Chapter 2Skeletal system

Anatomy and physiology

• Skeletal system composed of 206 separate bones.

• Bone is a type of connective tissue its matrix consists of calcium phosphate.

Periosteum: fibrous membrane that encloses all of the bone except the joint surface and is crucial to supplying blood to the underlying bone

Skeletal system

Axial skeleton80 bones

Appendicular skeleton126 bones

Anatomy of BoneAnatomy of Bone

periosteum

cancellous

Osteoblasts

Are bone forming cells that line the medullary canal and are Interspersed throughout the periosteum.

They are responsible for bone growth and thicknening.

Osteoclasts

Is a type of bone cells that removes (old) bone tissue by breaking down bone and releasing minerals resulting in transferring calcium from bone fluid to the blood (bone resorption) its function is maintenance and repair.

Osteoclasts and osteoblasts are instrumental in controlling the amount of bone tissue.

Osteoblasts form bone, osteoclasts resorp bone.

The bones of the skeletal system may also classified according to their shape

DiaphysisEpiphysisMetaphysis

Growth zone bet. Epi.&Dia.

Bone RadiographyPlain Films:

• Good for fracture, dislocation, tumors.

Bone Scan:

• Allows screening entire skeleton.

• Good for metastatic disease.

• Helps answer whether osteomyelitis.

CT:

• Allows cortical disruption, soft tissue extension to be assessed.

MR:

• Good for assessing marrow involvement.

• Good for soft tissues around joint (collateral ligaments, menisci in knee)

Normal Bone Appearance

• The radiographic image of the bone is due to its calcium content.

• Pathological lesions will be visible when there are:

• Change in structure continuity (as in fractures).

• Change in position (as in dislocations).

• Change in shape (as in congenital development defects).

• Lessening of density (reduced radio-opacity).

• Localized demineralization with disappearance of the trabeculae (bone erosion).

• Increased density from a high calcium content (bone sclerosis).

• New bone formation.

Metabolic bone diseaseGeneralized reduction of bone

density

• The main causes of generalized reduction in bone density are:

1- Osteoporosis.

2- Osteomalacia and rickets.

3- Hyperparathyroidism.

4- Multiple myloma• Gout • Paget disease

Osteoporosis-Osteoporosis-disease characterized by low bone mass &

structural deterioration of bone tissue

normal bone osteoporotic bone

Bone is a living, constantly changing tissue, and normally a balance exists between the amount of old bone being removed (an osteoclastic process) and the amount of new bone replacement (an osteoblastic process).

• Osteoporosis is usually caused by accelerated resorption of bone.

Causes:

• Endocrine disorders.

• Drug induced osteoporosis (prolonged steroid administration).

• Dietary deficiencies (especially in proteins).

• Post menopausal osteoporosis.

Radiographic appearance

• Loss of mineral salts causes osteoporotic bone to become more lucent than normal.

• This may be difficult to detect, because about 50% to 70% of the bone density must be lost before.

• So it is essential to use lowest practical kVp.

Osteomalacia العظام الكساح and rickets لين

• In histology, osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific proteins. When the osteoid becomes mineralized, it and the adjacent bone cells have developed into new bone tissue.

• When there is insufficient nutrient minerals or osteoblast dysfunction, the osteoid does not mineralize properly, and it accumulates. The resultant disorder is termed rickets in children and osteomalacia in adults.

Normal Abnormal

Causes:•Dietary deficiencies of vitamin D, or lack of exposure to sunlight.•Malabsorption causing impaired absorption of vitamin D and calcium from the gut.

Hyperparathyroidism

• Excess parathyroid hormone

secretion mobilizes calcium

from the bones resulting in

decrease in bone density.

• Causes:

Hyperparathyroidism may be:

• Primary, from hyperplasia or

tumor of the parathyroid

glands.

• Secondary to chronic renal

failure.

• The signs of

hyperparathyroidism

• A generalized loss of bone

density, with loss of different

ion between cortex and

medulla.

• Bone resorption (Fig.3a)

• Brown tumors (Fig.3b)

• Vascular calcification(Fig.4)

• Soft tissue calcification(Fig.5)

(Fig 3 a) (Fig 3 b)

(Fig 4) (Fig 5)