Medicine – Osteoporosis

Osteoporosis is a systemic skeletal disorder characterised by reduced bone strength, resulting in increased susceptibility to fragility fractures. Bone strength depends on both the amount of bone present and the quality of its internal structure.

The key pathological features are:

Reduced bone mass and bone mineral density.

Deterioration of bone microarchitecture.

Increased bone fragility and fracture risk.

Importantly, the bone that remains is generally normally mineralised. This distinguishes osteoporosis from osteomalacia, in which there is defective mineralisation of osteoid.

1. Normal Bone Remodelling

Bone is continuously renewed through a process of:

Bone resorption by osteoclasts

followed by:

Bone formation by osteoblasts.

In healthy adults, these processes are normally balanced sufficiently to maintain skeletal strength.

When bone resorption chronically exceeds bone formation:

Progressive bone loss occurs.

↓

Trabeculae become thinner and disconnected.

↓

Cortical bone becomes thinner and more porous.

↓

Bone strength decreases.

↓

Fragility fractures become more likely.

2. Reduced Bone Mass and Density

Osteoporosis causes a reduction in the quantity of bone.

This can be detected clinically by measuring:

Bone mineral density – BMD.

However, osteoporosis is not simply “low calcium in the bones.” It involves loss of the structural framework of bone itself.

Therefore routine serum:

Calcium, phosphate and ALP are usually normal.

3. Abnormal Bone Microarchitecture

The second major feature is deterioration of the microscopic architecture of bone.

In trabecular bone:

Trabeculae become thinner and may disappear or lose connectivity.

In cortical bone:

Cortical thickness decreases and porosity increases.

The result is a skeleton that is mechanically weaker even before a fracture occurs.

4. Primary Osteoporosis

Primary osteoporosis develops without another specific disease being primarily responsible.

Traditional teaching divides it into:

Type I – postmenopausal osteoporosis.

Type II – age-related or senile osteoporosis.

This classification remains useful for understanding the mechanisms, although modern clinical practice often discusses postmenopausal and age-related osteoporosis without rigidly separating them into Type I and Type II.

5. Type I – Postmenopausal Osteoporosis

Type I osteoporosis occurs predominantly following:

Menopause.

The major mechanism is:

Oestrogen deficiency.

Oestrogen normally helps restrain osteoclast-mediated bone resorption.

After menopause:

↓ Oestrogen

↓

↑ Osteoclast activity and bone turnover

↓

Bone resorption exceeds formation

↓

Accelerated bone loss.

6. Trabecular Bone in Postmenopausal Osteoporosis

Postmenopausal bone loss particularly affects:

Trabecular bone.

Trabecular bone is abundant in:

Vertebral bodies

and at several other fracture-prone skeletal sites.

Therefore postmenopausal osteoporosis is strongly associated with:

Vertebral compression fractures.

It also contributes to other fragility fractures, including hip and distal radius fractures.

7. Type II – Age-Related Osteoporosis

Type II osteoporosis occurs with:

Advancing age.

The mechanism is multifactorial and is not simply a reduction in osteoblast activity.

Ageing is associated with:

Reduced bone formation.

Altered bone remodelling.

Hormonal changes.

Reduced physical activity.

Reduced calcium and vitamin D availability in some individuals.

Loss of muscle mass and increased fall risk.

Both:

Cortical

and

Trabecular bone

are affected.

8. Fragility Fractures

The major clinical consequence of osteoporosis is:

Fragility fracture.

This means a fracture occurring after trauma that would not normally be expected to fracture healthy bone, classically:

A fall from standing height or less.

Common sites include:

Hip – proximal femur.

Vertebrae.

Distal radius – Colles-type fracture.

Proximal humerus.

9. Vertebral Compression Fractures

Vertebral fractures may occur with:

Minimal trauma

or even without a clearly remembered injury.

They can cause:

Back pain.

Loss of height.

Thoracic kyphosis.

Multiple vertebral compression fractures may progressively produce a:

Stooped posture.

