Bones (applied physiology)

Bones(Applied Physiology)DANISH HASSANLECTURER, UNIVERSITY OF SARGODHA

Diseases of Bone1. Osteoporosis2. Rickets3. Osteomlacia

Osteoporosis Bone disease characterized by the loss of bone

matrix and minerals. Osteoporosis means‘porous bones’. It involves a reduction in total bone mass, with

an equal loss of both bone mineral and organic matrix.

It is responsible for more than 1.5 million fractures annually, including 300,000 hip fractures, 700,000 vertebral fractures, 250,000 wrist fractures, and 300,000 fractures at other sites.

Nearly one third of people who have hip fractures end up in nursing homes within a year; nearly 20% die within a year.

A normal bone (Left) and an Osteoporotic bone (Right)

Causes of Osteoporosis1. Occurs due to excessive bone resorption and

decreased bone formation.2. Long-term dietary calcium deficiency can lead to

osteoporosis because bone mineral is mobilized to maintain plasma calcium levels.

3. Vitamin C deficiency can also result in a net loss of bone because vitamin C is required for normal collagen synthesis to occur.

4. A defect in matrix production and the inability to produce new bone eventually result in a net loss of bones.

5. A reduction in the mechanical stress placed on bone can lead to bone loss.

6. Immobilization or disuse of a limb, such as with a cast or paralysis, can result in localized osteoporosis of the affected limb.

7. Space flight can produce a type of disuse osteoporosis resulting from the condition of weightlessness.

Risk Factors1. Sedentary life2. Genetic factor3. Excessive smoking4. Excessive alcohol or caffeine intake5. Endocrine disorders like hypothyroidism, Cushing

syndrome, acromegaly and hypogonadism.

6. Being a woman (especially a postmenopausal woman)

7. Being of advanced age8. Having a family history of the disease 9. Having low testosterone levels (in men)

Loss of bone Mass with Age

Manifestations of Osteoporosis Loss of bone matrix and minerals leads to loss of

bone strength, associated with architectural deterioration of bone tissue.

Ultimately, the bones become fragile with high risk of fracture.

Commonly affected bones are vertebrae and hip.

People may not know that they have osteoporosis until they break a bone

Vertebral (spinal) fractures may initially be felt or seen in the form of

1. Persistent, unexplained back pain2. Loss of height3. Spinal deformities such as kyphosis or stooped

posture

Diagnosis of Osteoporosis: Bone density determines the degree of osteoporosis

and the fracture risk. The most common test for measuring bone density is

dual-energy x-ray absorptiometry (DEXA) scanning. DEXA uses x-rays to measure bone density and

provides two measures of how dense bone is T score Z score.

The T score compares the person’s bone density with the average bone density of young healthy adults of the same sex, a time when bone density is at its peak.

The Z score compares a person’s bone density with that of people of the same age, sex, and weight, and is less valuable in making predictions of risk of fracture or in making decisions about treatment.

Dual-energy X-ray Absorptiometry (DXA) Scan

Classification T-scoreNormal -1 or greater

Osteopenia Between -1 and -2.5Osteoporosis -2.5 or less

Severe Osteoporosis -2.5 or less and fragility fracture

Prevention of Osteoporosis The principal current approaches include:

1. Estrogen replacement therapy Estrogen decreases bone loss in postmenopausal

women by inhibiting bone resorption, resulting in a 5–10% increase in BMD over 1–3 years.

Calcium supplements enhance the effect of estrogen on BMD.

2. Bisphosphonates Bisphosphonates have a strong affinity for bone

apatite and are potent inhibitors of bone resorption.

These agents reduce the recruitment and activity of osteoclasts and increase their apoptosis.

3. Calcitonin Calcitonin reduces bone resorption by direct

inhibition of osteoclast activity. Intranasal calcitonin produces significant effects

on BMD. Calcitonin is less effective in prevention of cortical

bone loss than cancellous bone loss in postmenopausal women.

4. Parath-hormone: Intermittent administration of human

recombinant PTH restores bone strength by stimulating new bone formation at the periosteal (outer) and endosteal (inner) bone surfaces, thickening the cortices and existing trabeculae of the skeleton, and perhaps increasing trabecular numbers and their connectivity.

