Medicine – Osteomalacia and Rickets

Osteomalacia and rickets are metabolic bone disorders caused by defective mineralisation of newly formed osteoid. The fundamental abnormality is failure to adequately deposit calcium and phosphate crystals into the organic bone matrix.

The terminology depends mainly on whether the growth plates are still open:

Osteomalacia → defective mineralisation in adults after epiphyseal closure.

Rickets → defective mineralisation in children before epiphyseal closure, involving both bone and the growth plates.

The most important cause worldwide is vitamin D deficiency, although disorders of calcium, phosphate and renal tubular handling can produce the same fundamental defect.

1. Normal Bone Mineralisation

Osteoblasts first produce an organic bone matrix called:

Osteoid.

This matrix is subsequently mineralised predominantly with crystals containing:

Calcium + phosphate, mainly as hydroxyapatite.

Therefore normal bone formation requires adequate availability of:

Calcium.

Phosphate.

Vitamin D.

and normal renal, gastrointestinal and hormonal regulation of these minerals.

2. What Happens in Osteomalacia?

In osteomalacia, osteoblasts continue to produce:

Osteoid,

but the osteoid is inadequately mineralised.

Therefore:

Osteoid formation

↓

Insufficient Ca²⁺/PO₄³⁻ available for mineralisation

↓

Failure of normal hydroxyapatite deposition

↓

Accumulation of:

Unmineralised osteoid

↓

Soft, mechanically weak bone.

This causes:

Bone pain, muscle weakness, deformity and insufficiency fractures.

3. Osteomalacia Versus Osteoporosis

This distinction is extremely important.

In:

OSTEOMALACIA

there is:

Defective mineralisation of bone.

The bone is inadequately hardened.

In:

OSTEOPOROSIS

there is:

Reduced quantity of normally mineralised bone.

Therefore:

OSTEOMALACIA = poor mineralisation.

OSTEOPOROSIS = reduced bone mass.

Both can cause fractures, but their underlying pathology and biochemical patterns are different.

4. Rickets

Rickets is the childhood counterpart of osteomalacia.

Because children have open growth plates, defective mineralisation affects both:

Newly formed bone

and

Growth-plate cartilage.

This produces characteristic skeletal deformities that are generally not seen in adults with osteomalacia.

5. Major Causes

The original notes identify three major groups:

Vitamin D deficiency.

Abnormal calcium/mineral metabolism.

Proximal renal tubular disease.

A more complete modern classification includes disorders causing deficiency or impaired action of:

Vitamin D, calcium or phosphate.

6. Vitamin D Deficiency

The most important cause is:

Vitamin D deficiency.

Vitamin D is essential for maintaining adequate intestinal absorption of:

Calcium

and

Phosphate.

Therefore deficiency can prevent normal bone mineralisation.

7. Vitamin D Physiology

Vitamin D can be obtained through:

Skin synthesis after ultraviolet-B exposure

and from:

Dietary sources.

Vitamin D then undergoes two major activation steps.

First, in the:

Liver

it is converted to:

25-hydroxyvitamin D – 25(OH)D.

This is the major circulating form and the usual test used to assess:

Vitamin D status.

8. Renal Activation of Vitamin D

25-hydroxyvitamin D is subsequently converted in the:

Kidney

to:

1,25-dihydroxyvitamin D – calcitriol.

Calcitriol is the biologically active form.

It increases intestinal absorption of:

Calcium and phosphate.

Therefore adequate vitamin D activity provides the minerals required for normal skeletal mineralisation.

9. Causes of Vitamin D Deficiency

Vitamin D deficiency can result from:

Low sunlight exposure.

Poor dietary intake.

Malabsorption.

Chronic liver disease.

Certain medications that alter vitamin D metabolism.

Other factors may increase risk depending on lifestyle, age and underlying disease.

10. Malabsorption

Gastrointestinal disorders can impair absorption of:

Vitamin D

and sometimes:

Calcium.

Important examples include:

Coeliac disease.

Inflammatory bowel disease with significant malabsorption.

Pancreatic insufficiency.

Biliary disease.

Short-bowel states.

Some forms of bariatric surgery.