However, many vertebral fractures are initially clinically silent.

10. Secondary Osteoporosis

Secondary osteoporosis occurs because another disease, medication or environmental factor accelerates bone loss.

The original notes appropriately group the causes into:

Endocrine disorders.

Malignancy.

Gastrointestinal and nutritional disease.

Inflammatory disease.

Drugs.

Lifestyle and immobilisation.

11. Premature Menopause

The original notes correctly identify:

Premature menopause

as a major risk factor.

Earlier loss of ovarian oestrogen means a longer lifetime period of:

Oestrogen deficiency.

Therefore bone resorption increases earlier than expected.

Other causes of premature ovarian insufficiency can similarly increase osteoporosis risk.

12. Hypogonadism

Hypogonadism can cause osteoporosis in both:

Women

and

Men.

Reduced sex hormones increase bone turnover and reduce maintenance of skeletal mass.

Therefore:

↓ Oestrogen or testosterone → ↑ bone loss → osteoporosis.

This is why prolonged hypogonadism is an important secondary cause in younger patients.

13. Anorexia Nervosa

The original notes correctly include:

Anorexia nervosa.

Several mechanisms may contribute:

Low body weight.

Reduced sex hormones.

Nutritional deficiencies.

Reduced IGF-1 and other endocrine alterations.

The resulting reduction in bone formation and increase in skeletal fragility can produce markedly reduced BMD, particularly when the illness occurs during the years of normal peak bone-mass acquisition.

14. Cushing Syndrome

Excess glucocorticoid activity in:

Cushing syndrome

is an important cause of secondary osteoporosis.

Glucocorticoids reduce:

Osteoblast function and bone formation.

They can also alter calcium balance, muscle strength and gonadal function.

Therefore chronic glucocorticoid excess can produce substantial:

Bone loss and fracture risk.

15. Hyperparathyroidism

The original notes correctly include:

Hyperparathyroidism.

Excess PTH increases bone turnover and can promote:

Cortical bone loss.

Primary hyperparathyroidism is particularly suggested when osteoporosis is accompanied by:

Hypercalcaemia + inappropriately elevated PTH.

This differs from uncomplicated osteoporosis, where calcium and PTH are generally normal.

16. Hyperthyroidism

Excess thyroid hormone accelerates:

Bone turnover.

Although both formation and resorption increase, resorption can predominate, producing:

Net bone loss.

Therefore untreated or prolonged:

Hyperthyroidism

increases osteoporosis and fracture risk.

Excessive thyroid-hormone replacement causing persistent TSH suppression may also contribute in susceptible patients.

17. Multiple Myeloma

The original notes include:

Multiple myeloma.

Myeloma causes bone disease primarily through abnormal plasma-cell activity and increased osteoclast activation, producing:

Osteolytic lesions and pathological fractures.

It can therefore mimic or coexist with osteoporosis.

A patient with apparent osteoporosis plus features such as:

Anaemia, renal impairment, hypercalcaemia, unexplained bone pain or monoclonal protein

requires evaluation for myeloma rather than assuming uncomplicated primary osteoporosis.

18. Leukaemia and Other Malignancies

Certain haematological malignancies, including:

Leukaemia

and other malignant disorders, can adversely affect skeletal health through the disease itself, nutritional effects, hormonal disturbance or treatments such as:

Glucocorticoids and chemotherapy.

However, myeloma has a particularly important direct relationship with pathological bone loss.

19. Malabsorption Syndromes

The original notes correctly identify:

Malabsorption

as a cause.

Conditions such as:

Coeliac disease

can reduce absorption of:

Calcium and vitamin D.

This may lead to reduced BMD.

Depending on the severity and mechanism, patients may develop:

Osteoporosis, osteomalacia, or a combination of skeletal abnormalities.

Therefore abnormal calcium, phosphate, ALP or vitamin D results should raise the possibility of accompanying metabolic bone disease rather than simple osteoporosis alone.