5. Vitamin D analogs: Vitamin D analogs induce a small increase in BMD

that seems to be limited to the spine.

6. Exercise: Physical activity early in life contributes to high

peak bone mass. Walking, weight training, and high-impact

exercises induce a small (1–2%) increase in BMD at some skeletal sites.

Load-bearing exercise is more effective for increasing bone mass than are other types of exercise

Rickets Bone disease in children, characterized by

inadequate mineralization of bone matrix. It occurs due to vitamin D deficiency. Vitamin D deficiency develops due to

insufficiency in diet or due to inadequate exposure to sunlight.

Deficiency of vitamin D affects the reabsorption of calcium and phosphorus from renal tubules, resulting in calcium deficiency.

It causes inadequate mineralization of epiphyseal growth plate in growing bones.

This defect produces various manifestations

Causes of Rickets1. Deficiency of vitamin D2. Low dietary intake3. Inadequate synthesis in skin4. Reduced absorption from intestine5. Renal diseases6. Chronic renal failure7. Dialysis-induced bone disease8. Renal tubular acidosis

Features of Rickets Collapse of Chest wall

It occurs due to the flattening of sides of thorax with prominent sternum.

This deformity of the chest with projecting sternum is called pigeon chest/chicken chest/pectus carinatum.

Funnel Chest (Left) and Pigeon Chest (Right)

Rachitic Rosary A visible swelling where the ribs join their

cartilages. It is because of the development of nodules at

sternal end of ribs, which forms the rachitic rosary.

Kyphosis Extreme forward curvature of the upper back

bone (thoracic spine) with convexity backward (forward bending).

Severe kyphosis causes formation of a hump (protuberance) which is called humpback, hunchback or Pott curvature

Lordosis Extreme forward curvature of back bone in

lumbar region: also called hollow back /saddle back

Scoliosis Lateral curvature of spine

Harrison Sulcus: A groove in rib cage due to pulling of diaphragm

inwards. It may also appear in rickets because the patients lack

the mineralized calcium in their bones necessary to harden them.

Thus the diaphragm, which is always in tension, pulls the softened bone inward.

It is due to the indentation of lower ribs at the point of attachment of diaphragm.

Frontal Bossing If rickets occurs at a later age, thickening of the

skull develops. This produces frontal bossing and delays the

closure of the anterior fontanelle

Bowing of hands and legs It is due to inability of the limbs to bear body

weight (especially lower limbs)

Enlargement of liver and spleen

Tetany: In advanced stages, the patient may die because

of tetany, involving the respiratory muscles.

Decreases

in serum calcium, serum phosphorus, calcidiol, calcitriol, urinary calcium.

The most common laboratory findings in nutritional rickets are:

Increased Parathyroid hormone, alkaline phosphatase,urinary phosphorus levels are elevated.

Types of Rickets1. Nutritional Rickets

Nutritional rickets results from inadequate sunlight exposure or inadequate intake of dietary vitamin D, calcium, or phosphorus.

2. Vitamin D Dependent Rickets Vitamin D-dependent rickets, type I is

secondary to a defect in the gene that codes for the production of renal 25(OH)D3-1-alpha-hydroxylase

Vitamin D-dependent rickets, type II is a rare autosomal disorder caused by mutations in the vitamin D receptor. Type II does not respond to vitamin D treatment; elevated levels of circulating calcitriol differentiate this type from type I

3. Vitamin D Resistant Rickets Rickets refractory to vitamin D treatment may be

caused by the most common heritable form, known as vitamin D-resistant rickets or familial hypophosphatemic rickets.

Because of mutations of the phosphate-regulating gene on the X chromosome, renal wasting of phosphorus at the proximal tubule level results in hypophosphatemia. Normal levels of calcitriol are found in this disorder.

Osteomalacia Bone disease in adults, characterized by

inadequate mineralization of bone matrix. Rickets in adults is called osteomalacia or adult

rickets.

Causes of Osteomalacia Osteomalacia occurs because of deficiency of

vitamin D. It also occurs due to prolonged damage of kidney

(renal rickets).

Features of osteomalacia1. Vague pain2. Tenderness in bones and muscles3. Myopathy leading to waddling gait (gait means

the manner of walking).4. Occasional hypoglycemic tetany.