Diseases of the Musculoskeletal system

Diseases of the Musculoskeletal system

Various classifications of the diseases of the musculoskeletal system, based on clinical, pathological and etiological differences, are in use, but the simplest is that which divides the disease into degenerative and inflammatory types:
(1) The degenerative diseases of muscles, bones and joints :
Myopathy, osteodystrophy and arthropathy, respectively.
(2) The inflammatory diseases are: Myositis, osteomyelitis and arthritis.

The term myopathy describes the noninflammatory degeneration of skeletal muscle that is characterized clinically by muscle weakness and pathologically by hyaline degeneration of the muscle fibers.
The serum levels of some muscle enzymes are elevated and myoglobinuria is a common accompaniment.

Etiology and epidemiology:
The most important myopathies in farm animals are due to nutritional deficiencies of vitamin E and selenium and the effects of unaccustomed exercise.
The major causes of myopathy in farm animals and their epidemiological determinants are as follows.
1- Enzootic nutritional muscular dystrophy.
2- Exertional or post-exercise rhabdomyolysis.
3- Metabolic.
4- Degenerative myopathy.

Myositis may arise from direct or indirect trauma to muscle and occurs as part of a syndrome in a number of specific diseases including blackleg, bluetongue, ephemeral fever, swine influenza, sarcosporidiosis and trichinosis.
Injection site clostridial infections in horses and cattle:

Clostridial myositis, myonecrosis, cellulitis, and malignant edema are terms used to describe a syndrome of severe
necrotizing soft tissue infection associated with Clostridium spp.

Osteodystrophy is a general term used to describe those diseases of bones in which there is a failure of normal bone development, or abnormal metabolism of bone that is
already mature. The major clinical manifestations include
distortion and enlargement of the bones, susceptibility to
fractures and interference with gait and posture.

The common causes of osteodystrophy in
farm animals include the following:
-Nutritional causes
*Calcium, phosphorus and vitamin D
1- Absolute deficiencies or imbalances in calcium-phosphorus ratios in diets cause:
– Rickets in young animals, e.g., growing lambs fed a diet rich in wheat bran
– Osteomalacia in adult ruminants.

– Osteodystrophia fibrosa in the horse occurs most commonly in animals receiving a diet low in calcium and high in
– Osteodystrophia fibrosa in pigs occurs as a sequel to rickets and osteomalacia, which may occur together in young growing pigs that are placed on rations deficient in calcium, phosphorus and vitamin D following weaning.

*Copper deficiency
– Osteoporosis in lambs
– Epiphysitis in young cattle.

*Other nutritional causes
– Inadequate dietary protein and general under-nutrition of cattle and sheep can result in severe osteoporosis and a great increase in ease of fracture.
– Chronic parasitism can lead to osteodystrophy in young growing ruminants.
– Hypovitaminosis A and hypervitaminosis A can cause osteodystrophic changes in cattle and pigs.
– Prolonged feeding of a diet high in calcium to bulls can cause nutritional hypercalcitoninism combined with replacement of
trabecular bone in the vertebrae and long bones with compact bone.

*Chemical agents
1-Chronic lead poisoning is reputed to cause osteoporosis in lambs and foals.
2- Chronic fluorine poisoning causes the characteristic lesions of osteofluorosis, including osteoporosis and exostoses
Inherited and congenital causes
There are many inherited and congenital defects of bones of newborn farm animals.
Osteomyelitis is an infectious inflammatory disease process of bone and its marrow cavity, causing bone destruction. Infection may be localized to a single region of bone
or may involve several structures including marrow, cortex, periosteum, and surrounding soft tissue.

If only bone is affected, it is classified as osteitis.

Etiology :
Inflammation of bone is uncommon in farm animals except when infection is introduced by traumatic injury or by the hematogenous route.
Bacteria can reach bone by any of three routes:
•By extension from an adjacent focus of infection.
•By direct inoculation through trauma or surgery.

Non-inflammatory lesions of the articular surfaces of joints characterized by:
* Degeneration and erosion of articular cartilage
* Hypertrophy of bone surrounding the articular cartilage resulting in spur formation at the joint margins.

Inflammation of the synovial membrane and articular surfaces as a result of infection occurs commonly in farm animals.

It is characterized by varying degrees of lameness and a warm and swollen painful joint. The synovial fluid is usually abnormal, containing an increased leukocyte count and the pathogens causing the arthritis. The arthritis may be severe enough to cause systemic illness, and in some cases a draining sinus tract may occur.

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