20. Chronic Liver Disease

The original notes correctly include:

Chronic liver disease.

Chronic liver disorders can contribute to metabolic bone disease through multiple mechanisms, including:

Malnutrition.

Reduced physical activity.

Hormonal abnormalities.

Vitamin D disturbances.

Chronic inflammation.

The term hepatic osteodystrophy may be used for skeletal disease associated with chronic liver disease.

21. Inflammatory Bowel Disease

The original notes correctly identify:

Inflammatory bowel disease – IBD.

Osteoporosis risk can increase because of:

Chronic inflammation.

Malabsorption.

Low body weight.

Vitamin D deficiency.

Glucocorticoid treatment.

Therefore several mechanisms may operate simultaneously.

22. Rheumatoid Arthritis

The original notes correctly include:

Rheumatoid arthritis – RA.

Chronic systemic inflammation can promote bone loss.

Additional contributors include:

Reduced mobility.

Low body weight in some patients.

Glucocorticoid exposure.

Therefore osteoporosis is an important comorbidity in patients with chronic inflammatory disease.

23. Glucocorticoids

The most important medication-related cause in the original notes is:

Glucocorticoid therapy.

Long-term systemic glucocorticoids such as:

Prednisolone

can rapidly increase fracture risk.

Their effects include:

Reduced osteoblast activity.

Reduced bone formation.

Increased osteoblast/osteocyte apoptosis.

Reduced intestinal calcium absorption.

Increased renal calcium loss.

Muscle weakness and increased fall risk.

Therefore:

CHRONIC GLUCOCORTICOID USE → MAJOR SECONDARY OSTEOPOROSIS RISK.

24. Heparin

Prolonged exposure to:

Unfractionated heparin

can contribute to bone loss and osteoporosis.

This is mainly relevant with:

Long-term therapy.

The skeletal effect is less prominent with low-molecular-weight heparins, although prolonged exposure still requires appropriate clinical consideration.

25. Other Important Drug Causes

Modern secondary osteoporosis assessment also considers medications such as:

Aromatase inhibitors.

Androgen-deprivation therapy.

Some antiseizure medications.

Excess thyroid hormone replacement.

The patient’s complete medication history is therefore important when investigating unexpectedly low BMD or fragility fractures.

26. Immobilisation

The original notes correctly identify:

Immobilisation.

Mechanical loading is an important stimulus for maintaining bone.

Prolonged inactivity causes:

Reduced bone formation

and increased resorption.

Therefore prolonged:

Bed rest.

Paralysis.

Severe mobility restriction.

can accelerate bone loss.

27. Smoking

The original notes correctly include:

Smoking.

Smoking is associated with lower bone density and increased fracture risk through several mechanisms, including adverse effects on:

Bone cells, sex hormones and overall skeletal health.

Smoking cessation is therefore part of osteoporosis prevention and management.

28. Alcohol

The original notes include:

Alcoholism, better described clinically as chronic excessive alcohol intake.

Excessive alcohol can contribute through:

Poor nutrition.

Direct adverse effects on bone formation.

Hormonal abnormalities.

Liver disease.

Increased falls.

Moderating excessive alcohol intake is therefore an important preventive measure.

29. Other Important Risk Factors

Several important osteoporosis risk factors deserve addition to the original list.

These include:

Increasing age.

Previous fragility fracture.

Parental history of hip fracture.

Low body mass index.

Low physical activity.

Long-term glucocorticoid exposure.

Hypogonadism.

Smoking.

Excess alcohol.

Conditions associated with falls.

A previous fragility fracture is particularly important because it predicts a substantially increased risk of:

Future fractures.

30. Diagnosis

The diagnosis is based on:

Clinical fracture history

and/or

Bone mineral density assessment, depending on the circumstances.

The standard test for measuring BMD is:

Dual-energy X-ray absorptiometry – DXA or DEXA.

The usual sites assessed are:

Lumbar spine

and

Hip.