Therefore unexplained osteomalacia should prompt consideration of:

Malabsorption.

11. Vitamin D Deficiency and Calcium

When vitamin D is deficient:

↓ intestinal Ca²⁺ absorption

↓

Serum calcium tends to fall

↓

Parathyroid glands respond by increasing:

PTH.

This produces:

Secondary hyperparathyroidism.

12. Secondary Hyperparathyroidism

PTH attempts to maintain serum calcium.

It increases:

Renal calcium reabsorption

and promotes mechanisms that help preserve extracellular calcium.

However, PTH simultaneously reduces renal:

Phosphate reabsorption.

Therefore:

Vitamin D deficiency

↓

↓ Calcium absorption

↓

↑ PTH

↓

↑ Renal phosphate loss

↓

Hypophosphataemia

↓

Further impairment of bone mineralisation.

13. Why Calcium May Be Normal

The original biochemical table described calcium as:

Low.

This is possible, but calcium may also be:

Low-normal or even normal.

This occurs because secondary hyperparathyroidism helps maintain serum calcium despite inadequate vitamin D.

Therefore normal serum calcium does not exclude:

Vitamin D deficiency osteomalacia.

14. Typical Biochemical Pattern

In classical vitamin D deficiency osteomalacia:

Calcium: ↓ or low-normal

Phosphate: ↓

ALP: ↑

PTH: ↑

25-hydroxyvitamin D: ↓

This is the high-yield pattern.

15. Why ALP Is Raised

The original notes correctly emphasise:

↑ ALP.

In osteomalacia, osteoblasts remain active and attempt to produce and mineralise new bone.

The defective mineralisation leads to increased osteoblastic activity.

Therefore:

Bone alkaline phosphatase rises.

This makes elevated ALP an important clue to:

Osteomalacia/rickets.

16. Impaired Calcium Metabolism

The original phrase:

“Impaired calcium metabolism”

is broad.

Any disorder producing persistent inadequate availability of calcium for bone mineralisation can contribute.

Examples include:

Low calcium intake.

Calcium malabsorption.

Vitamin D deficiency or resistance.

However, phosphate availability is equally important, and several forms of osteomalacia are fundamentally:

Phosphate-wasting disorders.

17. Hypophosphataemia

Phosphate is essential for formation of:

Hydroxyapatite.

Therefore chronic severe:

Hypophosphataemia

can directly impair bone mineralisation.

This may occur because of:

Renal phosphate wasting

or other disorders of phosphate metabolism.

Therefore:

CHRONIC LOW PHOSPHATE → DEFECTIVE MINERALISATION → OSTEOMALACIA/RICKETS.

18. Proximal Renal Tubular Disease

The original notes correctly identify:

Proximal renal tubular disease.

The proximal tubule normally reabsorbs a large proportion of filtered:

Phosphate.

When proximal tubular function is impaired:

Phosphate is lost in urine.

This can produce:

Hypophosphataemia

and ultimately:

Osteomalacia or rickets.

19. Fanconi Syndrome

A classic proximal tubular disorder is:

Fanconi syndrome.

In Fanconi syndrome there is generalised impairment of proximal tubular reabsorption.

Urinary losses can include:

Phosphate.

Glucose despite normal blood glucose.

Amino acids.

Bicarbonate.

Uric acid.

Therefore phosphate wasting can lead to:

Hypophosphataemic osteomalacia/rickets.

20. Proximal RTA

Proximal tubular dysfunction can also produce:

Type 2 renal tubular acidosis – proximal RTA.

Because bicarbonate reabsorption is impaired:

Bicarbonate is lost in urine.

When proximal RTA occurs as part of Fanconi syndrome, simultaneous phosphate wasting can contribute significantly to:

Bone disease.

21. Chronic Kidney Disease – Important Distinction

Advanced CKD can also produce abnormal bone mineralisation through:

Reduced calcitriol production.

Phosphate retention.

Secondary hyperparathyroidism.

This forms part of:

CKD–mineral and bone disorder – CKD-MBD.

However, its biochemical pattern differs from straightforward vitamin D deficiency because advanced CKD commonly produces:

High phosphate rather than low phosphate.

