Living elements of bone which regulate flow of minerals in and out of the bone
Osteocytes
Living tissue composed of cells, calcium, collagen, proteins, and water
Bone
Examples are skull, sternum, and ribs
Flat bones
Type of bone for weight bearing
Long bones
Examples are carpals and tarsals
Short bones
Round and small bones which protect tendon
Sesamoid bones
Part of bone which forms the shaft
Diaphysis
Part of bone which forms the bone ends and supports the articular surface
Epiphysis
Part of bone found between diaphysis and epiphysis
Metaphysis
Part of bone between metaphysis and epiphysis
Physis (epiphyseal growth plate)
Cells responsible for bone resorption
Osteoclasts
Primary ossification center of bone
Medullary canal
Sheaths surrounding the haversian/central canal
Lamellae
Oblique channels connecting osteons/haversian systems
Volkmann's canals
Spaces within lamellar which serve as storage sites of osteocytes
Lacunae
Functions of bone
Protects vital structures
Enhances leverage
Provides attachment
Stores minerals
Important during palpation (serves as landmark)
Every change in the form and function of bone is followed by certain definite change in its internal architecture
Wolff's Law
Most widely used and validated tool to assess bone mineral density
Dual energy x-ray absorptiometry (DEXA) scan
Columns that are parallel to the long axis of bone
Haversian systems (osteons)
Microscopic canals between lacunae of ossified bone
Canaliculi
Normal BMD
1 SD above or below the mean average of young adults
1-2.5 SD below the mean average of young adults
Osteopenia
Osteoporosis BMD
>2.5 SD below the mean average of young adults
MC bone disease in adults
Osteoporosis
Racial characteristics associated with osteoporosis
Asian, Caucasian, Hispanic
Common sites of osteoporotic fractures
1. Midthoracic
2. Upper lumbar
3. Hip
4. Distal forearm
Epidemiology of osteoporosis
F>M until 75 years old
F=M after 75 years old
MC form of short-limb dwarfism
Achondroplasia
Endochondral osteogenesis is retarded and ceased early
Achondroplasia
Characteristics of achondroplasia
1. Short arms and legs
2. Height: 4 ft.
3. Broad forehead
4. Prominent jaw
5. Small face
6. Flat nose
7. Brachycephalic (decreased AP diameter of head)
8. Pudgy fingers
9. Main en trident (gap between 3rd and 4th fingers)
10. Bowing of femur and tibia
Isolated fracture of the iliac wing secondary to direct blow to the ilium
Duverney's fracture
Very rare autosomal dominant genetic condition characterized by symmetric expansion of diaphysis resulting to leg pain, gait abnormalities, muscle weakness, and increased fatigability
Group of skeletal dysplasias primary characterized by punctate calcifications in cartilage (calcific stippling)
Chondrodysplasia punctata
Genetic disorder characterized by osteoclast dysfunction that leads to excessive osteoid tissue formation
Osteopetrosis
Acquired disease in which the osteoclast dysfunction initially causes excessive removal of bone and is later deposited at different rates during the different stages of the disease
Paget's disease (osteitis deformans)
Softening of bone due to poor and delayed calcification
Osteomalacia
Bone disorder caused by mutation in fibroblast growth factor receptor 3
A) Achondroplasia
Osteoporosis is usually not visible on conventional radiographs until at least ___% of bone mineral has been lost
D) 25-30
Procedure of greatest clinical utility for measuring bone density
Dual-energy x-ray absorptiometry (DXA) scan
Senile and postmenopausal osteoporosis are examples of primary osteoporosis.
True
Meanwhile, secondary osteoporosis occurs in association with other conditons (e.g. rheumatoid arthritis, vitamin D deficiency), medications (e.g. phenytoin, corticosteroids), or disuse with immobility.
BMD is within 1 SD of a "young normal" adult
D) Normal
BMD is between 1 and 2.5 SDs below that of a "young normal" adult
A) Osteopenia
BMD is 2.5 SDs or more below that of a "young normal" adult
C) Osteoporosis
More fractures occur in persons with osteopenia compared to those with osteoporosis.