31. T-Score

The T-score compares the patient’s BMD with the mean BMD of a healthy young adult reference population.

In the appropriate population, the traditional diagnostic categories are:

Normal: T-score ≥ −1.0

Low bone mass/osteopenia: T-score between −1.0 and −2.5

Osteoporosis: T-score ≤ −2.5

A fragility fracture can also establish clinically important osteoporosis/high fracture risk even when the DXA value is not below −2.5, depending on the fracture and clinical context.

32. Z-Score

The:

Z-score

compares BMD with people of similar:

Age and sex.

It is particularly useful when evaluating younger individuals, where unexpectedly low BMD may suggest:

Secondary causes.

A markedly low Z-score should prompt careful investigation for underlying disease.

33. Blood Tests in Osteoporosis

The original notes correctly state:

Calcium = normal.

Phosphate = normal.

ALP = normal.

This is the classic pattern for:

Uncomplicated primary osteoporosis.

PTH is also generally:

Normal.

34. Why Blood Tests Are Normal

Osteoporosis represents:

Loss of normally mineralised bone.

It is not primarily caused by defective mineralisation.

Therefore serum mineral concentrations generally remain normal.

This gives an extremely useful distinction:

OSTEOPOROSIS → NORMAL Ca²⁺, PO₄³⁻ AND ALP.

35. Investigating Secondary Causes

Laboratory investigations are useful not because they directly diagnose primary osteoporosis, but because they may reveal:

Secondary causes.

Depending on the patient, investigations may include:

Calcium and phosphate.

ALP.

Renal function.

Liver tests.

25-hydroxyvitamin D.

Thyroid function.

Full blood count.

Further testing for PTH, coeliac disease, myeloma, hypogonadism or other conditions depends on the clinical picture.

36. Osteoporosis Versus Osteomalacia

This distinction is extremely important.

OSTEOPOROSIS:

The amount of bone is reduced.

The remaining bone is:

Normally mineralised.

Typical laboratory pattern:

Ca²⁺ normal.

PO₄³⁻ normal.

ALP normal.

OSTEOMALACIA:

There is:

Defective mineralisation of osteoid.

In typical vitamin D deficiency:

Ca²⁺ low or low-normal.

PO₄³⁻ low.

ALP high.

PTH high.

Therefore:

NORMAL BONE BIOCHEMISTRY → THINK OSTEOPOROSIS.

HIGH ALP + LOW PHOSPHATE → THINK OSTEOMALACIA, in the appropriate context.

37. Fracture-Risk Assessment

BMD is only one component of fracture risk.

Clinical tools such as:

FRAX

can estimate fracture probability using factors such as age, previous fracture, smoking, glucocorticoids and other clinical risks, with or without femoral-neck BMD.

Treatment decisions therefore depend on:

Overall fracture risk, not simply one DXA number.

38. Treatment – General Principles

The goals of treatment are to:

Prevent fractures.

Maintain or increase bone strength.

Treat secondary causes.

Reduce fall risk.

Maintain adequate calcium and vitamin D status.

Medication choice depends on fracture risk, previous fractures, renal function, age, sex, contraindications and other clinical factors.

39. Treat the Underlying Cause

In secondary osteoporosis, treatment should address the underlying disorder whenever possible.

Examples include:

Treat hyperthyroidism.

Correct hypogonadism where appropriate.

Treat malabsorption.

Correct vitamin D deficiency.

Minimise unnecessary systemic glucocorticoid exposure.

Address excessive alcohol and smoking.

40. Calcium and Vitamin D

The original notes correctly include:

Calcium and vitamin D.

Adequate calcium intake and vitamin D status are important components of bone health.

However, supplementation alone is generally not sufficient treatment for a patient at high fracture risk.

Dietary calcium is usually preferred where adequate, with supplementation used when required.

41. Exercise and Falls Prevention

Regular:

Weight-bearing exercise

and

Resistance exercise

help maintain musculoskeletal function.