22. Hypophosphataemic Rickets

Some inherited disorders cause excessive renal phosphate loss.

These include forms of:

FGF23-mediated hypophosphataemic rickets.

The best-known inherited example is:

X-linked hypophosphataemia.

These patients develop persistent renal phosphate wasting despite low serum phosphate.

23. Tumour-Induced Osteomalacia

An important acquired phosphate-wasting disorder is:

Tumour-induced osteomalacia.

Certain usually small mesenchymal tumours produce excessive:

FGF23.

FGF23 causes:

Renal phosphate wasting

and reduces appropriate calcitriol activity.

Therefore:

↑ FGF23 → ↓ renal phosphate reabsorption → hypophosphataemia → osteomalacia.

24. Clinical Features

The original notes correctly identify:

Pain.

Deformity.

Fractures.

Proximal myopathy.

These arise because inadequately mineralised bone cannot withstand normal mechanical stress.

25. Bone Pain

A common symptom is:

Diffuse bone pain or tenderness.

Pain may involve:

Hips.

Pelvis.

Lower back.

Ribs.

Legs.

It can sometimes be mistaken for musculoskeletal or rheumatological disease.

26. Proximal Muscle Weakness

The original notes correctly identify:

Proximal myopathy.

Patients may develop weakness of the:

Hip-girdle

and sometimes:

Shoulder-girdle muscles.

This can produce difficulty:

Rising from a chair.

Climbing stairs.

Walking normally.

27. Waddling Gait

Pelvic and proximal muscle weakness may produce a:

Waddling gait.

This is a useful clinical clue in significant osteomalacia.

The combination of:

Bone pain + proximal weakness + raised ALP

should strongly suggest a metabolic bone disorder such as osteomalacia.

28. Fractures

Poorly mineralised bone is mechanically weak.

Therefore patients may develop:

Insufficiency fractures.

These can occur after relatively minor mechanical stress.

Certain incomplete fractures associated with osteomalacia are called:

Looser zones

or

pseudofractures.

29. Looser Zones

Looser zones represent areas of incomplete mineralisation and stress-related structural failure.

They may appear radiographically as:

Transverse radiolucent lines

often with sclerotic margins.

They can occur in sites such as:

Femoral neck.

Pubic rami.

Ribs.

Scapula.

These are highly suggestive of:

Osteomalacia.

30. Bone Deformity

The original notes correctly include:

Deformity.

In adults, severe longstanding osteomalacia can cause skeletal deformity, but this is particularly striking in:

Rickets, because the growing skeleton is affected.

31. Clinical Features of Rickets

In children, defective growth-plate mineralisation can produce:

Bowing of the legs.

Knock knees.

Widened wrists and ankles.

Delayed growth.

Bone pain.

Muscle weakness.

32. Rachitic Rosary

Expansion of the costochondral junctions may produce palpable enlargements along the chest wall.

This is called:

Rachitic rosary.

It is a classic physical sign of:

Rickets.

33. Harrison Sulcus

Diaphragmatic traction on softened ribs may produce a horizontal depression of the lower chest wall known as:

Harrison sulcus.

This is another traditional clinical sign of significant rickets.

34. Skull Changes in Rickets

Young children may develop:

Craniotabes, representing softening of skull bones.

Other abnormalities can include delayed closure of the:

Fontanelle.

Dental development may also be affected.

35. Lower-Limb Deformities

Because weight-bearing acts on poorly mineralised growing bones, children may develop:

Genu varum – bow legs

or

Genu valgum – knock knees.

The exact deformity depends partly on age and mechanical loading.

36. Growth Disturbance

Because rickets involves the growth plate, affected children may develop:

Impaired linear growth.

Therefore rickets is not simply “osteomalacia in a small child”; the involvement of active growth plates produces distinctive:

Growth and skeletal deformities.

37. Diagnosis

Diagnosis requires integration of:

Clinical features.

Biochemical findings.

Vitamin D status.

Radiographic findings.

and identification of the:

Underlying cause.

38. Serum 25-Hydroxyvitamin D

The preferred biochemical marker for assessing vitamin D stores is:

25-hydroxyvitamin D – 25(OH)D.

