Bones and Joints Flashcards
What are the functions of bone cells?
Osteoblasts form new bone, whereas osteoclasts remove and remodel old bone under the influence of hormones.
Define epiphysis, metaphysis, and diaphysis and explain why a knowledge of these anatomic terms is important for pathology.
epiphysis = above the growth plate
diaphysis = the central part of long bones
metaphysis = the growth plate and adjacent terminal diaphysis which represent the most metabolically active segment of the long bones
Compare endochondral and intramembranous ossification.
endochondral ossification
osseous transformation of the cartilage in the growth plate
- ceases by the end of puberty (but can still occur during healing of bone fractures)
intramembranous ossification
bone formation that results from direct transformatio of fibrous matrix into osteoid, followed by mineralization
- accounts for subperiosteal bone formation of long bones
- continues through the normal life span
What are the main functions of bones?
- Mechanical support for the muscles, which makes possible the movement of limbs
- Protection of internal organs, such as the ribs forming the thorax or the skull protecting the brain
- Support of hematopoiesis, which occurs in the _bone marrow _
- Storage of calcium and phosphate salts
What is the basic structure and function of joints?
A joint is a junction between two or more bones, designed to provide support and structureal firmness and to allow movement.
**1) moveable diarthrodial or synovial joints: **knee, etc
2) limited mvmt synarthoses: head, trunk
What is achondroplasia?
Autosomal Dominant mutation in gene encoding fibroblast growth factor receptor 3.
Adversly affects endochondral ossification and growth of long bones = dwarfism.
What is osteogenesis imperfect?
Various mutations involving the encoding of collagen I.
Range of ages affected from in utero to later in life. Symptoms are not limited to the bones, and may have thin skin, thin dental enamel, defective heart valves, bluish hue to sclera.
What are the main causes of osteomyelitis?
Most common: staph aureus
Drug addicts: mixed flora hematogenous infections
Sickle cell: salmonella
Pott’s disease: mycobacterium, chronic osteomyelitis of the spine
Describe the principal pathologic feature of osteomyelitis.
The bacteria reach the metaphysis through the nutrient artery. Bacterial growth results in bone destruction and formation of an abscess.
From the abscess cavity, the pus spreads between the trabeculae into the medulla, through the cartilage into the joint, or through the haversian canals of the compact bones to the outside.
These sinuses traversing the bone persist for a long time and heal slowly. The pus destroys the bone and sequesters parts of it in the abscess cavity. Reactive new bone is formed around the focus of inflammation.
What are the possible causes of aseptic bone necrosis?
Sudden onset of ischemia caused by disruption or complete interruption of blood flow.
May be related to trauma, emboli, radiation, or drugs.
A disease of growing children, but also elderly
Describe the typical clinical features of aseptic bone necrosis.
Carpal bones are especially vulnerable because of their complex blood supply.
In elderly: most important site is head of the femur
What are the causes of osteoporosis?
**Primary: **disease of elderly
**Secondary: **can occur at any age
- hormone disturbance
- dietary insufficiency or malabsorption
- immobilization
- drugs
- tumors
Discuss the pathogenesis of osteoporosis.
*Bone resorption outpaces bone formation resulting in net bone loss. *
What are the complications of osteoporosis?
- Type 1: trabecular bone loss predominates, mostly in the vertebrae and distal radius
Major complications = crush fractures of vertebral bodies and distal end of radius
- Type 2: proportional loss of cortical and trabecular, head of femur, wedge fractures of vertebrae
What is osteomalacia?
Inadequate mineralization of the organic bone matrix, caused by disturances of either vitamin D or phosphate metabolism.
Osteomalacia of growing bones = rickets
Explain the role of vitamin D in calcium homeostasis.
Activation of vitamin D occurs in the liver and kidneys. Several active metabolites are fromed, of which the hydroxylated 1,25 vitamin D is the most important.
This vitamin D does three things:
1) stimulation of intestinal absorption of calcium and phosphorus
2) deposition of calcium into the osteoid and movilization of calcium from calcified bone; mineralization of osteoid
3) stimulation of teh PTH dependent resorption of calcium in the kidney
Compare rickets and osteomalacia.
Rickets
- growing bones
- endochonral ossification severely disturbed
- growth retardation, softening of growing bones (bowlegs), deformities
- *Osteomalacia**
- excess of osteoid around the calcified core of the trabeculae of spongy bone and ont he endocavitary side of compact bones
- often asymptomatic
- muscle weakness
How is osteomalacia diagnosed?
Based on
- clinical symptoms
- radiographic evidence of osteopenia
- laboratory: low vit D, calcium and phosphate; elevated PTH
*but in phosphate deficiency, the serum phosphate is low while calcium and PTH are normal