Falls prevention is also extremely important, particularly in older adults.

Measures may include addressing:

Muscle weakness.

Poor balance.

Visual impairment.

Sedating medications.

Environmental fall hazards.

Preventing the fall may prevent the fracture.

42. Bisphosphonates

The original notes correctly identify:

Bisphosphonates

as a major treatment.

Examples include:

Alendronate.

Risedronate.

Zoledronic acid.

Bisphosphonates bind to bone mineral and inhibit:

Osteoclast-mediated bone resorption.

Therefore:

↓ Osteoclast activity → ↓ bone loss → ↓ fracture risk.

They remain major first-line therapies for many patients.

43. Oral Bisphosphonate Administration

Oral bisphosphonates have specific administration requirements because absorption is poor and they can irritate the oesophagus.

They are generally taken:

On an empty stomach with plain water

and the patient remains:

Upright afterward.

Exact administration instructions depend on the preparation.

44. Important Bisphosphonate Adverse Effects

Potential adverse effects include:

Upper gastrointestinal irritation with oral preparations.

Acute-phase symptoms after some IV doses.

Rare but important long-term complications include:

Osteonecrosis of the jaw

and

Atypical femoral fractures.

These are uncommon, and treatment decisions balance these risks against the patient’s fracture risk.

Renal function is also relevant when selecting therapy.

45. Denosumab

An important modern treatment absent from the original list is:

Denosumab.

Denosumab is a monoclonal antibody against:

RANKL.

This suppresses osteoclast formation and activity, reducing:

Bone resorption.

It is an effective antiresorptive treatment in appropriately selected patients.

46. Important Point About Denosumab

Denosumab should not simply be stopped or substantially delayed without an appropriate management plan.

Stopping it can cause:

Rapid rebound bone turnover

and an increased risk of:

Multiple vertebral fractures.

Therefore another antiresorptive treatment is often required when denosumab is discontinued.

47. Anabolic Therapy

Patients at particularly high fracture risk may be considered for bone-forming therapy.

Examples include:

Teriparatide, a PTH analogue,

and in appropriate settings:

Romosozumab, which inhibits sclerostin and has substantial bone-building effects.

These treatments are generally used in selected high-risk patients according to local guidelines and contraindications.

48. Calcitonin – Important Update

The original notes include:

Calcitonin.

Calcitonin inhibits osteoclastic bone resorption, but it is no longer a major routine long-term treatment for osteoporosis because more effective fracture-prevention therapies are available.

It may have limited roles in selected situations, including short-term management of pain associated with some:

Acute vertebral compression fractures.

Therefore it should not be prioritised alongside modern first-line osteoporosis therapies.

49. Strontium Ranelate – Important Update

The original notes include:

Strontium ranelate.

This is now a limited or obsolete choice in many settings and is not a standard first-line osteoporosis treatment.

Its use became restricted because of safety concerns, particularly:

Cardiovascular and thromboembolic risks.

For modern study purposes, it is much more important to know:

Bisphosphonates.

Denosumab.

Anabolic therapy such as teriparatide.

and selected use of:

Romosozumab.

50. Osteoporosis – Causes in Note Form

PRIMARY OSTEOPOROSIS

Postmenopausal:

Oestrogen deficiency.

Accelerated bone resorption.

Particularly important effect on trabecular bone.

Age-related:

Ageing.

Reduced bone formation.

Altered remodelling.

Both cortical and trabecular bone affected.

SECONDARY – ENDOCRINE:

Premature menopause.

Hypogonadism.

Anorexia nervosa.

Cushing syndrome.

Hyperparathyroidism.

Hyperthyroidism.

SECONDARY – MALIGNANCY/HAEMATOLOGICAL:

Multiple myeloma.

Leukaemia and selected other malignancies.

SECONDARY – GI/NUTRITIONAL:

Malabsorption.

Coeliac disease.

Chronic liver disease.

Vitamin D/calcium deficiency where relevant.