In nutritional vitamin D deficiency it is:

Reduced.

Importantly, measuring active:

1,25-dihydroxyvitamin D

is generally not the routine test for determining vitamin D nutritional status.

39. ALP

ALP is commonly:

Elevated.

In children, interpretation requires age-appropriate reference ranges because normal skeletal growth itself produces higher:

Bone ALP levels.

Nevertheless, substantially elevated ALP in the correct clinical context supports active:

Rickets or osteomalacia.

40. PTH

In vitamin D deficiency, PTH is commonly:

Elevated.

This represents:

Secondary hyperparathyroidism.

Therefore:

LOW VITAMIN D + HIGH PTH

is a common pattern in significant deficiency.

41. Radiographs in Rickets

Rickets produces characteristic abnormalities around:

Growth plates, particularly rapidly growing metaphyses.

Typical changes include:

Widening of the growth plate.

Metaphyseal cupping.

Metaphyseal fraying.

Splaying.

These are classic radiological signs.

42. Radiographs in Osteomalacia

Adult osteomalacia may demonstrate:

Reduced bone density

and:

Looser zones/pseudofractures.

However, radiographic appearances can overlap with other metabolic bone disorders, so laboratory findings and clinical context are essential.

43. Treatment Principles

Treatment depends on the:

Underlying cause.

The goals are to restore the minerals necessary for normal bone mineralisation and correct the metabolic abnormality responsible for the disease.

44. Vitamin D Replacement

For nutritional vitamin D deficiency, treatment involves:

Vitamin D replacement.

Adequate calcium intake should also be ensured.

The exact dose and regimen depend on:

Severity of deficiency.

Age.

Malabsorption.

Underlying disease.

Local treatment guidance.

45. Calcium

Adequate:

Calcium intake

is essential for successful mineralisation.

Vitamin D treatment cannot fully restore bone mineralisation if the patient remains severely:

Calcium deficient.

Therefore dietary intake and supplementation requirements should be assessed together.

46. Treat Malabsorption

If deficiency is caused by:

Malabsorption,

the underlying gastrointestinal disorder should be treated whenever possible.

Patients with substantial malabsorption may require different vitamin D replacement strategies and closer monitoring.

47. Treat Phosphate-Wasting Disease

In phosphate-wasting osteomalacia or rickets, simply giving standard vitamin D may not correct the fundamental abnormality.

Treatment depends on the specific cause.

Selected disorders may require:

Phosphate replacement

and appropriate forms of:

Vitamin D therapy.

Certain FGF23-mediated disorders now have targeted treatments in selected patients.

48. Treat Proximal Tubular Disease

When proximal renal tubular dysfunction is responsible:

Correct the underlying tubular disorder where possible.

Treatment may require replacement of substances being lost, such as:

Phosphate

and

Bicarbonate, depending on the defect.

49. Monitoring Treatment

Response can be assessed using:

Symptoms.

Muscle strength.

Calcium.

Phosphate.

ALP.

PTH.

25-hydroxyvitamin D, where appropriate.

ALP may take time to return toward normal because skeletal healing continues after the metabolic abnormality begins to improve.

50. Osteomalacia – Note Form

DEFINITION:

Defective mineralisation of newly formed:

Osteoid in adults.

MAJOR CAUSES:

Vitamin D deficiency.

Calcium deficiency/malabsorption.

Chronic phosphate deficiency.

Renal phosphate wasting.

Proximal tubular disease/Fanconi syndrome.

Selected disorders of vitamin D metabolism or action.

CLINICAL FEATURES:

Diffuse bone pain.

Bone tenderness.

Proximal muscle weakness.

Difficulty rising/climbing stairs.

Waddling gait.

Insufficiency fractures.

Looser zones/pseudofractures.

Skeletal deformity in severe disease.

TYPICAL VITAMIN D DEFICIENCY BIOCHEMISTRY:

Calcium:

↓ or low-normal.

Phosphate:

↓.

ALP:

↑.

PTH:

↑.

25(OH) vitamin D:

↓.

51. Rickets – Note Form

DEFINITION:

Defective mineralisation of:

Growing bone + growth plates in children.