True
Persons with osteopenia far outnumber those with osteoporosis; thus, more fractures occur in the osteopenic population.
Recommended daily calcium intake for 19-50 years old
A) 1000 mg/d
Recommended daily calcium intake for >50 years old
C) 1200 mg/d
Which age range has the highest recommended daily calcium intake?
B) 9-18 years
The recommended daily intake for the following age ranges are as follows:
1. 0-6 months = 210 mg/d
2. 4-8 years = 800 mg/d
3. 9-18 years = 1300 mg/d
4. > 50 years = 1200 mg/d
Pregnant or lactating women who are 18 years or younger require higher daily calcium intake than their older counterparts.
True
Pregnant or lactating women who are 18 years old or younger require 1300 mg of calcium per day; whereas those who are aged 19-50 years only require 1000 mg/d.
At what age can a child begin to intake calcium via solid food?
C) 7-12 months
At 0-6 months of age, calcium intake only comes from human milk.
For men and women aged 50 or older, the current recommendation for daily intake of vitamin D is 800-1000 IU/day.
True
To aid in absorption of calcium and mineralization of bone, this is commonly prescribed as a supplement for patients who lack the 1-α-hydroxylase enzyme because of severe renal impairment
B) 1,25-dihydroxycholecalciferol
Vitamin D supplements can increase the risk for kidney stones, hypercalciuria, nephrolithias, or even nephrocalcinosis in patients at risk.
True
Vitamin D supplements can cause such risks because they increase calcium absorption in the gut.
For optimal bone health, an exercise program should include:
A) Both of the above
Most critical period of bone growth
A) Puberty and adolescence
What cell is responsible for the breakdown and resorbtion of the bone matrix?
B) Osteoclasts
Osteoclasts are the cells responsible for the breakdown and resorption of bone tissue for the purpose of remodelling in response to the stresses and pressures placed on it.
Osteoblasts are the cells responsible for creating new bone tissue after osteoclasts have resorbed old bone tissue, they are also responsible for turning hyaline cartilage into bone tissue during new bone growth and turning the fibrocartilaginous callous into new bone during fracture repair.
Osteocytes are the cells that make up healthy bone. These are found in the lacunae in the osteons of compact bone.
Periosteum is the outer layer of the bone. It provides blood supply and protection to the bone, the inner layer contains the osteogenic cells required to make new bone during growth and repair.
What is the pathogenesis of osteopetrosis (marble bone disease)?
A) Poor osteoclast function due to a carbonic anhydrase II mutation
An acidic environment is needed for osteoclasts to remove calcium from bone. A defect in maintaining this acidic environment leads to poor bone resorption by osteoclasts resulting in overgrowth and sclerosis of cortical bone. This abnormally thick bone fractures easily. Clinical features include bone fractures, anemia, thrombocytopenia (due to the bony replacement of marrow), and visual/ hearing loss due to cranial nerve compression. The patient can also develop renal tubular acidosis (defect in carbonic anhydrase leads to decreased reabsorption of bicarbonate) and hydrocephalus (due to narrowing of the foramen magnum).
Which bone disorder is caused by an autosomal dominant mutation that impairs the synthesis of type 1 collagen?
C) Osteogenesis imperfecta
Osteogenesis imperfecta is also known as ‘brittle bone disease’. It is a congenital defect of bone formation. Clinical findings include multiple pathologic fractures, blue sclera,and deafness due to fractures of the bones in the middle ear.
What is the pattern of inheritance of vitamin-D resistant rickets?
A) X-linked dominant
Other X-linked dominant conditions are fragile X syndrome and Alport syndrome.
X-linked recessive conditions include red-green color blindness, hemophilia A and B, and Duchenne and Becker's muscular dystrophy.
Autosomal dominant conditions include Huntington's disease, myotonic dystrophy, and Marfan's syndrome.
Autosomal recessive conditions include cystic fibrosis.