SECONDARY – INFLAMMATORY:

Inflammatory bowel disease.

Rheumatoid arthritis.

Other chronic inflammatory disease.

SECONDARY – DRUGS:

Long-term systemic glucocorticoids – particularly important.

Long-term unfractionated heparin.

Aromatase inhibitors.

Androgen-deprivation therapy.

Selected antiseizure medications.

SECONDARY – LIFESTYLE/MECHANICAL:

Prolonged immobilisation.

Smoking.

Excessive alcohol.

Low body weight.

Physical inactivity.

51. Diagnosis – Note Form

Bone mineral density:

Measured by:

DXA.

T-score ≤ −2.5:

Diagnostic of osteoporosis in the appropriate population.

Fragility fracture:

May establish clinically important osteoporosis/high fracture risk irrespective of whether the DXA reaches −2.5, depending on the clinical setting.

Serum calcium:

Normal.

Serum phosphate:

Normal.

ALP:

Normal.

PTH:

Usually:

Normal.

Abnormal biochemical results should prompt investigation for:

Secondary metabolic bone disease.

52. Treatment – Note Form

GENERAL:

Treat the underlying cause.

Adequate calcium and vitamin D.

Weight-bearing/resistance exercise.

Stop smoking.

Avoid excessive alcohol.

Falls prevention.

ANTIRESORPTIVE TREATMENT:

Bisphosphonates.

Denosumab in appropriate patients.

ANABOLIC/BONE-FORMING TREATMENT IN SELECTED HIGH-RISK PATIENTS:

Teriparatide.

Romosozumab where appropriate.

OLDER TREATMENTS:

Calcitonin – limited role, not routine long-term first-line therapy.

Strontium ranelate – now limited/not routinely used in many settings because of safety concerns.

53. Important Clarifications to the Original Notes

The traditional distinction between:

Type I postmenopausal

and

Type II age-related osteoporosis

is useful educationally, but osteoporosis in older adults is usually multifactorial and the two processes often overlap.

The statement:

“Type II = decreased osteoblastic activity”

is somewhat too simple. Age-related osteoporosis reflects multiple changes in:

Bone formation, resorption, hormonal physiology, nutrition, muscle function and physical activity.

The original diagnostic statement is correct:

Ca²⁺, phosphate and ALP are usually normal in uncomplicated osteoporosis.

This is one of the most useful distinctions from:

Osteomalacia.

The treatment list needs modernisation.

Bisphosphonates remain highly important, but modern treatment also includes:

Denosumab, teriparatide and romosozumab in selected patients.

Calcitonin is no longer routine long-term therapy, and strontium ranelate has a very limited role in modern practice.

Key Clinical Pattern

For rapid recall:

OSTEOPOROSIS = REDUCED QUANTITY AND QUALITY OF NORMALLY MINERALISED BONE.

Therefore:

Ca²⁺ = NORMAL

PO₄³⁻ = NORMAL

ALP = NORMAL

PTH = usually NORMAL.

POSTMENOPAUSAL OSTEOPOROSIS:

↓ OESTROGEN → ↑ BONE RESORPTION → particularly trabecular bone loss.

AGE-RELATED OSTEOPOROSIS:

Ageing → impaired bone maintenance/remodelling → cortical + trabecular bone loss.

Think secondary osteoporosis when there is:

GLUCOCORTICOID USE + HYPOGONADISM + HYPERTHYROIDISM + HYPERPARATHYROIDISM + MALABSORPTION + CHRONIC INFLAMMATORY DISEASE + IMMOBILISATION + SMOKING + EXCESS ALCOHOL.

The major clinical consequence is:

FRAGILITY FRACTURE, particularly involving the:

HIP + VERTEBRAE + DISTAL RADIUS.

And the high-yield distinction is:

OSTEOPOROSIS → NORMAL Ca/PO₄/ALP.

OSTEOMALACIA → DEFECTIVE MINERALISATION, typically ↑ ALP with ↓ phosphate in vitamin D deficiency.