1. Bone disease Osteomylitis :
Osteomyelitis is most often caused by staphylococcus aureus & usually affects infants & children.
The initial radiographs are normal as bone changes are not visible until days after the onset of the infection.
The TC 99m radionuclide bone scan and MRI show changes much earlier.
the earliest sings on plain radiographs are soft tissue swelling , and bone destruction in the metaphysis with a periosteal reaction that eventually may become very extensive and surround the bone to form an involucrum

2. part of the original bone may die and form a separate dense fragment known as a sequestrum

3. a radionuclide bone scan will show increased activity both on the early ( blood pool ) images reflecting hyperaemia and on the delayed bone phase images.

4. U/S can demonstrate sub periosteal collections of pus .
MRI is the imaging modality of choice & shows evidence of bone odema and pus accumulation in the bone & soft tissue .

5. distinction of neoplasm from osteomyelitis :
With malignant bone tumor the radiographs are usually abnormal
when the patient first presents , whereas with osteomyelitis the initial film are often normal .
The presence of fever & some times of discharging sinuses usually help to diagnose of infective lesion.
CT & MRI more informative.
Bone scanning is positive in both osteomyelitis & malignant tumour and can not be used in differentiation .

6. bone infarction :
Occurs most often in the intra –articular portions of the bones
Can occur in the shaft of a bone in several disease including caisson disease , sickle cell disease or following radiation therapy. . once healed , they appear as irregular calcification in the medulla of along bone.

7. Multiple focal lesions
Metastases :
Metastases are by far the commonest malignant bone tumor.
Metastases may be sclerotic , lytic or a mixture of lysis& sclerosis
Lytic metastases.
1- in adults most commonly arise from a carcinoma of the breast and bronchus , less commonly from carcinoma of the thyroid , kidney or colon .
2- in children from neuroblastoma or leukaemia .
Lytic metastases give rise to well defined or ill defined areas of bone destruction with out a sclerotic rim .the lesions vary from small holes to large areas of bone destruction.

9. Sclerotic metastases appear as ill-defined areas of increased density of varying size with ill-defined margins .
1-in men they are most commonly due to metastases from carcinoma of the prostate .
2-in women from carcinoma of breast , metastases with bone expansion occurs in primary tumour of the kidney & thyroid .

10. Mixed lytic & sclerotic metastases are not uncommon , they are often seen with carcinoma of beast .

11. A radionuclide bone scan is much more sensitive for detecting metastases than plain film .
MRI is better than radionuclide scanning for the detection of metastases, but it is more difficult to survey the whole skeleton .

12. Multiple myeloma :
frequently seen in bones with active haemopoiesislesions .may resemble lytic metastases in every way but are often better defined
- diffuse marrow involvement may give rise to generalized loss of bone density
MRI has good role in detecting multiple myloma lesions .

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14. Generalized decrease bone density ( osteopenia ):
Osteoporosis :
Is the consequence of a deficiency of protein matrix ( osteoid ) . the remaining bone is normally mineralized and appears normal histologically .
The most common causes of osteoporosis are :
idiopathic .
cushing disease& steroid therapy .
.disuse .

15. Changes of osteoporosis are best seen in the spine , decrease in bone density, compression fractures , vertebral bodies appearing wedged or biconcave , secondary widening of disc spaces .
Long bones have thin cortices .
Screening by measuring of bone mass using DEXA .

16. Rickets and osteomalacia :
In these condition there are poor mineralization of osteoid .if this occur before epiphyseal closure the condition is known as rickets , in adult the condition is known as osteomalacia .
The main causes of both above conditions :.
1- Dietary deficiency of vitamin D , or lack of exposure to sunlight.
2- malabsorption.
3-Renal disease.

17. In osteomalacia the features are
. loss of bone density
.Thinning of the trabeculae and the cortex
.looser zones
.bone deformity vertebral bodies are biconcave , the femora may be bowed & in severe cases the side walls of the pelvis may bend inwards , giving to the so called triradiate pelvis .

18. In rickets the changes are maximal where bone growth is occurring , so they are best seen at the knee, wrist and ankle .seen as . Deficient the zone of provisional calcification . .widening with irregularly mineralized metaphyses with cupping .increase distance between the visible epiphysis & the calcified portion of the metaphysis . .generalized decrease in bone density . . Deformities of the bones occur because the under mineralized bone is soft , green stick fractures are common .

19. Hyperparathyroidism:
Excess parathyroid hormone secretion mobilizes calcium from the bones , resulting in a decrease in bone density , it may be primary from hyperplasia or tumour of the parathyroid glands or secondary to chronic renal failure
. generalized loss of bone density.
. subperiosteal bone resorption.
. soft tissue calcification.
.brown tumour.

20. Generalized increase in bone density :
1. sclerotic metastases.
2.osteopetrosis myelosclerosis.

21. Alteration of the trabecular pattern & change in shape : occur in the following :
I- Paget disease:radiologically the affected bone showing thickening of the trabeculae and of the cortex leading to loss of corticomudellary differentiation & increased bone density together with enlargement of the affected bones .

22. II.Haemolytic anemia :
Radiological bony changes are seen in two main types ( thalassaemia & sickle cell disease ) & both show changes of marrow hyperplasia , but sickle cell disease can also showing signs of bone infarction & infection .

23. Changes in bone shape :