CLINICAL FEATURES:

Bone pain.

Growth impairment.

Widened wrists and ankles.

Bowing of legs.

Genu varum or genu valgum.

Rachitic rosary.

Harrison sulcus.

Craniotabes in younger children.

Muscle weakness.

X-RAY:

Growth-plate widening.

Metaphyseal:

Cupping.

Fraying.

Splaying.

52. Osteomalacia Versus Osteoporosis – Copyable Comparison

OSTEOMALACIA

Primary defect:

Defective mineralisation.

Bone quantity:

May appear reduced, but the fundamental problem is:

Unmineralised osteoid.

Bone pain:

Common.

Proximal muscle weakness:

Common.

Calcium:

Low or low-normal in typical vitamin D deficiency.

Phosphate:

Low.

ALP:

High.

PTH:

High in vitamin D deficiency.

Characteristic fracture:

Looser zone/pseudofracture.

OSTEOPOROSIS

Primary defect:

Reduced amount and impaired architecture of normally mineralised bone.

Bone pain:

Usually absent until:

Fracture occurs.

Proximal myopathy:

Not a characteristic primary feature.

Calcium:

Normal.

Phosphate:

Normal.

ALP:

Normal in uncomplicated disease.

PTH:

Usually:

Normal.

Characteristic problem:

Fragility fractures, especially hip, vertebral and distal radius.

53. Osteomalacia Versus Paget’s Disease

OSTEOMALACIA:

Mineralisation:

Defective.

Ca²⁺:

↓ or low-normal.

PO₄³⁻:

↓.

ALP:

↑.

PTH:

↑ in vitamin D deficiency.

PAGET’S DISEASE:

Mineralisation is not the primary problem.

There is:

Excessive, disorganised bone remodelling.

Ca²⁺:

Normal.

PO₄³⁻:

Normal.

ALP:

↑↑.

PTH:

Normal.

54. Important Clarifications to the Original Notes

The original statement:

“Decreased mineralisation of osteoid”

is correct.

More precisely:

OSTEOMALACIA = DEFECTIVE MINERALISATION OF NEWLY FORMED OSTEOID IN ADULTS.

RICKETS = DEFECTIVE MINERALISATION OF GROWING BONE AND GROWTH PLATES IN CHILDREN.

The original:

“Impaired calcium metabolism”

is too broad on its own.

Remember that successful mineralisation requires both:

Calcium and phosphate.

Therefore chronic:

Hypophosphataemia

is also an important mechanism.

The original:

“Proximal renal tubular disease”

is particularly important because proximal tubular dysfunction can cause:

Renal phosphate wasting.

Think especially of:

FANCONI SYNDROME → PHOSPHATURIA → HYPOPHOSPHATAEMIA → OSTEOMALACIA/RICKETS.

The original:

“↑ ALP”

is a major high-yield clue and should be retained.

Key Clinical Pattern

For rapid recall:

OSTEOMALACIA = SOFT BONE DUE TO DEFECTIVE MINERALISATION.

Think:

VITAMIN D DEFICIENCY

↓

↓ INTESTINAL Ca²⁺ ABSORPTION

↓

↑ PTH

↓

↑ RENAL PHOSPHATE LOSS

↓

↓ PO₄³⁻

↓

DEFECTIVE BONE MINERALISATION.

The classic vitamin D deficiency pattern is:

Ca²⁺ = ↓ / LOW-NORMAL

PO₄³⁻ = ↓

ALP = ↑

PTH = ↑

25(OH)D = ↓

The classic adult presentation is:

BONE PAIN + PROXIMAL MUSCLE WEAKNESS + FRACTURES/PSEUDOFRACTURES + ↑ ALP.

The classic childhood presentation is:

RICKETS → GROWTH-PLATE ABNORMALITY + BOWED LEGS + WIDENED WRISTS/ANKLES + RACHITIC ROSARY.

And the most useful distinction is:

OSTEOPOROSIS → NORMAL MINERALISATION, NORMAL Ca/PO₄/ALP.

OSTEOMALACIA → DEFECTIVE MINERALISATION, ↑ ALP with characteristic mineral abnormalities.