk.

Many people who have had a fracture due to osteoporosis do not receive follow-up treatment that helps reduce the chance of their getting another one.

There are wide variations throughout the UK in the quality and quantity of effort put into detecting and treating osteoporosis.

There are further divisions in the quality of care delivered to people from different social groups. In a recent study in Glasgow, people from the most deprived areas were eight times less likely to be referred for tests to detect osteoporosis than those from affluent areas.

The government has recognised the deficiencies that exist in osteoporosis management nationally. More funding is slowly coming through to expand the services, to be used for bone scanning machines to help diagnosis as well as specialists in osteoporosis.

What's classified as 'abnormally weak'?

It is normal for bone to get a bit weaker each year after the age of about 30, when our bones are at their maximum strength. Men tend to have greater bone mass than women of the same age.

For a few years after the menopause, women experience an increased rate of bone loss. This is secondary to the drop in oestrogen that is part of the hormone change of menopause – oestrogen has a protective effect upon bone strength.

Defining when bones are abnormally weak has to take account of what is normal for the two sexes and the different age groups.

Modern bone scanning devices can measure the density of bones and have allowed doctors to set a range for normal bone strength. Osteoporosis can therefore be diagnosed if a person’s bone density measurement is significantly low compared to these standards.

Low impact fractures

A person is also deemed to have osteoporosis if they have suffered a fracture too easily, ie a ‘low impact’ or ‘osteoporotic’ fracture.

A low trauma fracture is:

one that occurs from a fall from standing height or less
a fracture of the hip, wrist or forearm.

It's more difficult to categorise spinal fractures because they occur out of the blue and are not related to falls – sometimes they are not even accompanied by much pain.

However, the sudden onset of back pain should suggest there has been a collapsed vertebra, possibly due to osteoporosis.

Identifying people who have osteoporosis after they have suffered a fracture allows efforts at prevention to be concentrated on them. This can reduce the chance of them suffering another fracture later.

Causes of osteoporosis

Various factors are known to increase the rate at which bone loss occurs.

These can be divided into three groups:

factors you can do nothing about
things you can change
causes related to other medical conditions or drug therapy.

Listed below are the main conditions that can lead to osteoporosis.

Unchangeable causes of increased bone loss

Increasing age.
Family history of osteoporosis.
Being female.
Following menopause.
Being thin (see below).

Changeable causes of increased bone loss

Inactivity.
Poor diet (low in calcium).
Smoking.
Increased alcohol intake.

Medically related causes of increased bone loss

Steroid drug treatment, particularly if prolonged more than a few weeks.
Early menopause or the removal of the ovaries at a young age (under 45 years).
Hormone abnormalities, such as over-activity of the thyroid gland or the glands that produce the body's natural steroids, or under-production of testosterone in men.
Chronic liver or kidney disease.
Vitamin D deficiency.

Diagnosing osteoporosis

The best test to diagnose osteoporosis is a scan to determine the density of the bones.

Usually the same reference point in the skeleton is chosen, which allows better comparison between different people. The hip, forearm, heel bone or spine are all used, but exactly which varies according to local procedure.

DEXA scan

There are several ways in which a bone scan can be done, but the best is the‘DEXA’ scan. DEXA is short for dual-energy X-ray absorptiometry.

As the name implies, a DEXA scan uses X-rays to determine the density of bone.

Ultrasound

Ultrasound of the heel bone is another common technique for determining bone density. It uses cheaper equipment, but it's not yet clear if it is as accurate or reliable as DEXA scanning.

X-rays

Ordinary X-rays are not reliable as a tool for diagnosing osteoporosis. It can be possible to suspect from a standard X-ray that the person has less bone mass than normal, because the bone outline on the film might appear fainter.

However, the same appearance will show if the exposure of the film is slightly too high. Conversely, if the film is slightly underexposed, the bones will look normally dense.

As much as 30 per cent of bone mass needs to be lost before it shows up on ordinary X-rays.

Who can have a DEXA scan?

There are not enough DEXA scanners in the UK to make the test freely available, so some form of vetting procedure is used to ensure that those most at need are being scanned.

The details of these criteria vary across the UK, but could look like the list below, in which the presence of any one factor would justify a DEXA scan.

A woman over 50 who has had a low trauma fracture.
Anyone taking an oral steroid, eg prednisolone 5mg daily, or greater, for three months or more.
A woman under 45 who has had an early menopause or removal of the ovaries.
A man with a high alcohol consumption of more than 50 units of alcohol weekly.
A woman who is around the menopause with any two of the following:
- a body mass index (BMI) less than 21
- a history in her mother of a hip fracture below 80 years of age
- who smokes
- who drinks more than 35 units of alcohol weekly (see below).

Thinness

People who are unusually thin are more likely to develop osteoporosis, and the way to define ‘thinness’ is to measure your body mass index (BMI).

People with a BMI of 21 or less have a higher rate of bone loss than those who are heavier, and obese people have lower rates of bone loss than those who are ideal weight.

It is not known if a thin person who deliberately puts on a lot of weight will reduce their subsequent fracture risk.

Obesity, of course, carries with it many other health hazards.

Alcohol

Historically, the recommended maximum consumption of alcohol per week has been 21 units for women and 28 units for men.

High levels of alcohol intake (over 50 units per week in men or 35 units in women) are associated with osteoporosis, as well as the other serious health risks that accompany alcoholism.

It is possible that lower levels of alcohol consumption than this could still damage bone and be associated with problems such as raised blood pressure or diabetes.

Many experts therefore now recommend lower safe limits of alcohol consumption of 21 units weekly for men and 14 units weekly for women.

Prevention and treatment

There are some general measures that people can take to prevent and treat osteoporosis including changing their diet and modifying their lifestyle and attitude to exercise, as well as taking supplements or treatment prescribed by a doctor.

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